Combined Simulation and Experimental Study of Electrolysis Flow Cell for Continuous CO2 Conversion

Abstract

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.Reference 1. De Luna, P.; Hahn, C.; Higgins, D.; Jaffer, S. A.; Jaramillo, T. F.; Sargent, E. H., What would it take for renewably powered electrosynthesis to displace petrochemical processes? Science 2019, 364 (6438).2. Liu, M.; Pang, Y.; Zhang, B.; De Luna, P.; Voznyy, O.; Xu, J.; Zheng, X.; Dinh, C. T.; Fan, F.; Cao, C.; de Arquer, F. P. G.; Safaei, T. S.; Mepham, A.; Klinkova, A.; Kumacheva, E.; Filleter, T.; Sinton, D.; Kelley, S. O.; Sargent, E. H., Enhanced electrocatalytic CO2 reduction via field-induced reagent concentration. Nature 2016, 537 (7620), 382-386.3. Wen, G.; Lee, D. U.; Ren, B.; Hassan, F. M.; Jiang, G.; Cano, Z. P.; Gostick, J.; Croiset, E.; Bai, Z.; Yang, L.; Chen, Z., Orbital Interactions in Bi-Sn Bimetallic Electrocatalysts for Highly Selective Electrochemical CO2 Reduction toward Formate Production. Adv. Energy Mater. 2018, 8 (31), 1802427.4. Weng, L. C.; Bell, A. T.; Weber, A. Z., Modeling gas-diffusion electrodes for CO2 reduction. Phys Chem Chem Phys 2018, 20 (25), 16973-16984.5. Verma, S.; Hamasaki, Y.; Kim, C.; Huang, W.; Lu, S.; Jhong, H.-R. M.; Gewirth, A. A.; Fujigaya, T.; Nakashima, N.; Kenis, P. J. A., Insights into the Low Overpotential Electroreduction of CO2 to CO on a Supported Gold Catalyst in an Alkaline Flow Electrolyzer. ACS Energy Letters 2018, 3 (1), 193-198.