Surface-Sulfurized Zn-MOF Grown on Ni-Foam with Various Sulfurizing Agents for Aqueous Hybrid Supercapacitor Device Fabrication

Metal–organic frameworks (MOFs) are an emerging material with a high specific surface area, desired morphology, and tunable pore size. However, MOFs suffer due to low electrical conductivity. Transition-metal sulfides are excellent supercapacitor materials because of their large storage capacity and electrical conductivity. To preserve a high surface area and obtain high electrical conductivity, Zn-MOF is directly grown on Ni-foam, and its surface is modified through various sulfurizing agents. The as-fabricated Zn-MOF on Ni-foam exhibits a vertically oriented triangular rod-like morphology. Banana blossom, fiber, and rod-like morphologies are obtained due to the surface etching and surface sulfurization process by sulfurizing agents thioacetamide (TAA), sulfur (S), and thiourea (TU), respectively. The role of iR compensation in cyclic voltammetry analysis with higher mass-loading electrodes is established. The variations in its charge storage mechanism and charge-transfer kinetics corresponding to various sulfurizing agents are examined. Compared to other commonly used sulfurizing agents, TAA-assisted surface-sulfurized Zn-MOF provided excellent charge storage performance. It exhibits a maximum areal capacity of 4484 mC cm^–2 (specific capacity of 747.3 C g^–1) at a current density of 10 mA cm^–2. The as-fabricated aqueous hybrid supercapacitor device exhibits a maximum specific energy of 77.8 W h kg^–1 at a specific power of 0.73 kW kg^–1, even with a higher mass loading of 12.2 mg. The role and importance of mass loading are described by using an expanded Ragone plot.