Structural design and optimization of metal-organic framework-derived FeO @C/rGO anode materials for constructing high-performance hybrid supercapacitors

Hybrid supercapacitors are promising energy storage devices that bridge the performance gap between conventional capacitors and batteries. However, the backward development of anode materials is a key issue that hinders the performance improvement of the hybrid supercapacitors. Therefore, this study proposes a strategy to fabricate reliable FeOx-based (Fe2O3 or Fe3O4) anode materials using the Fe-based metal-organic framework (Fe-MOF) as a template. Polyvinyl pyrrolidone (PVP) was used to stabilize and regulate the morphology of the Fe-MOF template to ensure a desirable microstructure of the final product. A series of FeOx@Carbon nanocages/reduced graphene oxide (FeOx@C/rGO) nanocomposites were obtained by calcinating the templates. The optimized Fe2O3@C/rGO–2 nanocomposite possesses considerable specific surface area and pore volume, with ultrasmall Fe2O3 particles (<5 nm) stably embedded in the carbon nanocages. The unique microstructure of the Fe2O3@C/rGO–2 electrode results in improved ion/electron accessibility that ensures an admirable specific capacity (713 C g−1 at 1 A g−1) and rate capability (67.3% retention at 50 A g−1). Meanwhile, the impressive cycling stability (104% retention after 20000 cycles) originates from the dual protection of Fe2O3 particles by the carbon nanocages and rGO. Furthermore, a hybrid supercapacitor constructed from a Fe2O3@C/rGO–2 anode and a nickel foam-supported NiCo2O4 nanoneedles (NiCo2O4–NF) cathode exhibited a maximum energy density of 101.9 Wh kg−1, suggesting that the delicately designed anode material is a promising candidate for constructing advanced energy storage devices.