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 VRHE 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.