Sandwich-structured polypyrrole layer/KCl-polyacrylamide-gelatin hydrogel/polypyrrole layer as all-in-one polymer self-healing supercapacitor

The sandwich-structured polypyrrole layer/KCl-polyacrylamide-gelatin hydrogel/polypyrrole (PPy/KCl-PAM-Gela/PPy) is designed as all-in-one polymer self-healing supercapacitor for flexible electrochemical energy-storage. The self-healing properties of hydrogels are mainly due to the addition of Gela, which also decreases the impedance of hydrogels. The hydrogen bonding heterogeneous interface between electroactive PPy layer and KCl-PAM-Gela hydrogel contributes to lowering interfacial charge transfer resistance, which decreases from 1.46 Ω of PPy/KCl-PAM/PPy to 0.40 Ω of PPy/KCl-PAM-Gela/PPy. The hydrogen bonding homogeneous interface between PAM and Gela contributes to lowering diffusion impedance of KCl electrolyte, which decreases from 14,505 Ω of KCl-PAM to 13,306 Ω of KCl-PAM-Gela. PPy/KCl-PAM-Gela/PPy shows more lowered interface energy rather than PPy/KCl-PAM/PPy, indicating hydrogen bonding heterogeneous interface between PPy and KCl-PAM-Gela is more stable than interface between PPy and KCl-PAM. PPy/KCl-PAM-Gela/PPy shows the decreasing specific capacitance from 408.13 to 110.70 mF cm−2 when current density increases from 0.5 to 4.0 mA cm−2, indicating good rate capability of 27.12%. It also shows the decreasing specific capacitance from 352.41 to 319.20 mF cm−2 after 2000 cycles at 1.0 mA cm−2, indicating cycling capacitance retention of 86.96%. The elongation of PPy/KCl-PAM-Gela/PPy reached 300% and still keeps 225% after hydrogen bond-induced self-healing treatment, presenting good mechanical stability. The sandwich-structured PPy/KCl-PAM-Gela/PPy keeps the reasonable capacitance, mechanical and cycling stability, which acts well as all-in-one polymer self-healing supercapacitor for flexible energy storage application.