Study on the Reaction Mechanism of RuO_x and Its Enhanced Hydrogen Evolution Reaction Activity

Ruthenium oxide is a well-known electrocatalyst for water splitting. Despite many advantages, the reaction mechanism and the structure changes of ruthenium oxide are unclear during catalysis, and the catalytic efficiency of ruthenium oxides remains a concern. In this paper, a needle-shaped copper substrate was synthesized, and the performance of RuO_x was optimized. Reversible in situ Raman signals were found during the reaction process, which confirmed from the reversible surface reconstruction of RuO_x. Density Functional Theory calculations found that the actual catalytic species is Ru(II)O. A detailed reaction mechanism of the Volmer step on the surface of ruthenium oxide was proposed based on the findings. The results indicate that the needles can lower the overpotentials of RuO_x. At a current density of 10 $\mathrm{mA}·\mathrm{cm}$ ${}^{-2}$ , the overpotential of RuO_x@ndl. was 68% lower than that of RuO_x@b. f., which is much lower than the overpotential of commercial Pt(20wt.%)/C. This research provides a fundamental understanding of ruthenium oxide's reaction mechanism and gives insight into the design of the hydrogen evolution reaction catalysts.