Modification of the surface of activated carbon electrodes for capacitive mixing energy extraction from salinity differences

Abstract

The "capacitive mixing" (CAPMIX) is one of the techniques aimed at the extraction of energy from the salinity difference between sea and rivers. It is based on the rise of the voltage between two electrodes, taking place when the salt concentration of the solution in which they are dipped is changed. We study the rise of the potential of activated carbon electrodes in NaCl solutions, as a function of their charging state. We evaluate the effect of the modification of the materials obtained by adsorption of charged molecules. We observe a displacement of the potential at which the potential rise vanishes, as predicted by the electric double layer theories. Moreover, we observe a saturation of the potential rise at high charging states, to a value that is nearly independent of the analyzed material. This saturation represents the most relevant element that determines the performances of the CAPMIX cell under study; we attribute it to a kinetic effect.

Electrode kinetics in the “capacitive mixing” and “battery mixing” techniques for energy production from salinity differences

“…The measurement of the open-circuit potential in solutions with alternating salinity gives a potential rise of 82 mV, compatible with previously reported results[24].…”

“…In CDLE, where identical activated carbon electrodes are used, such a technique cannot be applied; instead, the circuit includes an external power supply and a fixed load in series with the cell; this more complicated circuit is needed for creating the oppositely charged electric double layers. The same circuit has been used, up to now, also for the functionalized activated carbons [22,23,24]; since this is an unnecessary complication in this case, in the present paper we will study the application of the galvanostatic operation also to the functionalized activated carbons.…”

“…The films made with NS30 are cast by means of the "doctor blade" tech- In this case, the AccMix cell is composed by two activated carbon electrodes with the two different functionalizations [24].…”

“…Functionalized activated carbon electrodes[22,23,24,25,26] Functional groups have been added to the surface of activated carbons with the aim of forming electric double layers, without the need of charging.According to the nature of such functional groups, the activated carbon spontaneously assumes either a positive or a negative potential when dipped into the solutions.…”

Harnessing ‘Blue energy’: A Review on Techniques and Preliminary Analysis

“…Optimization of distance between the electrodes in respect to the hydrodynamics of the flow of solution is recommended by them in order to improve this technique. Some works on CDP explaining the physics of the reaction, impact of electrode parameters, membrane and configuration are presented in [29].…”