Co-electrolysis of CO2 and H2O: From electrode reactions to cell-level development

Juan Herranz,Thomas J Schmidt,Alexandra Pătru,Emiliana Fabbri

doi:10.1016/j.coelec.2020.05.004

Juan Herranz, Thomas J Schmidt + Show 2 more

Open Access

https://doi.org/10.1016/j.coelec.2020.05.004

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Abstract

Abstract The electroreduction of CO2 into value-added products (e.g. CO) constitutes an excellent means of decreasing this greenhouse gas emissions, but limited efforts have been devoted to the implementation of this reaction within the so-called co-electrolysis cells operating at process-relevant currents >> 100 mA·cmgeom−2. Reaching such performances shall require a combination of gas-fed reactants and the corresponding diffusion electrodes, along with ion-exchange membranes and ionomers that set the operative pH at the cells' cathode and anode. The latter constitutes a key design parameter that must be combined with the need to minimize the crossover of reaction products and/or (bi)carbonate anions from the cathode to the anode, whereby their reoxidation to carbon dioxide leads to a decrease in the device's net CO2 consumption.

Highlights

Attaining the global temperature increase target of Electrochemical reactions and acid–base equilibria in co-electrolysis cells The extensive work devoted to the study of CO2 electroreduction kinetics discussed previously has served to establish the large variety of C-products that can be derived from this reaction (e.g. CH4, C2H4) [7,8], but recent technoeconomic analyses have concluded that the electrochemical production of CO has the greatest chance to become cost competitive with regard to current chemical routes (while the business case for www.sciencedirect.com90 Electrocatalysis Figure 1Schematic representation of an MEA-based co-electrolysis cell and of the three different catalyst layer -membrane interfaces discussed . (a) Co-electrolysis cell constituted by a cathode and an anode compartment fed with gaseous CO2 vs. water reactants that get reduced/oxidized to CO and O2, respectively. (b) Cell configuration implementing an anion-exchange membrane (AEM) that transports anions from cathode to anode, where they get oxidized back to CO2., (c) Cell with a reverse bias bipolar membrane (RB-BPM) in which water is split into protons and hydroxyl groups at the interface between cation- and anion-exchange layers (CEL, AELs). (d) Co-electrolyzer using a forward-bias bipolar membrane (FBBPM) in which (bi)carbonate anions and protons recombine at the AELCEL membrane yielding CO2 and H2O
Schematic representation of an MEA-based co-electrolysis cell and of the three different catalyst layer -membrane interfaces discussed . (a) Co-electrolysis cell constituted by a cathode and an anode compartment fed with gaseous CO2 vs. water reactants that get reduced/oxidized to CO and O2, respectively. (b) Cell configuration implementing an anion-exchange membrane (AEM) that transports anions from cathode to anode, where they get oxidized back to CO2., (c) Cell with a reverse bias bipolar membrane (RB-BPM) in which water is split into protons and hydroxyl groups at the interface between cation- and anion-exchange layers (CEL, AELs). (d) Co-electrolyzer using a forward-bias bipolar membrane (FBBPM) in whichcarbonate anions and protons recombine at the AELCEL membrane yielding CO2 and H2O
In summary, the aforementioned discussed studies demonstrate the potential of co-electrolysis cells to reduce CO2 into value-added products at applicationrelevant current densities, while highlighting the importance of numerous cell design aspects that were overlooked in previous electrocatalysis works but that are extremely relevant to the operation of such devices

Summary

Introduction

Attaining the global temperature increase target of Electrochemical reactions and acid–base equilibria in co-electrolysis cells The extensive work devoted to the study of CO2 electroreduction kinetics discussed previously has served to establish the large variety of C-products that can be derived from this reaction (e.g. CH4, C2H4) [7,8], but recent technoeconomic analyses have concluded that the electrochemical production of CO has the greatest chance to become cost competitive with regard to current chemical routes (while the business case for www.sciencedirect.com90 Electrocatalysis Figure 1Schematic representation of an MEA-based co-electrolysis cell and of the three different catalyst layer -membrane interfaces discussed . (a) Co-electrolysis cell constituted by a cathode and an anode compartment fed with gaseous CO2 vs. water reactants that get reduced/oxidized to CO and O2, respectively. (b) Cell configuration implementing an anion-exchange membrane (AEM) that transports anions from cathode to anode, where they get oxidized back to CO2., (c) Cell with a reverse bias bipolar membrane (RB-BPM) in which water is split into protons and hydroxyl groups at the interface between cation- and anion-exchange layers (CEL, AELs). (d) Co-electrolyzer using a forward-bias bipolar membrane (FBBPM) in which (bi)carbonate anions and protons recombine at the AELCEL membrane yielding CO2 and H2O. (b) Cell configuration implementing an anion-exchange membrane (AEM) that transports anions from cathode to anode, where they get oxidized back to CO2., (c) Cell with a reverse bias bipolar membrane (RB-BPM) in which water is split into protons and hydroxyl groups at the interface between cation- and anion-exchange layers (CEL, AELs).

Results

Conclusion