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.