Combined Simulation and Experimental Study of Electrolysis Flow Cell for Continuous CO2 Conversion
Authors: Wen Guobin , Ren Bohua , Gostick Jeff T. , Chen Zhongwei 
Published: May 2020

Electrochemical carbon dioxide reduction reaction (CO2RR) is a promising strategy to sequester CO2 while synthesizing valuable chemicals and utilizing intermittent renewable energy supply from solar and wind energy.1 Electrolysis is often studied in H-cells that are composed of planar electrodes immersed in an aqueous electrolyte, which have severely limited mass transport across the electrolyte and hydrodynamic boundary layer.2-3 To avoid these limitations alkaline flow cells with a gas diffusion electrode (GDE) operated in a flow-by mode are sometimes used to achieve more realistic conditions. Although they provide higher current densities (CD) and energy efficiencies (EE), they suffer from carbonate salt precipitation in the stagnant pores of the GDE, moreover in KOH electrolyte CO2 is parasitically converted to bicarbonate. To remedy the latter problem neutral electrolytes, such as K2SO4 or KHCO3, can replace alkaline electrolytes, but these have so far demonstrated low EE due to high ohmic resistance and overpotentials in the GDE.

In this work we present a flow-through compact membrane electrode assemble (MEA) electrolysis cell for continuous CO2RR, which has following advantages. Firstly, the neutral electrolytes flowed through the porous electrode with carbon in the form of dissolved CO2 and HCO3
—.4 Electrolysis was carried out to produce CO gas and formate ions, which only need to pass through a thin boundary layer with minimized mass transport resistance. The porous electrode was pressed onto the membrane to ensure good ionic conductivity at the electrode−electrolyte interface. Secondly, flowing electrolyte eliminated degradation related to electrolyte flooding and carbonate precipitation. Finally, the overpotential was lowered through catalyst tuning and localized alkaline environment,5 contributing to cost competitive electroreduction of CO2 to CO, which exhibited partial current density (PCDCO) exceeding 150 mA cm−2 at cell overpotentials (|ηcell|) less than 2 V.

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