Polyvinylpyrrolidone-Mediated Engineering of NiMn₂O₄ Nanocubes for Enhanced Energy Storage and Non-Enzymatic H₂O₂ Detection

Abstract

Developing polymer-assisted advanced materials for multifunctional energy storage and sensing platforms offers a viable path to address future energy demands and associated economic constraints. In this context, inverse spinel-structured NiMn₂O₄ has gained attention as a next-generation electrode material due to its high energy density, superior power delivery, and robust cycling stability. The incorporation of polyvinylpyrrolidone (PVP) as a polymeric surfactant during hydrothermal synthesis plays a pivotal role in tailoring the material's nanoscale architecture. PVP not only modulates nucleation and growth to achieve a mixed morphology of nanocubes and nanoflakes, thereby optimizing the surface-to-volume ratio, but also facilitates a shift from diffusion-controlled to surface-driven capacitive behavior. This transition significantly improves charge transport dynamics, energy density, and structural durability. The resulting electrodes deliver a high specific capacitance of 816 F g^-1 at 1 A g^-1 and retain excellent cyclic stability over 5000 cycles in 1 M KOH. The assembled asymmetric supercapacitor (ASC) device demonstrates 96% capacitance retention after 10,000 cycles, delivering an energy density of 8.8 Wh kg^-1 at 6400 W kg^-1 and reaching a peak energy density of 36.55 Wh kg^-1 at 400 W kg^-1. Complementary density functional theory (DFT) analysis provides insights into the polymer-modulated electronic structure and redox behavior. In addition, the non-enzymatic NiMn4/GCE-based H₂O₂ sensor showcases excellent sensitivity, a low detection limit, and high selectivity against various biological interferences, demonstrating the polymer-engineered NiMn₂O₄’s dual functionality in sustainable energy and biosensing applications.