Electronic mechanism for the enhanced hydrogen evolution reaction activity of Cu alloys

The low intrinsic activity hinders the development of Cu-based HER (hydrogen evolution reaction) electrocatalysts, and the doping of non-noble transition metals is a pragmatic approach for enhancement. However, since the HER process entails both H ₂O dissociation and H ⁺ adsorption, the calculated free energy of various adsorbed intermediates ( H ⁺, OH ⁻, and H ₂O) affects the activity, posing challenges in fully understanding alloying effects on the HER activity of Cu alloys. In this study, we combined experiments and first-principles calculations to elucidate the interplay between dopant elements, free energy, electronic structure, H ₂O dissociation, and activity. We found that doping of early and late transition elements significantly impacts the bonding of catalysts with OH ⁻ and H ⁺, respectively. The former dictates the energy barrier of H ₂O dissociation and has a crucial effect on the activity, whilst the latter only affects the kinetics of H ⁺adsorption and desorption. Electronic structure analysis reveals that the d-orbitals of doped early transition elements exhibit a significantly stronger coupling with O-2p orbitals compared to those of late transition elements. In addition, we proposed an optimal range of ΔG _OH for achieving desirable HER intrinsic activity of sites in Cu alloys, which was experimentally verified by the notable enhancement in activity upon the addition of an appropriate amount of Mn to Cu. Our findings provide not only a reliable guidance for the development of Cu-based HER electrocatalysts, but also new insights into understanding of electronic mechanisms of HER processes in general.