Calcination activation of three-dimensional cobalt organic phosphate nanoflake assemblies for supercapacitors

Abstract

Three-dimensional (3D) metal–organic framework (MOF) assemblies at the micro-nanoscale have garnered considerable interest because of their extensive applications. Herein, three-dimensional cobalt organic phosphate (COP) nanoflake precursors were obtained by a simple self-assembly method. Further, COP assemblies were obtained via the low-temperature calcination activation of the precursors in air, and the obtained assemblies preserved the nanoflake structure of the precursors by exposing an increased number of active sites. When the COP assemblies were directly used as electrode materials for supercapacitors (SCs), their performance greatly exceeded that of pure MOFs. As a proof of concept, a sample activated at 200 °C was used as the electrode material in SCs, and the specific capacitance reached 274.32 F g⁻¹ under 0.5 A g⁻¹. Moreover, an asymmetric SC device comprising COP//activated carbon was assembled, and it exhibited a long cycle stability, with a decay rate of only 0.39% after more than 3000 charge–discharge cycles. These results demonstrate that multilayer COP can potentially be applied as an electrode material for electrochemical capacitors.