Molecular Description of Electrosorption in a Nanoporous Carbon Electrode

A realistic molecular description is developed for electrosorption in nanoporous carbon electrodes, based on the replica reference interaction site model (replica RISM) approach to electrolyte solution sorbed in disordered nanoporous material. The theory properly accounts for the disordered structure of nanoporous carbon material and chemical specificity of sorbed solution species. The description is applied to the purification of ambient aqueous electrolyte solution of sodium chloride by nanoporous electrodes of carbonized polyvinylidene chloride (PVDC) and activated carbon. The solvation structure and thermodynamics of sorbed solution are discussed in detail. The specific sorption capacity and purification efficiency of the nanoporous electrodes are calculated. It is shown that the electrosorption mechanism and properties of a nanoporous electrode are very different from those of a planar electrochemical double layer. They are determined largely by the chemical potentials of ions sorbed in the nanoporous electrodes, rather than just by the potential drop in solution at the surface of nanopores.