S2 Light Driven Water Splitting
 
Wed Oct 24 2018
WatSpl S2.1
Chair: Christina Scheu
14:30 - 15:00
S2.1-I1
Fischer, Anna
Universität Freiburg
Improving BiVO4 thin Film Photoanodes for Light-Induced Water Oxidation
Anna Fischer
Universität Freiburg, DE

Since Aug. 2014:

Professor for “Inorganic Functional Materials” and head of the NANOMATERIAL group at the IAAC of the Ludwigs-Universität-Freiburg

2009 – 2014:

Group Leader within the framework of UniCat (DFG Exzellenz Cluster), Technische Universität Berlin, Institut für Chemie

Research on "Nanostructured electrodes for (bio)-electrocatalysis“

2008 – 2009:

Post-Doc at the MPIKG, Department of Biomaterials, Golm, Germany

2005 – 2008:

Dissertation at the Max-Planck-Institute of Colloids and Interfaces (MPIKG), Golm, Germany

“Synthesis of nanostructured metal nitrides through reactive hard-templating“

2000 – 2005:

Education in chemistry, Paris, France

Authors
Martin Rohloff a, b, c, Björn Anke c, Spark Zhang d, Christina Scheu d, Martin Lerch c, Anna Fischer a, b
Affiliations
a, University Freiburg, IAAC, Germany
b, University Freiburg, FIT, Germany, DE
c, Technical University of Berlin (TU), Straße des 17. Juni, Berlin, DE
d, Max-Planck-Institut für Eisenforschung, Germany
Abstract

The n-type semiconductor bismuth vanadate (BiVO4) is a promising material as photoanode for light induced water oxidation. Its absorption in the visible range (band gap energy of 2.4 eV), its suitable band edge positions compared to the OER half reaction, its stability against photo-corrosion as well as its low cost make BiVO4 one of the most interesting ternary oxide materials for light-induced oxygen evolution from water.1 One major drawback for BiVO4 is its poor electronic conductivity, which can however be overcome by applying three strategies: i) adjustment of thin film properties (especially thickness), ii) n-type doping by cation and more recently anion substitution and iii) heterojunction design (type II). Within the present talk, I will give an overview of the improvements we achieved for novel sol-gel based BiVO4 thin film photoanodes following each of these strategies allowing us to go all the way from low to high performance BiVO4 photoanodes.

First we developed a new, sol-gel-based synthesis involving simple dip-coating and calcination allowing the easy and reproducible fabrication of porous BiVO4 and Mo‑doped BiVO4 thin film photoanodes.2 The obtained thin films crystallize in the monoclinic scheelite structure in micrometre large, two-dimensional, single-crystalline porous domains with wall features in the range of the hole diffusion length of BiVO4. Optimization of the electron transport properties resulting in higher PEC performance was realized by cation and anion doping using Molybdenum and Fluorine, respectively.3 Finally, our new synthesis approach could be easily applied for the fabrication of BiVO4/WO3 type II heterojunctions following a simple layer-by-layer deposition. It is shown that precise control of the layer morphology and the overlapping interface between the layers is an indispensable prerequisite for high performance WO3/BiVO4 heterojunction photoanodes.

This work was funded by the DFG SPP1613 program.

1 Z.-F. Huang, L. Pan, J.-J. Zou, X. Zhang, L. Wang, Nanoscale 2014, 6, 14044.

2 M. Rohloff, B. Anke, S. Zhang, U. Gernert, C. Scheu, M. Lerch, A. Fischer, Sustainable Energy Fuels 2017, 1, 1830.

3 B. Anke, M. Rohloff, M. G. Willinger, W. Hetaba, A. Fischer, M. Lerch, Solid State Sci. 2017, 63, 1.

15:00 - 15:15
S2.1-O1
Granone, Luis Ignacio
Institute of Technical Chemistry, Gottfried Wilhelm Leibniz University Hannover, DE
Effect of the Degree of Inversion on the Photocatalytic Activity of Spinel ZnFe2O4
Luis Ignacio Granone
Institute of Technical Chemistry, Gottfried Wilhelm Leibniz University Hannover, DE, DE
Authors
Luis I. Granone a, b, Ralf Dillert a, b, Detlef W. Bahnemann a, b, c
Affiliations
a, Institute of Technical Chemistry, Gottfried Wilhelm Leibniz University Hannover, DE, Callinstraße, 3, Hannover, DE
b, Laboratory of Nano- and Quantum-Engineering (LNQE), Wilhelm Leibniz University Hannover, DE, Schneiderberg, 39, Hannover, DE
c, Laboratory “Photoactive Nanocomposite Materials”, Saint-Petersburg State University, Ulyanovskaya str. 1, 198504 Peterhof, Saint-Petersburg, Russia
Abstract

Recently, due to promising results in the fields of photocatalysis and photoelectrocatalysis, the attention has been focused on ferrites as new visible light-active materials [1,2]. Properties such as narrow band gap energies (≈ 2 eV), high stability, abundance, and low cost make ferrites promising for solar energy production and solar remediation. Zinc ferrite (ZnFe2O4) is one of the most widely studied compounds belonging to the spinel ferrite family. However, various and even contradictory results regarding the photocatalytic activity of ZnFe2O4 have been reported in the scientific literature [3]. ZnFe2O4 crystallize in a phase-centered cubic spinel structure with Fe3+ and Zn2+ ions occupying tetrahedral or octahedral sites[1]. When the Fe3+ and Zn2+ ions are arranged in octahedral and tetrahedral sites, respectively, the ferrite exhibits a so-called normal spinel structure (T[Zn]O[Fe2]O4). However, when all the Zn2+ ions at the tetrahedral sites are exchanged by Fe3+ ions from octahedral sites, the compound adopts a so-called inverse spinel structure (T[Fe]O[ZnFe]O4). The degree of inversion, x, defined as the fraction of Zn2+ ions occupying octahedral sites, can consequently adopt values from 0 (normal structure) to 1 (inverse structure) according to T[Zn1-xFex]O[ZnxFe2-x]O4 with 0 ≤ x ≤ 1. The degree of inversion closely depends on the synthetic route.

For the first time, the effect of the degree of inversion on the physicochemical properties affecting the photocatalytic behavior of ZnFe2O4 has been investigated. Interestingly, as the degree of inversion increases, the conductivity of the material increases exponentially and an influence on the photocatalytic activity is observed. Thus, the degree of inversion plays a fundamental role and is a parameter of utmost importance to be investigated in order to get a meaningful approach regarding the photocatalytic performance of spinel ferrites.

 

[1] R. Dillert, D. H. Taffa, M. Wark, T. Bredow and D. W. Bahnemann, APL Materials, 2015, 3, 104001.

[2] D. H. Taffa, R. Dillert, A. C. Ulpe, K. C. Bauerfeind, T. Bredow, D. W. Bahnemann and M. Wark, Journal of Photonics for Energy, 2016, 7, 012009.

[3] A. Arimi, L. Megatif, L. I. Granone, R. Dillert and D. W. Bahnemann, Journal of Photochemistry and Photobiology A: Chemistry, 2018, DOI: 10.1016/j.jphotochem.2018.03.014.

15:15 - 15:30
S2.1-O2
hajiyani, hamidreza
Universität Duisburg-Essen
Origin of Enhanced Efficiency of Tin-doped Ultrathin Hematite Photoanodes for Water-Splitting
hamidreza hajiyani
Universität Duisburg-Essen, DE
Authors
Hamidreza Hajiyani a, Alexander G. Hufnagel b, Siyuan Zhang c, Thomas Bein b, Dina Fattakhova-Rohlfing d, e, Christina Scheu c, Rossitza Pentcheva a
Affiliations
a, Department of Physics, Theoretical Physics and Center of Nanointegration (CENIDE), Universität Duisburg-Essen, Lotharstraße 1, 47057 Duisburg, Germany
b, University of Munich (LMU), Department of Chemistry and Center for Nanoscience (CeNS), 81377 Múnich, Alemania, Múnich, DE
c, Max-Planck-Institut für Eisenforschung GmbH, Max-Planck-Straße 1, 40237 Düsseldorf, Germany
d, Institut für Energie- und Klimaforschung, Forschungszentrum Jülich GmbH, Germany, Wilhelm-Johnen-Straße, Jülich, DE
e, Universität Duisburg-Essen, Germany
Abstract

Using a combination of experimental and theoretical methods we explore the beneficial effect of Sn(IV) doping in ultrathin hematite photoanodes for water oxidation. A series of hematite photoanodes with tailored Sn-doping profiles were prepared by alternating atomic layer deposition. Using data from spectrophotometry and intensity-modulated photocurrent spectroscopy we deconvoluted the overall efficiency and obtained the individual process efficiencies for light harvesting, charge separation and charge transfer. Photoanodes with Sn-doping both on the surface and in the subsurface region show the best performance with enhanced charge separation and charge transfer efficiency. Density functional theory calculations with a Hubbard U parameter were performed to investigate the causes of the efficiency improvement considering both Fe2O3 (0001), as well as Fe2O3 (11-26) surface orientation, as identified from micrographs at atomic resolution. The energetics of surface intermediates during the oxygen evolution reaction reveal that while Sn-doping decreases the overpotential on the (0001) surface, the Fe2O (11-26) orientation shows a significantly lower overpotential, one of the lowest reported for hematite so far. Electronic structure calculations demonstrate that Sn-doping on the surface also enhances the charge transfer efficiency by elimination of surface hole trap states (passivation). Moreover, the subsurface Sn-doping introduces a band bending that helps to improve the charge separation efficiency.

 

We acknowledge funding by SPP1613 and computational time at MagntUDE.

[1] A. G. Hufnagel, H. Hajiyani, S. Zhang, T. Li, O. Kasian, B. Gault, B. Breitbach, T. Bein, D. Fattakhova-Rohlfing, C. Scheu and R. Pentcheva, Adv. Funct. Mater. (accepted).

15:30 - 15:45
S2.1-O3
Eichberger, Rainer
Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Germany
The Transport Pathways of Charge Carriers in CuWO4 for Photocatalysis
Rainer Eichberger
Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Germany, DE
Authors
Sönke Müller a, James Hirst a, Hannes Hempel b, Daniel Peeters c, Alexander Sadlo c, Oliver Mendoza d, Dariusz Mitoraj d, Dennis Friedrich a, Anjana Devi c, Radim Beranek d, Rainer Eichberger a
Affiliations
a, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Germany, Berlin, DE
b, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Germany, Berlin, DE
c, Ruhr-Universität Bochum, Inorganic Materials Chemistry, Universitätsstraße, 150, Bochum, DE
d, University of Ulm, DE, Albert-Einstein-Allee 11, Ulm, DE
Abstract

We report on the carrier transport properties of CVD-grown CuWO4 films for solar water splitting with varying copper-to-tungsten stoichiometry within the borders of the binary metal oxides CuO and WO3. Time-resolved terahertz (TRTC) and microwave conductivity (TRMC) measurements addresses the bulk dynamics in different time windows from sub-ps to ms. In addition, photo-induced absorption (PIA) in a photo-electrochemical cell is applied to study the temporal behavior of excited carriers in the vicinity of the semiconductor/electrolyte interface under varying bias. A charge carrier mobility of ∼6× 103 cm2 V1 s1 and a diffusion length of and 30 nm is determined for a CuWO4 absorber film deposited with a copper-to-tungsten ratio (Cu/W) of 1.1 which also provides the best photocurrents in assembled photo-electrochemical cells. This value is comparable to undoped BiVO4 where poor carrier transport is governed by small polaron formation leading to slow mobility values. We compare the experimental results with measurements performed on dip-coated CuWO4 samples and other metal oxides such as BiVO4 and Cu2O. Our findings establish new insights into the advantages and limits of CuWO4-based photoanodes that can be possibly used in a tandem configuration on top of a highly absorbing semiconductor with optimal electronic properties.

 

[1] D. Peeters,  O. Mendoza Reyes,  L. Mai,  A. Sadlo,  S. Cwik,  D. Rogal, lH.-W. Becker, H. M.  Schütz, J. Hirst, S. Müller, D. Friedrich, D. Mitoraj, M. Nagli, M. Caspary Toroker, R.Eichberger, R. Beranek, A. Devi, J. Mater. Chem. A, adv. article (2018)

[1] M. Ziwritsch, S. Müller, H. Hempel, T. Unold, F. F. Abdi, R. v. d. Krol, D. Friedrich, R. Eichberger, ACS Energy Lett., 1 , 888 (2016)

[2] F. F. Abdi, T. J. Savenije, M. May, B. Dam, R. van de Krol, J. Phys. Chem. Lett. 4, 2752 (2013)

[4] J. Ravensbergen, F. F. Abdi, J. H. van Santen, R. N. Frese, B. Dam, R. van de Krol, J. T. M. Kennis, J. Phys. Chem. C, 118, 27793 (2014)

 

15:45 - 16:00
Discussion
16:00 - 16:30
S2.1-I2
Smirnov, Vladimir
Forschungszentrum Jülich GmbH, DE
Multijunction Si Solar Cells for Integrated Photo-Electrochemical Devices
Vladimir Smirnov
Forschungszentrum Jülich GmbH, DE, DE
Authors
Vladimir Smirnov a, Katharina Welter a
Affiliations
a, Forschungszentrum Jülich, Institute of Energy and Climate Research, IEK-5 Photovoltaics, Wilhelm-Johnen-Straße, Jülich, DE
Abstract

The application of multijunction solar cells in photoelectrochemical (PV-EC) devices for hydrogen production is addressed. Integrated PV-EC devices are composed of a ‘traditional’ photovoltaic (PV) cell combined with an electrochemical (EC) cell, presenting a promising approach to produce hydrogen and other fuels. The requirements for PV-EC devices and strategies for the solar cell development will be discussed. The results on the photovoltaic development of multijunction silicon based cells will be presented, focusing on a wide range of photovoltages and photocurrents in various systems, including the adoption of the cells to function on either cathode or anode sides of the system. A prototype integrated PV-EC system based on silicon multijunction solar cells can yield solar-to-hydrogen efficiencies (STH) of 9.5%.

The paths of device upscaling beyond laboratory size and the influence of varied illumination conditions close to obtained outdoor will also be discussed. This includes the effects of spectral quality, intensity and incident angle on the performance of both photovoltaic cells and PV-EC devices.

16:30 - 16:45
S2.1-O4
Melder, Jens
University of Freiburg, Freiburg Materials Research Center (FMF)
Electrochemical Water Oxidation by MnOx/CFP – pH Dependence of the Catalytic Activity
Jens Melder
University of Freiburg, Freiburg Materials Research Center (FMF), DE
Authors
Jens Melder a, Stefan Mebs b, Philipp Heizmann a, Holger Dau b, Philipp Kurz a
Affiliations
a, Institut für Anorganische und Analytische Chemie und Freiburger Materialforschungszentrum (FMF), Albert-Ludwigs-Universität Freiburg, Albertstraße 21, 79104 Freiburg
b, Freie Universität Berlin, Arnimallee 14, Berlin, DE
Abstract

The efficient catalysis of the four-electron oxidation of water to molecular oxygen (oxygen evolution reaction, OER) is a central challenge for the development of devices for the conversion of electrical energy, ideally from renewable sources, into storable chemical energy (e.g. by electrolysis or “artificial leaves”). Up to now, a plethora of earth-abundant, non-toxic catalysts (e.g. Ni/Fe, Co, Mn oxides)1 for OER is known. Most of these possess high activities and stabilities under strongly alkaline pH conditions. In contrast, the only convincing materials for OER in acidic media are based on the scarce elements Ru and Ir, while especially Ni and Co based electrodes suffer from corrosion and/or show little activity.2

Inspired by the oxygen evolving complex (OEC) of Photosystem II, the biological catalyst for this reaction, several manganese oxide (MnOx) polymorphs have been tested as heterogeneous water oxidation (electro-)catalysts. Here we found that amorphous layered or tunnelled manganese oxides show good activities and stabilities also for strong acidic reaction media.3 Recently, we developed a route to directly prepare coatings of amorphous MnOx on free-standing carbon based electrode supports (e.g. carbon-fiber-paper, CFP) by a simple, scalable redox deposition approach.4

This presentation will deal with a study where the electrocatalytic performance of such MnOx/CFP-anodes was tested under different electrolyte conditions. A special focus was laid on the influence of the pH on activity and stability. Additionally, the MnOx/CFP-electrodes were characterized before and after electrolysis by means of XRD, SEM/EDX, vibrational- and X-ray absorption spectroscopy. Details of the preparation, characterization, electrocatalytic performance and corrosion stability will be discussed together with possible reasons for the different behavior of the electrocatalyst at different pHs. We will report on an efficient catalyst for OER at acidic and near-neutral solution, a pH range highly desirable for (photo-)electrochemical devices, such as polymer electrolyte membrane (PEM) electrolysers or artificial leaves.

References

1 N.-T. Suen, S.-F. Hung, Q. Quan, N. Zhang, Y.-J. Xu and H. M. Chen, Chem. Soc. Rev., 2017, 46, 337–365.

2 L. C. Seitz, C. F. Dickens, K. Nishio, Y. Hikita, J. Montoya, A. Doyle, C. Kirk, A. Vojvodic, H. Y. Hwang, J. K. Nørskov and T. F. Jaramillo, Science, 2016, 353, 1011–1014.

3 C. E. Frey and P. Kurz, Chem. A Eur. J., 2015, 21, 14958–14968.

4 J. Melder, W. L. Kwong, D. Shevela, J. Messinger and P. Kurz, ChemSusChem, 2017, 4491–4502.

16:45 - 17:00
S2.1-O5
Ludwig, Alfred
Ruhr University Bochum, Germany
Combinatorial Fabrication and High-Throughput Characterization of Thin Film Metal Oxide Libraries for Solar water Splitting
Alfred Ludwig
Ruhr University Bochum, Germany, DE
Authors
Alfred Ludwig a, Mona Nowak a, Swati Kumari a, Helge S. Stein a, Ramona Gutkowski b, Joao Junqueira b, Wolfgang Schuhmann b
Affiliations
a, Ruhr-Universität Bochum, Institute for Materials, Universitätsstraße, 150, Bochum, DE
b, Ruhr-Universität Bochum, Analytical Chemistry, Center for Electrochemical Sciences (CES), Universitätsstraße, 150, Bochum, DE
Abstract

Semiconducting metal oxide thin films are promising candidates for photoelectrochemical (PEC) solar water-splitting applications due to their abundance, light absorption properties and stability in aqueous media. To identify materials with optimized properties, thin-film materials libraries, exhibiting combined thickness and compositional gradients, were synthesized by combinatorial reactive co-sputtering from elemental targets on platinized 100 mm diameter wafers in several complex multinary oxide systems: Fe-W-Ti-O, Fe-Cr-Al-O, Cu-Si-Ti-O, V-X-O, and Bi-V-X-O. High-throughput measurements of compositional, structural and functional data on the materials libraries were performed by automated thickness measurements, energy-dispersive x-ray analysis (EDX), X-ray diffraction (XRD) and PEC analyses using an optical scanning droplet cell in 342 measurement areas on each of the materials libraries. Furthermore, the microstructure of selected thin films was characterized by electron and atomic force microscopy. The analysis of the obtained data enables to establish correlations between composition, crystallinity, morphology, thickness, and photocurrent density. Several promising compositions were identified using the combinatorial approach. Furthermore, we demonstrate the combinatorial glancing angle sputter deposition (GLAD) approach for the fabrication of thin film materials libraries consisting of columnar nanostructures.

 
Thu Oct 25 2018
Plenary Session 5
Chair: Daniel Vanmaekelbergh
09:00 - 09:30
5-K1
Kovalenko, Maksym
ETH Zurich and Empa, CH
Colloidal Nanocrystals of APbX3 Perovskites [A=Cs+, CH(NH2)2+, X=Cl-, Br-, I-]: Surface Chemistry, Self-Assembly and Potential Applications
Maksym Kovalenko
ETH Zurich and Empa, CH

Maksym Kovalenko has been a tenure-track Assistant Professor of Inorganic Chemistry at ETH Zurich since July 2011 and Associate professor from January 2017. His group is also partially hosted by EMPA (Swiss Federal Laboratories for Materials Science and Technology) to support his highly interdisciplinary research program. He completed graduate studies at Johannes Kepler University Linz (Austria, 2004-2007, with Prof. Wolfgang Heiss), followed by postdoctoral training at the University of Chicago (USA, 2008-2011, with Prof. Dmitri Talapin). His present scientific focus is on the development of new synthesis methods for inorganic nanomaterials, their surface chemistry engineering, and assembly into macroscopically large solids. His ultimate, practical goal is to provide novel inorganic materials for optoelectronics, rechargeable Li-ion batteries, post-Li-battery materials, and catalysis. He is the recipient of an ERC Consolidator Grant 2018, ERC Starting Grant 2012, Ruzicka Preis 2013 and Werner Prize 2016. He is also a Highly Cited Researcher 2018 (by Clarivate Analytics).

Authors
Maksym Kovalenko a
Affiliations
a, ETH Zurich, Laboratory of Inorganic Chemistry, Department of Chemistry & Applied Biosciences, Vladimir-Prelog-Weg, 1, Zürich, CH
b, EMPA - Swiss Federal Laboratories for Materials Science and Technology, Überland Strasse, 129, Dübendorf, CH
Abstract

Colloidal lead halide perovskite nanocrystals (APbX3, NCs, A=Cs+, FA+, FA=formamidinium; X=Cl, Br, I) emerge as promising materials for optoelectronic applications such as in television displays, light-emitting devices, and solar cells. The sponaneous and stimulated emission spectra of these NCs are readily tunable over the entire visible spectral region of 410-700 nm [1-2]. The photoluminescence of these NCs is characterized by narrow emission line-widths of 12-42 nm, wide color gamut covering up to 140% of the NTSC color standard, and high quantum yields of up to 100%. Cs1-xFAxPbI3 and FAPbI3 reach the near-infrared wavelengths of 800 nm [3].  A particularly difficult challenge lies in warranting the practical utility of such semiconductor NCs in the red and infrared spectral regions. A promising approach lies in the formation of multinary compositions such as CsxFA1–xPb(Br1–yIy)3 NCs. We show that droplet-based microfluidics can successfully guide the synthesis of such complex compositions [4]. We could fine-tune the photoluminescence maxima of such multinary NCs between 700 and 800 nm, minimize their emission linewidths (to below 40nm), and maximize their photoluminescence quantum efficiencies (up to 89%) and phase/chemical stabilities. Most importantly, we demonstrate the excellent transference of reaction parameters from microfluidics to a conventional flask-based environment, thereby enabling up-scaling and further implementation in optoelectronic devices. As an example, CsxFA1–xPb(Br1–yIy)3 NCs with an emission maximum at 735 nm were integrated into light-emitting diodes, exhibiting high external quantum efficiency of 5.9% and very narrow electroluminescence spectral bandwidth of 27 nm.

The processing and optoelectronic applications of perovskite NCs are, however, hampered by the loss of colloidal stability and structural integrity due to the facile desorption of surface capping molecules during isolation and purification. To address this issue, we have developed a new ligand capping strategy utilizing common and inexpensive long-chain zwitterionic molecules, resulting in much improved chemical durability [5].

             Perovskite NCs also readily form long-range ordered asssemblies known as superlattices. These assemblies exhibit accelerated coherent emission (superfluorescence), not observed before in semiconductor nanocrystal superlattices [6].

 

 

L. Protesescu et al. Nano Letters 2015, 15, 3692–3696

M. V. Kovalenko et al. Science 2017, 358, 745-750

L. Protesescu et al. ACS Nano 2017, 11, 3119–3134

I. Lignos et al. ACS Nano 2018, DOI: 10.1021/acsnano.8b01122

F. Krieg et al. ACS Energy Letters 2018, 3, 641–646.

Raino, M. Becker, M. Bodnarchuk et al. 2018, submitted

WatSpl S2.2
Chair: Laurence Peter
09:00 - 09:30
S2.2-I1
Scheu, Christina
Max-Planck-Institut für Eisenforschung Düsseldorf
Nb3O7OH Nanoarrays for Photocatalytic Water Splitting: Defects, Dopants, and Stability of co-Catalysts
Christina Scheu
Max-Planck-Institut für Eisenforschung Düsseldorf, DE

Prof. Christina Scheu has a diploma degree in physics and did her doctorate at the Max-Planck-Institute for Metals Research in Stuttgart (Germany) in the field of material science. She spent two years as a Minerva Fellow at the Technion - Israel Institute of Technology – in Haifa, Israel. 2008 she was appointed as a full professor at the Ludwig-Maximilian-University (Munich, Germany). Since April 2014 she holds a joint position as a full professor at the RWTH Aachen, and as an independent group leader at the Max-Planck-Institut für Eisenforschung GmbH (MPIE) in Düsseldorf Germany. Her expertise is the structural and chemical analysis of functional materials with ex-situ and in-situ transmission electron microscopy and electron energy loss spectroscopy and correlation to optical, electronic and electrochemical properties. The investigated materials range from (photo)catalyst for hydrogen production to electrodes and membranes for polymer based fuel cells.

Authors
Sophia Betzler a, Thomas Gänsler b, Katharina Hengge b, Anna Frank b, Siyuan Zhang b, Christina Scheu b
Affiliations
a, Ludwig Maximilians University (LMU) Munich, Butenandtstr. 11, Munich, DE
b, Max-Planck-Institut für Eisenforschung Düsseldorf, Max-Planck-Straße, 1, Düsseldorf, DE
Abstract

Novel semiconducting nanostructured oxides have gained interest in photocatalytic water splitting where they can act as electrode material. One candidate is the n-type semiconductor Nb3O7(OH), which can be fabricated as 3D nanoarray using a hydrothermal synthesis approach [1]. The 3D nanoarray consists of nanowires arranged perpendicular to each other. The growth defects within the Nb3O7(OH) nanostructure such as stacking faults are the key parameters which determine the functionality as will be discussed in the talk. The nanostructures have been studied in-depth using advanced transmission electron microscopy including electron energy loss spectroscopy to determine the oxidation state of the individual atoms as well as to analyze the band gap on the nanometer scale. In addition, electron tomography and focused ion beam slicing have been used to obtain the 3D morphology of the Nb3O7(OH) array after various growth stages. The functional properties of the Nb3O7(OH) arrays can be improved by the incorporation of Ti within the orthorhombic crystal structure which leads to a higher hydrogen production rate in light driven water splitting experiments [2]. For these measurements, a Pt co-catalyst is deposited on the nanowire array. In order to understand the stability and degradation behavior of the co-catalyst we plan to perform identical location transmission electron microscopy measurements similar as we have done for a Pt/Ru electrocatalyst [3]. Such measurements enable tracking of individual nanoparticles and allow to determine the dominating degradation mechanisms such as catalyst dissolution or Oswald ripening down to the atomic scale. 

[1] S. B. Betzler, A. Wisnet, B. Breitbach, C. Mitterbauer, J. Weickert, L. Schmidt-Mende, and C. Scheu, J. Mater. Chem. A, 2014, 2, 12005.

[2] S. B. Betzler, F. Podjaski, K. Bader, M. Beetz, K. Hengge, A. Wisnet, M. Handloser, A. Hartschuh, B. V. Lotsch, C. Scheu, Chemistry of Materials, 2016, 28, 7666.

[3] K. Hengge, T. Gänsler, E. Pizzutilo, C. Heinzl, M. Beetz, K. J. J. Mayrhofer, C. Scheu, International Journal of Hydrogen Energy 2017, 42 (40), 25359.

[4] The author would like to thank the colleagues and co-workers who contributed to this work and the German Research Foundation (DFG) for financial support.

09:30 - 09:45
S2.2-O3
Ronge, Emanuel
University of Goettingen
In-Situ Transmission Electron Microscopy Analysis of a Calcium-Birnessite Water-Oxidation Catalyst
Emanuel Ronge
University of Goettingen, DE
Authors
Emanuel Ronge a, Vladimir Roddatis a, Jonas Ohms b, Philipp Kurz b, Christian Jooss a
Affiliations
a, University of Goettingen, Friedrich-Hund-Platz 1, Goettingen, DE
b, Albert-Ludwigs-Universität Freiburg, Albertstraße 21, Freiburg, 79104, DE
Abstract

Finding electro-catalysts for driving the oxygen evolution reaction (OER) at the minimum overpotential remains the bottle neck in water splitting. Birnessite is a promising earth-abundant electrode material, since its layered calcium manganese oxide structure with intercalated crystal water possibly allows bulk OER activity [1,2].

We study a nanocrystalline type of highly active electrode, prepared by dropping ink solutions on top of a substrate. The structure of the highly porous electrodes with a grain size down to a few nanometres are analysed with High Resolution Transmission Electron Microscopy (HRTEM) and Selected Area Electron Diffraction (SAED). To gain more information about the mechanism of water oxidation we investigated the interaction of the electrode with the electrolyte. Electron Energy Loss Spectroscopy (EELS) and Energy Dispersive X-Ray Spectroscopy (EDX) indicate an intercalation of the electrolyte cation phosphorous while calcium was depleted from the electrode. The exchange mainly happens at the surface and at grain boundaries.

To further explore the active centres of water oxidation with Birnessite we took steps towards in-situ TEM studies in water vapour. The Environmental TEM (ETEM) offers to investigate Birnessite active states in electric potentials close to operando conditions. Based on our studies we present conclusions on the involved OER mechanism and design strategies for highly active and stable electro-catalysts.

 

[1] S. Y. Lee, D. González-Flores, J. Ohms, T. Trost, H. Dau, I. Zaharieva and P. Kurz, ChemSusChem, 2014, 7, 3442-3451

[2] C. E. Frey and P. Kurz, Dalton Trans. , 2014, 43, 4370-4379

09:45 - 10:00
S2.2-O4
Petersen, Thorben
Carl von Ossietzky University Oldenburg
Quantum Chemical Investigation of Water Splitting on ideal TiO2-Anatase(101)
Thorben Petersen
Carl von Ossietzky University Oldenburg, DE
Authors
Thorben Petersen a, Thorsten Klüner a
Affiliations
a, Carl von Ossietzky University Oldenburg, Carl von Ossietzky Starß2 9-11, Oldenburg, 26129, DE
Abstract

Titania-based photocatalysts represent a promising class of materials to  split water in its elementary components due to their high abundancy and stability [1]. Albeit their low solar visible light exploitation, their crystal  structure and electronic properties are well-known and facilitate the  investigation of the several fundamental aspects involved in photocatalytic water splitting. A detailed understanding of these key steps will subsequently allow for the design of an appropriate photocatalyst.
Most recently, the anatase modification of titanium dioxide (a-TiO2) emerged as a widely applied material since it is the majority phase of TiO2-nanoparticles and shows enhanced photocatalytic activity [1,2]. The intermediates during the water oxidation pathway on the a-TiO2(101) surface were already identified on GGA-PBE level of theory [3]. The key step was determined to consist of the first proton removal induced through a photogenerated hole (H2O + h+ → OH + H+ ). The influence of the photogenerated hole on the dissociation process was addressed controversially by theoretical studies: whereas combined PBE/HSE06 studies indicate that hole-trapping only occurs after dissociation through the OH-anionic species [4], recent work employing the B3LYP functional gives evidence for a concerted proton/hole transfer [5]. In addition, as observed by experimental TPD and TOF methods, OH radicals are found to be ejected from a well-defined a-TiO2(101) surface after irradiation [6].
In order to get a more sophisticated insight into this yet indetermined reaction, we use two different theoretical approaches in this contribution: We firstly identify the active sites of the H2O/a-TiO2 system through periodic slab calculations using hybrid DFT functionals (PBE0/HSE06). Afterwards, these data will provide the basis for an embedded cluster approach allowing for accurate post-HF methods. As a result, we will present potential energy surfaces of a single water molecule on a-TiO2(101).

[1] F. De Angelis, C. Di Valentin, S. Fantacci et al., Chem. Rev. 114 (2014) 9708.
[2] A. Barnard, P. Zapol, L. Curtiss, Surf. Sci. 582 (2005), 173.
[3] Y.-F. Li, Z.-P. Liu, L. Lui, W. Gao, J. Am. Chem. Soc. 132 (2010) 13008.
[4] W.-N. Zhao, Z.-P. Liu, Chem. Sci. 5 (2014) 2256.
[5] C. Di Valentin, J. Phys.: Condens. Matter. 28 (2016) 074002.
[6] Z. Geng, X. Chen, W. Yang et al., J. Phys. Chem. C 120 (2016) 26807.

10:00 - 10:15
S2.2-O1
Fischer, Thomas
University of Cologne
Oxide Bilayers as High Efficiency Water Oxidation Catalysts through Electronically Coupled Phase Boundaries
Thomas Fischer
University of Cologne, DE
Authors
Sanjay Mathur a, Lasse Jürgensen a, Yakup Gönüllü a, Jennifer Leduc a, Thomas Fischer a
Affiliations
a, Department of Chemistry, Inorganic Chemistry, University of Cologne, Greinstr. 6, Cologne 50939, DE
Abstract

New semiconductor metal oxides capable of driving water-splitting reactions by solar irradiation alone are required for sustainable hydrogen production. Whereas most metal oxides only marginally deliver the photochemical energy to split water molecules, uranium oxides are efficient photoelectrocatalysts due to their absorption properties (Eg ~ 2.0 - 2.6 eV) and easy valence switching among uranium centers that additionally augment the photocatalytic efficiency. Although considered a scarce resource, the abundance of uranium compounds in the environment is manifested in the huge quantities of stored UF6 gas, produced as waste streams in the nuclear fuel enrichment process. Here we demonstrate that thin films of depleted uranium oxide (U3O8) and their bilayers with hematite (a-Fe2O3) are high activity water oxidation catalysts due to electronically coupled phase boundaries. The electronic structure of uranium oxides showed an optimal band edge alignment in U3O8//Fe2O3 bilayers (DFT calculations) resulting in improved charge-transfer at the heterojunction as supported by TAS and XAS measurements. The enhanced photocurrent density of the heterostructures with respect to well-known hematite offers unexplored potential of uranium oxide in artificial photosynthesis.

10:15 - 10:30
S2.2-O2
Lukic, Sasa
University of Duisburg-Essen
Generation of Zinc-Gallium-Oxynitride Nanoparticles from CVS Powders for Photocatalytic Water Splitting
Sasa Lukic
University of Duisburg-Essen, DE
Authors
Sasa Lukic a, Jasper Menze b, Martin Muhler b, Markus Winterer a
Affiliations
a, Nanoparticle Process Technology (NPPT), University of Duisburg-Essen, DE
b, Ruhr-University Bochum, Laboratory of Industrial Chemistry, DE
Abstract

The development of semiconductors that split water photocatalytically under visible-light irradiation is a path to the efficient conversion of solar energy. Various oxides with d0 and d10 electron configuration possess such photocatalytic activity, but suffer from poor oxygen and hydrogen evolution or work only in the ultraviolet regime [1]. Domen et. al. developed gallium-oxynitride (Ga1-xZnx)(N1-xOx) as such a material by nitriding mixture of Ga2O3 and ZnO in a solid solution. It is capable of absorbing visible light efficiently with a bandgap of 2,6 eV [2,3].

In the first step we are producing nanoparticles by Chemical Vapor Synthesis. By adjusting process parameters such as temperature, pressure and precursor evaporation rate, we vary the characteristics of the materials, such as: surface area, crystallinity and particle size [1]. Exploiting the advantages of the synthesis from the gas phase we are able to obtain pure phase or mixture of ZnO and β-Ga2O3, as well as the complex spinel phase ZnGa2O4. In second step these powders are nitrided thermally or with assistance of a microwave plasma to obtain the desired oxynitrides. It is known that photocatalytic activity of such a material strongly depends on crystallinity and its composition. Varying the nitridation time from 0.17 h to 10 h zinc and oxygen concentration in zinc-gallium oxyntrides decreases, which is associated with a change in band-gap energy.

Incorporation of nitrogen and elimination of oxygen and zinc during nitridation process should take place at the surface of β-Ga2O3 and ZnO nanoparticles, parallel with diffusion of the constituent ions to form the stoichiometric solid solution. X-Ray diffraction analyzed by Rietveld refinement reveals crystal phases, cell parameters, as well as atomic composition. These results are supported by High-Resolution Scanning-Electron Microscopy in combination with Energy Dispersive Spectroscopy. The specific surface area of the samples is analyzed by using low temperature nitrogen adsorption. The bandgap is determined by using Ultraviolet-visible Spectroscopy.

[1] S. Lukic et al., ChemSusChem, 10, (2017), 4190-4197.

[2] K. Maeda et al., J. Am. Chem. Soc. 127, (2005), 8286-8287.

[3] K. Maeda et al., J. Phys. Chem. B 109, (2005), 20504-20510.

10:30 - 11:00
Coffee Break
WatSpl S2.3
Chair: Bruce Parkinson
11:00 - 11:30
S2.3-I1
Marschall, Roland
University of Bayreuth, Germany
Nanostructured Spinel Ferrite Materials for Photoelectrochemical Water Splitting
Roland Marschall
University of Bayreuth, Germany, DE

Dr. Roland Marschall obtained his PhD in Physical Chemistry from the Leibniz University Hannover in 2008, working on mesoporous materials for fuel cell applications. After a one year postdoctoral research at the University of Queensland in the ARC Centre of Excellence for Functional Nanomaterials, he joined in 2010 the Fraunhofer Institute for Silicate Research ISC as project leader. In 2011, he joined the Industrial Chemistry Laboratory at Ruhr-University Bochum as young researcher. From 07/2013 to 08/2018, he was Emmy-Noether Young Investigator at the Justus-Liebig-University Giessen. Since 08/2018, he is Full Professor at the University of Bayreuth, Germany. His current research interests are heterogeneous photocatalysis, especially photocatalytic water splitting and nitrogen reduction using semiconductor mixed oxides, and synthesis of oxidic mesostructured materials for energy applications.

Authors
Kristin Kirchberg a, Roland Marschall a
Affiliations
a, Justus Liebig University Giessen, Heinrich Buff Ring 58, Giessen, DE
Abstract

We have developed a straightforward microwave synthesis protocol using acetylacetonate and acetate precursors to produce nanocrystals of the earth-abundant cubic spinel ferrites MgFe2O4 and ZnFe2O4[1,2], which are promising materials for both photoelectrochemical and photocatalytic water splitting under visible light irradiation due to their narrow band gaps (~ 2.0 eV) and matching band positions. The crystallite size can be tailored by post-synthetic heat treatment or seed-mediated growth method. Samples were characterized employing transmission electron microscopy (TEM), X-ray diffraction (XRD), dynamic light scattering (DLS), Raman spectroscopy and N2 physisorption, indicating highly-crystalline, single phase nanoparticles with specific surface areas of around 200 m²/g and good colloidal stability in non-polar solvents. Phase transfer into aqueous medium has been performed using different organic capping ligands, resulting in stable dispersions with a narrow size distribution. First results of photocatalytic experiments will be presented.

In addition, well-ordered mesoporous ZnFe2O4 thin films were fabricated by sol-gel synthesis, using a polymer-templating approach previously reported by Haetge et al.[3]. By means of the amphiphilic diblockcopolymer poly(isobutylene)-block-poly(ethylene oxide) (PIB50-b-PEO45), ordered mesopores are obtained after dip-coating by evaporation-induced self-assembly [4] followed by heat treatment. Scanning electron microscopy (SEM) confirms the porous morphology with average pore diameters of 12-15 nm. Raman spectroscopy and XRD Rietveld analysis revealed phase pure ZnFe2O4 with a crystallite size of 15 nm of. Furthermore, photocurrent and Mott‑Schottky measurements were performed at different pH values to determine the flat band potential and photocurrent density of the thin film electrodes calcined at various temperatures.

 

References

[1] C. Suchomski, B. Breitung, R. Witte, M. Knapp, S. Bauer, T. Baumbach, C. Reitz, T. Brezesinski, Beilstein J. Nanotechnol. 2016, 7, 1350

[2] K. Kirchberg, A. Becker, A. Bloesser, T. Weller, J. Timm, C. Suchomski, R. Marschall, J. Phys. Chem. C 121 (2017) 27126−27138

[2] J. Haetge, C. Suchomski, T. Brezesinski, Inorg. Chem. 2010, 49, 11619.

[3] C. J. Brinker et al., Adv. Mater. 1999, 11, 579.

11:30 - 11:45
S2.3-O1
Ahn, Hyo-Jin
A Strategy to Decrease the High Onset Potential of Hematite Photoanodes by Gradient Doping and Decoration with Zn-Co Layered Double Hydroxide
Hyo-Jin Ahn
Authors
Hyo-Jin Ahn a, b, Anandarup Goswami b, Francesca Riboni a, Stepan Kment b, Alberto Naldoni b, Radek Zboril b, Patrik Schmuki a
Affiliations
a, University of Erlangen-Nuremberg, Martensstraße, 7, Erlangen, DE
b, Regional Centre of Advanced Technologies and Materials
Abstract

Over the past years, α-Fe2O3 (hematite) has been considered as a promising photoanode material in photoelectrochemical (PEC) water splitting. In spite of significant success in obtaining relatively high PEC performance, the main drawbacks hindering practical application at hematite are related to an intrinsically poor charge transport and an inferior kinetics of the oxygen evolution reaction on the photoelectrode surface. In this presentation, we will discuss a strategy for reducing onset potential of hematite photoanode by coupling of gradient Sn4+ ion doping and Zn-Co LDH serving as a highly active OER catalyst. The gradient Sn doping in hematite influences the space charge layer (SCL), which is critical for charge separation and thus for an enhanced photoelectrochemical water splitting performance (PEC). The OER catalyst, i.e. Zn-Co LDH nano-sheets have been synthesized by a simple microwave treatment. The synergistic effect of Zn-Co LDH decoration and gradient Sn4+ doping results in decreasing the onset potential of more than 300 mV, from 0.86 VRHE to 0.54 VRHE, and in increasing the photocurrent density from 0.60 mA/cm2 to 2.00 mA/cm2 at 1.50 VRHE. Our approach demonstrates strategies to overcome onset potential limitations as well as poor OER properties of hematite and leads to a remarkably improved PEC water splitting performance.

11:45 - 12:00
S2.3-O2
Nong, Hong Nhan
Technical University of Berlin (TU)
Operando Studies of Hole-Doped IrNiOx core-shell electrocatalysts for Water Oxidation in acidic Environment
Hong Nhan Nong
Technical University of Berlin (TU), DE
Authors
Hong Nhan Nong a, d, Tobias Reier a, Paul Paciok b, Detre Teschner c, d, Marc Heggen b, Valeri Petkov e, Robert Schlögl c, d, Travis Jones d, Peter Strasser a
Affiliations
a, Dept. of Chemistry, Technical University Berlin, Strasse des 17. Juni 124, TC 03, 10623 Berlin, Germany
b, Forschungszentrum Jülich GmbH, DE, Wilhelm-Johnen-Straße, Jülich, DE
c, Dept. of Inorganic Chemistry, Fritz-Haber-Institute of the Max-Planck-Society, Faradayweg 4-6, 14195 Berlin, Germany
d, Max Planck Institute for Chemical Energy Conversion - Mülheim an der Ruhr, Stiftstraße, 34-36, Mülheim an der Ruhr, DE
e, Dept. of Physics, Central Michigan University, Mt. Pleasant, MI 48859, USA.
Abstract

The electro-oxidation of water to oxygen (oxygen evolution reaction, OER) in (photo-)electrolytic devices yields the electrons and protons required to form molecular fuels1,2: This is why it is expected to play a major role in the development of future (photo-)electrochemical energy conversion and storage technologies. However, the slow rate of water oxidation remains a key challenge that requires fundamental understanding and the design of more active and stable OER electrocatalysts3,4.

To further this development, we probe the local geometric ligand environment and the electronic metal states of O-coordinated Ir centers in Ni-leached IrNi@IrOx metal-oxide core-shell nanoparticles5 — one of the most active OER electrocatalysts known to date — under catalytic oxygen evolution condition using operando spectroscopic techniques, resonant high-energy XRD and differential atomic pair correlation analysis, with support of density functional theory (DFT) calculations. Ni-leaching generates lattice vacancies, which in turn produce uniquely shortened Ir-O metal-ligand bonds and an unusually large number of d-band holes in the Ir oxide shell under OER. DFT calculations show this increase in formal Ir oxidation state drives the formation of O 2p holes on the oxygen ligands in direct proximity to lattice vacancies, resulting in the highly covalent and uniquely short Ir-O bonds seen experimentally. We argue the electrophilic character of these ligands renders them susceptible to nucleophilic acid-base-type O-O bond formation at reduced kinetic barriers, resulting in strongly enhanced OER reactivities. Together, our findings advance both our fundamental understanding of the exceptional reactivity of bimetallic core-shell Ir catalysts and provide a roadmap to tailoring of other “hole-doped” core-shell catalysts for water oxidation at a molecular level.

References

Dau, H.; Limberg, C.; Reier, T.; Risch, M.; Roggan, S.; Strasser, P. Chemcatchem 2010, 2, 724.

Olah, G. A.; Goeppert, A.; Prakash, G. K. S. J. Org. Chem. 2009, 74, 487.

Suntivich, J.; May, K. J.; Gasteiger, H. A.; Goodenough, J. B.; Shao-Horn, Y. Science 2011, 334, 1383.

Reier, T.; Nong, H. N.; Teschner, D.; Schlögl, R.; Strasser, P. 2017, 7, 1601275.

Nong, H. N.; Gan, L.; Willinger, E.; Teschner, D.; Strasser, P. Chem. Sci. 2014, 5, 2955.

12:00 - 12:15
S2.3-O3
Toimil-Molares, Maria Eugenia
GSI Helmholtzzentrum
Photoelectrochemical Performance of Arrays of Cu2O/TiO2 and Au/Cu2O/TiO2 Nanowires Fabricated by Electrodeposition
Maria Eugenia Toimil-Molares
GSI Helmholtzzentrum, DE
Authors
Maria Eugenia Toimil-Molares a, Florent Yang a, Dimitri Korjakin a, Christina Trautmann a, b, Christopher Schröck a, b
Affiliations
a, GSI Helmholtz Centre for Heavy Ion Research, Planckstrasse 1, Darmstadt, 64291, DE
b, Institute of Material Science, Technische Universität Darmstadt, Germany, 64287 Darmstadt, Alemania, Darmstadt, DE
Abstract

For semiconductor nanowire structures the ratio of the minority charge carrier diffusion length over the light absorption depth is significantly reduced compared to bulk materials. In addition, nanostructured semiconductors exhibit larger surface-to-volume ratio. The dimensions of the nanostructures and their geometrical arrangement influence relevant processes such as light absorption, as well as charge separation and transport. Ion-track nanotechnology combined with electrodeposition and atomic layer deposition, enables the controlled synthesis of 3D architectures of semiconductor nanostructures with tailored composition, size and density.

Among the various materials studied as photocathodes for solar hydrogen production, Cu2O is a promising candidate with a predicted solar-to-hydrogen conversion efficiency of ~18%. Moreover, Cu2O is cheap, earth-abundant, non-toxic, and is also scalable and compatible with low-cost fabrication processes. Currently, the main challenge for Cu2O-based photocathodes is their chemical instability in aqueous solution, which can be improved by the use of suitable passivation coatings.

Here, we present the synthesis and characterization of two types of semiconductor nanowire-based photocathodes: (i) highly textured single-crystalline p-type Cu2O nanowire arrays prepared by electrodeposition in etched ion-track polymer membranes, (ii) Au/Cu2O core-shell nanowire arrays prepared by electrodeposition of Cu2O on arrays of free-standing single-crystalline Au nanowires. Polymer membranes with controlled nanochannel density (typically 108 - 1010cm-2) and channel diameter (~20 - 250 nm) are fabricated by swift heavy ion irradiation and selective chemical etching. Subsequently, either Cu2O or Au nanowires with lengths up to 10 µm are synthesized by electrodeposition in the etched nanochannels. Optimized deposition conditions yield single-crystalline nanowires of both materials. After electrodeposition, the polymer membranes are dissolved in an organic solvent. The from the template released Cu2O nanowire arrays are directly coated with a thin and conformal TiOpassivation film by atomic layer deposition (ALD). The Au nanowire arrays, in turn, are first coated with a Cu2O layer by electrodeposition and then with a TiOfilm by ALD. For optimization, the thickness of both layers is systematically varied during the synthesis.

The photoelectrochemical performance of both types of nanowire-based photoelectrodes is studied as a function of parameters such as nanowire length, diameter, and density. In particular, the influence of the core-shell geometry, and the resulting minimization of the diffusion length for both minority and majority charge carriers is discussed.

12:15 - 12:30
S2.3-O4
Bubeck, Cora
University of Stuttgart
Perovskite-type Oxynitrides LaTaO2N and LaTaON2 – Synthetic Strategies
Cora Bubeck
University of Stuttgart, DE
Authors
Cora Bubeck a, Marc Widenmeyer a, Gunther Richter b, Mauro Coduri c, Eduardo Salas Colera c, Songhak Yoon a, Frank Osterloh d, Anke Weidenkaff a
Affiliations
a, University of Stuttgart, Institute for Material Science, Stuttgart, Heisenbergstraße, 3, Stuttgart, DE
b, Central Scientific Facility Thin Film Laboratory, Max Planck Institute for Intelligent Systems, Stuttgart, Heisenbergstraße, 3, Stuttgart, DE
c, European Synchrotron Radiation Facility (ESRF), France, Avenue des Martyrs, 71, Grenoble, FR
d, Department of Chemistry, University of California, Davis, One Shields Avenue, Davis, CA, 95616, USA, Davis, US
Abstract

LaTaON21,2 is a well-known perovskite-type material with defined composition, oxidation state, and physical properties, which make it favorable for solar water splitting.3 This Ta5+-containing oxynitride can be synthesized, e.g. from LaTaO4. The crucial synthetic step for perovskite-type oxynitrides is the ammonolysis, typically a thermal treatment in flowing NH3. Several parameters such as temperature and heating ramp, reaction time, and gas flow rate have to be carefully adjusted.4,5 Besides, the anionic composition can be altered via the adjustment of the precursor reactivity. A thorough tuning of all above mentioned parameters allowed us a controlled variation of the anionic composition from LaTaON2 to LaTaO2N. This consequently leads to a reduction of Ta5+ to Ta4+. A great influence of this oxidation state change on the physical properties, particularly the light absorption, the charge separation, and the surface redox activity, is expected.6

References:

(1)         Marchand, R.; Pors, F.; Laurent, Y. Ann. Chim. Fr. 1991, 16, 553–560.

(2)         Marchand, R.; Antoine, P.; Laurent, Y. J. Solid State Chem. 1993, 107, 34–38.

(3)         Liu, M.; You, W.; Lei, Z.; Takata, T.; Domen, K.; Li, C. Chinese J. Catal. 2006, 27 (7), 556–558.

(4)         Ebbinghaus, S. G.; Abicht, H. P.; Dronskowski, R.; Müller, T.; Reller, A.; Weidenkaff, A. Prog. Solid State Chem. 2009, 37 (2-3), 173–205.

(5)         Widenmeyer, M.; Peng, C.; Baki, A.; Xie, W.; Niewa, R.; Weidenkaff, A. Solid Sate Sci. 2016, 54, 7–16.

(6)         Bubeck, C.; Widenmeyer, M.; Richter, G.; Coduri, M.; Salas Colera, E.; Yoon, S.; Osterloh, F.; Weidenkaff, A. in preparation.

12:30 - 14:30
Lunch
14:30 - 16:00
Internal Project Meeting
WatSpl S2.4
Chair: Krishnan Rajeshwar
16:00 - 16:30
S2.4-I1
May, Matthias
Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Germany
Challenges and Opportunities of Water Splitting with Multi-Junction Solar Absorbers
Matthias May
Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Germany, DE

Matthias May studied physics in Stuttgart, Grenoble, and Berlin, with a focus on condensed matter and computational physics. In his diploma thesis (2010), he investigated charge-density wave phase transitions using photoelectron spectroscopy. For his PhD studies at Humboldt-Universität zu Berlin and Helmholtz-Zentrum Berlin on III-V semiconductors for solar water splitting, he won a scholarship of Studienstiftung des deutschen Volkes. He received his PhD end of 2014 and worked in his first postdoctoral position on high-efficiency water splitting. From 2016 to 2018, he was postdoctoral fellow at the Chemistry Department of the University of Cambridge, funded by the German Academy of Sciences Leopoldina, modelling optical properties of solid-liquid interfaces. His main scientific interests lie in the area of highly correlated electron systems and semiconductor-interfaces, both from an experimental and modelling perspective.

Authors
Matthias M. May a, b
Affiliations
a, University of Heidelberg, Im Neuenheimer Feld, 267, Heidelberg, DE
b, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Germany, Berlin, DE
Abstract

Fossil fuels need to be replaced quickly and on a large scale to render our energy system compatible with current greenhouse gas emission targets. The scale of the transition is enormous and makes efficiency a key factor for its feasibility. The required pace of the transition, on the other hand, renders the modification of materials, that are already established in photovoltaics, for use in solar water splitting devices attractive.

In the case of light-driven water splitting, multi-junction absorbers are essential to provide enough photovoltage and -current for efficiencies beyond 10%. Challenges arising from the distribution of the solar spectrum over multiple sub-cells include appropriate internal band alignment, spectral shaping by (metallic) co-catalysts and the electrolyte as well as the reduction of reflection losses. In this talk, I will discuss current developments in the field of high-efficiency, immersed water splitting systems of currently up to 19% solar-to-hydrogen and outline the route towards efficiencies beyond 20%. Furthermore, I will outline the impact of efficiency on the potential of photoelectrochemical systems as a negative emission technology.

16:30 - 16:45
S2.4-O1
Pedesseau, Laurent
INSA, FOTON, UMR CNRS 6082
GaP Template on Si for Solar Water Splitting: Surface Energy Engineering
Laurent Pedesseau
INSA, FOTON, UMR CNRS 6082, FR

Dr Pedesseau is an Associate Professor at the INSA Rennes (FOTON Institute - CNRS) whose work is aimed at the understanding of physical processes in the III-V semiconductor nanostructures for silicon photonics, the hybrid perovskites and novel materials for photovoltaics, and optoelectronic device simulations for optical-communications. His recent scientific interests include: 1) polar surface and interface energies of semiconductors; 2) first principles simulation (including the spin-orbit effect) of mechanical stability, electronic, and optical properties of 3D and 2D semiconductors; 3) electronic structure theory beyond the DFT such as hybrid functionals (HSE), many-body corrections GW, and DFT-1/2; 4) HPC technology for exotic and highly demanding simulations in terms of the large memory footprint and extensive CPUs communications (thousands).

Authors
Laurent Pedesseau a, Ida Lucci a, Simon Charbonnier b, Maxime Vallet c, Pascal Turban b, Yoan Leger a, Tony Rohel a, Nicolas Bertru a, Antoine Létoublon a, Jean-Baptiste Rodriguez d, Laurent Cerutti d, Eric Tournié d, Anne Ponchet c, Gilles Patriarche e, Charles Cornet a
Affiliations
a, Univ Rennes, INSA Rennes, CNRS, Institut FOTON - UMR6082, France, FR
b, Institut de Physique de Rennes, CNRS, Université de Rennes 1, Rennes, FR
c, CEMES-CNRS Université de Toulouse UPS 29 rue Jeanne Marvig BP 94347 Toulouse, Cedex 04, France
d, IES Univ. Montpellier CNRS 860, France, Rue de Saint - Priest, Montpellier, FR
e, Centre de Nanosciences et de Nanotechnologies site de Marcoussis CNRS Université Paris Sud Université Paris Saclay route de Nozay 91460 Marcoussis, France
Abstract

The hydrogen production will play a major role for the energy transition. Recently, for water splitting context [1], [2], a demonstration of the efficiency enhancement of BiVO4 photoanodes has been shown in PEC devices[3] by simply a texturation of surfaces. Moreover, in the study of the semiconductor photocatalyst materials[4], GaP semiconductor appears to be a good candidate for photoelectrode in PEC devices[5]. One strong argument is to have at least 1.73 eV photopotential requirements for water splitting and its bandgap is larger and about 2.26 eV.

In this aim of water splitting applications, we propose a surface energy engineering for a large scale textured GaP template monolithically integrated on Si [6]. Based on experimental analysis and theory, the stability of the {114} facets is scrutinized by scanning tunneling microscopy images and also supported by density functional theory calculations. We then show that change of the surface energy for experimentally promoting the GaP(114) surface texturation can be achieved through (i) destabilizing the GaP(001) surface by using a vicinal Si substrate or through (ii) favoring the {114} facets formation by changing the group-V atmosphere above the surface on a miscut-free GaP substrate.

This work is supported by the French National Research Agency project ANTIPODE (Grant no. 14-CE26-0014-01) and Région Bretagne. The ab initio simulations have been performed on HPC resources of CINES under the allocation 2017-[x2017096724] made by GENCI (Grand Equipement National de Calcul Intensif).

[1] M. G. Walter et al., ‘Solar Water Splitting Cells’, Chem. Rev., vol. 110, no. 11, pp. 6446–6473, Nov. 2010.

[2] A. Fujishima and K. Honda, ‘Electrochemical Photolysis of Water at a Semiconductor Electrode’, Nature, vol. 238, no. 5358, p. 37, Jul. 1972.

[3] J. Zhao et al., ‘High-Performance Ultrathin BiVO4 Photoanode on Textured Polydimethylsiloxane Substrates for Solar Water Splitting’, ACS Energy Lett., vol. 1, no. 1, pp. 68–75, Jul. 2016.

[4] A. Kudo and Y. Miseki, ‘Heterogeneous photocatalyst materials for water splitting’, Chem. Soc. Rev., vol. 38, no. 1, pp. 253–278, 2009.

[5] E. E. Barton, D. M. Rampulla, and A. B. Bocarsly, ‘Selective Solar-Driven Reduction of CO2 to Methanol Using a Catalyzed p-GaP Based Photoelectrochemical Cell’, J. Am. Chem. Soc., vol. 130, no. 20, pp. 6342–6344, May 2008.

[6] I. Lucci at al., ‘A Stress‐Free and Textured GaP Template on Silicon for Solar Water Splitting’, Adv. Funct. Mat. Hot Topic: Water Splitting, 1801585, 2018

16:45 - 17:00
S2.4-O2
Cendula, Peter
University of Zilina
Elucidation of Photovoltage Enhancements and Charge Transport in Multijunction Cu2O Photocathode through Semiconductor Simulations
Peter Cendula
University of Zilina, SK
Authors
Peter Cendula a, Matthew T. Mayer b, c, Jingshan Luo d, Linfeng Pan e, Michael Grätzel b
Affiliations
a, University of Zilina, kpt. Nalepku 1390, L.Mikulas, SK
b, Laboratory of Photonics and Interfaces, Institute of Chemical Sciences and Engineering, École Polytechnique Fédérale de Lausanne (EPFL), Switzerland, Station 6, CH-1015 Lausanne, Lausanne, CH
c, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Germany, Berlin, DE
d, Nankai University, 94 Weijin Road, Nankai District, Tianjin 300071, CN
e, Ecole Polytechnique Federale de Lausanne (EPFL), Lausanne, CH
Abstract

Unassisted water splitting by this approach requires efficient, stable and low-cost photoelectrode materials. Of the material candidates for photocathodes, Cu2O stands out as best performing oxide for hydrogen production currently available. Although numerous experimental investigations greatly enhanced performance and stability of Cu2O photocathode, there is lack of detailed theoretical understanding of charge 
transport mechanism in Cu2O buried junction photocathodes. On the macroscopic scale within the drift-diffusion approximation of charge transport in semiconductors, device simulation studies so far studied Cu2O photovoltaics. The charge transport in photoelectrochemical Cu2O buried junctions has not been addressed so far by device simulation study.

In our work, we discuss existing belief that separation of the valence band of p-type Cu2O to conduction band of n-type buffer layer limits the available photovoltage, providing example calculation with Al:ZnO buffer layer, which does not follow this rule. To explain the measured low photovoltage obtained with Al:ZnO buffer layer, we identify recombination at defect-rich Al:ZnO/Cu2O interface as a responsible mechanism. Furthermore, our device simulations of onset voltage of TiO2/Ga2O3/Cu2O photocathode correspond well with the measured value. We describe how the two energy barriers for electron transport at Cu2O/Ga2Oand at TiO2/Ga2Ointerfaces cause anodic shift of the onset voltage. Numerical quantification of the drift and diffusion currents throughout the TiO2/Ga2O3/Cu2O photocathode brings us to conclusion that electron diffusion in Cu2O bulk close to Cu2O/Ga2O3 dominates the electron current at the onset voltage. Variation of electron affinity, mobility and doping of Ga2O3 buffer layer in our model result in important improvements on onset voltage up to 1.65 V vs RHE and ratiometric power-saved of the Cu2O photocathode, providing future ideas for experimental developments.

17:30 - 19:00
Poster session
 
Fri Oct 26 2018
Plenary session 6
Chair: Sascha Sadewasser
09:00 - 09:30
6-K1
Leite, Marina
University of California Davis
Probing Solar Cells at the Nanoscale through Real-Time Functional Imaging
Marina Leite
University of California Davis, US

Leite is an Associate Professor in Materials Science and Engineering at UC Davis. Her group investigates materials for energy harvesting and storage, from their nano-scale structural, electrical, and optical properties to their implementation in devices. Before joining UC Davis, Leite was an associate professor at the University of Maryland, she worked for two years at NIST and was a post-doctoral scholar at Caltech (Department of Applied Physics and Materials Science). She received her PhD in physics from Campinas State University in Brazil and the Synchrotron Light Source Laboratory. Leite's work has been recognized on the cover of ~30 scientific journals, by the presentation of >140 invited talks, by the 2016 APS Ovshinsky Sustainable Energy Fellowship from the American Physical Society (APS) and the 2014 Maryland Academy of Sciences Outstanding Young Scientist Award. Leite’s research has been funded by the National Science Foundation (NSF), the Army Research Office (ARO), the Defense Advanced Research Projects Agency (DARPA), etc.

Authors
Marina Leite a
Affiliations
a, University of Maryland, 2123 Chemical and Nuclear Engineering Building, College Park, 20742, US
Abstract

Our constantly increasing society’s need for energy has triggered a pressing need for the development of new materials for renewable sources. Concerning materials for energy harvesting, the most promising approaches for high-performance and low-cost photovoltaics rely in inhomogeneous compounds, such as perovskites and polycrystalline thin films (e.g. CIGS and CdTe). Thus, resolving their electrical and optical behavior at the nanoscale is imperative to advance their understanding. In this talk, I will share our scientific findings to image and quantify the local voltage response of nano- and mesoscale inhomogeneities in perovskites [1,2], CIGS [3], and CdTe through a variant of KPFM and NSOM [4-6]. By submitting the samples to illumination and humidity treatments under controlled conditions, we map the dynamic physical behavior of MAPI and triple-cation perovskites.

 

References:

[1] J. M. Howard et al. J. Phys Chem Letters, in press (2018)

[2] J. L. Garrett et al. Nano Letters 17, 2554 (2017).

[3] E. M. Tennyson et al. ACS Energy Letters 1, 899 (2016).

[4] E. M. Tennyson et al. ACS Energy Letters, 2, 2761 (2017). Invited Review

[5] E. M. Tennyson et al. ACS Energy Letters 2, 1825 (2017). Invited Perspective

[6] E. M. Tennyson et al. Advanced Energy Materials 5, 1501142 (2015).

WatSpl S2.5
Chair: Roland Marschall
09:30 - 10:00
S2.5-O1
Peter, Laurence
University of Bath
Understanding the Role of Nanostructuring in Photoelectrode Performance for Light-Driven Water Splitting
Laurence Peter
University of Bath, GB

Laurie Peter received his B.Sc. and Ph.D. from the University of Southampton (UK). After a period working at the Fritz Haber Institute in Berlin in the group of the late Heinz Gerischer, he returned to the Southampton before moving to the University of Bath, where he has been Professor of Physical Chemistry since 1993. He partially 'retired' in 2009 and is currently spending 6 months at the Ludwig Maximillian University in Munich working in the group of Professor Thomas Bein. Laurie Peter's interest sinclude fundamental studies of dye-sensitized solar cells (DSCs), research into inorganic thin film solar cells based on sustainable materials such a copper zinc tin sulfide and photoelectrochemical water splitting. He has developed a number of experimental techniques such as intensity modulated photocurrent spectroscopy (IMPS) and charge extraction that are used to characterize DSCs and water splitting systems. He has also developed in situ microwave methods for investigating photoelectrochemical reactions. At present he is attempting to understand the kinetics and mechanisms of light-driven oxygen evolution at iron oxide electrodes.

Authors
Laurence Peter a, - Gurudayal c, Lydia Helena Wong c, Fatwa Abdi b
Affiliations
a, Department of Chemistry, University of Bath, Claverton Down, University of Bath, Bath,UK, BA2 7AY, GB
b, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Germany, Berlin, DE
c, Nanyang Technological University (NTU), Singapore, SG
Abstract

 

Understanding water splitting at nanostructured electrodes presents some formidable challenges. Here, regular nanostructured photoelectrodes are considered using hematite nanorod arrays as an example. Since Mott Schottky plots are often reported for nanostructured electrodes, we revisit the effects of the cylindrical nanorod geometry on the capacitance-voltage behaviour. The limiting case of complete depletion is discussed in terms of the residual geometric capacity at the base of the nanorods. Since nanorod arrays generally leave areas of the substrate exposed, it is also necessary to consider the parallel capacitance associated with the fraction of uncovered surface. We then turn to the enhancement of external quantum efficiency (EQE) achieved by nanostructuring, again using hematite nanorod arrays as experimental examples. We show that, although very substantial EQE enhancement should be achieved by simple geometric effects, the performance of nanostructured hematite electrodes in the visible region of the spectrum is considerably lower than predicted if all charge carriers generated in the space charge region (SCR) were collected. Further analysis reveals that the internal quantum efficiency increases with photon energy, suggesting that the probability of generating free, rather than bound, electron-hole pairs in hematite depends on the excess energy hν - Egap.

  

10:00 - 10:15
S2.5-O2
Selim, Shababa
Imperial College London, United Kingdom
Investigating the Influence of Nanostructuring on Photoanode Performance
Shababa Selim
Imperial College London, United Kingdom, GB
Authors
Shababa Selim a, Laia Francas a, Camilo Mesa a, Andreas Kafizas a, Dongho Lee b, Kyoung-Shin Choi b, James R. Durrant a
Affiliations
a, Department of Chemistry, Imperial College London, South Kensington Campus London, London, GB
b, Department of Chemistry, University of Wisconsin–Madison, Madison, WI 53706, USA
Abstract

The performance of semiconducting materials as photoanodes is continually optimised overtime. With the aid of nanostructuring, noteworthy performance enhancements for the water oxidation reaction are obtained when coupled with electrocatalysts such as FeOOH/NiOOH and Co-Fe Prussian Blue.1,2 In the longstanding compromise between the light penetration depth and charge diffusion lengths, nanostructuring provides an effective tool. However, it is not often efficacious unless coupled with co-catalyst or in presence of hole scavengers. This highlights the presence of significant surface recombination that is especially critical for kinetically demanding reactions such as the four hole oxidation of water, requiring the accumulation of holes on the surface.

In this talk, we will discuss the structure performance relationship between densely packed and mesoporous structures of bismuth vanadate alongside other n-type materials such as titania and hematite. Using techniques such as transient photocurrent measurements (TPC) and photo induced absorption spectroscopy (PIAS), we can directly probe the influence of porosity and increased surface area on electron transport and photo-catalysis.

 

References:

1         T. W. Kim and K.-S. Choi, Science (80-. )., 2014, 343, 990–994.

2         F. S. Hegner, I. Herraiz-Cardona, D. Cardenas-Morcoso, N. López, J. R. Galán-Mascarós and S. Gimenez, ACS Appl. Mater. Interfaces, 2017, 9, 37671–37681.

10:15 - 10:30
S2.5-O3
Xi, Fanxing
Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Germany
Activation of amorphous MoSx as a hydrogen evolving catalyst in aqueous electrolysis
Fanxing Xi
Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Germany, DE
Authors
Fanxing Xi a, Peter Bogdanoff a, Sebastian Fiechter a
Affiliations
a, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Germany, Berlin, DE
Abstract

Solar water splitting is a sustainable and in principle environmentally sound approach to solve the high energy demand of mankind using renewable energies[1], because of the high energy density of hydrogen and no CO2 emission when used as a fuel. To provide hydrogen in large quantities, nontoxic, earth abundant and cheap catalysts are in demand to replace costly platinum for reducing the overpotential in the hydrogen evolving reaction (HER) process[2].

In our study, molybdenum sulfide layers of different crystallinity and morphology have been prepared by reactive magnetron sputtering and tested as HER catalyst. Best performance was obtained starting from an amorphous MoSx layer deposited at room temperature on FTO (η10=180mV at pH 0 sulfuric acid electrolyte), which in Raman spectroscopy shows similar vibrations as the highly efficient HER catalyst, (NH4)2Mo3S13[3]. However, during electrochemical measurement, production of hydrogen was proved along with the release of H2S especially during the first 20min of CV (activation step). Afterwards, only hydrogen was evolved from the electrode. A structural change of the material from amorphous MoSx to MoS2 layered structure happens during CV was proved by Raman measurement with the disappearance of terminal and bridging [S2]2- units and the emergence of the characteristic vibration mode A1g (out of plane S bonding) from layer structured MoS2. Mo atoms at the edges of formed MoS2 nano-islands are oxidized to Mo(VI) after removal from the electrolyte. From the ratio of Mo (IV) to Mo(VI) in the XPS spectra, the size of MoS2 nano-islands could evaluated. The high number of this Mo atoms at the edges explains the good performance of the HER electrode. For stability test, room temperature sputtered MoSx electrode was measured under CV conditions for 10h exhibiting an increase in overpotential of 46 mV.

1.            Lewis, N.S. and D.G. Nocera, Powering the planet: chemical challenges in solar energy utilization. Proc Natl Acad Sci U S A, 2006. 103(43): p. 15729-35.

2.            McCrory, C.C., et al., Benchmarking hydrogen evolving reaction and oxygen evolving reaction electrocatalysts for solar water splitting devices. J Am Chem Soc, 2015. 137(13): p. 4347-57.

3.            Kibsgaard, J., T.F. Jaramillo, and F. Besenbacher, Building an appropriate active-site motif into a hydrogen-evolution catalyst with thiomolybdate Mo3S13 (2-) clusters. Nature Chemistry, 2014. 6(3): p. 248-253.

WatSpl S2.6
Chair: Matthias May
11:00 - 11:30
S2.6-O1
Rajeshwar, Krishnan
University of Texas, Arlington,US
New Families of Ternary Rare Earth Chalcogenides for Photoelectrochemical Applications
Krishnan Rajeshwar
University of Texas, Arlington,US, US
Authors
Krishnan Rajeshwar a
Affiliations
a, University of Texas, Arlington,US, US
Abstract

Even after ca. four decades of R&D effort, we still do not have a "magic bullet" inorganic semiconductor to photoelectrochemically generate fuels or chemicals from sunlight in a sustainable, efficient and environment-friendly manner. While it is unlikely that a single semiconductor candidate will emerge that simultaneously satisfies all the optical, electrical, surface chemical, and electrochemical prerequisites for efficient solar conversion, complex oxides or chalcogenides (or derivatives thereof, e.g., oxynitrides) do provide a versatile framework for rational design of the "perfect beast" in a chemical architectural sense. Ultimately two or more such semiconductor compositions can be combined in a composite design much like complementary functionalities are combined in photosynthetic assemblies in Nature. In such designs, the semiconductor(s) and the photoactive junction can even be separated from the electrolyte and the electrocatalyst component in a "buried junction" design. In this vein, the author's laboratory has been engaged in the development of time- and energy-efficient methods for synthesizing new families of photoelectrode or photocatalyst materials. In this particular talk, the author will provide first a context for the key role that solid-state chemistry paradigms and principles can play in photoelectrode designs for driving multi-electron processes typical of solar fuel generation. A representative ternary semiconductor system, namely, M-Ln-X (M = divalent metal, e.g., Ba, Ln = lanthanide element, e.g., Ce, and X = chalcogen, e.g., S) will be discussed in this talk.

11:30 - 11:45
S2.6-O2
Schuhmann, Wolfgang
Ruhr University Bochum, Germany
Improving the Photoelectrocatalytic Activity of Metal-Doped BiVO4-Based Photoabsorbers by Means of Oxygen Evolution Co-Catalysts
Wolfgang Schuhmann
Ruhr University Bochum, Germany, DE
Authors
Wolfgang Schuhmann a, Ramona Gutkowski a, Joao Junqueira a, Tim Bobrowski a, Olga Krysiak a
Affiliations
a, Ruhr-Universität Bochum, Analytical Chemistry, Center for Electrochemical Sciences (CES), Universitätsstraße, 150, Bochum, DE
Abstract

The recombination of photogenerated electron-hole pairs is one of the major limiting factor in photo­electrocatalysts absorbing in the visible region of the solar spectrum. The performance as expressed by the incident photon-to-current efficiency (IPCE) strongly depends on the loading and thickness of the active material. Especially for BiVO4 the slow electron transport to the back contact facilitates charge carrier recombination and thus does not allow to exploit the entire potential of the photo­absorber. Hence, thin layers are favoured to avoid excessive charge carrier recombination, however, on the expense of a low absorption of the incident light with the result of low photocurrent output of such electrodes.

We present the development of different strategies to address the limitations evoked by charge carrier recombination of BiVO4-based photoabsorbers. The electrochemically-induced deposition of Pt-nanoparticles enhanced the contact between electrochemically deposited BiVO4 films and fluorine doped tin oxide (FTO) electrodes which showed significantly lower recombination rates during frontside illumination1. Modifications of BiVO4 films by doping with different metals showed enhancements of the IPCE by more than 30% at 1.2 V vs. RHE for Mo/Zn and Mo/B doped systems during light driven oxygen evolution reaction (OER)1. High-throughput screening showed highest improvement of photocurrents by a factor of 10 for Bi(V-Mo-X)O4 material libraries as compared to a BiVO4 reference material2. To further improve the performance of BiVO4-based photoabsorbers a systematic characterisation of different co-deposited OER catalysts onto pre-modified Mo-doped BiVO4 films was performed revealing the necessity for an optimal deposition technique and loading of the co-catalyst in question such as electrodeposition, photoassisted electrodeposition and photo­deposition. Moreover, an alternative technique for simple electrode preparation and modification based on an air brush-type spray-coater system is proposed which allows to easily tune the layer thickness of photoabsorber films and is able to deposit gradients of additives or OER co-catalysts. Using the spray-coating technique in combination with an optical scanning droplet cell allowed for a quick and easy but precise tuning of the investigated systems for further enhancing the performance of BiVO4-based photoabsorbers.

References

R. Gutkowski, D. Peeters, W. Schuhmann, J. Mater. Chem. A, 2016, 4, 7875–7882.

R. Gutkowski, C. Khare, F. Conzuelo, Y. Kayran, A. Ludwig, W. Schuhmann, Energy Environ. Sci., 2017, 10, 1213–1221.

Acknowledgements

The authors are grateful to the financial support of the DFG within the framework of the SPP1613 (SCHU929/12-1 and 12-2).

11:45 - 12:00
S2.6-O3
Gimenez Julia, Sixto
Universitat Jaume I, Institute of Advanced Materials (INAM) - Spain
Water oxidation with metal oxide semiconductor materials
Sixto Gimenez Julia
Universitat Jaume I, Institute of Advanced Materials (INAM) - Spain, ES

Sixto Giménez (M. Sc. Physics 1996, Ph. D. Physics 2002) is Associate Professor at Universitat Jaume I de Castelló (Spain). His professional career has been focused on the study of micro and nanostructured materials for different applications spanning from structural components to optoelectronic devices. During his PhD thesis at the University of Navarra, he studied the relationship between processing of metallic and ceramic powders, their sintering behavior and mechanical properties. He took a Post-Doc position at the Katholiek Universiteit Leuven where he focused on the development of non-destructive and in-situ characterization techniques of the sintering behavior of metallic porous materials.  In January 2008, he joined the Group of Photovoltaic and Optoelectronic Devices of University Jaume I where he is involved in the development of new concepts for photovoltaic and photoelectrochemical devices based on nanoscaled materials, particularly studying the optoelectronic and electrochemical responses of the devices by electrical impedance spectroscopy. He has co-authored more than 80 scientific papers in international journals and has received more than 5000 citations. His current h-index is 31. 

Authors
Sixto Gimenez Julia a, MIguel García-Tecedor a, Drialys Cardenas-Moscoso a, Roser Fernández-Climent a
Affiliations
a, Universitat Jaume I, Institute of Advanced Materials (INAM) - Spain, Avinguda de Vicent Sos Baynat, Castelló de la Plana, ES
Abstract

The development of photoelectrochemical strategies for the production of added-value chemicals and fuels using solar light is particularly attractive to overcome the dependence of fossil fuels at a global scale.[1] Specifically, the photoelectrochemical oxidation of H2O to produce solar H2 as a clean energy vector or valuable chemical precursor stands out as one of the most promising approaches in this direction. Different approaches have been followed to achieve competitive devices, targeting Solar To Hydrogen (STH) efficiency of 10%, durability of 10 years and cost of 2-4 $/kg of dispensed Hydrogen.[2] For this purpose, the use of low-cost, earth-abundant, stable materials synthesized by easily up-scalable methods is essential.[3] In the present talk, we will discuss about the suitability of earth-abundant metal oxides to achieve these targets. Different examples of the synergistic combination of metal oxides (Fe2O3[4], and BiVO4[5],[6]) with catalytic layers (Fe-Co Prussian Blue, Ag3PO4, etc…) will be described, emphasizing the mechanistic insights leading to enhanced performance. Our studies focus on the correlation of the photoelectrochemical response of the materials with a detailed structural and mechanistic characterization carried out by different microscopic and spectroscopic tools.

12:00 - 12:30
S2.6-O4
Parkinson, Bruce
University of Wyoming
The Past, Present and Future of Solar Fuels
Bruce Parkinson
University of Wyoming, US
Bruce Parkinson received his BS in chemistry at Iowa State University in 1972 and his PhD from Caltech in 1977 and was a post-doctoral scientist at Bell Laboratories in 1978. He then spent time at the Ames Laboratory and the Solar Energy Research Institute (now known as the National Renewable Energy Laboratory). He moved to the Central Research and Development Department of the DuPont Company in 1985 and in 1991 he became Professor of Chemistry at Colorado State University until his recent departure to join the Department of Chemistry and the School of Energy Resources at the University of Wyoming. His current research covers a wide range of areas including materials chemistry, surface chemistry and photoelectrochemical energy conversion. He has more than 220 peer-reviewed publications and holds 5 US patents.
Authors
Bruce Parkinson a
Affiliations
a, Department of Chemistry, University of Wyoming, Laramie, WY, USA, Laramie, Wyoming 82071, EE. UU., Laramie, US
Abstract

The interest in the direct storage of solar energy as a chemical fuel in a semiconductor based photoelectrochemical system started with the demonstration of solar photoelectrolysis of water with large band gap oxide semiconductor electrodes in the late 1970s. In the last decade or so there has been both and increased interest and increased funding towards achieving a goal of efficiently producing cost effective fuels from solar energy with either water or carbon dioxide as a feedstock. This talk will review the progress towards this goal considering recent developments. One of these developments is that the cost of photovoltaic systems has been decreasing rapidly to where currently the cost of the solar panels is now exceeded by balance of systems cost. The cost of electrolyzers will be also decrease as they are improved and scaled. Connecting these two existing technologies has the advantage of producing hydrogen where and when it is needed and at pressure. These facts mean that the window for direct solar photoelectrolysis is rapidly closing. One possible breakthrough is that a new stable, efficient, inexpensive, defect-tolerant and scalable new materials are identified that can quickly improve the efficiency of photoelectrolysis much like the hybrid perovskites are have done for photovoltaic devices. This talk will review the progress in combinatorial approaches to discover new materials for photoelectrolysis with some examples including one from the Solar Hydrogen activity Research Kit (SHArK) Project, a distributed science project that provides undergraduates and high school students with the resources to produce and screen metal oxide semiconductors for photoelectrolysis activity. In addition the reasons for producing hydrogen from water rather than direct carbon dioxide reduction to produce fuels will be reviewed. A new system for storing solar energy directly as redox equivalents, a solar chargeable redox flow battery, will also be introduced and its advantages and disadvantages compared to solar hydrogen generation will be discussed.

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