Tuning Spatial Product Selectivity of Electrochemical CO 2 Reduction in Gas Diffusion Systems via Mass-Transport Control

Electrochemical CO 2 reduction on copper is a promising path to green C 1 and C 2 + chemicals and fuels, but its complexity, due to branching pathways 1 , adsorbate coverages 2 , and mass-transport coupling, has hindered systematic electrolyzer design. This work addresses this challenge using a pioneering first-principles 3 -driven multi-scale modeling approach on state-of-the-art gas diffusion layer-based electrodes 4 . By creating digital twins of experimental systems, we decipher two key cell design parameter groups: (1) the electrochemical surface area, influencing currents across the whole catalyst layer and voltage range, and (2) properties of the catalyst layer substrate critical at active sites close to the gas inlet under mass-transport-limited conditions. These attributes also enable them to control the spatial product selectivity of C 1 vs. C 2 product formation. Comparisons with experiments 5 show promising agreement while suggesting additional complexities, such as the presence of various active sites or alternate transport channels. These insights are unlocked solely due to the non-fitted nature of the kinetic model, setting the stage for first-principles-driven multi-scale design. References: Seger, B., Kastlunger, G., Bagger, A. & Scott, S. B. A perspective on the reaction mechanisms of CO 2 electrolysis. ACS Energy Lett. 2212–2227 (2025). Kastlunger, G. et al. Using pH Dependence to Understand Mechanisms in Electrochemical CO Reduction. ACS Catal. 12 , 4344–4357 (2022). Liu, X. et al. pH effects on the electrochemical reduction of CO (2) towards C 2 products on stepped copper. Nat. Commun. 10 , 1–10 (2019). Weng, L.-C., Bell, A. T. & Weber, A. Z. Modeling gas-diffusion electrodes for CO 2 reduction. Phys. Chem. Chem. Phys. 20 , 16973–16984 (2018). Jung, Y. et al. Understanding the role of gas diffusion electrodes in steering the CO 2 electroreduction pathway. Nano Energy 147 , 111602 (2026).