Rapid microwave-assisted vs. hydrothermal synthesis of hierarchical sheet-like NiO/NiMoO_4 hybrid nanostructures for high performance extrinsic pseudocapacitor application

摘要

Combinations of pseudocapacitive materials such as metal oxides and metal molybdates are one of the extensively interested hybrid electrode materials for pseudocapacitor application. Various synthetic protocols along with structural parameters of the obtained products are crucial to achieve desired electrochemical properties for electrode materials. Herein, sheet-like hierarchical NiO/NiMoO4 (NNMO) hybrid nanostructures are synthesized by one-step rapid & energy saving green microwave-assisted approach (M-NNMO) and compared their physicochemical-electrochemical properties with hydrothermally synthesized H-NNMO. The as-synthesized materials are characterized by various spectroscopic and microscopic techniques. As an electroactive pseudocapacitive material, M-NNMO shows maximum specific capacity of 459.0 Cg(-1) (1147.5 Fg(-1)), while H-NNMO delivers specific capacity of 271.1 Cg(-1) (677.8 Fg(-1)) at a current density of 1 Ag-1. The superior performance of the M-NNMO is closely related to its low crystallinity, high bulk (147.9 m(2) g(-1))/electroactive surface area (26.7 cm(2)), and mesoporosity within hierarchical assembly. Furthermore, asymmetric supercapacitors are fabricated by NNMOs nanostructures as the positive and commercial activated carbon as the negative electrode. MNNMO//AC device exhibits maximum specific capacity of 203.0 Cg(-1), promising specific energy/power of 38.6 Whkg(-1)/685.2 WKg(-1), while H-NNMO//AC shows specific capacity of 169.5 Cg(-1), specific energy and power of 32.4 Whkg(-1) and 688.6 WKg(-1), respectively, at a current density of 1 Ag-1. Maximum cyclability (similar to 84% capacity retention after 2250 cycles) of H-NNMO//AC may be correlated with better crystallinity and thermal/ structural stability of H-NNMO hybrid nanostructure. Based on results, we suggest that the NNMO hybrid nanostructures can be promising electrode materials for electrochemical energy storage application.