Ultrathin two-dimensional metal–organic frameworks (MOFs) have convincing performances in energy storage, which can be put down to their accessible active sites with rapid charge transfer. Herein, NiCo-layered double hydroxide (LDH) nanosheet arrays are used as self-sacrificial templates to in situ fabricate ultrathin NiCo-MOF nanosheet arrays on Ni foam (NS/NF) by using organic ligands without adding metal sources. Two ultrathin MOF nanosheets with different ligands, terephthalate (BDC) and 2-aminoterephthalate (NH2-BDC), are synthesized, characterized, and discussed in detail. Specifically, NiCo-NH2-BDC-MOF NS/NF exhibits the best electrochemical performance as a battery-type electrode for supercapacitors, achieves an areal capacitance of 12.13 F cm–2 at a current density of 2 mA cm–2, and retains the original capacitance of 73.08 % after 5000 cycles at a current density of 50 mA cm–2. Furthermore, when NiCo-NH2-BDC-MOF NS/NF is assembled with activated carbon (AC) to form an asymmetric supercapacitor (ASC), an energy density of 0.81 mWh cm–2 can be provided at a power density of 1.60 mW cm–2. These results offer an effective and controllable synthetic strategy to in situ prepare ultrathin MOF nanosheet arrays with different ligands and metal ions from LDH precursors.

Metal-organosulfide coordination polymers (MOSCPs) are important functional materials with attractive application prospects. Herein a two-dimensional structural MOSCP was fabricated on nickel foam with nanosheet array morphology. When as the binder-free battery-type electrode for a supercapacitor, the as-prepared Co-based MOSCP showed high specific capacitance (759 F g–1/379.5 C g–1/105.4 mAh g–1 at 0.5 A g–1), excellent rate performance (58.8% after the current density increased 20 times), and good cycle stability (73.4% after 5000 cycles). In addition, a maximum energy density of 31.97 Wh kg–1 was obtained at a power density of 375.01 W kg–1 in the assembled asymmetric supercapacitor device. These results indicated that this work would open up a new path to design and prepare the battery-type electrode for a supercapacitor by exploring nanoscale MOSCP materials.

The design and controlled preparation of hollow and porous metal sulfide arrays are an important issue for electrochemical energy storage and conversion because of their unique structural merits including large surface areas, shortened diffusion paths, and rich reaction sites. Herein, a hollow and porous Co 9 S 8 microplate array (MPA) was successfully fabricated by a facile self-sacrifice template strategy, which involved the uniform growth of a metal−organic framework microplate template on Ni foam (NF) and annealing in air, followed by an anion-exchange reaction with S 2− ions. The resulting Co 9 S 8 -MPA/ NF as a binder-free electrode for a supercapacitor shows a high specific capacitance of 1852 F g −1 (926 C g −1 ) at 1 A g −1 and an excellent cycling stability (86% retention after 5000 cycles at 20 A g −1 ). Moreover, a hybrid supercapacitor (HSC) constructed with Co 9 S 8 -MPA/NF and activated carbon exhibits an outstanding energy density of 25.49 Wh kg −1 at a high power density of 800 W kg −1 and a long-term stability of 92% capacitance retention after 5000 cycles at 10 A g −1 . It is worth noting that the prepared allsolid-state HSC can light a red light-emitting diode for 2 min, proving to be a great practical application prospect. These excellent electrochemical behaviors show that this effective conversion strategy offers more possibilities for the development of highperformance energy storage metal sulfide materials.

No abstract