Abstract
Abstractα‐SnWO4 is a promising metal oxide photoanode material for direct photoelectrochemical water splitting. With a band gap of 1.9 eV, it ideally matches the requirements as a top absorber in a tandem device theoretically capable of achieving solar‐to‐hydrogen (STH) efficiencies above 20%. It suffers from photoelectrochemical instability, but NiOx protection layers have been shown to help overcome this limitation. At the same time, however, such protection layers seem to reduce the photovoltage that can be generated at the solid/electrolyte junction. In this study, an extensive analysis of the α‐SnWO4/NiOx interface is performed by synchrotron‐based hard X‐ray photoelectron spectroscopy (HAXPES). NiOx deposition introduces a favorable upwards band bending, but also oxidizes Sn2+ to Sn4+ at the interface. By combining the HAXPES data with open circuit potential (OCP) analysis, density functional theory (DFT) calculations, and Monte Carlo‐based photoemission spectra simulation, the presence of a thin oxide layer at the α‐SnWO4/NiOx interface is suggested and shown to be responsible for the limited photovoltage. Based on this new‐found understanding, suitable mitigation strategies can be proposed. Overall, this study demonstrates the complex nature of solid‐state interfaces in multi‐layer photoelectrodes, which needs to be unraveled to design efficient heterostructured photoelectrodes for solar water splitting.
Highlights
In order to establish a clean and sustainable future energy supply, significant research efforts have been devoted to developing novel renewable energy technologies
We performed a detailed investigation of the α-SnWO4/NiOx interface using synchrotron-based hard X-ray photoelectron spectroscopy (HAXPES) in order to understand the origin of the limited photovoltage in NiOx-coated α-SnWO4 films
NiOx deposition was found to introduce a favorable upwards band bending at the α-SnWO4/ NiOx interface
Summary
In order to establish a clean and sustainable future energy supply, significant research efforts have been devoted to developing novel renewable energy technologies. Which can be stored and used directly as fuel or used as a feedstock to synthesize other chemical fuels.[3,4,5] Metal oxide semiopen circuit potential (OCP) analysis, density functional theory (DFT) calculaconductors have been considered as viable tions, and Monte Carlo-based photoemission spectra simulation, the presence of a thin oxide layer at the α-SnWO4/NiOx interface is suggested and shown to be responsible for the limited photovoltage Based on this new-found understanding, suitable mitigation strategies can be proposed. The HAXPES data are complemented with ΔOCP analysis, density functional theory (DFT) calculations, and Monte Carlo-based photoemission peak intensity simulation Based on this comprehensive analysis we are able to unravel the origin of the limitation at the α-SnWO4/ NiOx interface and propose suitable mitigation strategies
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