Toward a high specific power and high stability polypyrrole supercapacitors

Polypyrrole (PPy) films doped by p-toluenesulfonic (PTS) are prepared by pulse current polymerization (PCP PPy) in aqueous solutions. Cations (H+, Li+, Na+, and K+ ions) in working electrolyte solutions have a great influence on the electrochemical properties of PCP PPy films for supercapacitors. In 3 M aqueous chloride solutions, the smaller cations lead to the better electrochemical properties of PCP PPy films. PCP PPy films show ideally capacitive characteristics with a very high specific power of 110.9 kW kg−1 in 3 M HCl when its specific energy reaches 18.4 Wh kg−1. PCP PPy films are very stable in 3 M HCl, showing less than 4% decay over 160,000 and 20,000 charge/discharge cycles at current density of 40 A g−1 within voltage range of 0–0.4 V and 0–0.8 V, respectively. The results of SEM show that many pits and grooves appear on the surface of PPy anode in 3 M KCl after 30,000 cycles, which should be main reason of rapid decay of PPy capacitance in 3 M KCl.