Synthesis of Mesoporous ZIF-8 Nanoribbons and their Conversion into Carbon Nanoribbons for High-Performance Supercapacitors

Al-MOF-derived spindle-like hierarchical porous activated carbon for advanced supercapacitors

Metal organic frameworks (MOFs) and their derivatives have been widely used in electrochemistry due to their adjustable pore size and high specific surface area (SSA). Herein, a spindle-like hierarchical porous activated carbon (SPC) was synthesized through carbonizing the Al-BTEC precursor and then alkaline washing with NaOH. The fabricated SPC has a uniform shuttle-shaped structure, showing a large BET surface area of 1895 m² g^-1 and an average pore size of 2.4 nm. The SPC product displays a high specific capacitance (SC) of 337 F g^-1 at 1 mV s^-1 and 334 F g^-1 at 1 A g^-1. The retention of SC is about 95% after 100 000 cycles when the current density is 50 A g^-1, indicating its excellent stability. Furthermore, the assembled symmetrical capacitor with a two-electrode system exhibits a high SC of 173 F g^-1 at 1 A g^-1 and an energy density of 15.3 W h kg^-1 at a power density of 336 W kg^-1. This work would provide a new pathway to design and synthesize carbon materials for supercapacitors with excellent properties in the future.

Nitrogen-Doped Carbon Networks with Consecutive Conductive Pathways from a Facile Competitive Carbonization-Etching Strategy for High-Performance Energy Storage

Recently, new carbonization strategies for synthesizing structure-controlled and high-performance carbon electrode materials have attracted great attentions in the field of energy storage and conversion. Here a competitive carbonization-etching strategy to prepare nitrogen-doped carbon polyhedron@carbon nanosheet (NCP@CNS) hybrids derived from zeolitic imidazolate framework-8 is presented. Consecutive conductive networks are constructed in the NCP@CNS hybrids during a unique carbonization-etching pyrolysis, where a competition between the formation of NCPs and CNSs exists. When the NCP@CNS hybrids are employed as supercapacitor electrodes, their hierarchically porous NCPs serve as ion-buffering reservoirs for offering fast ion transport channels, and the CNSs within hybrids not only link the NCPs together to build electron transfer pathways but also restrict the volume fluctuation of electrodes during charging and discharging process. As a result, the as-fabricated NCP@CNS electrode displays excellent electrochemical performances including a superior specific capacitance of 320 F g^-1 , a high energy density of 22.2 W h kg^-1 (5.6 W h kg^-1 for symmetric device), and a long cycle life with capacitance retention of ≈101.8% after 5000 cycles. This study opens an encouraging avenue toward the tailored synthesis of metal-organic frameworks (MOFs)-derived carbon electrodes for renewable energy storage applications and devices.

The solvent and zinc source dual-induced synthesis of a two dimensional zeolitic imidazolate framework with a farfalle-shape and its crystal transformation to zeolitic imidazolate framework-8

Exploring new zeolitic imidazolate frameworks (ZIFs) with specific topologies and pore structures is important for extending applications and improving performances. In this work, a new farfalle-shaped ZIF with an ordered hierarchical structure (named ZIF-F) was easily built with zinc acetate and 2-methylimidazole (MeIm) in an aqueous system at room temperature. The synthesis mechanism of ZIF-F is a dual-induction interaction of a solvent and zinc source based on the synthesis protocol of ZIF-8. The prepared ZIF-F is a 3-5 μm dispersible particle constructed from numerous nanoplates with the same building units as ZIF-8. ZIF-F has a rich 4 nm inter-particle spacing with a 0.1074 cm3 g-1 total pore volume and exhibits high thermo- and solvent stability. It is worth noting that crystal transformation could occur from ZIF-F to ZIF-8 in methanol via the dissolution-recrystallization route. Regarding the adsorption of Congo red (CR), ZIF-F exhibits better adsorption capacity (182.82 mg g-1) than ZIF-8 (149.25 mg g-1) with 6 times higher adsorption rate than that of ZIF-8 because of the positive effect of its larger pore size and hierarchical structure.