( Invited) Mechanistic Insights into Electrochemical Reactions at Solid-Liquid Interfaces: Role of Solvents and Ions

Electrochemical CO 2 reduction reaction (CO 2 RR) is a cornerstone technology for renewable fuel and chemical production in a carbon-neutral energy cycle. Despite extensive research, the molecular origins of electrolyte effects, particularly the coupled roles of cations, anions, and solvent structure, remain elusive at solid-liquid interfaces. [1] Understanding how these species modulate charge/proton transfer and interfacial reactivity is essential for advancing electrocatalyst design and improving selectivity. In this talk, I will present our recent efforts to elucidate the interfacial mechanisms of CO 2 RR at electrode-electrolyte interfaces using density functional theory (DFT), ab initio molecular dynamics (AIMD), enhanced sampling technique , constrained DFT, and Marcus theory. We construct complete reaction energy landscapes for both inner- and outer-sphere CO 2 reduction pathways at Au-water interfaces with the presence of ions, explicitly accounting for cation-solvent coordination and hydrogen-bond dynamics. Our simulations reveal that alkali cations stabilize key intermediates and promote inner-sphere reaction kinetics while suppressing the competing hydrogen evolution reaction (HER) via the modulation of crucial water network. [2][3] The outer-sphere CO 2 activation is tuned by cations due to the induced differences in solvent reorganization energies, and we establish how both short-range Coulomb interactions and long-range field effects from ions cooperatively modulate reaction energetics. [4] I will also talk about the recent emerging anion effect on interfacial understanding in heterogeneous electrocatalysis, with crucial roles on cation distribution, H-bond connectivity, reaction energy under various applied potential conditions. [5] These mechanistic insights provide a unified picture of how electrolyte structures (solvents, cations, and anions) and dynamic interactions at solid-liquid interfaces influence the molecule activation/reduction and multi-electron transfer pathways. By combining theoretical simulations with data-driven modeling and experimental collaboration, we aim for bridging atomic-scale understanding with macroscopic catalytic performance, guiding the rational design of catalysts and electrolytes for efficient and sustainable energy conversion. [1] X.P. Qin*, R. Sechi, H.A. Hansen*, Curr. Opin. Electrochem. 2025, 49, 101614. [2] X.P. Qin, T. Vegge, H.A. Hansen*, J. Chem. Phys. 2021, 155, 134703. [3] X.P. Qin, T. Vegge, H.A. Hansen*, J. Am. Chem. Soc. 2023, 145, 1897–1905. [4] X.P. Qin*, H.A. Hansen, K. Honkala, M.M. Melander*, Nat.Commun. 2023, 14, 7607. [5] K. Wan, Y. Cui, J. Francisco*, X. Shi*, X. Zeng*, J. Am. Chem. Soc. 2025, 147, 38301–38310