Comparative studies on electrochemical energy storage of NiFe-S nanoflake and NiFe-OH towards aqueous supercapacitor

In this study, electrochemical energy storage performances of an efficient Ni–Fe sulfide and hydroxide supported on porous nickel foam are compared. X-ray diffraction (XRD), X-rayphotoelectron spectroscopy (XPS) and energy-dispersive X-ray spectrometer (EDS) results confirmed the formation of Ni–Fe–S and Ni–Fe–OH electrodes. In addition, Brunauer–Emmett Teller (BET) was used to determine the specific surface area of the prepared materials. Moreover, the morphologies were observed by scanning electron microscopy (SEM). The brilliant characteristics of Ni–Fe–S could be attributed to transport acceleration in electrolyte ions and electrons, occurrence of redox reactions as well as the higher conductivity of the sample. From stand point of comparison, the capacitance of Ni–Fe–S is more than that of Ni–Fe–OH. Therefore, the exchange of O²⁻ with S²⁻ in Ni–Fe–OH lattice obviously improves the electrochemical performance. The as-fabricated Ni–Fe sulfide electrode exhibits a tremendous specific capacitance of 884.9 F g⁻¹ at 1 A g⁻¹. Furthermore, an assembled asymmetric supercapacitor device using the activated carbon as negative electrode and this smart configuration (Ni–Fe–S) as positive electrode also provided a maximum specific power and specific energy of 8000 W kg⁻¹, 37.9 Wh kg⁻¹, respectively. Also, it shows cycling stability with 88.8% capacitance retention after 1700 cycles in aqueous electrolyte, demonstrating its potential application in the next-generation high-performance supercapacitors used for energy storage.