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.