Crystalline phase transformation of Co-MOF derivatives on ordered mesoporous carbons for high-performance supercapacitor applications

Abstract

Metal–organic frameworks (MOFs) are regarded as self-sacrificial templates to prepare various transition metal-based electrode materials. However, there is still a lack of information on the electrochemical performance difference of MOF-derived hydroxides, oxides and phosphates in recent research. In addition, the rate capability is still a problem that hampers the application of MOF-based derivatives. Hence, it is necessary to choose suitable materials with outstanding electrical conductivity for MOF-based derivatives. In this study, a series of MOF-based derivatives, namely, Co-MOFs, NiCo-LDH (layered double hydroxide), NiCoO₂, NiCoP, SAC@NiCo-LDH and SAC@NiCoP were prepared by combining suitable methods such as ion exchange, hydrothermal processes, oxidation and phosphorization. The electrochemical performance of these samples at 1 A g⁻¹ was found in the order of SAC@NiCoP > SAC@NiCo-LDH > NiCoP > NiCo-LDH > NiCoO₂. SAC@NiCoP exhibits the best specific capacitance and cycling stability when compared with the remaining materials. Phosphating enhances the electrical conductivity, the layer structure facilitates the intercalation/deintercalation of electrolyte ions, and oxidation inhibits the release of electrochemical performance. Hence, the enhancement effect is arranged as follows: phosphorization > layer structure > oxidation. This work analyzes the performance differences of MOF-based materials with different modification methods and crystal structures carefully and provides reliable criteria for the design and screening of advanced electrode materials.