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.

Effects of Polyelectrolyte Surface Coating on the Energy Storage Performance in Supercapacitors

“…We note that we reach this point under the condition of fixed surface charge density, and the surface voltage varies as PE coating applies, as discussed above. However, in practical cases , and many conventional studies, , the surface voltage is fixed rather than the surface charge density. To further interpret the PE coating effect, we need to convert the capacitance–voltage relation to the conventional capacitance–charge relation.…”

Double-Edged Sword of Ion-Size Asymmetry in Energy Storage of Supercapacitors

“…The embedded pore is modeled as a structureless slit pore with a fixed width, L = 1.6 nm. 49,50 Generally, both sides of this slit pore carry the same charges, i.e., positive charges in anode and negative charges in cathode, as shown in panels a and b of Figure 1, respectively. Those pores are named as like-charge slit pores.…”

“…Otherwise, the preferential attractive interaction upon cations can further enhance the charge inversion. 49 Second, the dielectric constant is fixed throughout this work. In fact, the interfacial accumulation of ions will reduce the dielectric constant because of the solvent polarization effect.…”

“…As shown in the top panel of Figure , the charging process inside the porous electrode is simulated through the embedded pores under a grand canonical ensemble (i.e., μVT ensemble; see the Supporting Information for details), where μ, V , and T are chemical potential, volume, and temperature, respectively. The embedded pore is modeled as a structureless slit pore with a fixed width, L = 1.6 nm. , Generally, both sides of this slit pore carry the same charges, i.e., positive charges in anode and negative charges in cathode, as shown in panels a and b of Figure , respectively. Those pores are named as like-charge slit pores.…”

“…For short-ranged external potential, excess accumulation of cations can be neutralized by the preferential attractive interactions upon anions, thereby suppressing the charge inversion. Otherwise, the preferential attractive interaction upon cations can further enhance the charge inversion . Second, the dielectric constant is fixed throughout this work.…”