Desorption of Hydrogen from Graphene Induced by Charge Injection

Abstract

Hydrogen adsorbed on a graphene electrode in contact with an aqueous solution is in a metastable state. Here, its desorption induced by a small positive charge pulse was studied by molecular dynamics with a tight binding method based on density functional theory. The efficiency of the code allowed to follow the trajectory of the desorbed particle in detail. Desorption was triggered by an oxygen atom of water, which was attracted to the surface and approached the adsorbed hydrogen. Charge transfer occured, and the hydrogen was attached to the water molecule to form a hydronium ion, which drifted into the solution, changed its solvation and underwent Grotthus steps. The reverse process, adsorption of a proton from the solution, required a pulse with a high negative charge. The reaction was governed by the field right in front of the electrode, and not by the electrode potential. The time that the proton transfer takes is much shorter than the relaxation time of the double layer, so that simulations performed with a constant electrode potential may not be realistic.