The rising share of renewable electricity is testament to the increasing importance of solar/wind-electric routes to harvest sun light in form of potential differences and flowing free electrons. While some electricity is used directly or stored capacitively, an increasing portion calls for direct conversion into valuable molecular solar fuels or chemicals. This conversion in the dark is made possible by heterogeneous electrocatalysis on the surface of solid electrodes. Electrocatalysis at the electrode surface orchestrates the stepwise making or breaking of molecular chemical bonds by means of electronic charge transfer across the electrified solid electrode/electrolyte interface. Kinetic barriers of elementary reaction steps – associated with suboptimal chemisorption or stabilization of intermediates – typically limit the efficiency of the overall reaction process. Fundamental understanding of the origin of the kinetic barriers arising along the reaction coordinate aids in the design of more efficient, tailor-made electrochemical interfaces.

In this presentation, I will report on recent advances in our understanding of “dark” electrocatalytic materials, interfaces and mechanisms relevant to the conversion of solar energy into value-added molecular compounds, using, among others, in-situ/operando X-ray spectroscopic, microscopic, scattering or spectrometric techniques. Examples include the electrochemistry of small molecules as they occur in low-temperature water- and CO₂ electrolyzers.

The electroreduction of CO2 to chemicals has the potential to enable a transition from fossil to renewable sources in the vast chemical industry – for example to produce clean fuels and materials for manufacturing. The technoeconomic viability of the CO2 reduction (CO2R) technology depends on achieving sufficient product selectivity, productivity (or current density), energy efficiency, and stability. I will present recent advances that, based on the manipulation of catalyst environment, achieve CO2R to key multicarbon chemicals such as ethylene, ethanol, and propanol at high selectivity and productivity. With these increasing performance metrics, a crucial limiting factor in the CO2R technology is CO2 reactant loss – a result of rapid carbonate formation in alkaline and neutral electrolytes – which brings additional energy penalties. To conclude, I will provide an overview of some emerging strategies to address this challenge.                             

Graphitic materials are largely explored as redox-active supports for metal species in acid/base catalysis, redox catalysis and electrocatalysis. [1] Edge terminations and in-plane point defects, such non 6-membered rings and vacancies on the basal planes of the graphene layers can be functionalized with other heteroatoms, such as O, N, B and P for anchoring metal active species. Of interest, N species offer opportunities for the enhancement of a generally poor stability of these metal species on carbon supports as well as a tuning of the reactivity and selectivity. Thus, offering a platform for comparative mechanistic studies aimed at aiding materials design. In this contribution I will present on the dynamics of metal species on various carbon supports, with focus on Fe and Cu systems, during electrocatalytic CO2 reduction as monitored in recent work [2] by complementary surface and bulk sensitive in situ X-ray Spectroscopy.] These dynamics are correlated to the electrocatalysts´ performances to develop robust structure/function relationships. The discussion will be centred on the nature of the active sites as well as the beneficial role of the N species.

During recent years, 2D Surface Optical Reflectance (2D-SOR) [1,2] microscopy [3] has emerged as a valuable surface characterization tool for model catalysts or electrodes [4] when performing operando investigations in harsh environments. In particular, 2D-SOR microscopy is favorably used as a complementary technique to other photon-in-photon-out techniques which do not carry direct information on the surface 2D morphology. In this presentation we will present the development and examples of 2D-SOR instrumentation and investigations from single and poly-crystalline samples in combination with Planar Laser Induced Fluorescence (PLIF) [2, 3], High Energy Surface X-Ray Diffraction (HESXRD) [5,6,7] and Polarization Modulation-Infrared Reflection Absorption Spectroscopy (PM-IRRAS) [8] coupled to Mass Spectrometry (MS) and Cyclic Voltammetry (CV) in thermal catalysis, electrocatalysis and corrosion.

Illustrating examples of the versatility of the technique will be shown including reflectance changes during the thermal CO oxidation over Pd(100) and Pd polycrystalline surfaces. We show that reflectance changes during the reaction can be associated with the formation of thin Pd oxides by the combination of 2D-SOR and Surface X-Ray Diffraction (SXRD). The combined measurements demonstrate a sensitivity of 2D-SOR to the formation of a 2-3 Å thin Pd oxide film.

During Cyclic Voltammetry (CV) in an acidic electrolyte using a Au(111) surface as an electrode, we show that the differential of the change in 2D-SOR reflectance correlate to various current features in the CV curve. This observation can be used to differentiate current features in the CV curve from a polycrystalline Au surface, demonstrating that the different grains contribute to the current at different potentials due to the different surface orientations.

Finally, we show that 2D-SOR is a cheap and useful technique to investigate the corrosion of applied materials such as duplex stainless steels and Ni alloys.

Graphics: a) The 2D-SOR experimental setup for thermal catalysis. b) Side view of the electrochemical flow-cell showing the electrode configuration and a window at the top for the 2D-SOR LED light.

References

[1] W. G. Onderwaater et al Rev. Sci. Instrum., 88 (2017) 023704.

[2] J. Zhou et al, J. Phys. Chem. C 121 (2017) 23511.

[3] S. Pfaff et al, ACS Appl. Mater. Interfaces 13 (2021) 19530.

[4] W. Linpe, et al, Rev. Sci. Instrum., 91 (2020) 044101.

[5] S. Pfaff, et al Rev. Sci. Instrum. 90 (2019) 033703.

[6] S. Albertin, et al, J. Phys. D: Appl. Phys. 53 (2020) 224001.

[7] W. Linpé, et al J. Electrochem. Soc. 168 (2021) 096511.

[8] L. Rämisch et al, Appl. Surf. Sci. 578 (2022) 152048

The improvement of spectroscopic techniques has enabled the in situ characterization of catalysts under operating conditions, often revealing a highly dynamic behavior of the active phase. For example, metals and metal-oxides usually employed as catalysts frequently undergo significant chemical and structural transformations during operation. In contrast, the conceptual framework and structural models used to rationalize the catalytic properties of such materials has traditionally relied on a rather static picture of the catalyst substrate. In addition to this so-called environmental complexity, the structural complexity of such these nanostructured materials further hinders the characterization of their response to reaction conditions [1].

Establishing reliable structural models of working catalysts is particularly relevant in computational modeling studies relying on quantum mechanical calculations. To overcome these challenges, novel computational approaches have been developed to determine the structure and composition of targeted materials and conditions, combining quantum mechanics, structure prediction (i.e. global optimization) algorithms, ab initio thermodynamics, and, more recently, also machine-learning methods [2].

During my talk, I will introduce some of these approaches and showcase their capacity by presenting different case studies involving the characterization of the structure and oxidation states of technologically relevant catalytic materials [3, 4].  

Oxide-derived copper electrodes have displayed a boost in activity and selectivity toward valuable base chemicals in the electrochemical carbon dioxide reduction reaction (CO2RR), but the exact interplay between the dynamic restructuring of copper oxide electrodes and their activity and selectivity is not fully understood. In this contribution, the utilization of time-resolved surface-enhanced Raman spectroscopy (TR-SERS) during CO₂ electroreduction will be discussed, which shows the dynamic restructuring of the copper (oxide) electrode surface and the adsorption of reaction intermediates during cyclic voltammetry (CV) and pulsed electrolysis (PE). By coupling the electrochemical data to the spectral features in TR-SERS, we studied the dynamic activation of and reactions on the electrode surface and find that CO₂ is already activated to carbon monoxide (CO) during PE (10% Faradaic efficiency, 1% under static applied potential) at low overpotentials (−0.35 VRHE). PE at varying cathodic bias on different timescales revealed that stochastic CO is dominant directly after the cathodic bias onset, whereas no CO intermediates were observed after prolonged application of low overpotentials. An increase in cathodic bias (−0.55 V_RHE) resulted in the formation of static adsorbed CO intermediates, while the overall contribution of stochastic CO decreased. The low overpotential CO₂-to-CO activation is attributed to a combination of selective Cu(111) facet exposure, partially oxidized surfaces during PE, and the formation of copper-carbonate-hydroxide complex intermediates during the anodic pulses. This work sheds light on the restructuring of oxide-derived copper electrodes and low-overpotential CO formation and highlights the power of the combination of electrochemistry and time-resolved vibrational spectroscopy to elucidate CO2RR mechanisms.

In catalysis and energy conversion, fundamentals behind poor charge transfer, electrode corrosion or moderate catalytic activity and selectivity remain elusive. Conventional techniques cannot spatially resolve performance-determining properties of electrode-electrolyte interfaces, particularly local electric conductance in liquids, thus hindering rational innovation of key catalytic reactions.

We introduce in situ correlative atomic force microscopy for simultaneously imaging an electrode’s conductivity, chemical-frictional and morphological properties. We visualize conductivity variations across electrocatalyst surfaces, which were chosen with a view to CO₂ electroreduction. For bimetallic copper(oxide) - gold electrocatalysts in air, water and bicarbonate electrolyte, current-voltage curves show highly resistive copper(oxide) islands, in agreement with current contrasts. For nanocrystalline gold, we observe current contrasts that indicate resistive grain boundaries, electrocatalytically passive adlayer regions and hydration layer heterogeneities. The combined measurement of the friction force with the current provides the opportunity to interrogate the hydration layer and analyse its effect on the interfacial electron transfer, as the hydration layer molecular ordering may modulate both the mechanical resistance to the tip sliding motion and the electric resistance. In the light of the implemented in situ microscopy method, we outline prospects for establishing structure-property relationships but also for fundamental studies beyond (photo)electrocatalysis, e.g. to investigate solid-liquid interfaces in electrochemical energy storage systems.

The electrochemical CO₂ reduction can be a key technology for a fossil free future but for industrial applications it is necessary to analyse and understand the cathode. As one of the main problems is the low utilization efficiency of CO₂ in AEM approaches due to the carbonate formation we have to find solutions to solve carbonate formation by maintain high selectivity.

In this work we investigated NiNC cathode GDEs for CO₂ reduction to CO in a zero-gap MEA cell regarding their activity in a classic AEM and CEM approach. We show that the CO₂ access of the catalyst is important to achieve high performances. In an AEM approach with near neutral conditions on the anode we can reach 85% FE towards CO at 300 mA cm^-2 at 3.6 V with single pass conversion of 40% which is close to the theoretical maximum. In addition, we can report high energy efficiency but only a utilization efficiency of around 50%.

Our newly introduced CCC value give information about the consumption of CO₂ by the produced OH^- during the CO2RR. The CCC value in combination with the selectivity enable insights in the mass transfer during the CO₂ reduction in an AEM setup and get information about the accessibility of the catalyst and we can monitor the flooding.

On the other Hand, we show that our NiNC GDE is stable under acidic conditions in a PEM zero-gap cell. We added a protective layer on our catalyst to remain a local high pH at our active sites to maintain selectivity towards CO. The protons help to increase the utilization efficiency as the carbonate will react back to CO₂ and water to 100%. Therefore, we investigated the activity with DI water and diluted H₂SO₄ at the anode. In pure water, 0.01 and 0.1M H₂SO₄ we can achieve a selectivity above 80% towards CO at 100 mA cm^-2 with cell potentials around 3 V which are comparable to the AEM configuration with 0.1M KHCO₃.

The CCC value is in the perfect case 0 as we do not consume any additional CO₂ but can indicating flooding as the CCC is rising. This indicates water accumulation which can hinder the neutralization of the carbonate/OH^- and CO₂ will be consumed.

To mitigate excess anthropogenic carbon dioxide emissions (~4 GtC yr⁻¹) and realise the Paris Agreement on the climate change agenda of 2⁰C target, circular carbon economy is considered an impactful technology which is getting cheaper with decreasing costs of renewable energies. Converting CO₂ into methanol which can be used as a fuel for methanol fuel cells or to upscale for different factory chemicals, currently derived from fossil fuels, can help in achieving net-zero or negative emissions^[1]. Electrochemical carbon dioxide reduction (ECO2R) is paired with an anodic half-reaction which is limited by high overpotentials and low stability^[2]. An efficient anodic valorisation process integrated with ECO2R is crucial for small cell voltage and long-lasting devices. Oxygen evolution reaction (OER) is the most common anodic half-reaction paired with ECO2R. In a membrane electrode assembly, anodic reaction releases electrons and protons that are used at the cathode to reduce CO₂ and higher O₂ generation rate modulates the ECO2R towards higher faradaic efficiency.

One of the constraints for OER is the stability of the electrocatalyst at high current densities, which corrodes to form an inactive surface layer which limits currents or leaches out into the alkaline/neutral solution. Here, we co-electrodeposited thin films of poly-metal oxides of Ni, Fe and Cu^[3] from a slightly acidic solution through pulsed currents on Tantalum foil. These poly-metal oxide-based films were analysed in 1M KOH and recorded an overpotential of 270 mV for a benchmark current of 10 mA/cm² and cell voltage of 1.83 V (RHE) at 100 mA/cm² current stable for 25 hours of the OER process.

To mitigate the corrosion of metal substrates with KOH, which can lead to decrease in OER activity, we have deposited a range of Cu, Fe, and Ni-based catalysts on highly conductive substrates such as Ni foam and porous carbon papers to enhance current density and stability simultaneously. We have also deposited Mxenes, polyvinylidene fluoride (PVDF) and other piezoelectric functional coatings on poly-metal oxides thin films to induce piezopotential through mechanical deformation of coatings by the anolyte flow. This extra potential is aligned in a direction to lower the overpotential and enhance the stability of CuFeNi electrocatalysts for both alkaline and near-neutral OER. We will also present our studies on the impact of the anodic environment on the selectivity and activity of copper-based catalysts for ECO2R to frame a roadmap for anodes in alkaline and polymer electrolyte membrane CO₂ electrolysers. Our study will pave the way toward the fabrication of next generation electrochemical system for sustainable direct CO₂ capture and utilization/storage as clean solar fuel.

Understanding Pt surface oxidation is of key importance for the development of durable oxygen reduction reaction catalysts as used in low temperature fuel cells. The formation of an ultra-thin surface oxide on Pt electrodes causes atomic-scale restructuring of the electrode surface and Pt dissolution, which promotes the degradation of Pt-based catalysts. However, the precise role of the Pt surface oxides during Pt dissolution is still unclear, although a strong influence is evident, since dissolution mostly occurs transiently during oxide formation and reduction [1,2]. For a better understanding of Pt dissolution and Pt electrode restructuring, a detailed atomistic picture of the oxide structure is required, which only existed previously for the Pt(111) electrode [3,4].

In this study, we have used high energy surface X-ray diffraction [5,6] to analyse the atomic-scale surface structure of Pt(111) and Pt(100) during oxide formation and reduction in 0.1 M HClO₄ and 0.1 M H₂SO₄. These surfaces exhibit distinct differences in stability versus restructuring after oxidation/reduction cycles. For example on Pt(111), almost no surface roughening can be observed even after oxidation at potentials of up to 1.15 V, while Pt(100) immediately degrades upon oxidation. The Pt dissolution mirrors this trend and is one order of magnitude higher on Pt(100) as shown in our complementary dissolution measurements using inductively coupled plasma mass spectrometry [6]. To elucidate this difference we performed a detailed analysis of the crystal truncation rods from the onset of oxide formation up to the onset of oxygen evolution to determine the location and potential-dependent coverage of the Pt atoms in the oxide on Pt(100). Two phases of Pt oxides were found, a stripe-like oxide consisting of Pt rows [6] and an amorphous oxide at a higher vertical distance from the surface. Based on the geometry of these oxides we were able to find an oxide growth mechanism for Pt(100) which inherently leads to surface roughening and thereby explains the difference in structural stability. Comparison of the coverage of the two oxide phases with the corresponding dissolution reveals a correlation of the dissolution during oxide formation and reduction with either of the two oxide phases.

Alkaline water electrolysis is one of the simplest methods used for renewable hydrogen production [1]. In contrast to electrolyzers relying on acidic electrolytes, alkaline electrolyzers reach high conversion efficiency with abundant metals such as Ni-Fe alloys [2]. The outstanding properties can be mainly traced back to the host material Ni, which is both stable and electro-catalytically active in alkaline media. We demonstrate that this peculiarity can be related to its ability to form various compounds with hydrogen and oxygen (NiO, Ni(OH)₂, NiOOH), which are known to stabilize Ni when in contact with electrolyte solutions as categorized in equilibrium Pourbaix diagrams. However, the surface is subject to a dynamic equilibrium, and the presence of specific phases depends on the presently applied conditions as well as on the history of the sample. We give a comprehensive overview of the evolution of the oxy-hydroxide surfaces from the ultrahigh vacuum clean Ni surface to water and oxygen gas exposure, liquid water contract, and under electrochemical conditions. Bridging these informations requires the use of APXPS setup at the Swiss Light Source [3] and a combination of soft- and hard x-ray photoelectron spectroscopy with electro-chemical impedance spectroscopy. Main outcome is that the high intrinsic electronic conductivity comes together with an increasing water intercalation into the oxy-hydroxide, which is experimental evidence for a water mediated OH^- diffusion mechanism.

Understanding the nature of the active site and the reaction mechanisms is crucial for the design of cost-effective and highly efficient (electro)catalysts for the energy transition. Despite its relevance, the complexity of catalytic systems and the time scale of (electro)chemical reactions hinder gaining atomic level insights on the reaction intermediates under the catalyst operating conditions. In this talk we show how by combining first principles calculations with experimental characterization it is possible to unambiguously identify the active sites and the reaction intermediates at the surface of perovskite oxide ABO3 catalysts. Specifically, we show how by tuning the oxide electronic structure with A-site substitution, the reaction mechanism for the oxygen evolution reaction can be modified from a mechanism centered on the B-site to a mechanism involving the lattice oxygen, and we discuss the implication for the oxide electrocatalytic activity and stability [1, 2]. Moreover, we further demonstrate that the lattice oxygen activity, which is determined by the position of the oxygen electronic states, is linked to the catalytic activity for the NO oxidation reaction on La_1−xSr_xCoO₃ perovskites, where La_0.8Sr_0.2CoO₃ presents the highest intrinsic activity, comparable to state-of-the-art catalysts, thanks to the optimal binding energy of NO to the lattice oxygen site for this composition which maximizes the oxidation kinetics [3]. These results show the critical role of the catalyst electronic structure in determining reaction mechanisms and catalytic activity, providing a framework for the rational design of novel oxide catalysts.

In situ characterization of electrochemical processes in model materials are central to fundamental electrochemistry as they provide precise potential-dependent quantities that can be used to accurately assess theoretical models and predictions. As such, structural evolution of materials under highly oxidizing conditions represents a particular challenge. To gain the necessary insight into the surface and bulk behavior, one should combine advanced in situ characterization techniques with well-defined materials that are essential for modeling.

In this talk, I will discuss how a combination of in situ microscopy techniques can provide insight into the surface and bulk behavior of electrocatalysts during electrocatalytic water splitting (OER). Specifically, I will show how operando electrochemical atomic force microscopy (EC-AFM) can be used to record nanoscale changes in the surface morphology during anodic corrosion of the perovskite SrIrO₃ surface. I will also discuss how operando EC-AFM can be combined with other microscopy techniques to probe the evolution and reactivity of single particles of Co(OH)₂. Additionally, I will briefly cover the state of the art in operando microscopy and relevant experiments for electrocatalysis.

The charge transport properties in solids play an important role in the selection of materials for electrochemical devices. Spinels are a special class of solids that are very versatile and possess different properties based on changes in stoichiometry and cation distribution. In that way, their properties can be tailored to fit certain uses. Here we report a density functional theory study of the electronic structures of nine normal and inverse ternary AB₂O₄ (A, B = Fe, Co, Ni, Mn) and A₃O₄ spinels. Bulk-based band alignment results are also reported for the spinels in this work in order to design materials with preferred charge transport pathways.

References:

Y. Elbaz, A. Rosenfeld, N. Anati, M. Caspary Toroker, “Electronic structure study of various transition metal oxide spinels reveals a possible design strategy for charge transport pathways”, J. Electrochem. Soc. 169 (4), 040542 (2022).

A. Bhargava, C. Y. Chen, K. Dhaka, Y. Yao, A. Nelson, K. D. Finkelstein, C. J. Pollock, M. Caspary Toroker, and R. Robinson, "Mn cations control electronic transport in spinel CoxMn3-xO4 nanoparticles", Chemistry of Materials 31(11), 4228 (2019).

A. Bhargava, R. Eppstein, J. Sun, M. A. Smeaton, H. Paik, L. F. Kourkoutis, D. G. Scholm, M. Caspary Toroker, R. D. Robinson, “Breakdown of the small-polaron hopping model in higher-order spinels”, Adv. Mat., 2004490 (2020).

R. Eppstein and M. Caspary Toroker, “On the interplay between oxygen vacancies and small polarons in manganese iron spinel oxides”, ACS Materials Au 2, 269 (2022).

Photoelectrochemical (PEC) water splitting combines light absorption and electrocatalysis into the same device or material. In so-called "emerging" materials systems, which are less well characterized and understood, it is often unclear where the problem lies when the performance begins to decay with time. The light absorber material itself could be changing, resulting in a decaying photovoltage output, or the surface catalyst may be changing in some may, reducing its efficacy. We have developed a novel implementation of the dual working electrode (DWE) technique that can deconvolute the photovoltaic performance from the surface catalytic performance under normal water splitting conditions (i.e., operando), in order to identify the problematic part of the device. I will then discuss our work towards developing a suitable model for electrochemical impedance spectroscopy (EIS) of multilayered photocathode materials, where the processes taking place in each layer can be characterized and the problematic interfaces can be identified, enabling optimization. Examples of interface treatments that improve the performance of thin film-based water splitting photoelectrodes, such as the deposition of molecular dipole layers, will also be discussed.

Using renewable energy to convert carbon dioxide to fuels and chemical is a goal pursued worldwide, but neither electro- nor photocatalytic processes have reached a maturity that would invite their application on the industrial scale. Performance, stability, and selectivity issues occur in either process option to different extents. Although progress is reported in the scientific literature almost daily, fundamental insight is still lacking that would allow a knowledge-driven improvement of photo- and electrocatalysts.

As will be shown in the current contribution, systematic studies in photocatalysis are severely hindered by the non-standardized and often irreproducible reaction conditions. Therefore, standardization approaches were undertaken that use, as a prerequisite, high-purity reaction conditions free of any (carbon-)impurity. Using, in addition, reaction engineering tools known from classical catalysis allows to determine the interdependence of yields and selectivity on the reaction conditions. This is not only a first step towards an understanding of the reaction fundamentals, but also builds a bridge towards machine learning approaches for (photo)catalyst improvement.

It will be shown that despite its absorption in the UV range, titania is still the best performing semiconductor for photocatalytic carbon dioxide reduction. However, oxidation and reduction reaction are inherently coupled because the pathway from carbon dioxide to methane on the titania surface also contains oxidative elementary steps involving photogenerated holes. On bare titania, methane and oxygen thus cannot be formed at the same time. Other approaches are needed in which new catalytic active sites allow a continuous reduction sequence. Furthermore, it will be shown how reduction and oxidation reaction can be separated onto different semiconductors in Z scheme and heterojunction systems, which also allows the development of switchable photocatalyst composites.

Strongly correlated compositions catalyse the most important reactions for life and are the future of greener catalysis. The understanding of quantum correlations within catalysts is an active and advanced research field, necessary when attempting to describe all the relevant electronic factors in catalysis. In our research, we concluded that the most promising electronic interactions to improve the optimization of technological applications based on magnetic materials are quantum spin exchange interactions (QSEI), nonclassical orbital mechanisms that considerably reduce the Coulomb repulsion between electrons with the same spin. QSEI can stabilize open-shell orbital configurations with unpaired electrons in magnetic compositions. These indirect spin-potentials significantly influence and differentiate the catalytic properties of magnetic materials. As a rule of thumb, reaction kinetics (thus catalytic activity) generally increase when interatomic ferromagnetic (FM) interactions are dominant, while it sensibly decreases when antiferromagnetic (AFM) interactions prevail. The influence of magnetic patterns and spin-potentials can be easily spotted in several reactions, including the most important biocatalytic reactions like photosynthesis, for instance. Moreover, we also add the concept of quantum excitation interactions (QEXI) as a crucial factor to establish the band gap in materials and as a key factor to efficiently mediate electron transfer reactions. In this talk, we will show a general conceptual overview on the importance of strongly correlated electrons and their interactions during catalytic events. We will present the physical principles and meanings behind quantum exchange in a way that facilitates a comprehensive understanding of the electronic interactions in catalysis from their quantum roots; we explore the issue via mathematical treatment as well as via intuitive visual space/time diagrams to expand the potential readership beyond the domain of physicists and quantum chemists.

Conversion of CO₂ to multi-carbon products using renewable electricity is a viable strategy to reduce the greenhouse gas effects and produce high-value chemicals in a sustainable manner. However, the commercial viability of this process is severely affected due to the low selectivities, or faradaic efficiencies (FEs) of the hydrocarbons and alcohols produced. Even though there has been a lot of research towards finding better catalysts for converting CO₂ to C₂₊ products selectively, copper remains the state-of-the-art catalyst for this conversion[1]. Recent work has shown that larger hydrocarbons beyond C₂ can be formed on oxide-derived Cu and Ni catalysts with non-trivial faradaic efficiencies (~25%) [2,3]. This remains a widely underexplored area and holds great prominence due to the high value of C₃₊ products, which can further improve the economics of e-CO2RR. Even though promising, the reaction mechanisms for C₃₊ product formation involve large reaction networks with several surface intermediates (>100). In addition, electrolyte effects including pH and cation are found to influence the CO₂ activation and C-C bond formation reaction steps [1]. Therefore, in this study, we develop a detailed microkinetic model to first understand the reaction mechanism towards the various C₂ and C₃ products on Cu catalysts. We also test the influence of cations on the rate determining steps to evaluate their effect on different product selectivities. 

Firstly, we identified all the possible reaction paths for the C₂₊ products using an in-house graph-theory based algorithm ‘r-net’. We then found all the unique sites on the Cu (100) and automatically placed the reaction intermediates on the identified sites using the ‘catkit’ algorithm. Once the transition state energies were evaluated, all the energetics data has been stored in a python-based ASE database. This database serves as an input for our microkinetic modelling code ‘pyMKM’. The initial results from the model showed that most abundant surface intermediate is CO* for which the coverages are high. Hence, we performed a coverage dependent analysis on the most important reaction intermediates and reaction steps that are found through the degree of rate control analysis. Additionally, we evaluated the effect of cations on these pathways through which the lower on-set potential of C₂ products as compared to C₁ products was correctly predicted. The selectivity determining C-C bond steps that lead to propanol formation have also been ascertained. The ultimate aim of the study would be to further evaluate the identified pathways on oxide-derived Cu models to understand the influence of Cu oxidation state towards selectivity of hydrocarbon products. 

Multi-Scale modeling has been the standard to explain and predict activity and selectivity of chemical reactions during the last 20 years^[1,2]. This procedure allowed us to predict semiquantitatively the activity trends, recovering the classical volcano plots. The later models lead to successful catalyst optimization using a reduced set of energy descriptors. However, the accuracy of Multi-Scale modeling confronts several limitations with complexity, mainly caused by the coverage effects, the catalyst phase or surface reconstructions, large reaction networks, and highly dynamic materials^[1-3]. Statistical Learning (SL) techniques can overcome such limitations. Nevertheless, the black-box nature of most of the SL techniques hinders the physical interpretation of the results. In this work, we present a procedure to generate physical interpretable models able to correlate experimental activity and selectivity with ab-initio Density Functional Theory (DFT)-based descriptors. Here, we applied our methodology on the CH2X2 (X=Cl, Br) hydrodehalogenation reaction family catalyzed by transition metals^[3].  Even if this study is based on thermochemical systems, it provides a starting point to solve more complex chemical problems, such as explaining the dynamic charge exchange of single metal atoms on Ceria^[4] or electrochemistry.

One of the main obstacles in the implementation of hydrogen fuel cells (HFC) lies in the efficiency loss due to the overpotential of the oxygen reduction reaction (ORR). Nowadays, one of the best catalysts for cathodes in HFC are Pt-Co nanostructures [1], as confirmed by commercially available Fuell Cell Vehicles (FCV) (https://www.toyota-europe.com/download/cms/euen/Toyota%20Mirai%20FCV_Posters_LR_tcm-11-564265.pdf). The superior activity of these magnetic Pt-alloys, compared to metallic platinum, correlates with the milder chemisorption of the oxygenated intermediates on the surfaces of the alloy.

We present a study on magnetic Pt₃Co(111) nanostructures conducted via spin-polarized DFT+U calculations (PBEsol). The study begins with a detailed structural screening of Pt₃Co slab models with different atomic distributions. The outcome of this screening highlights that the most stable atomic arrangement is an ordered structure with a multilayer organization between the magnetic and the nonmagnetic components (the same trend is observed in magnetic Pt₃Fe(111) and Pt₃Ni(111)) [2,3]. The chemisorption enthalpy value of O* atoms on the most stable AFM (A-type) and FM nanolayers show weaker binding of the adsorbate compared to isostructural Pt(111) materials [3]. Chemical effects and magnetic effects are so analysed and quantified to understand the origin of this milder chemisorption values. From this analysis cooperative spin potentials, associated with open-shell orbital configurations such as Pt₃Co(111), emerges as active actors in determining the chemisorption properties of magnetic catalysts [2,3]. Moreover, these cooperative spin potentials unequivocally lead to decreased enthalpies of adsorption for O* atoms [2,3].

Hence, a complete and realistic treatment of the structure−activity relationships in heterogeneous catalysis relies upon the correct evaluation of orbital magnetism: spin-dependent potentials are key factors to design optimal ORR catalysts.

Artificial photosynthesis, inspired by natural photosynthesis, is considered a promising technology to store solar energy into chemical bonds, such as NH₃, H₂ or carbon-based fuels via (photo)electrochemical water splitting, ammonia reduction or CO₂ reduction. This process is usually limited by the oxidation reaction taking place at the photoanode, in particular n metal-oxide photoanodes. The photoelectrochemical performance of these photoanodes vary depending on their synthetic route and post-synthesis treatment that can lead to crystal defects such as oxygen vacancies. However, the chemical nature of such oxygen vacancies and their role in photoelectrochemical oxidation of water or organic substrates to produce high added-value chemicals is still in debate.

In this talk, I will present a spectroscopic, microscopic and electrochemical analysis of the chemical nature of light-induced oxygen vacancies in one of the most studied photoanodes such as BiVO₄. Oxygen vacancies in these BiVO₄ photoanodes were produced by light exposure treatments and are associated with the migration of Bi towards the surface forming nanoparticles.^[1] Additionally, I will show the role of oxygen vacancies in the photoelectrochemical behaviour of BiVO₄, WO₃^[2] and a-Fe₂O₃^[3] photoanodes and their role in the water oxidation mechanism as example.

Converting solar energy into chemical commodities (such as, hydrogen, hydrocarbons) via photoelectrochemical devices has become the topic of vital importance, since such a technique provides an efficient strategy for addressing solar energy intermittency problem and supplying feedstocks to the commodity chemicals industry on a global scale. Employing organic conjugated semiconductors in photoelectrochemical devices, including small molecules, linear polymers and covalent organic frameworks (COFs), is attracting an increasing interest in recent years, due to their tunable optoelectronic properties at the atomic level.[1] So far, developing molecular designs and photoelectrode architectures toward achieving comparable performance and stability with inorganic counterparts remains as the major task of organic photoelectrodes. In this presentation, strategies for advancing the performance and operational stability of organic photoelectrodes will be discussed.[2, 3] The deactivation pathway of organic semiconductors for photoelectrochemical application is studied by in-situ spectroelectrochemical characterizations. Furthermore, a novel approach for fabricating high quality COF thin films and constructing donor polymer/COF heterojunction based photocathode for solar-to-hydrogen conversion will also be presented.[4]