Co-Electrolysis Cell Configurations for CO2 Electrochemical Reduction Using Gold Electrodes
Authors: Patru Alexandra , Durst Julien , Herranz Juan , Permyakova Anastasia A. , Schmidt Thomas J. 
Published: February 2020

The electrical power produced by renewable energies can be chemically stored as hydrogen and other fuels via electrolysis. CO2 together with H2O can be used in this context as a feed in order to produce valuable chemical products, such as CO, CH4, C2H4, HCOO-, or CH3OH. This process will not only allow storing excess energy but also close the CO2 cycle, i.e., recycle this greenhouse gas. The main challenges of the CO2 reduction reaction (CO2RR) are related to reduce the associated overpotential, increase the overall faradaic efficiency and better control the product selectivity [1].
CO2RR kinetics and products identification and quantification are mostly carried out in half-cell configurations using liquid electrolytes. This fundamental approach of studying CO2RR is limited by the low solubility of CO2 in water, the maximum CO2 reduction current reported in the literature being in the range of 0.01- 0.02 A/cm2. In order to overcome the solubility problem and to reach higher operating current densities, CO2 reduction can be carried out in a co-electrolysis system where pure or diluted gaseous CO2 is used. To make co-electrolysis system economical feasible, efforts have to be concentrated on design of highly efficient cells, development of catalysts and their incorporation into efficient co-electrolyser designed for high current-density operation.
Recently it was shown that, from an economic perspective, products such as syngas (CO + H2) and formate (HCOO-) are the most suitable to be obtained from the electrochemical reduction of CO2 [2]. Based on this assumption the present study is focused on CO and HCOO- production.
To reach similar current densities to those featured in alkaline water electrolysers (0.2 A/cm2) different cell configurations were tested and the reaction products analysed by on-line mass spectroscopy. The cathode electrodes were based on gold catalyst since it can be used in different pH ranges without major chemical stability issues [3]. Au-black and Au-nanoparticles supported on carbon were used in a gas diffusion electrode configuration and their performances were compared with a pure gold mesh electrode. Each type of gold electrode was tested in various membrane-electrode assembly (MEAs, 1cm2) configurations. These configurations consist in an electrochemical cell with a proton exchange membrane or an anion exchange membrane as a unique core electrolyte or in a modified electrochemical cell with a stable pH-buffer layer of aqueous KHCO3 between the cathode catalyst and the membrane [4].
The co-electrolyser performances and selectivity’s of the various MEAs are examined in details.

Acknowledgements

Financial support of this work by the Commission of Technology and Innovation Switzerland (CTI) and the Swiss Competence Center for Energy Research Heat and Electricity Storage are greatly acknowledged.

References

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