High-Performance Titanium Oxynitride Thin Films for Electrocatalytic Water Oxidation

TiNxOy (TiNO) thin films with superior electrochemical properties have been synthesized in situ using a pulsed laser deposition method and a varied oxygen partial pressure from 5 to 25 mTorr. The electrochemical overpotential of these TiNO films for water oxidation was found to be as low as 290 mV at 10 mA/cm2, which is among the lowest overpotential values reported. The Tafel slopes, indicative of a rate of increase of electrode potential with respect to current, for these films are determined to be in the range of 85–57 mV/decade. These results further demonstrate the superiority of TiNO thin film as electrocatalyst for water oxidation to generate fossil-free fuels. The improvement in the electrocatalytic behavior of the semiconducting TiNO thin films is explained based on an adjustment in the valence band maximum edge and an enhancement in the number of electrochemically active sites. Both effects are realized by the substitution of N by O, forming a TiNO lattice that is isostructural with the rock-salt TiN lattice. These findings appear to assume significant importance in light of water electrolysis to produce fuels for the development of environmentally friendly power sources.