Bifunctional spinel ZnMn2O4 nanostructures for efficient supercapacitors and water splitting electrocatalysts: a synergistic experimental and modeling study
Abstract
Designing multifunctional nanostructures for sustainable energy solutions is crucial for advancing next-generation energy storage and conversion technologies. Herein, spinel ZnMn2O4 nanostructures are synthesized via a modified chemical route and optimized by annealing at different temperatures. The SZMO 5 sample, annealed at 500 °C, exhibits superior electrochemical performance with a high specific capacitance of 1281.14 F g−1 at 1 A g−1 and excellent cycling stability, retaining 91.2% capacitance after 2000 cycles. This performance is attributed to its mesoporous structure, improved surface area (85.92 m2 g−1), and efficient charge transfer kinetics. Symmetric and asymmetric supercapacitor devices are fabricated with PVA/H2SO4 gel electrolyte, and the asymmetric supercapacitor device shows superior electrochemical performance, with an energy density of 138 W h kg−1 at a power density of 510 W kg−1. To gain deeper insight into device-level charge transport dynamics, COMSOL Multiphysics simulations are employed for the first time, visualizing the potential distribution and current density evolution during operation. Simultaneously, SZMO 5 demonstrates outstanding catalytic activity for the hydrogen evolution reaction (HER), with a low overpotential of 376 mV at 10 mA cm−2 and a Tafel slope of 148 mV dec−1. The redox activity of Zn and Mn ions, coupled with the optimized structure, makes ZnMn2O4 a potential bifunctional material for supercapacitors and HER electrocatalysts, offering a sustainable pathway for clean energy technologies.