Proton-coupled pseudocapacitive behavior of a manganese oxide-decorated nitrogen-rich COP for sustainable high-performance energy storage devices

Abstract

A hierarchical hybrid material (Mn₂O₃@COP) with dual charge storage capabilities was created by synthesizing a triazine-based covalent organic polymer (COP) that is rich in nitrogen functionalities and integrating it with Mn₂O₃ nanoparticles. Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), Brunauer–Emmett–Teller (BET) studies, and X-ray photoelectron spectroscopy (XPS) demonstrated a distinct architecture: Mn₂O₃ nanoparticles were uniformly embedded in a stable, porous COP matrix. Mn₂O₃ loading caused a modest decrease in surface area, but the composite still had the mesoporosity needed for quick ion diffusion. The existence of electroactive nitrogen centers—pyridinic, pyrrolic, and graphitic—and mixed-valence Mn³⁺/Mn⁴⁺ species, which together improve redox kinetics and charge transfer routes, was verified by XPS analysis. An intriguing combination of electric double-layer capacitance (EDLC) and pseudocapacitive behavior was demonstrated by electrochemical experiments in a 1 M H₂SO₄ electrolyte. The Mn₂O₃@COP composite electrode in the three-electrode system had a high specific capacitance of 113 F g⁻¹ at 5 mV s⁻¹ and 69.1 F g⁻¹ at 0.1 A g⁻¹, an energy density of 9.6 Wh kg⁻¹ and a power density of 500 W kg⁻¹ at 0.1 A g⁻¹. The fabricated symmetric supercapacitor device maintained 95% of its capacitance after 10 000 charge–discharge cycles at 0.5 A g⁻¹ and provided a specific capacitance of 16.2 F g⁻¹ and energy density and power density of 2.25 Wh kg⁻¹ and 250 W kg⁻¹ at 0.2 A g⁻¹, respectively. This study offers a viable method for combining the energy density of transition metal oxides with the quick kinetics of conductive organic networks, opening the door to long-lasting, highly effective energy storage devices.