Phosphomolybdic acid-doped polypyrrole as electrode for integrated hydrogel supercapacitors

Integrated hydrogel supercapacitors have attracted increasing attention owing to their low interfacial contact resistance and excellent electrochemical performance even under folding and bending. Herein, phosphomolybdic acid-doped polypyrrole (PPy) was deposited in situ on the surface of a hydroxypropyl cellulose/polyvinyl alcohol (HPC/PVA) hydrogel to fabricate integrated hydrogel supercapacitors. The negatively charged phosphomolybdic acid (PMo 12 ) was anchored onto the positively charged PPy chain to prevent its dissolution in the electrolyte thereby enhancing its pseudocapacitive performance. PMo 12 also can dope and modify PPy, providing additional pseudocapacitance and thereby improving the energy storage capacity of the supercapacitor. The supercapacitor achieved a high areal specific capacitance (350 mF cm −2 at 0.5 mA cm −2 ) and demonstrated a remarkable energy density (24.0 \(\upmu\) Wh cm −2 at 1000 \(\upmu\) W cm −2 ). After 1000 galvanostatic charge–discharge cycles at a high current density of 10 mA cm −2 , it retained 71.3% of its initial capacitance and maintained 98% Coulombic efficiency.