Spinel-MgMn2O4 nanofibers: An attractive material for high performance aqueous symmetric supercapacitor

It is a known fact that morphology greatly influences the energy storage performance of a material. In this work, spinel magnesium manganese oxide (MgMn2O4) having nanofibric morphology has successfully been prepared for the first time using a versatile and cost-effective electrospinning technique. The morphology and the pore size are altered and optimized by varying the process parameters in the electrospinning process, and their corresponding effect on supercapacitive properties are also studied thoroughly. The aligned, mesoporous, and high aspect ratio of spinel-MgMn2O4 nanofiber exhibit the specific capacitance of ∼345 Fg−1 at 1 Ag−1 and 250 Fg−1 at 4 Ag−1 as well as demonstrate an outstanding rate capability and good capacity retention (∼90%) after 10,000 successive cycles at 4 Ag−1 in a three-electrode configuration. The improved energy storage performance of MgMn2O4 active material on graphite substrate is ascribed to its nanofibric morphology with interconnected particles having pores/voids in between, which impart a higher diffusion coefficient (D= 3.226 × 10−10 cm2s−1) and a small relaxation time constant (τ = 0.1 s). The quantitative capacitive contribution generating from EDLC and/or the surface pseudocapacitance reactions and the contribution from diffusion-controlled redox reactions to the total current have also been determined. The assembled symmetric all-solid-state supercapacitor (ASSSC) shows the high specific energy of ∼30 W h kg−1 at the specific power of ∼510 W kg−1 in the potential window of 0.0 V to 2 V with PVA-H2SO4 gel electrolyte. This performance is superior to that exhibited by many ASSSC reported recently. Two ASSSC devices connected in series can light up parallelly connected 55 red LEDs for more than 3 min, indicating practical applicability of our designed symmetric supercapacitor in electronics appliances. The outstanding electrochemical performance of the MgMn2O4 nanofiber reveals its potential to be a promising electrode material for supercapacitors.