Flower-like bimetal Ni/Co-based metal–organic-framework materials with adjustable components toward high performance solid-state supercapacitors

Abstract

The design and fabrication of electrode materials with excellent electrochemical performance are the key measures to improve the energy density of devices. Since cobalt-based materials have excellent conductivity and stability while nickel-based materials have ultra-high theoretical capacitance, a series of bimetal Ni/Co metal–organic-framework materials with adjustable components were synthesized via a facile one-step solvothermal method. Moreover, due to the similarity of the atomic radius and chemical valence state between Co and Ni, the in situ replacement was achieved by adjusting the initial proportion of Co²⁺ to Ni²⁺ during the synthetic process. The optimal sample not only retained the stability and electrical conductivity of Co-based MOF materials, but also demonstrated outstanding electrochemical performance with a high specific capacitance (1230.3 F g⁻¹ at 1 A g⁻¹), excellent rate capability (87.0%, from 1 A g⁻¹ to 10 A g⁻¹) and great cycle stability (80%, 4000 cycles at 10 A g⁻¹). Besides, the assembled solid-state supercapacitor using the optimal sample as the positive electrode and active carbon as the negative electrode exhibited an ultra-high energy density of 116 W h kg⁻¹ at a power density of 0.795 kW kg⁻¹ and a superior stability with 92.1% initial capacity retention even after 6000 cycles at 10 A g⁻¹. In brief, this work could provide novel insight into the controllable synthesis of high performance polymetallic-based MOF materials with adjustable components for energy storage and conversion.