Preferential Ion Adsorption in Blue Energy Applications

Abstract

The available blue energy (or salinity gradient energy) in a capacitive double-layer expansion (CDLE) process is directly determined by the interplay between adsorption and release of ions from the electrodes at different salt concentrations. In this work, we explore the effect of asymmetric preferential ion adsorption at nanoporous anode and cathode surfaces as a means to enhance the available blue energy. We find that preferential adsorption can not only enhance the available energy output but also shift the supplied potential difference in the CDLE process toward the "spontaneous voltage". We determine the maximum available energy for the CDLE process as a function of the pore size and the degree of asymmetric adsorption. In the mixing of river water and saltwater, we find that preferential adsorption can give as much as 10% more available energy compared to indifferent electrode surfaces.

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