Mechanistic origin of alloy-induced activity enhancement for alkaline hydrogen evolution

The alkaline hydrogen evolution reaction (HER) remains limited by sluggish water dissociation and slow release of adsorbed hydrogen intermediates. Despite the growing interest in alloy catalysts, the fundamental origin of the alloy-induced HER enhancement remains unclear because of the lack of in situ evidence linking the role of metal species to catalytic dynamics. Here, we synthesize ultrathin Rh-based binary alloy nanosheets (RhM-NS, M = Fe, Co, Cu), whose atomic-layer thickness and homogeneous solid-solution structures provide an ideal platform for mechanistic investigation. Electrochemical measurements reveal that RhFe-NS exhibits substantially higher alkaline HER activity than Rh-NS. In situ XAFS measurements show that both Rh and Fe remain metallic under operating conditions and that Fe does not primarily serve as an oxygen adsorption site, indicating that the enhanced activity does not derive from facilitated O-H bond cleavage. In situ Raman spectroscopy reveals an attenuated Rh–H vibrational feature in RhFe-NS compared with the pronounced Rh–H band observed in Rh-NS, indicating a substantially lower surface coverage of the adsorbed hydrogen intermediate (H_ad) and consequently accelerated desorption of H_ad toward H₂ formation. These results indicate that alloying enhances the alkaline HER by promoting H_ad desorption rather than accelerating water dissociation. This study provides a clear mechanistic picture of the alloy-induced enhancement of the alkaline HER and establishes a foundation for the rational design of next-generation alloy electrocatalysts.

J. Colloid and Interface Sci. 2026, 722, 140812