Unraveling how the crystal phase and dispersion of mesoporous carbon-confined Ru nanoclusters govern full-pH hydrogen evolution performance.

The design and fabrication of highly active hydrogen evolution reaction (HER) electrocatalysts that can outperform Pt/C are extremely desirable but remain challenging. Herein, S-doped hollow mesoporous carbon-anchored Ru nanoclusters (Ru NCs/S-HMCs) are fabricated as a novel and highly active HER electrocatalyst through a modified Stöber process and subsequent hydrothermal treatment, in which Ru NCs (1.64 nm in size) are uniformly anchored onto S-HMCs channels. Benefiting from the unique electronic structure induced by S doping and the spatial confinement effect of the mesoporous carbon, the Ru NCs/S-HMCs catalyst exhibits excellent pH-universal HER activity, requiring overpotentials of only 3.5, 61.0, and 63.5 mV to achieve a current density of 10 mA cm-2 in alkaline, neutral, and acidic electrolytes, respectively. In 1 M KOH, 0.5 M H2SO4, and 0.5 M PBS solutions, Ru NCs/S0.5-HMCs exhibits high mass activities of 21542, 2998 and 7088 mA mgRu-1, respectively, at an overpotential of -50 mV. The excellent activity stems from (1) the pore confinement effect, which promotes the formation of ultrasmall Ru NCs (1.64 nm) and suppresses metal leaching; (2) the S doping, which modulates the electronic structure of Ru and reduces the water dissociation barrier; and (3) the hollow mesoporous architecture, which accelerates mass and electron transport. This work provides insights for designing high-efficiency pH-universal electrocatalysts.