Enhanced Interfacial Affinity of the Supercapacitor Electrode with a Hydrogel Electrolyte by a Preadsorbed Polyzwitterion Layer

Polymer hydrogel-based solid-state supercapacitors exhibit great potential applications in flexible devices. Nevertheless, the poor electrode–electrolyte interfacial properties restrict their advances. Herein, by taking the well-developed polyvinyl alcohol (PVA)/H2SO4 gel electrolyte and the graphene film electrode as the prototype, a very simple strategy is demonstrated to improve the interfacial affinity between the electrode and the hydrogel electrolyte by a preadsorbed highly hydrophilic polyzwitterion layer of poly(propylsulfonate dimethylammonium propylmethacrylamide) (PPDP) on the electrode surface. Electrochemical measurements confirm that the charge-transfer resistance on the interface is effectively reduced after modification with PPDP. Consequently, the obtained areal capacitance experiences a 3-fold increase compared to the unmodified ones. Results from electrochemical quartz crystal microbalance with dissipation demonstrate that more ions can be reversibly transferred on the modified interface during the change–discharge cycles, suggesting that the accessible surface area on the electrode is also increased. The hydrophilic PVA layer shows a similar function but with a much smaller efficiency. The strategy depicted here is highly universalizable and can be generalized to different electrode/electrolyte systems or other electrochemical energy storage devices.