Adsorption of Molecular Nitrogen in Electrical Double Layers near Planar and Atomically Sharp Electrodes

The adsorption of gas molecules at electrode-electrolyte interfaces is an important step in electrochemical reactions. Using molecular dynamics simulations, we investigate the adsorption of dissolved N₂ in the electrical double layers (EDLs) of an aqueous electrolyte near planar and 1 nm radius spherical carbon electrodes. The adsorption of N₂ is found to be overall enriched near neutral electrodes regardless of their surface curvature, although it can be locally enriched or depleted depending on the distance from the electrode surface. In comparison, the adsorption of N₂ in the EDL near negatively charged electrodes is found to increase under a moderate surface charge density, but decrease under a high surface charge density, especially near a planar electrode. By analyzing the potential of mean force for dissolved N₂, the solvent-induced effects are found to play important roles in influencing the adsorption of N₂ in the EDLs. The adsorption behavior of N₂ molecules, especially their dependence on the surface charge and curvature of electrodes, is further rationalized by examining the structure of interfacial water molecules, their interference with the hydration shell of N₂, and their modification by the electrification of electrodes.