Cation solvation engineering for enhanced CO2 electroreduction

Abstract

Electrochemical CO₂ reduction (CO₂RR) holds promise for carbon-neutral fuel production but is hindered by the competing hydrogen evolution reaction (HER) and slow kinetics. This study investigates how cationic solvation engineering with 18-crown-6 ether (18C6) impacts CO₂RR by selectively coordinating potassium ions (K⁺). 18C6 disrupts the K⁺ hydration shell, shifting the proton source from water to bicarbonate, suppressing HER, and enhancing CO₂RR. Experimental results show a 7.3-fold increase in CO faradaic efficiency (FE) with optimized 18C6 concentrations in 1 M KHCO₃. The non-monotonic relationship between CO production rates and 18C6 concentration highlights the balance between water and bicarbonate protonation processes. In situ ATR-FTIR and Raman analyses reveal reduced water adsorption and enhanced carbonate interactions at the electrode interface. Temperature-dependent electrochemical impedance spectroscopy demonstrates a lowered desolvation energy barrier (83.4 vs. 32.1 kJ mol⁻¹), indicating facilitated dehydration of solvated K⁺. This work provides insights into the mechanistic role of cationic solvation, offering a strategy for improving CO₂RR efficiency.