Unraveling molecular structures and ion effects of electric double layers at metal water interfaces

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Electrocatalysis is a decisive factor determining the practicability of green energy technologies. Electric double layers (EDLs) provide suitable chemical environments for electrocatalysis, having direct impact on their activity. However, little is known about EDL structures and dielectric properties. Aiming to address these issues, here we perform ab initio molecular dynamics simulations of electrified Ag(111)/water interfaces, and our calculations are able to reproduce the subtle difference in experimental capacitance curves due to ion effects. It is interesting to find that, on weak binding, Ag(111) water chemisorption can be strengthened when positively charged, contributing to the hump in differential capacitance owing to electronic effects. Bulky ClO4−, compared with small F−, increases the EDL width and decreases the water content at interfaces. Furthermore, steric repulsion between ClO4− forces the formation of a second layer of the ions at very positive potentials. These detailed factors dictate the EDL capacitances that depend on the nature of counter ions.