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Hierarchical FeCo2S4 nanosheet arrays for highperformance asymmetric supercapacitors Roghayeh Asadi1, Seyed Naser Azizi1,*, and Saied Saeed Hosseiny Davarani2,*

1 2

Faculty of Chemistry, University of Mazandaran, Babolsar, Iran Faculty of Chemistry, Shahid Beheshti University, G. C., Evin, 1983963113 Tehran, Iran

Received: 29 March 2020

ABSTRACT

Accepted: 5 September 2020

Metal sulfides (MSs) with porous structures are highly desirable materials for supercapacitor (SC) applications, due to their good electrical conductivity and electrochemical activity. Herein, a facile hydrothermal strategy is introduced to fabricate spinel FeCo2S4 nanosheet (FCSNS) arrays as a promising binder-free electrode for SC applications. The FCSNS electrode indicated significant properties with a good capacity of 260.5 mAh g-1 at 1 A g-1, excellent rate performance of 71.2%, and exceptional durableness of 95.4%. Most importantly, an asymmetric device (FCSNS//AC (active carbon)) was then established, indicating a good capacitance of 143.6 F g-1 at 1 A g-1 and a satisfactory energy density (EnDe) of 44.87 Wh kg-1.

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Springer Science+Business

Media, LLC, part of Springer Nature 2020

1 Introduction With the increasing environmental pollution and scarcity of fossil fuels due to global warming, the exploration of high-efficiency energy storage systems (ESSs) is becoming urgent. Among the plentiful ESSs, supercapacitors (SCs) have attracted notable attention as one of the most favorable kinds, owing to their rapid charge/discharge, outstanding durableness, high-power-density, and great reliability [1–5]. Accordingly, supercapacitors have been largely used in diverse electronics such as memory devices, portable electronics, military devices, and electric vehicles. In the last decade, metal oxides (MOs) have been intensely employed for SCs due to their low toxicity,

and good capacitance, and inexpensive [6–8]. The intrinsically poor conductivity of MOs leads to low durability and rate capability. Many studies have demonstrated that metal sulfides (MSs) generally indicate better electrochemical activities compared with MOs [9, 10]. Especially, spinels such as MCo2S4 (M = Ni, Zn, Cu, etc.) reflect superior electrochemical activity and performance than single metallic sulfides owing to their boosting charge transfer between various metal ions and rich redox sites [11, 12]. For example, our group fabricated a CuCo2S4@Ni-Mo-S by hydrothermal method on the nickel foam (NF) electrode with the exceptional performance [13]. Ma et al. reported a spinel NiCo2S4via an anion exchange procedure with an acceptable capacity of 249 mAh/g and superb durability [14]. However, current reports

Address correspondence to E-mail: [email protected]; [email protected]

https://doi.org/10.1007/s10854-020-04437-w

J Mater Sci: Mater Electron

mostly focused on the Mn-Co, Cu-Co, Zn-Co, Ni-Co metallic sulfides. Recently, Huang et al. constructed an electrode for SC applications by MnCo2S4@FeCo2S4 using the facile method, which showed significant performance [15]