Immobilized Tetraalkylammonium Cations Enable Metal‐free CO2 Electroreduction in Acid and Pure Water

Abstract Carbon dioxide reduction reaction (CO 2 RR) provides an efficient pathway to convert CO 2 into desirable products, yet its commercialization is greatly hindered by the huge energy cost due to CO 2 loss and regeneration. Performing CO 2 RR under acidic conditions containing alkali cations can potentially address the issue, but still causes (bi)carbonate deposition at high current densities, compromising product Faradaic efficiencies (FEs) in present‐day acid‐fed membrane electrode assemblies. Herein, we present a strategy using a positively charged polyelectrolyte—poly(diallyldimethylammonium) immobilized on graphene oxide via electrostatic interactions to displace alkali cations. This enables a FE of 85 %, a carbon efficiency of 93 %, and an energy efficiency (EE) of 35 % for CO at 100 mA cm −2 on modified Ag catalysts in acid. In a pure‐water‐fed reactor, we obtained a 78 % CO FE with a 30 % EE at 100 mA cm −2 at 40 °C. All the performance metrics are comparable to or even exceed those attained in the presence of alkali metal cations.