Surface Single Atom Alloys for Alkaline Hydrogen Evolution Reaction

Single atom catalysts (SACs) achieve 100% utilization of metal atoms and have versatile support effects, whereas single atom alloys (SAAs) with metallic bonds own the free-atom-like electronic structure. Herein, surface single atom alloys (SSAAs) are developed that integrate the advantages of SACs and SAAs via incorporating an ultrathin metallic layer during the synthetic process of SACs. It is shown that the Pt single atom preferentially coordinates with metallic Mo nanolayer, thereby forming a Pt₁-Mo_L surface atom alloy on Mo₂C (marked as Pt₁-Mo_L-Mo₂C SSAAs). Comprehensive spectroscopic and theoretical calculations reveal that the Mo nanolayer in SSAAs not only functions as an electron buffer between Pt₁ and Mo₂C, leading to a free-atom-like d state at Pt₁ sites and thereby balancing the adsorption and desorption of H, but also enhances the aggregation, adsorption, and activation of H₂O. Consequently, the Pt₁-Mo_L-Mo₂C SSAAs exhibit superior alkaline hydrogen evolution reaction (HER) performance compared to Pt₁/Mo₂C SACs, achieving a low overpotential of 12 mV at 10 mA cm^-2 and a low Tafel slope of 17 mV dec^-1. This work provides novel insights into the design of advanced single-site catalysts.