Vertically Aligned Co 3 O 4 Nanoarrays With High Mass Loading and Controlled Oxygen Vacancy for Advanced Supercapacitor Applications

Co3O4 obtained from zeolitic imidazolate framework-67 (ZIF-67) has great potential for supercapacitor applications owing to its exceptional electrochemical behavior and adjustable structural characteristics. However, Co3O4 in powder form and conventional slurry coating methods suffer from problems like poor electrical conductivity and ion diffusion, weak electrode integration, complex processing, and particle aggregation. Growing vertically aligned Co3O4 directly on conductive substrates to construct binder-free integrated electrodes seems to be an effective strategy to address these problems and enhance the electrochemical performance and stability. In this study, vertically aligned Co3O4 nanoarrays (Co3O4/NA) with a high mass loading were successfully synthesized on carbon fabric by combining a static growth method with heat treatment. By optimizing the growth time of ZIF-67 (4, 6, 8, and 10 h), the electrode obtained at 8 h exhibited the best performance, delivering an areal capacitance of 466.07 mF·cm–2 at 1 mA·cm–2. Furthermore, based on the optimized growth time (8 h), a subsequent annealing strategy (vacuum annealing followed by air annealing) was employed, which effectively regulated the morphology, specific surface area, pore structure, and introduced oxygen vacancies, thereby further boosting the capacitance to 952 mF·cm–2 at 1 mA·cm–2 under a high mass loading (4.7 mg·cm–2). Asymmetric supercapacitors fabricated using activated carbon and ZIF-67-derived Co3O4 nanoarrays displayed an impressive specific energy of 99 μWh·cm–2. Moreover, it retained 82% of the initial capacitance when subjected to 5000 tests at 5 mA·cm–2. Thus, the design of vertically aligned Co3O4 nanoarrays shows great potential in supercapacitor applications.