Design of RuO_<i>x</i> Electrocatalysts Containing Metallic Ru on the Surface to Accelerate the Alkaline Hydrogen Evolution 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.