Chapter 2 - Kinetics of Ion Transport in a Porous Electrode

Abstract

Abstract In this chapter we go into some details of the kinetics of the processes of ions and salt adsorption in the micropores of active electrodes. This analysis is important from two points of view: understanding the phenomena involved and using this knowledge for explaining experimental results and, even more important, predicting improvements in the implementation. Consideration is first paid to the case of energy harvesting by EDL expansion (capacitive-mixing double layer expansion, CDLE). A 1-D model is described that allows predicting the time evolution of charge and potential inside the macro- and micropores after application of a step electric field. The same model yields the potential rises and drops when salty and fresh solutions are exchanged. The same treatment can be applied, with slight modifications, to the evaluation of the kinetics of capacitive deionization, which can be considered the long-time limit of the solutions found for the first problem. The cases of treated (soft electrode CDI) and membrane-coated electrodes (MCDI) are also considered. An excellent agreement with experimental data is reported, indicating that the physics of the CDI processes is in fact captured.