Double-phase engineering of cobalt sulfide/oxyhydroxide on metal-organic frameworks derived iron carbide-integrated porous carbon nanofibers for asymmetric supercapacitors

Designing advanced functional electrode materials with a tunable structure and multiphase/composition comprising a single metal via a one-step synthesis process for supercapacitor applications is challenging. Here, a dual-phase cobalt sulfide/cobalt oxyhydroxide (Co_1-xS/HCoO₂) hexagonal nanostructure on iron metal-organic framework (MIL-88A) derived iron carbide (Fe₃C) integrated porous carbon nanofibers (PCNFs) is synthesized using a wet-chemical curing technique. MIL-88A is integrated by a physical blending process into a PAN/PMMA polymer matrix during the PCNFs preparation process. The integrated MIL-88A-derived iron carbide nanomaterial contributes to improving the electrochemical performance of electrode materials by lowering the inherent resistance. The optimal (Co_1-xS/HCoO₂)-1@Fe₃C/PCNFs electrode exhibits a high specific capacitance of 1724 F g⁻¹ at 1 A g⁻¹ with an improved rate capability and exceptional cycling stability with 89.8% retention even after 10,000 cycles. These excellent electrochemical capabilities are predominantly attributed to the double-phase hybrid composites, which have a variety of abundant sites, a large active surface area, rapid electron and ion transport capability, and strong structural stability. A Co_1-xS/HCoO₂-1@Fe₃C/PCNFs//Fe₂O₃/NPC@PCNFs asymmetric supercapacitor (ASC) demonstrates excellent electrochemical energy storage behavior, with a maximum energy density of 65.68 Wh kg⁻¹ at a power density of 752.7 W kg⁻¹ and excellent cycling stability (90.3% capacitance retention after 10,000 charge-discharge cycles at a constant current density of 20 A g⁻¹). These electrochemical results indicate that this ASC outperforms previously reported asymmetric supercapacitors, showing that the heterophasic electrode (Co_1-xS/HCoO₂)-1@Fe₃C/PCNFs has the potential to be applied in supercapacitor devices.