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

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.