Optimizing the Selectivity of CH₄ Electrosynthesis from CO₂ Over Cuprates Through Cu─O Bond Length Descriptor

Precisely controlling the nature of Cu─O bond in Cu-based oxide catalysts and understanding its correlation with CH₄ electrosynthesis (from CO₂) for selectivity optimization is a long-standing challenge. Herein, taking a specific type of cuprates structured with CuO₄ square-planar motifs as the platform, we report a selectivity descriptor of Cu─O bond length for screening highly selective catalysts toward CH₄ electrosynthesis. We establish the descriptor by systematic investigations of several proof-of-concept cuprates. Their Cu─O bond lengths are precisely controlled ranging from 1.944 to 1.970 Å and these bonds remain stable in CH₄ selectivity evaluation. Our investigations demonstrate that the CH₄ selectivity exhibits a volcano-type dependence on the Cu─O bond length, and the optimized value is accessible at about 1.951 Å. This could be attributed to the optimal (neither too strong nor too weak) *CO adsorption created by the moderate Cu─O bond length, facilitating *CO hydrogenation. Furthermore, utilizing this descriptor, we predict three highly selective cuprates for CH₄ electrosynthesis, with superior selectivity that is near the top of the volcano plot. And importantly, in an acidic electrolyte (pH = 1), they outperform the reported catalysts, achieving CH₄ selectivity of up to 61.7% at 300 mA cm^-2.