Theoretical Insight into Charge-Recombination Center in Ta3N5 Photocatalyst: Interstitial Hydrogen

Ideal Ta3N5 is a promising candidate photocatalyst for solar water splitting. In a common synthetie route, both oxygen and hydrogen impurities are inevitably formed during the nitridation of TaOx precursor by ammonia. The introduced hydrogen impurities would bond with oxygen in the form of hydroxyl groups, resulting in additional bands bracketing band edges. This configuration adds Ta3N5 electron hole recombination centers, leading to a high Onset potential. Hydrogen impurities would also introduce hydrogen bonds which aggravate charge recombination by additional charge transport paths from anions to hydroxyl recombination centers. In addition, hydride ions of hydroxyl groups may be activated into protons at high bias and may relay hole transport in Ta3N5, endowing the material with high saturated photocurrent. In summary, hydrogen impurities would aggravate the onset potential of Ta3N5 in the way of high electron hole recombination. More broadly, hydrogen impurities may be common in (oxy)nitrides and other covalent materials; they may add to the photocatalysts' high onset-potential via electron localizations and might introduce high charge recombination for covalent semiconductors.