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Green Synthesis of Plant Mediated-Based MnO2 Electrocatalysts Using Clerodendrum infortunatum L. for Enhanced Oxygen Reduction and Evolution in Solid-Electrolyte Zinc-Air Batteries

Manat Jaimasith, Wanrudee Kaewmesri, Arrak Klinbumrung

Abstract


This study investigated the green synthesis of MnO2-based electrocatalysts using Clerodendrum infortunatum L. flower and leaf extracts as natural reducing and capping agents via a comproportionating reaction. Bioactive compounds facilitated Mn⁷⁺ to Mn⁴⁺ reduction and stabilized the resulting flower-mediated (FM) and leaf-mediated (LM) composites. Characterization via UV–Visible spectroscopy, XRD, and SEM-EDS confirmed aggregated nanoparticle clusters (50–200 nm) with uniform Mn, O, and C distribution. High carbon content confirmed MnO2–organic carbon composite formation, which improved electrical conductivity and structural stability. The composites were fabricated into electrodes (FME and LME) and evaluated as air cathodes for solid-electrolyte zinc–air batteries. Both exhibited Oxygen Evolution Reaction (OER) performance comparable to commercial Pt/C (onset potentials: 1.5–1.6 V; overpotentials: 450–460 mV). For Oxygen Reduction Reaction (ORR), onset potentials of 0.7–0.8 V vs. RHE were recorded, with steeper slopes than Pt/C, indicating superior kinetics. Batteries discharged at 2 mA/cm² showed that FME delivered a discharge capacity of 6.00 mAh/cm², approximately 9 times that of Pt/C (0.63 mAh/cm²), while maintaining 1.05 V over 180 minutes. The utilization of plant extracts as natural reducing agents in the green synthesis approach offers a promising and environmentally responsible alternative for the fabrication of electrocatalysts in next-generation zinc-air battery applications, although a comprehensive techno-economic analysis remains necessary to fully validate its potential economic advantages.

Keywords



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DOI: 10.14416/j.asep.2026.08.006

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