Immobilized Tetraalkylammonium Cations Enable Metal-free CO 2 Electroreduction in Acid and Pure Water.

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.