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.