Hematite photoelectrodes grown on porous CuO–Sb₂O₅–SnO₂ ceramics for photoelectrochemical water splitting

Photoelectrodes capable of cost-effective hydrogen production on a large scale, via photoelectrochemical water splitting under solar light, could offer an elegant solution to many current problems of humankind caused by over-reliance on fossil fuels and the resulting environmental pollution. The search and design of low-cost photoelectrode materials and substrates for practical applications are required. In this work, unmodified hematite photoanodes grown by metal-organic chemical vapor deposition (MO-CVD) onto CuO–Sb₂O₅–SnO₂ ceramic substrates are reported. The deposition time of hematite precursor varied between 10 min, 60 min, and 90 min. The photoanode grown for 60 min exhibits the highest photocurrent density recorded at 1.23 V vs RHE (reversible hydrogen electrode): 4.79 mA/cm² under blue light of Thorlabs LED M455L2 (455 nm), 0.41 mA/cm² under the radiation of the real sun in Mexico, and 0.38 mA/cm² under AM1.5G solar simulator conditions. The high porosity of CuO–Sb₂O₅–SnO₂ ceramics permits the permeation of the hematite precursor into the substrate bulk, which results in 3D-growth of a thin Fe₂O₃-coating (50 nm or less) on conductive SnO₂-grains in the ceramics to a depth of ca. 5 μm. The thick photocatalytic layer (SnO₂-grains coated by hematite) of several micrometers assures a good light harvesting by the photoelectrode, while the nano-sized Fe₂O₃-films on conductive SnO₂-grains is favorable for charge diffusion. This architecture of the photoelectrode results in good photoelectrochemical characteristics and is promising for further development.