Coordination-Engineered Interfacial Pathway Partitioning for Electrocatalytic CO₂ Conversion and Downstream Upgrading

Electrochemical CO₂ reduction (eCO₂RR) is increasingly capable of delivering downstream-compatible carbon products, yet the interfacial origin of pathway selection remains insufficiently understood. Here, coordination-environment-tunable Cu-Sn catalysts are employed to partition CO₂ electrosynthesis between a Sn-centered formate-selective pathway and a Cu-centered CO-selective pathway. In situ spectroscopy reveals coordination-dependent evolution of adsorbed intermediate and interfacial water structures, while H/D kinetic isotope analysis and in situ electrochemical impedance spectroscopy-distribution of relaxation times (EIS-DRT) measurements resolve distinct proton-coupled and polarization-sensitive kinetic regimes. Density functional theory calculations further elucidate the energetic origin of pathway bifurcation through coordination-dependent reconstruction of adsorption geometry and interfacial energetics. Sn-centered medium-coordination regimes favor oxygen-bound intermediates and a proton-coupled formate pathway, whereas Cu-centered medium-coordination regimes promote carbon-bound adsorption and CO-selective reactivity. In the downstream modules, electrodialysis achieves a 98.1% HCOOK-to-HCOOH conversion with 93.97% Faradaic efficiency (FE) at 300 mA cm^-2, while CO₂-NH₃ route delivers formamide with a maximum FE of 45.2% and a production rate of 840 µmol cm^-2 h^-1. This work establishes coordination-engineered interfacial partitioning as a strategy for integrated CO₂ electrosynthesis with downstream upgrading.