Cathodic shift of a photo-potential on a Ta₃N₅ photoanode by post-heating a TiO₂ passivation layer

Ta₃N₅ is a promising photoanode material for solar water splitting due to its suitable band gap and high theoretical solar energy conversion. A high onset potential of Ta₃N₅ limits its photoelectrochemical performance due to serious surface charge recombination. In a previous study, a TiO₂ passivation layer was usually coated on the surface of Ta₃N₅ to reduce the surface recombination and improve the performance of a sample. However, to date, there are no studies on the effect of conductivity of the TiO₂ passivation layer on the photoelectrochemical properties of a Ta₃N₅ photoanode. In this work, for the first time, the conductivity of TiO₂ is increased by post-heating of a TiO₂ passivation layer, leading to a 90 mV cathodic shift of the photo-potential of Ta₃N₅. After further loading with a Ni(OH)_x/FeOOH bi-layer electrocatalyst, the Ta₃N₅ photoanode achieves a current density of 6.4 mA cm^-2 at 1.23 V_RHE and a HC-STH (half-cell solar to hydrogen efficiency) of 0.72% under a sunlight simulator (100 mW cm^-2), which are the highest values among the Ta₃N₅ photoanodes prepared by thermal oxidation and nitridation of Ta foil.