Electrochemical reaction of CO 2 to CO on a catalyst coated cation exchange membrane enabled by ammonium proton shuttling

CO 2 reduction (CO 2 RR) can convert CO 2 into feedstock for the chemical industry. In aqueous CO 2 electrolysis a key challenge is how to combine the CO 2 educt with a neutral or alkaline electrolyte and achieve a stable cell operation. We propose a novel cell design and operation mode based on a catalyst coated cation exchange membrane: a cationic acid (NH 4 + ), with a volatile conjugate base (NH 3 ), replaces the protons usually present for ion transport. The approach avoids a high proton concentration at the cathode catalyst while still removing all products within the gas phase. In this paper different cell concepts are investigated to identify a pathway to a stable, efficient and scalable operation mode. In a completely novel cell design a FE CO > 50% was already maintained for over 35 h at 50 mA cm −2 , and at 200 mA cm −2 a cell voltage of 3.6 V (FE CO > 60%) was achieved. Surprisingly, ammonium oxidation at the anode was fully supressed under the reaction conditions.