Pseudocapacitive Behaviors of Polypyrrole Grafted Activated Carbon and MnO_2 Electrodes to Enable Fast and Efficient Membrane-Free Capacitive Deionization

摘要

Capacitive deionization (CDI) has emerged as a promising technique for brackish water desalination. Here, composites of polypyrrole grafted activated carbon (Ppy/AC) were prepared via in situ chemical oxidative polymerization of pyrrole on AC particles. The Ppy/AC cathode was then coupled with a MnO_2 anode for desalination in a membrane-free CDI cell. Both the Ppy/AC and MnO_2 electrodes exhibited pseudocapacitive behaviors, which can selectively and reversibly intercalate Cl~- (Ppy/AC) and Na~+ (MnO_2) ions. Compared to AC electrodes, the specific capacitances of Ppy/AC electrodes increased concurrently with the pyrrole ratios from 0 to 10%, while the charge transfer and ionic diffusion resistances decreased. As a result, the 10%Ppy/AC-MnO_2 cell showed a maximum salt removal capacity of 52.93 mg g~(-1) (total mass of active materials) and 34.15 mg g~(-1) (total mass of electrodes), which was higher than those of conventional, membrane, and hybrid CDI cells. More notably, the salt removal rate of the 10%Ppy/AC-MnO_2 cell (max 0.46 mg g~(-1) s~(-1) to the total mass of active materials and 0.30 mg g~(-1) s~(-1) to the total mass of electrodes) was nearly 1 order of magnitude higher than those in most previous CDI studies, and this fast and efficient desalination performance was stabilized over 50 cycles.