Water gating in CO2 electrolysis: interfacial water controls catalyst selectivity at industrial current density

Researchers at ICFO and ICIQ used operando Raman spectroscopy inside a working membrane electrode assembly to watch how interfacial water affects CO2 electrolysis on copper catalysts. At current densities up to 1 A/cm2, they found that the ordered layer of water molecules acts as a gate: when three-hydrogen-bond water dominates, CO2 reduction to multicarbon products is favored; when a denser four-hydrogen-bond water layer forms, hydrogen evolution takes over. Selectivity for multicarbon products reached 45 percent around 0.2 A/cm2, where the water structure was most productive. The study, published in Nature Catalysis, combines spectroscopy with ab initio molecular dynamics to explain how potassium cations and adsorbed species reshape the water network. That points to practical design levers: surface functionalization, electrolyte composition, and water-exchange membranes could keep the interface in the productive regime. For anyone working on CO2 utilization, green chemicals, or electrolyser scale-up, the key takeaway is that water management at the molecular scale may matter as much as catalyst composition.