Unveiling a Cooperative Mechanism for the Alkaline Hydrogen Evolution Reaction: Role of Built‐in Electric Field

Abstract The work function has a significant influence on surface charge distribution, particularly when a built‐in electric field (BIEF) is present. Recent research is focused on leveraging BIEFs at the interface of different electronic environments to improve hydrogen production. Therefore, analyzing and correlating parameters such as the work function, BIEF, and Gibbs free energy is crucial for understanding the reaction mechanism. Herein, a p‐n heterojunction of CuO‐CuWO 4 is created to form a moderate space‐charge region at the interface. The Gibbs free energy (∆G) in the depletion regime displays behavior that contrasts with that of the bulk region, facilitating the hydrogen evolution reaction (HER). Along the heterojunction interface, the ∆G indicates high adsorption affinity of protons toward the CuO phase and significant desorption at the CuWO 4 phase. The catalyst effectively fine‐tunes its ∆G value relative to surface coverage and exhibits a negative cooperative effect. The Gibbs free energy of the catalyst shows that up to 80% surface coverage, the catalyst surface maintains a high proton adsorption affinity (−1.05 eV), which gradually decreases to −0.05 eV at 100% coverage. The catalyst surpassed commercial Pt/C, demonstrating higher efficiency and achieving a current density of 10 mA cm − 2 at an overpotential of just 21 mV.