Metal-Programmable Heterogeneous Graphene Hydrogel Monoliths

Self-assembly of two-dimensional (2D) building blocks offers an effective route to architecturally and chemically complex porous materials, yet strategies to program spatial heterogeneity within a single monolith remain scarce. Here, we report a metal-dependent gelation mechanism that enables the direct fabrication of monolithic graphene hydrogels with well-defined spatial heterogeneity simply by immersing multimetal templates into aqueous graphene oxide dispersions. Interfacial electrochemical reduction, driven by differences in standard reduction potentials between the graphene oxide building blocks and the underlying metals, induces spontaneous deoxygenation and self-assembly of graphene oxide sheets into highly porous, freestanding graphene hydrogels without additional binders. The elemental identity of the metal substrate governs the reduction level, interlayer arrangement, and surface hydrophobicity, thereby encoding metal patterns into a single monolithic graphene hydrogel with sharply delineated regions in chemical composition, pore architecture, and wetting behavior. This built-in spatial heterogeneity is further exploited for region-selective postfunctionalization of graphene hydrogels, including controlled N-doping and localized formation of Pt nanoparticles with tunable density and size across distinct regions. Moreover, the gelation mechanism enables the unprecedented seamless integration of multiple hydrogel units into complex 3D architectures. This versatile, metal-dependent gelation platform provides a general strategy for realizing structurally and chemically programmable graphene hydrogel monoliths for advanced electrochemical, catalytic, and energy-related applications.