(5f) Theoretical Analysis of Electrochemical CO? Reduction in Seawater Electrolytes

Methane-selective electrochemical CO₂ reduction in seawater is a promising approach to sustainable fuel production. Seawater offers advantages such as low cost and high availability, but the presence of divalent cations like Mg²⁺ and Ca²⁺ significantly limits catalytic performance through salt precipitation and catalyst deactivation. Recent experiments have shown that Cu-based catalysts combined with ethylenediaminetetraacetic acid (EDTA) enhance CH₄ selectivity, yet the atomistic mechanisms underlying this improvement remain poorly understood.

In this study, we investigate the roles of surface structure and electrolyte environment in CO₂ reduction via density functional theory (DFT) and ab initio molecular dynamics (AIMD) simulations. DFT calculations were performed to analyze the reaction pathway of the CO₂ reduction reaction (CO₂RR) on low-coordinated Cu(111) surfaces and Cu(111), showing that the low-coordinated surfaces lower the energy barriers associated with CH₄ formation. AIMD simulations were conducted to examine the interactions between EDTA, divalent cations, and water. The results indicate that EDTA effectively chelates Mg²⁺ and Ca²⁺, reducing their concentration near the surface and mitigating salt precipitation. In addition, EDTA alters the hydrogen-bonding network of water molecules, thereby enhancing local proton availability at the interface.

This work provides theoretical insights into how surface coordination and electrolyte additives synergistically influence CH₄ selectivity in seawater-based CO₂RR systems. These findings offer guidance for the rational design of nanostructured catalysts and electrolyte systems for electrochemical energy conversion under realistic conditions.