Acidity-Controlled Reduction Level and Porous Architecture of Graphene Hydrogels via Zn-Induced Interfacial Gelation

Graphene hydrogels are attractive electrode materials for aqueous electrochemical devices. The reduction level of their graphene building blocks governs the balance between electron transport and electrolyte accessibility, but has rarely been tuned within a single gelation process. Here, we report an acidity-controlled Zn-induced interfacial gelation that concurrently achieves the self-assembly of 3D porous graphene hydrogels and systematic control of their reduction level. Simple addition of HCl to an aqueous graphene oxide dispersion modulates interfacial reduction and assembly on a Zn surface, raising the residual oxygen content of the reduced graphene oxide framework from 15.4 to a maximum of 23.2 at.% and modifying the porous architecture. At an intermediate HCl addition, the moderately reduced hydrogel combines a restored π-conjugated carbon network with retained oxygen functionality and develops the largest gel thickness and specific surface area. A supercapacitor based on this hydrogel delivers the highest specific capacitance of 70.2 F g−1 among the hydrogels, with sustained rate capability and cycling stability. These findings highlight the reduction level as a key design parameter for graphene hydrogel electrodes, demonstrating a facile route for concurrently tuning surface chemistry and porous architecture during interfacial gelation.