Recent study demonstrated that the performance of α-SnWO4/NiOx photoabsorbers prepared by pulsed laser deposition (PLD) is limited by the interfacial properties; [1] understanding this interface is therefore crucial for further improvement. A thorough α-SnWO4/NiOx interface investigation by means of hard X-ray photoelectron spectroscopy (HAXPES) is presented and correlated with photoelectrochemistry measurements. PLD NiOx introduces strong upwards band bending (~500 meV) at the interface. However, photoemission spectra simulation indicates that at the same time a thin SnO2 layer is formed at the interface. The implications of this SnO2 layer to the interface junction properties and the limited photovoltage will be discussed. [1] Kölbach et al. Chem Mater. 30 (2018) 8322-8331
Local build-up of pH gradients is a major concern in near-neutral photoelectrochemical water splitting since it leads to efficiency losses due to concentration overpotentials. Here, we monitor in-situ pH changes during water splitting in a (photo)electrochemical cell by a fluorescence-based technique and compared with multi-physics simulations. We found that the pH distribution within the cell is affected by natural convection generated by the electrochemical reactions. Based on this observation, we developed a model that considers natural convection driven by buoyancy forces due to local changes in the density of the electrolyte. Only when the buoyancy effect is considered does the model accurately reproduces the measured pH profile. This study reveals the importance of natural convection driven by electrochemical reactions and highlights the implications for designing efficient photoelectrochemical devices.
In this work, we investigate the initial interaction of water and oxygen with different surface reconstructions of GaP(100) applying photoelectron spectroscopy, low-energy electron diffraction, and reflection anisotropy spectroscopy. Surfaces were prepared by metal-organic vapour phase epitaxy, transferred to ultra-high vacuum, and exposed to oxygen or water vapour at room temperature. The (2 4) reconstructed, Ga-rich surface is more sensitive and reactive to adsorption, bearing a less ordered surface reconstruction upon exposure and indicating a mixture of dissociative and molecular water adsorption. The p(2 2)=c(4 2) P-rich surface, on the other hand, is less reactive, but shows a new surface symmetry after water adsorption. Correlating findings of photoelectron spectroscopy with reflection anisotropy spectroscopy could pave the way towards optical in-situ monitoring of electrochemical surface modifications with reflection anisotropy spectroscopy.
The properties of thin film InVO4 photoanodes for water splitting have been studied. Compact films of InVO4 were prepared by spray pyrolysis and are found to be stable between pH 3 and 11. Although the indirect bandgap is 3.2 eV, a modest amount of visible light absorption is observed. The origin of this absorption is attributed to the presence of deep donor states at ∼0.7 eV below the conduction band. These donor states presumably correspond to oxygen vacancies, which form as a result of small but unavoidable deviations of In:V from the ideal 1:1 stoichiometry during the wet-chemical synthesis process. Shallow donors are absent in this material, in contrast to what is normally observed for metal oxides. The deep donor model explains the much stronger visible light absorption of powders compared to thin films. The defect chemical reactions that lead to the formation of the deep donors are shown, and are supported by photoluminescence data.
The properties of thin film InVO4 photoanodes for water splitting have been studied. Compact films of InVO4 were
prepared by spray pyrolysis and are found to be stable between pH 3 - 11. Although the indirect bandgap is 3.2 eV, a
modest amount of visible light absorption is observed. The origin of this absorption is attributed to the presence of deep
donor states at ~0.7 eV below the conduction band. Shallow donors are absent in this material, in contrast to what is
normally observed for metal oxides. The deep donor model explains the much stronger visible light absorption of
powders compared to thin films, and is supported by photoluminescence data. The origin of the deep donors is attributed
to deviations in the In:V ratio, and the corresponding defect-chemical reactions will be discussed.
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