(450b) Liquid and Solid Electrolyte Optimization from First Principles Multiscale Modeling of Electrochemical CO2 Reduction

We built a multiscale model including the cation at all scales. The transport in the vicinity of an Ag electrode is modeled by generalized modified Poisson-Nernst-Planck equations, and a microkinetic model where the number of active sites depends on the local cation concentration is used to calculate the current densities of CO₂ reduction to CO and reduction of water and H⁺ to H₂ based on local conditions and kinetic rate constants obtained from atomic-scale calculations (DFT and AIMD).

Current densities and FEs are evaluated, and the effect of different alkali bicarbonate buffers and starting buffer concentrations (from 0.01 M to 2 M) on the performance of the system over a large potential window (-0.4 to -1.7 V vs. RHE) is assessed. At slightly negative potentials, higher cation concentrations lead to improved activity, while at strongly negative potentials, cation accumulation due to double layer charging leads to transport limitations and reduced CO current density. The fixed organic cation in an AEM in 0.1 M KHCO₃ solution also provides microenvironments promoting eCO₂R. K⁺ is still present at the electrode, and the CO current density from organic microenvironments is in the same order of magnitude as that from K⁺ microenvironments. Reduced membrane hydration leads to reduced water activity and CO₂ transport limitations.

We optimize the catalyst-electrolyte microenvironment and predict the optimal electrolyte and operating conditions. The model paves the way for a fully first-principles multiscale electrolyte and ionomer design for electrochemical interfaces.