Highly Flexible OPBI Membrane as Solid‐State Electrolyte for Organic‐Polymer‐Based Supercapacitor Applications

ABSTRACT In this work, we design poly(4,4′‐diphenylether‐5,5′‐bibenzimidazole) (OPBI) as a promising electrolyte membrane for high‐performance flexible supercapacitors. The solid‐polymer electrolyte membrane is designed by immersing the OPBI membrane in phosphoric acid (H3PO4) and it was paired with polyaniline (PANI)‐treated multiwall carbon nanotubes (TMWCNTs) or poly(3,4‐ethylenedioxythiophene)‐poly (styrene sulfonate) (PEDOT: PSS) with TMWCNTs as the active electrode materials. Specifically, the PANI/TMWCNT‐based supercapacitor, integrated with the OPBI membrane electrolyte (OPBIME), demonstrated a high specific capacitance (Cs) of 519 F/g at a current density of 2.2 A/g. In contrast, a conventional cellulose‐PVA gel electrolyte yielded a reduced specific capacitance of 405 F/g under the same conditions. Further testing with PEDOT: PSS/TMWCNT electrodes and OPBIME resulted in a specific capacitance of 14 F/g at a current density of 0.5 A/g, along with excellent capacitance retention of 92% after 2000 cycles. Overall, these findings highlighted the dual role of OPBI membranes as both an electrolyte and a separator, significantly improving the performance of flexible supercapacitors. Their high ionic conductivity, electrochemical stability, and flexibility enable superior specific capacitance and long‐term cycling stability, positioning them as a promising electrolyte for next‐generation energy storage applications.