Engineering multi-source biomass carbon hybrid integrated with MWCNTs and TiO₂ for high-performance supercapacitors...

This project was designed to investigate the electrode performance of a sustainable biomass-derived carbon hybrid P₁ (AC) sourced from mango leaves, moringa leaves, and spent tea waste, alongside its binary P₂, P₃ (AC@MWCNTs, AC@TiO₂) and ternary P₄ (AC-MWCNTs@TiO₂) composites for supercapacitors and oxygen evolution reaction (OER) water splitting applications. X-ray diffraction (XRD), scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDX), and Fourier-transform infrared spectroscopy (FTIR) were used to confirm the successful synthesis of the as-prepared materials via structural, compositional, and morphological attributes. Electrochemical characterization using cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) chronopotentiometry revealed significantly enhanced supercapacitive performance for the composites compared to the pristine biomass carbon hybrid. Among all tested materials, the P₄ ternary composite emerged as the most promising supercapacitor electrode, delivering a superior specific capacitance (C _s) of 651 F g^-1 at 2 mV s^-1 (via CV) and 312.5 F g^-1 at 0.8 A g^-1 (via GCD), a longer discharge time (d _t ) of 168 s, a high energy density (E _d) of 12.13 Wh kg^-1, and an excellent capacitance retention of 96%. Furthermore, OER electrocatalytic evaluations conducted via CV and linear sweep voltammetry (LSV) demonstrated that the same P₄ composite exhibited a low onset potential of 1.50 V, a minimized overpotential (η) of 198 mV at 10 mA cm^-2, and a low Tafel slope of 64.28 mV dec^-1. Long-term electrocatalytic stability was successfully authenticated via controlled potential electrolysis (CPE) chronoamperometry, showing steady performance at a current density of 98 mA cm^-2. Electrochemical impedance spectroscopy (EIS) corroborated the rapid charge kinetics of P₄, which yielded the lowest solution resistance (R ₁ = 1.20 ohm) and charge transfer resistance (R ₂ = 1.70 ohm). Therefore, driven by these benchmark performances, the P₄ ternary composite stands out as a viable, dual-functional electrode candidate for next-generation supercapacitors and OER applications.