Materials Science in Semiconductor Processing 109 (2020) 104925 1369-8001/© 2020 Elsevier Ltd. All rights reserved. Cobalt sulfide nanoparticles: Synthesis, water splitting and supercapacitance studies Rehana Akram a , Malik Dilshad Khan b, c, *** , Camila Zequine d , Chen Zhao d , Ram K. Gupta d , Masood Akhtar b, c , Javeed Akhtar e, ** , Mohammad Azad Malik b, c , Neerish Revaprasadu c, * , Moazzam H. Bhatti a a Department of Chemistry, Allama Iqbal Open University, H/8 Islamabad, Pakistan b School of Materials, The University of Manchester, Oxford Road, Manchester, M13 9PL, UK c Department of Chemistry, University of Zululand, Private Bag X1001, KwaDlangezwa, 3880, South Africa d Department of Chemistry, Pittsburg State University, Pittsburg, KS, USA e Department of Chemistry Materials Laboratory, Mirpur University of Science & Technology (MUST), Mirpur, 10250, AJK, Pakistan A R T I C L E INFO Keywords: Charge storage Hydrogen evolution Solventless Supercapacitance Water splitting ABSTRACT Different alkyl xanthate complexes of cobalt (alkyl ¼ Ethyl, Hexyl, Octyl) were synthesized and used for the synthesis of nanoparticles by a solvent-less route. The p-XRD of the nanoparticles showed the formation of the CoS phase only from all precursors. The effect of size and surface capping on energy generation and energy storage applications was investigated. The electrocatalytic performance of the synthesized samples for hydrogen (HER) and oxygen evolution reaction (OER), indicates that CoS synthesized from the octyl xanthate complex (CoS-Oct) showed higher electrocatalytic performance. A lower over potential of 325 mV and 200 mV was observed for CoS-Oct, at a current density of 10 mA/cm 2 , for OER and HER, respectively. The charge storage performance was also investigated, where an inverse trend was observed i.e. the highest specific capacitance (1500 F/g, at scan rate 2 mV/s) was observed for the CoS sample synthesized from ethyl xanthate (CoS-ET). Similarly, the discharge time for CoS-ET was longer as compared to the other samples, suggesting better per- formance for the charge storage applications. The use of cobalt xanthate complexes for the preparation of CoS by melt method, and the effect of self-capped and uncapped surface of CoS on supercapacitance and OER/HER performance, has never been investigated before. 1. Introduction The ever-increasing energy demand due to the technological ad- vancements, and limited amount of fossil fuels, increases the necessity to search for sustainable alternative energy sources for energy generation and/or energy storage. For energy generation, one of the cheapest and eco-friendly sources of the green fuels, is the generation of hydrogen and oxygen by water splitting [1–3]. The process of electrocatalytic water splitting consists of the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), which should ideally occur at 1.23 V (vs RHE) [4,5]. However, water is thermodynamically highly stable and without the presence of any suitable electrocatalyst, a much higher overpotential is required for HER and/or OER. Noble metals, such as platinum has the advantage of being very electroactive with high electrochemical sta- bility, however, the exorbitant cost and scarcity hinder its widespread use. Water splitting using nanostructures avoiding precious metals such as platinum, gold and ruthenium is highly desirable to meet the competitive market demands. Therefore, the current research focus is primarily on the synthesis of cost-effective, earth-abundant and high-performance electrocatalysts, which can reduce the overpotential for water splitting. Likewise, for energy storage applications, electro- chemical capacitors are considered superior to conventional batteries for charge storage, due to their high energy capacity and long cycle life associated with them along with quick energy storage and release time [6,7]. Transition metal sulphides (TMSs) are potentially suitable materials * Corresponding author. ** Corresponding author. *** Corresponding author. School of Materials, The University of Manchester, Oxford Road, Manchester, M13 9PL, UK. E-mail addresses: azad.malik@manchester.ac.uk (M.D. Khan), javeedkt@gmail.com (J. Akhtar), RevaprasaduN@unizulu.ac.za (N. Revaprasadu). Contents lists available at ScienceDirect Materials Science in Semiconductor Processing journal homepage: http://www.elsevier.com/locate/mssp https://doi.org/10.1016/j.mssp.2020.104925 Received 18 September 2019; Received in revised form 27 December 2019; Accepted 6 January 2020