Redox-active doped polypyrrole microspheres induced by phosphomolybdic acid as supercapacitor electrode materials

Abstract Microsphere-structured polypyrrole (PPy) induced and doped by phosphomolybdic acid with high redox activity is synthesized by a facile in situ polymerization method. The diameter of the microsphere can be controlled in the range of 100˜120 nm by the introduction of p-toluene sulfonic acid (TSA), which can also be used as co-dopant for PPy. The electrochemical performances the resulted PPy microspheres have been greatly improved. When the molar ratio of TSA:pyrrole is 0.5:1, PPy microsphere can provide the highest specific capacitance of 400 F/g, which is more than 3 times as much as that of pristine PPy. In this study, phosphomolybdic acid played multi-functional roles as the oxidant, redox-active dopant as well as spherical inducing agent for PPy. The improved capacitance could be attributed to the bipolaronic structure evidenced by Fourier-transform infrared spectroscopy, Raman and electron spin resonance measurements originating from the codoping effect. The formation mechanism of the PPy mircospheres is also proposed.