Promoting Cu-catalysed CO2 electroreduction to multicarbon products by tuning the activity of H2O
Tuning water activity in concentrated salt electrolytes from 0.97 to 0.47 controls C–C coupling vs. C1 product formation on Cu, achieving ~73% faradaic efficiency toward C2+ at −110 mA cm⁻² at modest overpotentials. Lower H₂O activity raises CO surface coverage and shifts C2+/C1 ratios up to 20-fold — establishing thermodynamic water activity as a practical selectivity lever for CO₂ reduction.