A back-to-back flexible supercapacitor based on novel polyvinyl alcohol-4-carboxyphenylboronic acid hydrogel coated graphite paper current collector

Flexible supercapacitors (SCs) with a sandwich structure constructed using traditional current collectors usually exhibit poor utilization of electroactive materials and unsatisfactory mechanical deformation stability. In this work, a novel polyvinyl alcohol-4-carboxyphenylboronic acid hydrogel-coated graphite paper (PVA-CPBA/GP) current collector is developed. The CPBA dopants covalently immobilized on PVA chains act as anchoring sites, promoting the dispersed growth of polypyrrole (PPy) within the 3D hydrogel network. The resulting PPy@PVA-CPBA electrode with an interpenetrating network structure shows evidently enhanced electrochemical performance compared to PPy/PVA and PPy electrodes. Using the PVA-CPBA/GP current collector, a separator-free back-to-back flexible SC is also constructed successfully. The device exhibits an areal capacitance of 110.2 mF cm⁻² at 0.5 mA cm⁻², retains 82.6 % of its initial capacitance after 10,000 cycles, and maintains 83.8 % of its initial capacitance after 1000 bending cycles. These performance metrics are significantly higher than those of the PPy/PVA SC as a control. This work demonstrates that the developed PVA-CPBA/GP current collector not only promotes the highly efficient utilization of PPy, enhancing the capacitive performance and cycling stability of the SC, but also enables the construction of a separator-free back-to-back flexible SC, thereby improving its mechanical deformation stability. The hydrogel-based current collector we propose presents a new perspective for developing high-performance flexible SCs.