Molecular picture of electric double layers with weakly adsorbed water

M Jia and JY Wang and QX Liu and XH Yang and C Zhang, JOURNAL OF CHEMICAL PHYSICS, 161, 104702 (2024).

DOI: 10.1063/5.0226111

Water adsorption energy, E-ads, is a key physical quantity in sustainable chemical technologies such as (photo)electrocatalytic water splitting, water desalination, and water harvesting. In many of these applications, the electrode surface is operated outside the point (potential) of zero charge, which attracts counter-ions to form the electric double layer and controls the surface properties. Here, by applying density functional theory-based finite-field molecular dynamics simulations, we have studied the effect of water adsorption energy E-ads on surface acidity and the Helmholtz capacitance of BiVO4 as an example of metal oxide electrodes with weakly chemisorbed water. This allows us to establish the effect of E-ads on the coordination number, the H-bond network, and the orientation of chemisorbed water by comparing an oxide series composed of BiVO4, TiO2, and SnO2. In particular, it is found that a positive correlation exists between the degree of asymmetry Delta CH in the Helmholtz capacitance and the strength of E-ads. This correlation is verified and extended further to graphene-like systems with physisorbed water, where the electric double layers (EDLs) are controlled by electronic charge rather than proton charge as in the oxide series. Therefore, this work reveals a general relationship between water adsorption energy E-ads and EDLs, which is relevant to both electrochemical reactivity and the electrowetting of aqueous interfaces.

Return to Publications page