Solvent-regulated synthesis and phosphating of nickel-cobalt bimetal organic framework microflowers with hierarchical structure for high-performance supercapacitors

Bimetallic metal-organic frameworks (MOFs) with a controlled morphology are potential materials for boosting the electrochemical performance of supercapacitors owing to their unique structural merits. Herein, a solvent-regulated strategy was proposed to synthesize bimetallic MOFs with various morphologies, such as microflowers, microspheres , and nanosheets , and the possible mechanisms of morphology control during nucleation and crystal growth were analyzed. When employed as electrode materials for supercapacitors, the NiCo-MOF microflowers possessed the biggest specific capacitance, which could achieve 1086 F g −1 at a current density of 1 A g −1 . To further improve the electrochemical performance of materials, NiCo-P was prepared via a low-temperature phosphating method using NiCo-MOF microflowers as the precursor. Electrochemical studies displayed that the NiCo-P(6) microflowers exhibited good capacitance and superior rate capability with specific capacitances of 1592 and 1384 F g −1 at 1 and 20 A g −1 , respectively. Furthermore, an asymmetric supercapacitor assembled by NiCo-P(6) and active carbon exhibited a high energy density of 51.2 Wh kg −1 at a power density of 749.8 W kg −1 and outstanding cycling stability. This work is easy to operate and can be extended to the preparation of other MOF-based electrode materials. The delivered excellent electrochemical performance suggests the resulted flower-like NiCo-P is a promising electrode material for advanced energy storage devices.