Tuning Water Microenvironments with Polar Organic Solvents to Steer Electrochemical Selectivity

Tuning interfacial microenvironments offers a powerful strategy to steer selectivity in electrocatalysis. Here, we show that tailoring solvent–water hydrogen-bond networks in aprotic solvents suppresses the competing hydrogen evolution reaction (HER) while maintaining high CO₂ reduction (CO₂R) activity. Strong hydrogen-bond solvents confine water reactivity, shifting HER onset potentials by nearly 1 V and enabling ~100% CO Faradaic efficiency at water concentrations up to 3 M with both gold and zinc catalysts. Bulk solvation characterization using infrared and NMR spectroscopy reveals that solvents with higher donor numbers form stronger hydrogen-bond networks, decreasing the fraction of free water and slowing hydrogen bonding dynamics. These bulk solvation descriptors correlate directly with interfacial phenomena observed by in situ surface-enhanced Raman spectroscopy, where restricted water accumulation at the electrode surface underpins HER suppression. These findings establish microenvironmental engineering as a design principle for selective CO₂ electrocatalysis and could be extended to other relevant transformations, including aqueous batteries, hydrogen evolution, and nitrogen reduction. Figure 1