Engineering Rhynchostylis retusa-like heterostructured α-nickel molybdate with enhanced redox properties for high-performance rechargeable asymmetric supercapacitors

The demand for battery-type materials having hierarchical architectures, large surface areas, and excellent redox properties, to develop high energy density asymmetric supercapacitors (ASCs), is increasing. Herein, a facile single-step wet chemical method is proposed, which allows an engineered combination of alpha-NiMoO4 hierarchical heterostructures to be used as advanced battery-type electrodes for ASCs. The as-synthesized architectures consist of versatile nanogeometries including nanowires, nanosheets, and nanoparticles in the form of Rhynchostylis retusa-like heterostructures, which synergistically enhance the energy storage properties; specifically, at a current density of 2 A g(-1), heterostructured alpha-NiMoO4 exhibits a superior specific capacitance of 1061 F g(-1) and an outstanding cycling stability of 96%. Moreover, an aqueous ASC is fabricated by combining such a redox-type alpha-NiMoO4 heterostructure and activated porous carbon as the positive and negative electrodes, respectively, separated with a piece of filter paper. This device shows high energy and power densities (31.8 W h kg(-1) and 786.5 W kg(-1), respectively), which are useful to operate various portable electronic appliances. Together with the excellent cycling stability and energy storage properties, the synthesized heterostructured metal molybdates exemplify a new approach to develop novel electrode materials for high-performance aqueous ASCs.