Influence of dopant structure and charge on supercapacitive behavior of polypyrrole electrodes with high mass loading

Chromotropic acid disodium salt (CHR) and its derivatives, such as 2,7-Bis(2-sulfophenylazo)chromotropic acid tetrasodium salt (CHR-BS), 2-(phenylazo)chromotropic acid disodium salt (CHR-P) and 2-(1-naphthyldiazenyl)chromotropic acid disodium salt (CHR-N) were investigated as new anionic dopants for chemical polymerization of polypyrrole (PPy) for application in electrodes of electrochemical supercapacitors (ES). The analysis of electron microscopy data and electrochemical testing results provided an insight into the influence of dopant structure, size and charge on the PPy powder morphology and electrochemical performance of PPy electrodes. The increase in the size and charge of the dopant molecules resulted in reduced powder agglomeration and lower particle size. The use of CHR-BS allowed the fabrication of non-agglomerated PPy powders with particle size below 50 nm. It was found that new anionic dopants allowed the fabrication of ES electrodes with high mass loading in the range of 20–40 mg cm−2 and good electrochemical performance. Due to the higher charge to mass ratio of CHR and CHR-BS, compared to CHR-P and CHR-N, the CHR and CHR-BS doped PPy showed higher capacitance. The specific capacitance of 7.2 F cm−2 was achieved using CHR-BS doped PPy. Moreover, CHR-BS doped PPy electrodes showed excellent cycling stability. The ES cells, containing CHR-BS doped PPy electrodes showed promising electrochemical performance.