Proton tunneling interfacial engineering enables selective CO₂ electroreduction on CoZn oxide nanoflowers

Abstract

The electrochemical CO₂ reduction reaction (CO₂RR) holds great promise for closing the anthropogenic carbon cycle, yet conventional aqueous electrolytes epitomized by KHCO₃ suffer from intrinsically low CO₂ solubility, sluggish mass transport, and poor product selectivity, which collectively hamper catalytic efficiency and pathway controllability. Here, we report a rationally designed hybrid electrolyte system comprising 1-ethyl-3-methylimidazolium chloride ([EMIM]Cl) supplemented with KHCO₃, integrated with composition-tunable CoZn oxide nanoflower catalysts, that enables highly efficient and precisely switchable conversion of CO₂ to either CO or formic acid (HCOOH). Through an integrated approach combining electrochemical measurements, in situ infrared spectroscopy, and multiscale theoretical simulations (density functional theory + ab initio molecular dynamics), we uncover a previously unrecognized cooperative proton tunneling mechanism: water molecules act as proton-bridging mediators, constructing a linear [EMIM]-H···O-H···O-C(O)^- pre-reaction complex at the electrode interface that dramatically lowers the activation barrier of the proton-coupled electron transfer step. Critically, the Co:Zn ratio dictates the electronic structure of active sites; Co centers stabilize *COOH intermediates for CO evolution, whereas Zn centers favor *OCHO stabilization for HCOOH formation. Under optimized conditions, the Co:Zn = 2:1 catalyst achieves a Faradaic efficiency of 80.4% for CO, whereas the Co:Zn = 1:2 counterpart delivers 70.9% for HCOOH. This work establishes a paradigm of “proton tunneling channel engineering” via electrolyte-catalyst synergy, offering a molecular-level blueprint for precise control over multi-electron electrochemical transformations beyond CO₂RR.

Keywords

Carbon dioxide reduction reaction / cooperative proton tunneling / bimetallic cobalt-zinc catalyst / product selectivity engineering / electrolyte-catalyst interface

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