Steering Hydrogenation Pathways via Construction of Multivalence Cu Electrocatalysts for Boosting Electrocatalytic...

The electrochemical reduction of CO₂ to CH₄ in neutral electrolytes represents a compelling route toward carbon-neutral energy systems. Nonetheless, realizing a high Faradaic efficiency (FE) at industrially relevant current densities remains a formidable challenge, primarily due to the intrinsically slow kinetics of the multistep proton-coupled electron transfer (PCET) processes from CO₂ to CH₄. In this study, we propose an alternative active hydrogen (•H) transfer (AHT) process that significantly facilitates both CO₂ activation and subsequent intermediate hydrogenation, thereby markedly enhancing the kinetics of CO₂-to-CH₄ conversion by designing a multivalent copper-based catalyst comprising Cu(0) nanoparticles and Cu(I) single atoms on an Al-MgO support. This novel catalyst achieved a CH₄ Faradaic efficiency of ∼93.5% at a high current density of 350 mA cm^-2 in a flow cell, substantially outperforming its monovalent counterpart (Cu(0)/Al-MgO, FE 55.4% at 300 mA cm^-2) governed by a PCET-mediated pathway. Experimental studies and theoretical calculations demonstrate that the Cu(I) sites significantly lower the energy barrier for H₂O dissociation, generating •H species that subsequently migrate to adjacent Cu(0) sites. These •H species effectively promote the hydrogenation of *CO to *CHO on Cu(0) sites, a key step in CH₄ formation. Our findings highlight the critical role of tailoring hydrogenation pathways from traditional PCET to AHT mechanisms for advancing the efficiency and selectivity of electrocatalytic CO₂-to-CH₄ conversion.