Potential-modulated orbital interactions determine domino CO/methanol selectivity for CO2 electroreduction on cobalt phthalocyanine.

Heterogenized cobalt phthalocyanine (hetero-CoPc) molecular catalysts exhibit domino CO/methanol selectivity during CO2 electroreduction. However, the origin of this selectivity is not well understood, impeding the strategic optimization for methanol generation. Here, we show potential-modulated orbital interaction mechanisms governing the selectivity in hetero-CoPc based on first-principles calculations with consideration of carbon support and electrochemical interfaces. Specifically, constant-potential orbital-resolved analyses reveal that electrons introduced by applied potentials initially occupy the semi-occupied Co-3dz2 orbital, thus suppressing CO-5σ → Co-3dz2 electron donation. This induces gradual weakening of *CO adsorption while establishing high *CO hydrogenation barriers (restricting the product to CO) over the medium potential range. With further decreasing potentials, a progressive electron population occurs in the Co-3dyz/dxz orbitals, promoting the Co-3dxz/dyz → CO-2π* back-donation. This facilitates the activation of the C─O bond of *CO, thereby reducing its hydrogenation barriers and enabling methanol production at more negative potentials. Similar analyses also rationalize experimental observations for other heterogenized metal phthalocyanines, showing the importance of potential-modulated orbital interactions for selectivity engineering.