WO3 and W2N nanowire arrays for photoelectrochemical hydrogen production

Tungsten oxide (WO3) nanowire array samples were nitrided in a NH3 atmosphere to get complete conversion to tungsten nitride (W2N) nanowires. UV–vis absorption spectroscopy shows that the band gap of WO3 reduced from 2.9 eV to 2.2 eV after nitridation to W2N. Photoelectrochemical properties of both WO3 and W2N nanowire array electrodes were investigated. WO3 nanowire arrays show maximum incident photon-to-current conversion efficiency of 85% at 370 nm at 1.2 V vs. SCE. The high quantum efficiency is attributed to the nanowire architecture which ensures efficient light absorption and charge transport. The nanowire arrays were stable even up to 8 h of continuous gas evolution. W2N nanowire arrays showed good photoactivity even at moderate bias. However, the pure W2N electrodes were unstable with respect to photocorrosion. The mixed phase W2N–WO3 nanowires showed improvement in stability compared to pure W2N nanowire arrays.