Beyond the vacuum: modeling the solid-liquid interface for gas-involving electrocatalysis

The electrochemical reduction of small molecules, particularly CO₂ and N₂ (CO₂RR and NRR), offers a promising pathway for sustainable energy conversion; however, the complex nature of the electrified solid-liquid interface presents a formidable challenge for accurate theoretical modeling. Standard density functional theory (DFT) calculations frequently rely on simplified vacuum approximations, neglecting critical interfacial phenomena such as electric fields, solvation effects, and local microenvironments. To move beyond these vacuum limitations, a hierarchy of solvation models has been progressively developed to simulate the realistic reaction environment. This review systematically summarizes this methodological evolution for gas-involving electrocatalysis. First, the critical physicochemical features of the solid-liquid interface, including electric double layer structures, local ionic microenvironments, and reactant desolvation penalties, are outlined. Subsequently, current computational approaches are critically assessed, ranging from the foundational computational hydrogen electrode (CHE) and implicit continuum schemes to advanced explicit and hybrid implicit/explicit frameworks. Particular emphasis is placed on the capability of these models to capture solvent-mediated proton transfer and field-dependent kinetics. Finally, future frontiers driven by grand canonical DFT (GC-DFT), AI-accelerated sampling, and in situ spectroscopic integration are highlighted to guide the rational design of next-generation electrocatalysts.