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.