Asymmetric Electronic Modulation Accelerating Proton-Coupled Electron Transfer and CO₂ Reduction at Strongly Negative Potentials.

Abstract

Electrochemical CO₂ reduction to value-added chemicals offers a sustainable route toward carbon neutrality under mild conditions. Yet, it faces an intrinsic proton-electron imbalance at strongly negative potentials, where the hydrogen evolution reaction (HER) dominates, depletes interfacial protons, and severely compromises CO₂ reduction selectivity. Here, we report an asymmetric Ni-Fe dual-atom electrocatalyst that restores efficient proton-coupled electron transfer (PCET) through cross-site synergy. Electron migration from Fe to Ni establishes a local asymmetric electric field that enhances CO₂ adsorption and induces molecular bending at Ni sites, thereby weakening the C═O bond. Simultaneously, electron-deficient Fe sites exhibit moderated H adsorption, suppressing HER while serving as transient proton reservoirs for adjacent Ni centers. This spatially separated yet temporally synchronized PCET pathway accelerates the rate-determining CO₂ → COOH step and sustains efficient CO₂-to-CO conversion under deeply cathodic conditions. Consequently, the Ni─Fe dual-atom electrocatalyst maintains CO selectivity exceeding 95% across a wide potential window from -0.9 to -1.4 V and reaches 99.1% at -1.2 V, markedly outperforming monometallic analogues that exhibit volcano-type selectivity decay due to unbalanced PCET-HER kinetics. This work highlights asymmetric electronic modulation as an effective strategy to resolve the intrinsic PCET-HER selectivity conflict in CO₂ reduction.