Construction of Complex CoS Hollow Structures with Enhanced Electrochemical Properties for Hybrid Supercapacitors

Hierarchical hollow nanostructures with complex shell structures are attractive for efficient storage of electrochemical energy. However, reports on the designed formation of such delicate architectures are rare. Starting from a framework of Co-based zeolitic imidazolate (ZIF-67) nanocubes, we demonstrate a template-engaged formation of double-shelled hollow structures with CoS-nanoparticle-assembled nanoboxes surrounded by outer CoS-nanosheet-constructed shells (denoted as CoS-NP/CoS-NS DSNBs). Delicate manipulation of the template-engaged reaction between ZIF-67 and water leads to the formation of ZIF-67/Co(OH)2-nanosheet yolk-shelled structures, which are then transformed into CoS-NP/CoS-NS DSNBs through the reactions with Na2S. As a result of the unique assembly of subunits with different dimensionalities, the CoS-NP/CoS-NS DSNBs have a high specific surface area, suitable mesopores, and good structural robustness, which contribute to exceptional performance as a battery-type electrode. Moreover, a hybrid supercapacitor is fabricated by using CoS-NP/CoS-NS DSNBs as the positive electrode and activated carbon as the negative electrode. Impressively, these optimized devices can be operated stably in a wide potential range of 1.6 V with greatly enhanced energy density and power capability. The device is stable for 10,000 cycles with a capacitance retention of 88%.