Design Principles of Bipolar Electrochemical Co-Electrolysis Cells for Efficient Reduction of Carbon Dioxide from Gas Phase at Low Temperature

Alexandra Pătru,Tobias Binninger,Bernhard Pribyl,Thomas J Schmidt

doi:10.1149/2.1221816jes

Abstract

Cell designs for the electrochemical reduction of CO2 from gas phase were developed and investigated, and the critical elements for an efficient process were identified. Various types of polymeric membrane were used to build membrane electrode assembly adapted for CO2 reduction in gas phase: protonic and anion exchange membrane (AEM), bipolar membrane and a modified bipolar like membrane configuration. Configurations using anion exchange ionomer in the cathodic catalytic layer in contact with an AEM allow for a great enhancement of the cathode reaction selectivity toward CO. However, a severe problem was identified when co-electrolysis is performed using only an AEM: this type of membrane acts as a CO2 “pump” meaning that for each molecule of CO2 reduced at the cathode, one or two CO2 molecules are produced at the anode by oxidation of the carbonate/bicarbonate anion transported in the membrane. A bipolar membrane system was shown to soften this problem, but only a newly developed cell design was able to fully prevent the parasitic CO2 pumping. Using this new cell configuration, the faradaic efficiency of an alkaline environment is maintained, the parasitic CO2 pumping to the anode side is completely suppressed, and the overall cell voltage efficiency is highly improved.

Highlights

The electrochemical reduction of carbon dioxide is a very attractive proposition for minimizing the level of atmospheric CO2, for reutilizing CO2 emissions from fossil fuel sources, and for storing energy when it is coupled to a renewable energy source such as wind or solar PV
Carbon dioxide is converted to fuels or chemical feedstock, which, depending on the process efficiency, could be generated at a competitive price when compared with chemicals that are conventionally derived from petroleum.[1,2]
Influence of ionomer/membrane pH on CO2 reduction reaction (CO2RR).—The CO2RR is pH dependent and in gas phase co-electrolysis systems, the reaction pH is defined by the type of polymer electrolyte like in similar electrochemical devices, e.g. fuel cells and electrolyzers.[5]

Summary

Introduction

The electrochemical reduction of carbon dioxide is a very attractive proposition for minimizing the level of atmospheric CO2, for reutilizing CO2 emissions from fossil fuel sources, and for storing energy when it is coupled to a renewable energy source such as wind or solar PV. The selectivity for CO was superior in the alkaline cell, with results shown in Fig. 2b: Using acidic ionomer/membrane, small amounts of CO were obtained only at low overpotentials, whereas at higher overpotentials only H2 could be detected as cathode reaction product.

Results

Conclusion