Local-strain-induced CO₂ adsorption geometries and electrochemical reduction pathway shift

Unravelling the influence of strain and geometric effects on the electrochemical reduction of carbon dioxide (CO₂RR) on Cu-based (or Pd-based) alloys remains challenging due to complex local microenvironment variables. Herein, we employ two PdCu alloys (nanoparticles and nanodendrites) to demonstrate how CO₂RR selectivity can shift from CO to HCOO^-. Despite sharing consistent phases, exposed crystal facets, and overall oxidative states, these alloys exhibit different local strain profiles due to their distinct geometries. By integrating experimental data, in-situ spectroscopy, and density functional theory calculations, we revealed that CO₂ prefers adsorption on tensile-strained areas with carbon-side geometry, following a *COOH-to-CO pathway. Conversely, on some compressive-strained regions induced by the dendrite-like morphology, CO₂ adopts an oxygen-side geometry, favoring an *OCHO-to-HCOO pathway due to the downshift of the d-band center. Notably, our findings elucidate a dominant *OCHO-to-HCOO^- pathway in catalysts when featuring both adsorption geometries. This research provides a comprehensive model for local environment of bimetallic alloys, and establishes a clear relationship between the CO₂RR pathway shift and variation in local strain environments of PdCu alloys.