Ternary nanocomposite ReMIL-CN (ReSe ₂ @MIL-53(Fe)@g-C ₃ N ₄ ) for energy storage and electroactive integrated H ₂ O ₂ sensor application

Integrated electrochemical systems capable of simultaneous charge storage and biochemical sensing response have gained prominence in modern materials science and biomedical engineering by offering multifunctionality for next-generation smart devices. The present comprehensive study is focused on the synthesis and characterization of a ternary nanocomposite material, focusing on its applications in integrated electrode systems for BHSCs and hydrogen peroxide (H₂O₂) sensing. The synthesized ReMIL-CN (ReSe₂@MIL-53(Fe)@g-C₃N₄) nanocomposite exhibits an average crystallite size of 27.27 nm, a specific surface area of 154 m² g^-1, and a specific pore volume of 0.022 cm³ g^-1. The ReMIL-CN electrode offers maximum specific capacities (<i>Q</i> _s) of 1925.5 C g^-1 in a three-electrode testing setup and 423 C g^-1 in a ReMIL-CN//AC full-cell setup. The values of the oxidation and reduction diffusion coefficients (<i>D</i> _oxidation and <i>D</i> _reduction) of the ReMIL-CN compound are 4.59 × 10^-8 m² s^-1 and 1.45 × 10^-8 m² s^-1, respectively. The highest obtained values of the energy density (<i>E</i> _d) and power density (<i>P</i> _d) are 50 Wh kg^-1 and 2060 W kg^-1, respectively. The ReMIL-CN//AC hybrid device demonstrates high stability response, with 95% capacity retention, 90% columbic efficiency, and 90% and 84% charge-discharge time retention over a prolonged period of 10 000 repeated cycles. The measured <i>b</i>-values of 0.59, 0.68, and 0.70 suggest the hybrid-natured operational mechanism of the ReMIL-CN//AC device. Moreover, the present composite-based electrode exhibits a sensitivity of <i>S</i> = 0.185 μA μM^-1 cm² with a linear operational range of 50-1000 μM for the H₂O₂ detection system. The device maintains 95% signal stability after 1000 cycles, with an LOD of 0.1 μM, a linear regression value of <i>R</i> ² = 0.998, and a minimal response time of less than 3 seconds, demonstrating the excellent selectivity of the device. The outstanding electrochemical charge storage and sensing capabilities of this ternary nanomaterial enable its integration into real-time, self-powered bioelectrochemical monitoring for next-generation portable and wearable bioelectronics.