Flexible Ni‐Based Bimetallic Spinel Oxide (NiM2O4, M = Mn, Fe, Co) Electrodes for Supercapacitor Applications

Herein, the single‐phase Ni‐based bimetallic spinel oxide (NiM 2 O 4 , M = Mn, Fe, Co) nanoparticles are successfully synthesized by sol–gel method and coated on a carbon cloth substrate to form flexible electrodes for supercapacitor applications. The effects of transition metal activity, calcination temperature, surface, and textural properties on the electrochemical properties of spinel electrode materials are demonstrated. It is found that lowering the calcination temperature results in a decrease in crystallite size and particle size, leading to an increase in surface area and pore volume. X‐Ray absorption spectroscopy reveals the presence of Mn 2+/3+ , Fe 2+/3+ , and Co 2+/3+ in materials. According to the electrochemical studies, NiMn 2 O 4 electrode in Na 2 SO 4 electrolyte exhibits electrical double‐layer capacitance behavior, while NiFe 2 O 4 and NiCo 2 O 4 electrodes in KOH electrolyte exhibit pseudocapacitive behavior. All electrode materials have low solution resistance and charge transfer resistance. NiCo 2 O 4 provides the highest specific capacitance (85.60 F g −1 at 2.5 A g −1 ) followed by NiFe 2 O 4 and NiMn 2 O 4 . It seems likely that the high electrochemical activity of Co 2+/3+ and small particle size of NiCo 2 O 4 nanoparticles play an important role in improving the redox process and charge transfer, which may enhance the electrochemical performance of this electrode material.