Immobilization of phosphotungstate through doping in polypyrrole for supercapacitors.

Immobilization of phosphotungstate is achieved through doping in polypyrrole via the electrochemical deposition of polypyrrole (PPy) in the presence of the phosphotungstate anions (PW12) on carbon nanotube film. Electrochemical stability in neutral solution is realized for PW12 in the prepared ECNT-PPy/5PW12, owing to the proton sponge provided by PPy. ECNT-PPy/5PW12 shows a high areal capacitance of 1300.0 mF cm-2 in LiCl solution at 1 mA cm-2. ECNT-PPy/5PW12 also displays high rate capability and good cyclic stability due to the interaction of incorporated PW12 and the polymer matrix. ECNT-PPy/5PW12 can retain 78.6% and 92.0% of its capacitance with 40-fold current increase and after 10 000 galvanostatic charge/discharge cycles, respectively. An asymmetric supercapacitor with the ECNT-PPy/5PW12 anode and CNT-MnO2 cathode demonstrates high volumetric energy density (4.71 mW h cm-3 at 13.85 mW cm-3) and long cycle life (90.0% capacitance retention after 10 000 charge/discharge cycles).