Bucket Effect: A Metal–Organic Framework Derived High-Performance FeS₂/Fe₂O₃@S-rGO Negative Material for Enhanced Overall Supercapacitor Capacitance

Over the past decades, great achievements of supercapacitor positive electrode materials have been developed, but the exploration of negative electrode materials is obviously lagging and mainly focuses on low-capacity electrochemical double-layer capacitor-based carbon materials (≤300 F g–1, commonly), which limits the overall capacitance of supercapacitor devices for further application. In this work, using the gifted MIL-88A@GO as a precursor, we fabricate a FeS2/Fe2O3 heterostructure-coupled S-functionalized 3D rGO network (FeS2/Fe2O3@S-rGO) by a diffusion-controlled etching and vulcanizing process. The formation of heterogeneous interfaces and the strongly coupled interaction between the FeS2/Fe2O3 heterostructure and 3D S-rGO can provide high surface area for more electrochemical active sites, a rich pathway for the rapid transmission of the electron and electrolyte, and effectively alleviate the volume variation in the charging and discharging process. Therefore, the as-obtained FeS2/Fe2O3@S-rGO presents an outstanding capacity of 219.4 mA h g–1 (790 F g–1) at a current density of 2 A g–1, which is higher than that of most reported Fe-based negative materials. Then, a positive electrode of hierarchical 2D/3D Ni3S2/Co3S4 (NCS) is prepared and further fabricated with a FeS2/Fe2O3@S-rGO electrode to obtain a hybrid supercapacitor device (NCS//FeS2/Fe2O3@S-rGO), which delivers an outstanding overall capacitance value of 114.2 mA h g–1 (274 F g–1) at 1 A g–1 and provides a remarkable energy density of 85.63 Wh kg–1 corresponding to a power density of 0.75 kW kg–1.