A hematite photoelectrode grown on porous and conductive SnO₂ ceramics for solar-driven water splitting

Photoelectrochemical water splitting using solar energy is a highly promising technology to produce hydrogen as an environmentally friendly and renewable fuel with high-energy density. This approach requires the development of appropriate photoelectrode materials and substrates, which are low-cost and applicable for the fabrication of large area electrodes. In this work, hematite photoelectrodes are grown by aerosol assisted chemical vapour deposition (AA-CVD) onto highly-conductive and bulk porous SnO₂ (Sb-doped) ceramic substrates. For such photoelectrodes, the photocurrent density of 2.8 mA cm^-2 is achieved in aqueous 0.1 M NaOH under blue LED illumination (λ = 455 nm; 198 mW cm^-2) at 1.23 V vs. RHE (reversible hydrogen electrode). This relatively good photoelectrochemical performance of the photoelectrode is achieved despite the simple fabrication process. Good performance is suggested to be related to the three-dimensional morphology of the porous ceramic substrate resulting in excellent light-driven charge carrier harvesting. The porosity of the ceramic substrate allows growth of the photoactive layer (SnO₂-grains covered by hematite) to a depth of some micrometers, whereas the thickness of Fe₂O₃-coating on individual grains is only about 100–150 nm. This architecture of the photoactive layer assures a good light absorption and it creates favourable conditions for charge separation and transport.