Synthesis of a (NiFe)9S8 nanorod array as a negative electrode for a high-performance hybrid supercapacitor

Abstract

Inspired by morphological control and element doping, nanorod NFS-X ((NiFe)₉S₈ with different Ni : Fe molar ratios) was synthesized by a hydrothermal method. In this work, uniform and dense NF-X (X = 0, 1, 3, 5, 7, 9 and 10) materials were prepared on NiFe foam, and as a precursor, the nanorod was formed in situ by sulfurization in ethanol. NFS-X (X = 0, 1, 3, 5, 7, 9 and 10) with nanorod morphology was successfully obtained by controlling the Ni and Fe ratio. The optimized NFS-3 has a unique nanorod structure, which provides abundant electrochemical active sites and sufficient electron and electrolyte migration paths for fast and deep Faraday reactions. A specific capacitance of 3620 mF cm⁻² at 2 mA cm⁻² was obtained with significant cycling performance (83.3% retention after 7000 cycles at 20 mA cm⁻²). Furthermore, asymmetric supercapacitor CNHC//NFS-3 was prepared by using NFS-3 nanorods as a cathode and double-shell layer Co/Ni-based alkaline carbonate (CNHC) as an anode. The device presents an excellent energy density of 68.9 Wh kg⁻¹ at a power density of 0.74 kW kg⁻¹ while driving a small fan for operation, exhibiting potential for practical applications.