Operando Surface Dynamics Govern the pH-Universal Activity and Stability of Cobalt Phosphide for Hydrogen Evolution

Abstract

Cobalt phosphide (CoP) has been established as a highly promising, pH-universal electrocatalyst for the hydrogen evolution reaction (HER). However, the operando surface structure–activity relationship and the mechanistic origins of its high stability remain elusive. Here, we combine large-scale data mining (2,282 experimental observations), surface Pourbaix diagrams, ab initio molecular dynamics (AIMD), and microkinetic modeling to reveal the operando surface configurations of CoP. We demonstrate that at low overpotentials (<100 mV), the surface is dominated by HO*-covered configurations featuring P–OH groups. This P–OH enrichment critically modulates the electronic structure of adjacent Co active sites, optimizing H* adsorption and facilitating water activation. At high overpotentials (>100 mV), the surface undergoes a structural transition to a dense H* coverage (comprising Co–H and P–H species), which maintains highly favorable adsorption thermodynamics of H* near the Sabatier optimum (ΔGH* = 0 eV) across the wide pH range of 0–14 under the applied electric field. Surface coverage mapping and 2D microkinetic volcano analyses, using ΔGHO* and ΔGH* as key descriptors, further corroborate these potential-dependent surface species and the resulting high HER activity. Crucially, these potential-dependent surface adsorbates protect CoP from detrimental element leaching. Moreover, comprehensive experimental characterizations validate our theoretical predictions. This work exemplifies the capabilities of combining AI-driven data platforms with precise simulations in accelerating scientific discoveries and uncovering underlying catalytic mechanisms.