Zn-substituted Co3O4 Crystal Anchored on Porous Carbon Nanofibers for High Performance Supercapacitors

Metal-organic frameworks (MOFs) are a promising class of electrode materials for supercapacitors. In this work, MOF-derived transition metal oxide/carbon nanofiber composites (ZnCoO/C) are synthesized through a freeze-drying method followed by a carbonization process. The crystal structure of the ZnCoO/C product is regulated by changing the ratio of Co to Zn, which in turn influences its electrode properties. The electrochemical tests reveal that the ZnCoO/C-2 electrode demonstrates an impressive specific capacitance of 356.3 F g-1 at 1 A g-1 and maintains a capacitance retention exceeding 77% after 10,000 cycles, which exhibits a good cycling stability. It is found that appropriate Zn substitution can diminish the crystallinity of the material, augment the active sites, and enhance the specific capacitance of the electrode material. Considering the heteroatom substitution tends to introduce vacancy defects in the crystals, this work theoretically explores the effect of oxygen vacancies on the electrode materials. As the oxygen vacancy concentration increases, the band gap and the adsorption energy of the models decrease; conversely, the formation energy of the models shows an increasing tendency. This indicates that an increase in oxygen vacancies can enhance the electrical conductivity of electrode materials and facilitate their kinetic process but destroy the stability of crystal. This research explores the interplay between the microstructure and the electrochemical performance of electrode materials, providing a foundational reference for the design of structurally optimized high-performance electrodes and further elucidating the energy storage mechanisms in supercapacitors.