Optimum hydrogen binding energy at the atomic-level interfaces of Rh atoms/ultrasmall Rh nanoparticles for boosting hydrogen electrocatalysis

Optimizing the intrinsic hydrogen binding energy at atomic-level interfaces is beneficial and challenging for hydrogen electrocatalysis to improve the mass activity of platinum-group metal. Here, we develop a bifunctional hydrogen electrocatalyst featuring atomically dispersed Rh-N₄ sites alongside ultrasmall Rh nanoparticles (Rh_SA+NP/NC). For the hydroxide oxidation reaction, the mass activity (9.14 A mg_Rh⁻¹) of Rh_SA+NP/NC is 101 times that of commercial Pt/C. For the hydrogen evolution reaction, the overpotential is merely 14 mV at an extremely low Rh loading (1.91 μg cm⁻²). The anion-exchange membrane fuel cell and anion-exchange membrane water electrolyzer equipped with Rh_SA+NP/NC achieve a high peak power density (25.7 W mg_Rh⁻¹) and a low cell voltage (1.77 V at 1 A cm⁻²), respectively. Experimental and computational results indicate that the atomic-level interface formed by Rh single atoms and nanoparticles optimizes the adsorption behavior of active species and accelerates the hydrogen conversion kinetics. This study designs cost-effective hydrogen electrocatalysts through atomic-level interface engineering, providing a feasible strategy for accelerating the realization of a sustainable hydrogen circular economy.