Template and co-precipitation routed NiMn2O4 microfiber for aqueous hybrid supercapacitor

Manganese-based transition metal oxides have attracted considerable attention in the field of electrochemical energy storage owing to their natural abundance, environmental compatibility, rich redox chemistry, and outstanding electrochemical performance. However, there is still a lack of scalable methods capable of simultaneously achieving well-defined fibrous structures and high surface-area-to-volume utilization. Therefore, in this study, NiMn 2 O 4 nanomaterial is prepared by easiest co-precipitation method that uses tissue paper as a biotemplate to directly construct NiMn 2 O 4 microfibers with a continuous, interconnected fibrous morphology. This biomorphic route is operationally simple, reagent-light, and avoids high-pressure hydrothermal or MOF-derived precursors commonly used for NiMn 2 O 4 nanostructuring. The resulting NiMn 2 O 4 microfiber electrode delivers the specific capacitance of 711 in 2 M KOH and 565 F g −1 in 2 M LiOH at the current density of 1 A g −1 , highlighting electrolyte-dependent redox kinetics of the Ni 2+ /Ni 3+ and Mn 3+ /Mn 4+ couples in alkaline media. Furthermore, the NiMn 2 O 4 electrode exhibits 92% capacitance retention and 97% coulombic efficiency after 10,000 cycles at 6 A g −1 in 2 M KOH, and 91.4% retention with 95% efficiency under the same conditions in 2 M LiOH. An aqueous hybrid supercapacitor (HSC) is subsequently assembled using NiMn 2 O 4 microfiber (+ve electrode), activated carbon (AC) (−ve electrode) and 2 M KOH electrolyte. The resulting NiMn 2 O 4 //AC device delivers an energy density of 34.32 W h kg −1 at a power density of 800 W kg −1 , while retaining 88% of its initial capacitance and a corresponding coulombic efficiency of 89.36% after 10,000 charging-discharging cycles at 5 A g −1 . Practical viability is demonstrated by powering LEDs, a thermo-hydrometer, a kitchen timer, and a toy motor fan using two series-connected NiMn 2 O 4 //AC cells. Collectively, this work establishes tissue paper as an effective, low-cost biotemplate for engineering fibrous NiMn 2 O 4 electrodes, offering a scalable pathway to high-performance, environmentally benign energy storage.