High-Performance Titanium Oxynitride Thin Films for 2 Electrocatalytic Water Oxidation

TiNxOy (TiNO) thin films with superior electrochemical6 properties have been synthesized in situ using a pulsed laser deposition7 method and a varied oxygen partial pressure from 5 to 25 mTorr. The8 electrochemical overpotential of these TiNO films for water oxidation was9 found to be as low as 290 mV at 10 mA/cm2, which is among the lowest10 overpotential values reported. The Tafel slopes, indicative of a rate of11 increase of electrode potential with respect to current, for these films are12 determined to be in the range of 85−57 mV/decade. These results further13 demonstrate the superiority of TiNO thin film as electrocatalyst for water14 oxidation to generate fossil-free fuels. The improvement in the15 electrocatalytic behavior of the semiconducting TiNO thin films is16 explained based on an adjustment in the valence band maximum edge and17 an enhancement in the number of electrochemically active sites. Both18 effects are realized by the substitution of N by O, forming a TiNO lattice that is isostructural with the rock-salt TiN lattice. These19 findings appear to assume significant importance in light of water electrolysis to produce fuels for the development of20 environmentally friendly power sources.