Role of Oxygen Concentration in Reactive Sputtering of RuO2 Thin Films: Tuning Surface Chemistry for Enhanced Electrocatalytic Performance

Developing active electrocatalysts for water splitting is a great challenge due to slow four-electron transfer oxygen evolution reaction. Here, we report the effect of variable oxygen concentrations in sputtered RuO2 thin films on electrochemical performance. The impact of Ar/O2 ratios on the structural, chemical, and optical properties of sputtered RuO2 films is systematically investigated. The as-deposited amorphous RuO2 showed higher catalytic activity as compared to its annealed crystalline counterparts. The X-ray photoelectron spectroscopy results showed controlled stoichiometry with 20% oxygen. The electrochemical measurements of the RuO2 deposited with a 4:1 Ar:O2 ratio showed superior performance in cyclic voltammetry, linear sweep voltammetry, and Tafel slope. Transformation of as-deposited amorphous RuO2 into polycrystalline films is observed at 400 °C of annealing temperature. Film thickness is increased with increasing O2 concentration during deposition. This study highlights that sputtered RuO2 thin films with varying oxygen concentration during deposition can influence the electrocatalytic activities in water-splitting applications.