Fiber-in-tube RuxCr1−xOy as highly efficient electrocatalysts for pH-universal water oxidation via facile bubble desorption

Abstract

Electrospun Ru_xCr_1−xO_y nanomaterials were produced using an electrospinning technique followed by a thermal annealing process under oxidative atmospheric conditions. The morphology of the materials was controlled by adjusting the atmospheric O₂ concentration during calcination, resulting in various shapes, including core–shell structures and nanofibers. The electrocatalytic activity of Ru_xCr_1−xO_y nanomaterials for the oxygen evolution reaction (OER) was assessed with voltammetry under various pH conditions. Specifically, Ru_xCr_1−xO_y_20 nanofibers (synthesized in a calcination environment composed of 20% oxygen and 80% helium gases), featuring a fiber-in-tube structure, exhibited the lowest potentials (V vs. RHE) at 10 mA cm⁻², reaching 1.47 V under alkaline, 1.49 V under neutral, and 1.44 V under acidic conditions. Furthermore, these nanomaterials displayed the smallest Tafel slopes of 37.5 mV dec⁻¹ in alkaline, 68.9 mV dec⁻¹ in neutral, and 40.8 mV dec⁻¹ in acidic environments. These results clearly indicate the superior OER activity of Ru_xCr_1−xO_y_20 in comparison to that of commercial Ir (Ir/C), pure RuO_x (Ru/RuO₂), and Ru-based electrocatalysts reported in the literature. Additionally, it displayed remarkable stability over 20 h continuous chronopotentiometry tests across all pH ranges and facilitated the desorption of oxygen bubbles generated during the OER process, leading to improved OER activity. The unique core–shell structure of Ru_xCr_1−xO_y_20, which dilutes expensive Ru with cheap Cr, presents excellent feasibility as a practical and cost-effective OER catalyst, especially considering the scarcity of pH-universal OER catalysts reported.