Porous Co₃O₄ materials prepared by solid-state thermolysis of a novel Co-MOF crystal and their superior energy storage performances for supercapacitors

In this work, porous Co₃O₄ materials were prepared via a solid-state conversion process of a freshly prepared cobalt-based metal–organic framework (Co-MOF) crystal. Herein, the unique Co-MOF crystal was formed via the specific chemical coordination between the carboxylic ligand azobenzene-3,5,4′-tricarboxylic acid (H₃ABTC) and the auxiliary ligand 4,4′-bipyridine (bpy) to construct 2-dimensional (2D) bilayer structural intermediates, which subsequently formed a 3D polycatenation supramolecular array architecture with the assistance of π–π stacking and hydrogen bonding interactions. Subsequently, porous Co₃O₄ particles were obtained by simple thermolysis of the Co-MOF crystals via a two-step calcination treatment. The results demonstrated that the as-made Co3O4 displays crystalline and well-defined porous features and can be applied as a supercapacitor electrode, and its energy storage performances were investigated in 2 M KOH electrolyte. The electrochemical results showed that the porous Co₃O₄ particles exhibit a high specific capacitance of 150 F g^-1 at a current density of 1 A g^-1 and retain slightly enhanced capacitance after 3400 cycles, which could be ascribed to its higher specific surface area and accessible channel structural features. The present approach is facile, controllable, and reproducible. Importantly, this specific solid-state thermal conversion strategy could be easily extended to prepare other porous metal and/or
metal oxide nanomaterials with specific surface textures and morphologies.