Morphology Variations in Copper Sulfide Nanostructures as Anode Materials for Na-Ion Capacitors

Abstract

The electrochemical behavior of copper sulfide (CuS) as an electrode material for a Na-ion capacitor (NIC) is closely related to its morphology. Here, various CuS nanostructures, including nanoparticles (50–100 nm), nanotubes (600–700 nm), hexagonal coins (100–150 nm), cross-linked nanotubes (600–700 nm), and nanoworms (200–250 nm), are synthesized by simple chemical routes and investigated for NICs in an aqueous system. For the first time, we are reporting the CuS cross-linked nanotubes (CLNTs) and various nanostructures’ electrochemical performance for NICs. It is observed that CLNTs reveal a superior gravimetric capacitance of 275 F g–1 at 0.5 A g–1 in three-electrode configurations, as compared to the other investigated CuS nanostructures. The uniformly distributed hollow nature of CLNTs facilitates electrolyte infiltration and provides a more active surface for the interaction of more Na+ ions. The symmetric configuration of two electrodes with CLNTs shows a gravimetric capacitance of 315 F g–1 at 1 A g–1 followed by device fabrication with a maximum working potential of 2.5 V. The device lights up a red LED of 1.2 V and can hold a charge for ∼111 s at 1 A g–1. CuS CLNTs have high potential for large-scale energy storage devices due to their exceptional electrochemical performance and higher conversion reaction.

Unraveling the Role of Sodium Thiosulfate in Copper Sulfide Synthesis

“…The resulting copper sulfide was in the form of hollow tubes with a maintained cross section of the template. On the other hand, in the literature dedicated to the reaction of copper salts and Na 2 S 2 O 3 in the water/EG mixtures, the characteristic hexagonal tubular morphology of the as-obtained CuS has been primarily attributed to the coordination ability of EG and its interaction with water molecules, ensuring appropriate solubility of copper sulfide and diffusion of reactants. ,,,,, It was supported by the fact that in the aqueous medium, the final product was in the form of spheres.…”

“…The widely reported influence of material morphology on its various physicochemical properties has led to intensive studies on synthesis procedures enabling shape control of the final particles . Recently, a strong emphasis has been placed on the development of methods that not only allow for tailoring the morphology but can also be adapted for large-scale production. − A concise set of guidelines for the sustainable design of new materials and processes was compiled by Anastas and Warner as The Twelve Principles of Green Chemistry. , The main assumptions of this approach are oriented toward increasing the energy efficiency and reaction yield, eliminating or reducing the use of harmful precursors, solvents, surfactants, additives, and byproducts, as well as ensuring nontoxicity of the final product and/or its innocuous degradation after the life cycle.…”

“…Among various pathways for CuS synthesis, the method involving the reaction between copper salt and sodium thiosulfate in water and/or ethylene glycol (EG) has retained considerable attention throughout the years. ,,,, This procedure not only offers the possibility of obtaining tunable hierarchical structures , but also meets the guidelines of green chemistry . It does not require elevated temperatures (<100 °C) or the addition of any surfactants and stabilizing agents.…”

“…Apart from that, some misconceptions have arisen about the role of EG in shaping the final structures. In the majority of reports, the authors claim that the mixture of water and EG (1:1 or 1:3) is essential to achieve the tubular morphology of the final product, while conducting the reaction in pure water (or water-dominated solvent) results in obtaining spherical particles. ,,,, In opposition to this, Zhang et al synthesized copper sulfide tubes from an aqueous solution using the same precursors at 150 °C with a reaction time of 12 h . In another study, this research group observed that the yellow precipitate obtained as an intermediate product from aqueous solution at room temperature itself has a rod-like shape .…”