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

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.