An in situ growth strategy of NiCo-MOF nanosheets with more activity sites for asymmetric supercapacitors

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An in situ growth strategy of NiCo-MOF nanosheets with more activity sites for asymmetric supercapacitors Runping Jia 1 & Cheng Zhao 1 & Zhixiong Huang 1 & Xin Liu 1 & Dayang Wang 1 & Zi Hui 1 & Xiaowei Xu 1 Received: 17 June 2020 / Revised: 19 July 2020 / Accepted: 1 August 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020

Abstract NiCo layered double hydroxides (LDHs) for supercapacitors have been studied by virtue of the high specific capacitance theoretical values. However, less active sites limit the further increase of their specific capacitances. Metal-organic framework (MOF), as a promising material, has attracted intense attention with enormous specific area and adjustable structure. Herein, a practical strategy was designed to improve the active sites of the binder-free electrode by potentiostatic deposition and soaking NiCo-LDHs in 2-methylimidazole for in situ growth of MOF. This layered NiCo-MOF was obtained at room temperature which can retain more active sites to enhance capacitive properties. In particular, the prepared layered NiCo-MOF obtained a superior capacitance (1289 F g−1 at 0.5 A g−1), along with a remarkable rate capability (767 F g−1 at 20 A g−1). In addition, the as-prepared asymmetric supercapacitor exhibited a maximum specific energy of 57.8 Wh kg−1 at 748.7 W kg−1 (at a working potential of 1.5 V), and it retained 71.40% capacitance after 6000 cycles. All of these findings suggest that this work gives a practical way to synthesize NiCo-MOF nanosheets, and it exhibits excellent prospect in further energy field. Keywords Metal-organic frameworks . NiCo-LDHs . Binder-free . Electrodeposition . Asymmetric supercapacitor

Introduction As energy source and environmental disruption are ever-decreasing, it is urgent to develop the next-generation electronics, such as lithium-ion batteries, fuel cells, and supercapacitors, to achieve sustainable utilization of resources in the future [1–4]. Especially, supercapacitors have aroused wide research interest for their excellent power density, rapid energy storage function, and durable lifespan. But the energy density of supercapacitors cannot perform as higher as lithium-ion batteries, obstructing their comprehensive development in the contemporary electronics [5–9]. As a result, the recent researchers who interest in supercapacitor electrodes have made the suitable selection from these materials to get high-performance electrodes.

Electronic supplementary material The online version of this article (https://doi.org/10.1007/s11581-020-03727-x) contains supplementary material, which is available to authorized users. * Xiaowei Xu [email protected] 1

School of Materials Science and Engineering, Shanghai Institute of Technology, Shanghai 201418, People’s Republic of China

Among the recent studies, many researchers have been devoted to study diverse materials, such as transition metal hydroxides/oxides [10–16], conductive polymers [17, 18], and transition metal sulfides [19, 20]. In particular, transition metal hyd

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