Effect of dopants on the adsorbing performance of polypyrrole/graphite electrodes for capacitive deionization process

Polypyrrole/graphite electrodes (PPy/G-Cl, PPy/G-p-TS and PPy/G-DBS) were synthesized by electrochemical polymerization process. The three type of electrodes were then used as anode respectively to study the effect of dopants on the adsorbing performance of PPy/G electrodes in capacitive deionization process. The morphology, thickness, conductivity of PPy layers and the surface area of the PPy/G electrodes were characterized and tested respectively, all of which depend on the type of dopants. The electrochemical impedance spectroscopies infer that the adsorbing processes of the PPy/G electrodes are controlled by Warburg diffusion. Also, the PPy/G-Cl and PPy/G-p-TS electrodes show better conductivity than the PPy/G-DBS electrode in CDI cells. The ion exchange capability of the PPy layers was measured by an electrochemical quartz crystal microbalance (EQCM), which proves that the ion exchange capability of the PPy layers is in the order of: PPy-p-TS > PPy-Cl > PPy-DBS. The results of adsorbing experiments indicate that the specific adsorption capacities of PPy/G electrodes to Cl− vary with the type of dopants and follow the order of: PPy/G-p-TS > PPy/G-Cl > PPy/G-DBS. Further, it can be obtained that dopants dominate the electrochemically switchable ion exchange (ESIE), and the specific adsorption capacities of the PPy/G electrodes are mainly determined by the ESIE.