To tackle the issue of the low specific capacity (372 mA h g⁻¹) of graphite as the anode material for lithium-ion batteries (LIBs), an effective and controllable strategy was developed to construct porous bimetallic Co/Zn embedded N-doped carbon (Co–Zn/N–C) polyhedral nanocages via annealing a ZIF-8@ZIF-67 precursor at 800 °C under Ar atmosphere. The results clearly displayed that metallic Co and Zn particles are uniformly dispersed in the carbon matrix. Porous Co–Zn/N–C polyhedral nanocages have a large specific surface area of 349.12 m² g⁻¹ and contain plenty of micropores and mesopores, which benefit from the carbonization of organic ligands and the catalytic effect of cobalt in the calcination process. As anodes for LIBs, the porous Co–Zn/N–C polyhedral nanocages showed an initial discharge capacity of 809 mA h g⁻¹ and a capacity retention of 702 mA h g⁻¹ after 400 cycles at a current density of 0.2 A g⁻¹. Furthermore, a reversible capacity of 444 mA h g⁻¹ was obtained at a much higher current density of 2 A g⁻¹. The improved electrochemical performance was attributed to the synergistic effect of Zn and Co, the unique porous hollow structure as well as N doping, which relieved the impact of volume changes, maintained perfect electrical conductivity throughout the electrode and enhanced the electrochemical activities of lithium storage.

This study presents a facile strategy to construct three-dimensional graphene network (3DGN) and metal–organic framework (MOF)-derived metal oxide composites as free-standing electrodes for supercapacitors for the first time. A Mn-based MOF is first grown in situ on a 3DGN substrate through a simple solution immersion method, and then a high-temperature treatment has resulted in the formation of a 3DGN decorated with Mn₂O₃ with a nanowire stacking flower-like morphology. The structure and morphology of the as-prepared samples are investigated by powder X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy analysis, scanning electron microscopy, elemental mapping, and transmission electron microscopy. The designed 3DGN/Mn₂O₃ electrode material exhibits a high specific capacitance of 471.1 F g⁻¹ (0.21 F cm⁻²) at 0.2 A g⁻¹, good rate capability of 57.3% at 5 A g⁻¹ relative to the initial value at 0.2 A g⁻¹, and excellent long-cycle stability without decaying after 1800 charge–discharge cycles. The remarkable electrochemical performances originate from the synergistic effect of the high electrical conductivity and large surface area of the 3DGN along with the superior pseudocapacitance activity of Mn₂O₃ nanowires. This result suggests that the 3DGN/MOF-derived metal oxide composites are promising and efficient binder-free electrode materials for high-performance supercapacitors.

Carbon-coated α-Fe ₂ O ₃ hollow nanospindles and varied-phase Fe ₂ O ₃ @C (γ-Fe ₂ O ₃ @C, αγ-Fe ₂ O ₃ @C, and α-Fe ₂ O ₃ @C) nanobipyramids were prepared by controlling pyrolysis of MIL-88A nanobipyramids at different temperature and time in air or nitrogen, exhibiting advanced lithium storage capacities.