Photoelectrochemical Hydrogen Production Using a CaFe2O4 Electrode Coated with TiO2 As a Surface Protective Layer

Abstract

CaFe2O4 is a p-type semiconductor with a bandgap of 1.9 eV that can function as a photocathode for photoelectrochemical (PEC) hydrogen production from water. However, there is one issue in that the CaFe2O4 photocathode is likely to decompose during the PEC reaction, which results in a decrease in the photocathodic current. In this study, a TiO2 thin layer was coated on the CaFe2O4 surface by pulsed laser deposition to suppress decomposition.The onset potential was slightly shifted to the negative side by coating of the photocathode with TiO2. Although the photocathodic current was slightly decreased compared with the CaFe2O4 electrode without the TiO2 layer, the decrease in the photocurrent during the PEC hydrogen production reaction was suppressed. In the case of amorphous-like TiO2-coated CaFe2O4, the photocurrent was increased during the PEC hydrogen production reaction. The ratio of the photocurrent after 6 h reaction to the photocurrent at the initial stage of the reaction (5 min) was 120/100. After the PEC reaction, there were no cracks evident on the electrode surface, and the surface morphology was almost the same as the initial morphology. This result indicates that surface degradation of the CaFe2O4 electrode can be suppressed by coating with a thin TiO2 layer.