Copper (Cu) is the unique known metal catalyst that is capable of catalyzing CO₂ electro-reduction (eCO₂RR) into C₂₊ chemicals (e.g., ethylene (C₂H₄), ethanol (C₂H₅OH), and n-propanol (n-C₃H₇OH)) and methanol (CH₃OH). However, Cu has a wide product distribution. The intricate reaction network of eCO₂RR to C₂₊ product restricts the rational design of advanced Cu catalysts or catalysts even beyond Cu for a single product formation. Nevertheless, based on the state-of-the-art eCO₂RR mechanism, the reaction pathway can be divided into two stages: C-C coupling, which is the rate-determining step (RDS) for overall C₂₊ product generation, and post-C-C coupling, which is the selectivity determining step (SDS) branching single C₂₊ product formation. A lot of previous effort has been put into lowering the kinetic barrier of C-C coupling reaction and subsequently increasing the overall selectivity of C₂₊ products. The prior strategies in these efforts all revolved around *CO manipulation to improve the *CO adsorption strength and/or *CO coverage, two interdependent parameters measuring the interaction between the catalyst surface and the *CO intermediate. The control over reaction path bifurcation in the post-C-C coupling stage, which is often neglected in previous design attempts, plays an equally important role in determining the selectivity towards a specific C₂ product. We will present our recent work on identifying the key SDS and selectivity determining intermediate (SDI) dividing C₂H₄ versus C₂H₅OH formation based on a theory prediction-experimental validation loop. We harnessed the SDI and used a reaction descriptor, oxophilicity of the metal surface, to guide the design of catalysts for precise control over post-C-C coupling selectivity. The single-site doping into the Cu surface effectively tunes metal-oxygen binding strength, thus navigating the activity and productivity toward C₂H₄ or C₂H₅OH. The optimal single-site doped Cu catalyst exhibits 70% FE of C₂H₄ at a partial current density of >1.5 A cm^-2. We further extend this strategy of modulating the surface oxophilicity to control the selectivity of CH₃OH over CH₄ and HCOO^-versus CO, all of which involve an oxygen-bound SDI. For example, the single-site doped indium achieves HCOO^-productivity to > 1.0 A cm^-2 while maintaining > 95% FE. Our work demonstrates the importance of controlling SDI adsorption configuration and strength in directing the selectivity to a single product.

Zhengyuan Li

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