Intrinsic Activity of Face-Dependent Hydrogen Evolution Reaction Induced by Cu, Cu2O, and CuO Surfaces

Abstract

The hydrogen evolution reaction (HER) is central to electrochemical water splitting and renewable hydrogen production. Here, we use DFT+U, continuum solvation, ab initio thermodynamics, and the computational hydrogen electrode to compare the intrinsic HER thermodynamics of Cu, Cu2O, and CuO surfaces with different crystallographic orientations under acidic and alkaline conditions. Metallic Cu provides hydrogen adsorption energies closer to thermoneutrality than the oxide surfaces, but it exhibits unfavorable water activation in alkaline media. Cu2O and CuO directly bind and activate *H2O, *H, and *OH at lattice Cu–O sites, yet their strong stabilization of hydrogen-containing intermediates penalizes H2 release. Thus, the overall activity ranking depends on the criterion considered: metallic Cu gives the lowest calculated thermodynamic overpotentials, whereas Cu2O, especially its stepped surface. Surface topology further modulates these trends through low-coordination sites. Importantly, we show that surface topology further modulates this balance, with low-coordination sites enhancing reactivity but amplifying adsorption asymmetries.