Scalable Solid‐State Synthesis of Highly Dispersed Uncapped Metal (Rh, Ru, Ir) Nanoparticles for Efficient Hydrogen Evolution

Green and scalable syntheses of highly dispersed supported metal nanocatalysts (SMNCs) are of significant importance for heterogeneous catalysis in industry. In order to achieve nanosized SMNCs and prevent metal nanoparticles (NPs) from aggregation, the traditional liquid syntheses commonly require organic capping agents and low metal loading, which are unfavorable for practical production of SMNCs. Herein, a green and facile solid‐state approach is reported for a general synthesis of Rh, Ru, and Ir NPs highly dispersed on different carbon supports via a room‐temperature mortar grinding. The synthesis is easy to scale up and no organic solvent is needed. Metal NPs are free of capping agents and in a couple of nanometers with a uniform size distribution. Benefiting from the above features and high intrinsic activity, Rh NP/C shows the superior activity for hydrogen evolution reaction (HER) in terms of an ultralow overpotential of 7 mV at 10 mA cm−2, outperforming the state‐of‐the‐art HER electrocatalysts. The cell voltage to output a stable current density of 10 mA cm−2 is only 1.53 V for the electrolyzer with Rh NP/C cathode. These results indicate that the present scalable solid‐state synthetic strategy paves a new avenue for mass production of highly efficient SMNCs for diverse applications.