(292h) Membrane-Free Electrochemical CO2 Conversion Using Bicarbonate Solutions

Integrating CO₂ capture and utilization using electrochemical methods is a promising approach to addressing current energy and climate challenges.^{1, 2} Conventional gas-fed membrane-based CO₂ electrolyzers have shown promise in this aspect, but several key challenges must be overcome for successful commercialization: i) large pH gradients that result in conversion of CO₂ into (bi)carbonate at the cathode and subsequent release of CO₂ at the anode,³ ii) the degradation of polymeric membranes,⁴ and iii) the decreased performance of membranes and electrodes caused by deposition of impurity species.⁵

In this work, we demonstrate a design of packed-bed membraneless electrolyzers (PBME) with a series of alternating porous electrodes to simultaneously address these three issues. By flowing a bicarbonate electrolyte resembling a carbon-capture solution through proton-generating anodes and CO₂ reduction cathodes, the pH of the electrolyte was balanced between electrodes while CO₂ was generated immediately upstream of the cathode, as evidenced by in-situ colorimetric imaging measurements.⁶ This helps minimize the back-conversion from CO₂ to (bi)carbonate that results in low CO₂ conversion per pass. We show that the PBME design is scalable and that CO₂ utilization is expected to exceed 80% in an optimized multi-cell system. By adding chelating agents to scavenge metal impurities and ultra-thin metal oxide layers to encapsulate the electrocatalysts, impurity deposition was minimized and the electrode stability was significantly enhanced, as evidenced by electrochemical and product measurements, as well as electrode characterization. We also evaluated operations at elevated pressures, where the performance is expected to be improved due to the higher solubility of CO₂, hence resulting in a larger amount of CO₂ that can participate in the reaction.

This work demonstrates a simple, affordable, and scalable electrolyzer design that will enable the decarbonization of energy-intensive industrial processes through electrification in a sustainable energy future.

References

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(5) Hori, Y.; Konishi, H.; Futamura, T.; Murata, A.; Koga, O.; Sakurai, H.; Oguma, K. “Deactivation of copper electrode” in electrochemical reduction of CO2. Electrochimica Acta 2005, 50 (27), 5354-5369. DOI: https://doi.org/10.1016/j.electacta.2005.03.015.

(6) Pang, X.; Verma, S.; Liu, C.; Esposito, D. V. Membrane-free electrochemical CO2 conversion using serially connected porous flow-through electrodes. Joule 2022, 6 (12), 2745-2761. DOI: https://doi.org/10.1016/j.joule.2022.11.003.