Graphene-directed zinc-MOF sulfidation for flexible solid-state supercapacitors with high practical energy density

Electrochemical energy storage requires high-energy, high-power, mechanically flexible devices that remain competitive when realistic metrics are applied. Transition-metal-based electrodes, including metal sulfides, offer rich redox chemistry but typically underperform in devices because of insulating interfaces, particle coarsening, and the resulting sluggish charge transport. Here we employ graphene acid (GA) for the directed sulfidation of zeolitic imidazolate framework-8 (ZIF-8) crystals toward a seamless ZnS/graphene architecture to unlock the redox activity of ZnS through Zn–carboxylate coordination. The interfacial bonding suppresses aggregation and insulating sulfur-rich surface species. It prevents GA restacking, and affords a mesoporous, higher-surface-area architecture that improves proton access, and enhances fast charge transport pathways, as confirmed by scanning electrochemical microscopy (SECM). These properties enable effective operation of ZnS/GA without the need for heavy metallic foam-based current collectors. Thus, it yields superior full-electrode-mass metrics (i.e., including the current collector mass) relative to prior systems. A ZnS/GA∥GA asymmetric solid-state supercapacitor with a polyvinyl-alcohol (PVA)–H 2 SO 4 gel as electrolyte and an ultrathin graphite-foil current collector operates at 2.0 V. It achieves 27.6 Wh kg −1 at a power density of 2.1 kW kg −1 with 92% capacitance retention after 5000 cycles and stable performance under extreme bending. This approach demonstrates a versatile route to overcome the inherent limitations of metal sulfides and unlock their latent redox properties, enabling their use in high-performance, flexible energy storage. • Graphene acid directs ZIF-8 sulfidation into seamless ZnS/graphene, unlocking ZnS redox activity. • Zn–carboxylate bonding suppresses aggregation, sulfur-rich insulation, and enables fast charge transport. • SECM confirms enhanced interfacial charge transport and proton accessibility in mesoporous ZnS/graphene electrodes. • Flexible solid-state ZnS/GA∥GA device delivers 27.6 Wh kg −1 at 2.0 V with 92% retention after 5000 cycles.