Contents lists available at ScienceDirect Journal of Energy Storage journal homepage: www.elsevier.com/locate/est Diferent controlled nanostructures of Mn-doped ZnS for high-performance supercapacitor applications Iftikhar Hussain a,1 , Debananda Mohapatra a,1 , Ganesh Dhakal a,1 , Charmaine Lamiel a,b , Saad Gomaa Mohamed a,c , Mostafa Saad Sayed a , Jae-Jin Shim a, ⁎ a School of Chemical Engineering, Yeungnam University, Gyeongsan, Gyeongbuk 38541, Republic of Korea b School of Chemical Engineering, University of Queensland, Australia c Mining and Metallurgy Engineering Department, Tabbin Institute for Metallurgical Studies (TIMS), Tabbin, Helwan 109, Cairo 11421, Egypt ARTICLEINFO Keywords: Mn-doped ZnS Nanosheet Nanofake Nanoneedle Asymmetric supercapacitor ABSTRACT Various Mn-doped ZnS controlled nanostructures were synthesized directly on the nickel foam to develop a binder-free, high-performance positive electrode for supercapacitors, where specifc energy, specifc power, and cycling stability are the crucial parameters. We achieved Mn-doped ZnS based diferent nanostructures, such as nanosheets, nanofakes, and nanoneedles just by monitoring the reaction temperature. Among those three morphologies, the nanosheets showed the highest specifc capacitance of1905Fg −1 atacurrentdensityof1A g −1 and93.1%capacityretentionafter10,000cyclesinathree-electrodesystem.Anasymmetricsupercapacitor (ASC) device was assembled using Mn-doped ZnS nanosheets and activated carbon as a positive and negative electrode, respectively. The ASC device showed a high capacitance of 140 F g −1 (210Cg −1 ), delivered a high specifcenergyof43.3Whkg −1 ,andahighspecifcpowerof6.8kWkg −1 .TheASCdeviceretained93.3%with excellent coulombic efciency of 95.7% after 8,000 cycles. Importantly, two serially connected ASC devices illuminated52redlight-emittingdiodes.ThishighlightsthepotentialoftheMn-dopedZnSbasedASCdevicefor the next generation supercapacitors. 1. Introduction The energy crisis and environmental pollution from burning fossil fuels have prompted universal eforts to explore renewable and clean energy sources [1]. Over the last two decades, the attention of re- searchers has turned towards emerging energy storage devices, such as fuel cells, batteries, or supercapacitors. Of these, supercapacitors have signifcant features that connect the gap between conventional capa- citorsandbatteriesintermsofpowerdensity,energydensity,andcycle life [2,3]. Supercapacitors store and release energy instantaneously, hold long-term retention, and are much safer to handle [4]. These features make them attractive for use in consumer electronics, electric vehicles, and other applications [5,6]. Supercapacitors can broadly be divided into two types; electric double-layer capacitor (EDLC) and pseudocapacitor [7–9]. Electric double-layer capacitors based on car- bonaceousmaterialshavealimitedenergydensity [7,10].Ontheother hand, pseudocapacitors generally deliver a high specifc capacitance, and redox reactions occur at the surface of the electroactive materials. Besides, conducting polymers exhibit poor stability during charge- discharge cycling. Pseudocapacitive materials, such as transition metal oxides (TMOs), transition metal nitrides (TMNs), and transition metal chalcogenides (TMCs) have attracted considerable attention in recent years [11–19]. However, the synthesis of TMNs involves time-con- suming, complex processes. TMOs and TMCs have attracted particular attention as promising electrode materials for the next generation ul- tracapacitors owing to their multiple oxidation states for the feasible the redox reactions [20]. Recently, TMCs have been reported to show superior electrical conductivity, thermal and mechanical stability, and higher electro- chemical performance than their corresponding metal oxide[1,21,22]. Compared to the single metal sulfdes, binary metal sulfdes exhibit more productive redox reactions and higher electronic conductivity, resulting in signifcant improvement of the electrochemical perfor- mance [23]. In addition, binary transition metal sulfdes, such as zinc cobalt sulfde, were reported to show a much lower optical band gap and much higher electrical conductivity than their single transition metal sulfde counterparts [24–27]. Studies have found that the re- placement of oxygen with sulfur may produce a more fexible structure https://doi.org/10.1016/j.est.2020.101767 Received 5 April 2020; Received in revised form 23 July 2020; Accepted 10 August 2020 ⁎ Corresponding author. E-mail address: jjshim@yu.ac.kr (J.-J. Shim). 1 These authors are equally contributed. Journal of Energy Storage 32 (2020) 101767 2352-152X/ © 2020 Elsevier Ltd. All rights reserved. T