Hematite-based photoelectrode for solar water splitting with very high photovoltage

Abstract

Hematite photoelectrode is a promising candidate for photoelectrochemical (PEC) water splitting. However, the high density of surface defects and slow kinetics for oxygen evolution have restricted the PEC performance of hematite photoelectrodes, mainly their low photovoltage. This study provides the hematite surface modification combining two strategies, annealing at high temperatures (800 degrees C) and coating with RuO2 and IrO2/RuO2 co-catalysts. IrO2/RuO2-coated hematite thin film exhibited a low turn-on potential of 0.48 V-RHE and a final photovoltage of 1.20 V, which is the highest photovoltage reported for hematite-based photoelectrodes. A photocurrent density of ca. 1.52 mA cm(-2) was obtained at 1.23 V-RHE, corresponding to ca. 140% increase compared to bare hematite; the photocurrent obtained at 0.60 V-RHE was 0.34 mA cm(-2), the highest value ever reported. The IrO2/RuO2-coated hematite photoelectrode showed a quite stable performance at 0.80 V-RHE for over 72 h. The water oxidation efficiency was therefore enhanced with values above 90% for potentials higher than 1.00 V-RHE due to faster charge transfer and reduced electron-hole recombination at its surface.