Coincorporation of N and Ta into TiO₂ Nanowires for Visible Light Driven Photoelectrochemical Water Oxidation

Abstract

We report a synthesis of N- and Ta-coincorporated TiO2 (N,Ta:TiO2) and Ta-incorporated TiO2 (Ta:TiO2) nanowire (NW) arrays and their application as photoanodes for water photooxidation. Tantalum is incorporated into TiO2 NWs with concentrations ranging from 0.11 to 3.47 atomic % by a simple solvothermal synthesis. N,Ta:TiO2 nanowires are prepared via nitridation of Ta:TiO2 nanowires in NH3 flow at a relatively low temperature (500 °C). N,Ta:TiO2 NWs with the optimum Ta concentration of 0.29 atomic % also demonstrate significant enhancement in photoelectrochemical performance with the photocurrent reaching 0.52 and 0.18 mA/cm2 under AM 1.5 G and visible light (>420 nm) illumination, compared with 0.26 and 0.13 mA/cm2 for that of N:TiO2 NWs, although the active spectrum of the N,Ta:TiO2 NW sample only extends to ∼520 nm (2.38 eV), compared to ∼540 nm (2.30 eV) for N:TiO2 NWs. We believe that the enhancement shown by the N,Ta-coincorporated sample is due to fewer recombination centers from charge compensation effects and suppression of the formation of an amorphous layer on the nanowires during the nitridation process.