Reducing the surface defects of Ta3N5 photoanode towards enhanced photoelectrochemical water oxidation

Abstract

Tuning the concentration and location of defects in semiconductors has been found to be effective in modifying their photoelectrochemical (PEC) performance. Herein, we present the fabrication of Ta₃N₅ photoanodes with reduced surface defects through the nitridation of a two-step-flame-heating-derived Ta₂O₅ precursor (TSFH-Ta₂O₅). We found that by using TSFH-Ta₂O₅ instead of the one-step-flame-heating-derived Ta₂O₅ (OSFH-Ta₂O₅), the concentrations of low valence Ta species on the surface of Ta₂O₅ and the resulting Ta₃N₅ photoelectrodes are reduced. Moreover, we clarified that low valence Ta species on the Ta₃N₅ surface led to the formation of undesirable surface states, which induces severe Fermi level pinning and aggravates charge recombination. Therefore, TSFH-Ta₃N₅ delivered enhanced charge separation and injection efficiencies for PEC water oxidation reaction. A photocurrent density of 6.8 mA cm⁻² at 1.23 V vs. reversible hydrogen electrode (RHE) was obtained on TSFH-Ta₃N₅ after loading a Co(OH)_x cocatalyst, which is among the highest values reported for planar Ta₃N₅ photoanodes.