Design of RuO_<i>x</i> ElectrocatalystsContaining Metallic Ru on the Surface to Accelerate the Alkaline HydrogenEvolution Reaction

The development of water splitting technology in alkaline medium requires the exploration of electrocatalysts superior to Pt/C to boost the alkaline hydrogen evolution reaction (HER). Ruthenium oxides with strong water dissociation ability are promising candidates; however, the lack of hydrogen combination sites immensely limits their performance. Herein, we reported a unique RuO_<i>x</i> catalyst with metallic Ru on its surface through a simple cation exchange method. We demonstrated that the formation of metallic Ru on RuO_<i>x</i> greatly enhances the interaction between the catalyst and adsorbed hydrogen (*H), resulting in extremely high HER activity in alkaline media. Moreover, we proposed the potential of zero charge (<i>E</i>_pzc) as a descriptor of ruthenium-base catalysts for alkaline HER for the first time and revealed that the existence of metallic Ru optimizes the <i>E</i>_pzc of RuO_<i>x</i> toward the hydrogen region. As a result, the designed RuO_<i>x</i> catalyst achieves an overpotential of only 18 mV at the current density of 10 mA cm^–2. Furthermore, RuO_<i>x</i> requires 1.80 V to reach 800 mA cm^–2 in the anion exchange membrane water electrolyzer, outperforming the benchmark Pt/C.