Electrochemical reaction of CO2 to CO on a catalyst coated cation exchange membrane enabled by ammonium proton shuttling

Abstract

CO₂ reduction (CO₂RR) can convert CO₂ into feedstock for the chemical industry. In aqueous CO₂ electrolysis a key challenge is how to combine the CO₂ 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 (NH₄⁺), with a volatile conjugate base (NH₃), 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.