Steering Hydrogenation Pathways via Construction of Multivalence Cu Electrocatalysts for Boosting Electrocatalytic CO ₂ Reduction to CH ₄

The electrochemical reduction of CO 2 to CH 4 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 CO 2 to CH 4 . In this study, we propose an alternative active hydrogen (•H) transfer (AHT) process that significantly facilitates both CO 2 activation and subsequent intermediate hydrogenation, thereby markedly enhancing the kinetics of CO 2 -to-CH 4 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 CH 4 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 H 2 O 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 CH 4 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 CO 2 -to-CH 4 conversion.