Synergistic effect of substrate and ion-containing water in graphene based hydrovoltaic generators

Electricity generation from graphene based hydrovoltaic generators is a promising field for energy harvesting devices. Here by first-principles calculations we have systematically investigated the role of ion-containing water and substrates including polymer, silicon dioxide and transition metal dichalcogenides in charge exchange and doping on monolayer graphene coatings. The synergistic effect of water containing Na⁺ ions and the electronegativity of substrates dominates the p-type or n-type doping states of graphene and can significantly enhance charge transfer on graphene. Charge accumulations always occur on the surfaces of graphene covered substrates in the presence of Na⁺ solutions, which facilitates the formation of electric double layers with Na⁺ ions. According to the charge differences in graphene between graphene covered substrates with and without Na⁺ solutions, we estimate ideal currents and voltages generated in graphene when a Na⁺ containing water droplet moves on graphene covered substrates.