Dual-ion charge storage mechanism in polypyrrole cathodes for zinc-ion hybrid capacitors

The development of cathode materials that are well-matched with zinc anodes is critical for the advancement of zinc-ion hybrid capacitors (ZIHCs). Among various candidates, polypyrrole (PPy), a representative conductive polymer, has been extensively investigated as a cathode material due to its intrinsic conductivity and reversible redox activity. However, the practical application of PPy remains limited by an incomplete understanding of its charge storage mechanism. In this study, a straightforward approach is proposed to elucidate the charge storage behavior of PPy cathodes in ZIHCs. Specifically, using p-toluenesulfonic acid sodium as a dopant, PPy-coated carbon cloth electrode (denoted as PPy-CC) prepared of electrochemical deposition was employed as the cathode. In 1 M ZnSO 4 electrolyte, this electrode delivered a specific capacity of 124 mAh g −1 at a current density of 0.2 A g −1 and demonstrated excellent long-term cycling stability, retaining 71.2 % of its capacity after 5000 cycles at 5 A g −1 . To probe the underlying charge storage mechanism, X-ray photoelectron spectroscopy, X-ray diffraction, and in situ pH monitoring were conducted, revealing a dual-ion storage process involving both anion and cation participation during the electrochemical reactions. This work offers new insights into the charge storage mechanism of PPy-based cathodes and provides valuable guidance for the design of high-performance ZIHCs.