CO₂ electrolysis by renewable energy is one crucial strategy to realize the closed loop of carbon cycle for the sustainable future.^[1] Among various CO₂ electrolysis products, the CO shows a high economical and commercial feasibility, due to its high market demands and the facile two-electron transfer reaction.^[2] Zero-gap membrane electrode CO₂ electrolysis is the most promising technology to produce CO at industrially relevant current densities, however, it still suffers from low CO₂ utilization and serious HCO₃^-/CO₃^2- crossover at large j (> 300 mA cm^-2), leading to low faradic efficiency (FE) and energy efficiency (EE).^[3]

Based on the baseline silver catalyst, this work will explore how the changes of CO₂ supply mode (e.g. flow rate, partial pressure, etc.) influences the local CO₂ concentration and local pH value on catalyst surface. By combining a series of well-designed experiments with theoretical mode calculation, we proposed that surface accessible CO₂ (SA-CO₂) supply on catalyst, which depends on surface OH^- content and surface structure, decides the CO₂ reduction reaction performance. At large current density, although the total CO₂ supply is higher than the requirement for electrolysis, the local CO₂ content is still limited by the in-situ generated hydroxide due to the high CO₂ hydration (HCO₃^-/CO₃^2-). Accordingly, a pulsed-electrochemical method was developed to improve the SA-CO₂ supply by introducing a pulse-relax time to decrease the surface OH^- content. When applying the same current, this baseline silver catalyst can implement a j_CO of > 225 mA cm^-2 with FE_CO > 75 % via pulsed-electrochemical method, much larger than the normal galvanostatic method with j_CO of 150 mA cm^-2.

Reference

[1] S. Nitopi, E. Bertheussen, S.B. Scott, X. Liu, A.K. Engstfeld, S. Horch, B. Seger, I.E.L. Stephens, K. Chan, C. Hahn, J.K. Nørskov, T.F. Jaramillo, I. Chorkendorff, Chem. Rev. 2019, 119, 7610-7672.

[2] B. Endrődi, E. Kecsenovity, A. Samu, T. Halmágyi, S. Rojas-Carbonell, L. Wang, Y. Yan, C. Janáky, Energy Environ. Sci., 2020, 13, 4098-4105.

[3] W. Lee, Y. Ko, Y. Choi, S. Lee, C. Choi, Y. Hwang, B. Min, P. Strasser, H. Oh, Nano Energy, 2020, 76, 105030.