The large library of two-dimensional materials can be exploited to master interface properties of perovskite solar cells. Here, I will present the results of the use of 2D materials in perovskite cells, modules and panels. In particular I will focus on a new class of 2D, namely Titanium Carbide MXenes (such as Ti3C2). Beside exceptional chemical and mechanical properties, MXenes offer a wide tunabilty of work function (WF) by varying their surface termination. WF can ranges from ≈2 eV (for OH-termination) to ≈6 eV (for O-termination). In particular, by producing well exfoliated Ti₃C₂Tx MXenes with a relatively low WF (~3.7eV) we demonstrate the capability to tune both perovskite absorber and electron transporting layer (ETL) WFs.[1] This strategy has been applied to nip [1] and pin [2] cells structure and exploited on large area modules [3]. We show that MXene interface engineering used on the n side of pin cell (NiO/perovskite/C60/BCP/Cu) permitx to increase enormously the stability of the cell with a T90 exceeding the 2000 h under continuous light soaking at Maximum Power Point (in ambient conditions) and T80>1000h for thermal stress (85 °C). [4]

The use of a combination of 2D materials to improve performance and stability of perovskite technology has been extended to panels (9 panels of 0.5 sqm each) that have been tested for more than a year in a Solar Farm in Crete.[5] The results of this outodoor test in a real environment will be presented and performance and stability will be discussed.

Using green energy or increasing energy efficiency is the key to a sustainable world.  2D materials can be used to build a sustainable world in terms of low-cost H₂ generation, low-power-consuming devices, and IA-enabled optimization of novel materials. In this talk, I will briefly discuss how we use 2D materials as an ideal platform to explore the mechanism of semiconducting catalysis. 

It is known that semiconducting catalysts are great candidates to replace noble metals to make green energy such as H₂ due to their low cost. Using 2D materials as the model system, we revisited the semiconductor-electrolyte interface and unraveled a universal self-gating phenomenon through micro-cell-based measurements. [1] We unveiled a surface conductance mechanism that dominates the charge transport in semiconductor electrocatalysts. Based on this, we provided a guideline on how to design a high-performance semiconductor electrocatalyst. We also demonstrate the synthesis of amorphous PtSex and its use in high-performance electrocatalyst. [2]

Breakthrough discoveries in high-throughput formulation of abundant materials and advanced engineering
approaches are both in utter need as prerequisites for developing novel large-scale energy conversion
technologies required to address our planet’s rising energy demands. Nowadays, the rapid deployment of
Internet of Things (IoT) associated with a distributed network of power-demanding smart devices,
concurrently urges for miniaturized systems powered by ambient energy harvesting. Graphene and other
related two-dimensional materials (GRM) consist a perfect fit to drive this innovation owing to their
extraordinary optoelectronic, physical and chemical properties that emerge at the limit of two-dimensions.
In this review, after a critical analysis of GRM’s emerging properties that are beneficial for power generation,
novel approaches are presented for developing ambient energy conversion devices covering a wide range
of scales. Notable examples vary from GRM-enabled large-scale photovoltaic panels and fuel cells, smart
hydrovoltaics and blue energy conversion routes, to miniaturized radio frequency, piezoelectric, triboelectric,
and thermoelectric energy harvesters. This presentation will focus on GRM-enabled energy
harvesters that have the potential to revolutionize the way that grid-electricity is provided in the cities of the future. At the end of the discussion, perspectives on the trends, limitations and commercialisation potential of these emerging, up-scalable energy conversion technologies are provided.
 

In the present study the analytical modelling of graphene/PMMA nanocomposite under hygro-thermo-mechanical loading is performed. The 2D analytical method consists of the use of the stress-function variational method, which was validated with experimental data in our previous paper [1]. Three cases of loading – heating, cooling and mixed (hygro-thermo-mechanical) are considered and compared with mechanical one. It was found, that all resultant stresses for heating in the layers show the same behavior like mechanical ones with slight increase in amplitude. At cooling the stresses look as a mirror image in respect to the heating case. Also, at heating, the axial stress in graphene increases with increasing the temperature, but the axial stress in the substrate PMMA decreases at the same time. At cooling the stresses show an opposite behavior. The parametric analysis for the influence of external mechanical, temperature and moisture loading, is performed. It was found, that mechanical loading influences significantly the mixed interface shear stress. There is a critical mechanical load of 350 MPa, after that the delamination takes place for mixed case. Without this loading, delamination is not possible nevertheless of applied thermal and/or moisture load. The interface delamination appears from the left and from the right length side of the structure simultaneously.

Electrochemical reduction of CO₂ to valuable chemical fuels provides a promising pathway for reducing the continuously growing global carbon footprint. One of the critical components of an efficient electrochemical CO₂ reduction system is the catalyst which accelerates the reaction’s kinetics.

Metal-Organic Frameworks (MOFs) are a class of crystalline coordination polymers with high surface area, consisting of metal clusters and organic multi-topic linkers. MOFs were highly useful in chemical catalysis because of their unique physical properties, such as high surface area and porosity. These unique properties allow us to use MOFs for integrating the fundamental functional elements needed for the efficient electrocatalytic system: 1) immobilization of high concentration of the molecular catalysts, 2) installation of the redox shuttles for charge transport to and from the catalytic sites, 3) optimization of the mass transport channels through the MOFs pores, and 4) modulation of the catalyst's secondary chemical environment. The notion of using MOF to immobilize high concentrations of molecular electrocatalysts to drive electrochemical reactions was demonstrated. Yet, the modulation of the active-site’s immediate chemical environment to boost electrocatalysis rate and selectivity has rarely been shown..

Herein we demonstrate that in a FeTCPP-Based 2D MOF, using an heterogeneous incorporation of ligands bearing a fixed cationic charge, one can electrostatically-stabilize FeTCPP-bound COO^- intermediate, and thus systematically tune its CO₂-to-CO selectivity up to practically 100%. As such, we believe that these results will widen our understanding of MOF-based electrocatalytic systems and accelerate their implementation is energy-conversion schemes.

Photoelectrocatalytic hydrogen evolution from water is a promising topic for producing H₂ efficiently and environmentally friendly. However, the efficiency of hydrogen production in these photoelectrocatalysis systems is still low. Therefore, the discovery of more efficient phototelectrocatalysts has been considered as one of the important directions in the field of clean and renewable energy. 2D BiOBr is emerging as an interesting photoelectrocatalysts because of its unique internal electric field and band structure that facilitate the separation and mobility of the charge carriers[1,2]. However, pure 2D BiOBr suffers from low catalytic efficiency and photocorrosion from the light source. In order to optimize the catalytic efficiency and stability of 2D BiOBr, a 2D BiOBr/MoS₂ heterojunctions with 1 wt%, 5 wt%, 10 wt% and 50 wt% of MoS₂ were fabricated by a simple liquid-phase exfoliation method. Raman spectra prove the existence of strong interactions between the MoS₂ and BiOBr 2D nanosheets in the heterojunctions. The heterojunction containing 1 wt% of MoS₂ shows the best performance and stability in photoelectrocatalytic hydrogen evolution than the other samples. The calculation of the heterojuntions shows a better charge transfer inside the heterojunction than the pure 2D materials as well.

Semiconductor polymeric carbon nitride (CNs) are a family of 2D materials that exhibit excellent photocatalytic properties for diverse chemical transformations thanks to their tunable band gap, suitable energy-band position, high stability under harsh chemical conditions, and low cost. Unfortunately, despite progress in the last decade, their utilization as the photoactive layer in photoelectrochemical (PEC) cells has yet to reach the performance of state-of-the-art metal-oxide-based systems. The main challenges thus far have been the difficulty in depositing high-quality and homogenous CN layers of controlled thickness on substrates, the wide band gap of ‘intrinsic’ CN ca. 2.7 eV, poor charge-separation efficiency, and low electronic conductivity.^[1]

We present some noteworthy progress we have recently achieved in both stability and performance towards water-splitting as a result of tackling some of these limitations, mainly through variation of precursor deposition methods,^[2–6] externally adding CN-precursor vapor during thermal polymerization,^[5] incorporation of conductive carbons,^[6,7] and successful incorporation of a Ni_xFe_1–xO_yH_z oxidation co-catalyst.^[7] The latter is unique due to the difficulty of forming stable organic–inorganic heterojunctions in porous materials. This was accomplished by in-situ electrochemical transformation inside the porous CN matrix of a solvothermally-deposited pre-catalyst—a Ni/Fe-MIL-53 metal-organic framework (MOF)—into the co-catalyst. This configuration reaches photocurrents of 472 ± 20 µA cm^–2 with faradaic efficiency towards O₂ and H₂ > 80% in 0.1 M KOH solution at 1.23 V vs. RHE. We show stable operation up to 35 h, where degradation occurs due to slow leaching of the co-catalyst.

In this study, we present interface modification of lead halide perovskite solar cells in normal configuration by means of deposition of functionalized Mxene (Ti3C2) nanosheets. H3PP ligand as used as functionalizing and passivation agent molecule at the interface of perovskite-Spiro OMeTAD layers. MXene nanosheets were prepared by delamination of MXene bulk powers with a novel method then dispersed in a pre-dissolved H3pp (0.5 mg/ml) solution. JV measurements showed a PCE of 20.03% for modified device while the reference device PCE was 19.63%. Impedance Spectroscopy analyses and Mott-Schottky analysis revealed the increase of recombination resistance and reduction of trap state densities, respectively, for modified device. Stability studies by means of MPP tracking under N2 atmosphere for 1000 h showed enhanced stability for devices modified by pure MXene nanosheets and H3PP modified MXene nanosheets devices. In addition to that, MPP tracking of encapsulated devices under outdoor conditions  showed clear indication of higher stability in performance of H3PP/Mxene modified devices.In this study, we present interface modification of lead halide perovskite solar cells in normal configuration by means of deposition of functionalized Mxene (Ti3C2) nanosheets. H3PP ligand as used as functionalizing and passivation agent molecule at the interface of perovskite-Spiro OMeTAD layers. MXene nanosheets were prepared by delamination of MXene bulk powers with a novel method then dispersed in a pre-dissolved H3pp (0.5 mg/ml) solution. JV measurements showed a PCE of 20.03% for modified device while the reference device PCE was 19.63%. Impedance Spectroscopy analyses and Mott-Schottky analysis revealed the increase of recombination resistance and reduction of trap state densities, respectively, for modified device. Stability studies by means of MPP tracking under N2 atmosphere for 1000 h showed enhanced stability for devices modified by pure MXene nanosheets and H3PP modified MXene nanosheets devices. In addition to that, MPP tracking of encapsulated devices under outdoor conditions  showed clear indication of higher stability in performance of H3PP/Mxene modified devices.

 Two-dimensional van der Waals layered materials possess strong Coulomb interactions, giving rise to large exciton binding energies, and weak exciton-phonon coupling, allowing lower carrier cooling rates. Tuning the interface is paramount to pushing the device's performance including its optoelectrical properties. Engineering the interface with various 2D-materials (Transition Metal Dichalcogenides, carbon nitride, and Mxenes) at hole transport layers and perovskite, can eliminate defective charge build-up and suppress the charge carrier recombination rate to induce accelerated photo-induced charge transfer. This in turn minimizes voltage deficit. In some cases, where inorganic hole transport layers are used it also avoids direct contact with metal oxide (eg. NiOx with perovskite, overcoming the possible instability of the active layer via iodide oxidation and deprotonation of cationic amines). The use of 2D materials will serve as an effective interfacial layer for reliability in photovoltaics. We will show examples to optimize the interface and band alignment for efficient charge extraction, push the performance and reliability of the perovskite solar cells, and will decipher device kinetics.

Rechargeable Na-O2 batteries have received a great deal of attention as an alternative to current lithium-ion batteries, mainly due to their potential to provide higher energy densities. Na–O2 batteries are still in an early stage of development, with several challenges that need to be addressed, including limiting kinetics at the air cathode. In this regard, the use of suitable cathode materials is a point of major concern as they are responsible for achieving efficient deposition/redissolution of the solid discharge products formed during battery cycling.

Carbon materials have been widely used as air cathodes due to their low cost, high surface area, chemical and mechanical stability, high electrical conductivity, well-developed porosity and intrinsic catalytic activity towards ORR/OER. In particular, graphene has gained attention due to its superior electrical conductivity and highly accessible 2D area. The real integration of graphene as electrode material in energy storage devices, however, requires the development of sustainable and scalable approaches for its production and processing.

In this talk, graphene aerogels prepared by the graphite oxide route and the electrochemical exfoliation of graphite will be discussed. First, graphene aerogels with different pore sizes obtained by the graphite oxide route revealed a trade-off between pore texture and battery performance. This route, however, is not environmentally friendly and involves multiple steps, including a reduction step to tune the sheet conductivity. As an alternative, we have used a simpler, faster and more eco-friendly route to access high-quality graphene by electrochemical exfoliation of graphite, resorting to natural nucleotides as both exfoliating electrolytes and colloidal stabilizers. An aerogel prepared from this graphene suspension delivered a large discharge capacity and longer cycle life than those cathodes prepared by the graphene oxide route. The origin of such good performance is attributed to the participation of the nucleotide molecules in key chemical processes taking place at the battery cathode, including oxygen electrocatalysis and nucleation of the discharge products.The present work highlights not only the interest on this electrochemical method over more traditional routes when it comes to manufacturing graphene, but also the direct potential benefits of the resulting graphene in novel electrochemical energy storage technologies.

REFERENCES

M. Enterría, C. Botas, J.L. Gómez-Urbano, B. Acebedo, J.M. López del Amo, D. Carriazo, T. Rojo, N. Ortiz-Vitoriano, Journal of Materials Chemistry A, 42 (2018) 20778.

M. Enterría, J.L. Gómez‐Urbano, J.M. Munuera, S. Villar‐Rodil, D. Carriazo, J.I. Paredes, N. Ortiz‐Vitoriano, Small, 17 (2021) 2005034.

Over the last years, models have evolved to allow us to address the properties

of materials in energy. I will revise some of the local effects for the most relevant

applications including the oxygen evolution reaction and the CO2 reduction with

showing where the most important bottlenecks are present.