Enhancing edge chemistry in HCP-Ru catalysts through crystalline domain engineering for efficient alkaline hydrogen evolution

Engineering the nanoscale domain structure of transition metal catalysts offers a promising pathway to enhance their intrinsic activity by tailoring surface coordination and electronic states. Here, we report a MgO-assisted solvothermal strategy for synthesizing hexagonal close-packed (HCP) Ru nanospheres from Ru(acac)₃ in isopropanol, in which MgO templates modulate the crystallization pathway to preferentially expose the (100) and (002) facets while suppressing the (101) facet. This facet-selective growth leads to the formation of well-defined crystalline domains with abundant low-coordination edge sites and oxygen vacancies at domain boundaries. Such domain-induced surface reconstruction gives rise to edge-rich chemistry – a catalytic environment characterized by enhanced interfacial charge transfer, strengthened water adsorption, and optimized hydrogen binding at under-coordinated Ru⁰ sites. Mechanistic studies, including in situ Raman spectroscopy, reveal that the edge-enriched Ru_domains promotes earlier onset of hydrogen adsorption and accelerates H₂ evolution by facilitating both the Volmer and Heyrovsky steps. Benefiting from these structural and electronic advantages, the resulting Ru_domains achieves an ultralow overpotential of 23.5 mV at 10 mA cm⁻² and a small Tafel slope of 34.4 mV dec⁻¹ in alkaline media, outperforming commercial Pt/C and most Ru-based HER catalysts. This work highlights a general and scalable strategy for activating edge sites through oxide-directed facet/domain engineering, providing new insight into the design of HER electrocatalysts based on edge-rich chemistry.