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Published July 20, 2023 | public
Journal Article

Local microenvironment tuning induces switching between electrochemical CO₂ reduction pathways


Gas diffusion layers (GDL) have become a critical component in electrochemical CO₂ reduction (CO₂R) systems because they can enable high current densities needed for industrially relevant productivity. Besides this function, it is often assumed that the choice of catalyst and electrolyte play much more important roles than the GDL in influencing the observed product selectivity. Here, we show that tuning of the GDL pore size can be used to control the local microenvironment of the catalyst and hence, effect significant changes in catalytic outcomes. This concept is demonstrated using sputtered Ag films on hydrophobic PTFE substrates with 6 different pore sizes. Although Ag is known to be a predominantly CO generating catalyst, we find that smaller pore sizes favor the generation of formate up to a faradaic efficiency of 43%. Combined experimental and simulation results show that this is due to the influence of the pore size on CO₂ mass transport, which alters the local pH at the electrode, resulting in reaction pathway switching between CO and formate. Our results highlight the importance of the local microenvironment as an experimental knob that can be rationally tuned for controlling product selectivity: a key consideration in the design of CO₂R systems.

Additional Information

© The Royal Society of Chemistry 2023. This article is part of the themed collection: Journal of Materials Chemistry A: Emerging Investigators. Y. L. acknowledges support and funding from the A*STAR (Agency for Science, Technology and Research) under its LCERFI program (Award No. U2102d2002) and A*STAR Career Development Award (Project No. 202D800037). A. B., H. A. A., A. Z. W., and A. J. K. would like to acknowledge support from the Liquid Sunlight Alliance, which is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Fuels from Sunlight Hub under Award Number DE-SC0021266. A. J. K. acknowledges funding from the National Science Foundation Graduate Research Fellowship under Grant No. DGE 2146752. Z. F. and X. M. acknowledges funding from National Natural Science Foundation of China (22178265, U21B2096 and 21938008). W. R. L. would like to acknowledge the A*STAR Career Development Award (Grant number: C210112053) and Young Individual Research Grant (Grant number: A2084c0180). Author contributions. Y. L. and H. A. A. supervised the project. Y. L. conceived the idea and designed the experiments. S. B. D. carried out all the experimental work. A. B. performed and analyzed the confocal microscopy experiments. Z. F. and A. J. K. performed the multiphysics simulations. A. Z. W. and E. K. supervised the multiphysics simulations. A. Q. F., A. D. H., W. R. L. and X. M. contributed to data analysis and manuscript editing. Y. L., A. B. and S. B. D. co-wrote the manuscript. All authors discussed the results and assisted during the manuscript preparation. The authors declare no competing interests.

Additional details

August 22, 2023
October 20, 2023