N-Doped activated carbon derived from water hyacinth for ultra-stable metal-free bifunctional electrode for zinc-air battery

Abstract

Activated N-doped carbon derived from water hyacinth leaves (WHL) was prepared and investigated as metal-free bi-functional catalyst for oxygen reduction and evolution (ORR/OER) in zinc-air batteries (ZABs). Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and Brunauer–Emmett–Teller (BET) methods were used to examine the morphology, elemental composition and the specific surface area of the samples, respectively. Linear sweep voltammetry (LSV) at rotating disk electrodes (RDEs) and rotating ring-disk electrodes (RRDEs) were employed to characterize the electrocatalytic activities. The electrochemical studies reveal that N-doped porous carbon from N-WHLs exhibited remarkable electrocatalytic activity for ORR, with an onset potential of 0.95 V and half-wave potential of 0.88 V comparable to commercial Pt/C catalyst. It also displays promising activity towards OER, with an overall potential of 1.86 V versus RHE to reach a current density of 10 mAcm^, resulting in an oxygen electrode activity (OEA) value of 0.98 V. The percentage of hydrogen peroxide produced was significantly low, with average electron transfer number value of 3.94 at 0.8 V for N-WHL. Furthermore, the ZAB using N-WHL catalysts as an air cathode displayed a power density of 84 mW cm⁻² and superior stability over 450 hours.

KEY WORDS: Bifunctional catalyst, Oxygen reduction reaction, Oxygen evolution reaction, Water hyacinth, Zinc-air battery.

Bull. Chem. Soc. Ethiop. 2025, 39(3), 571-584.                                                          

DOI: https://dx.doi.org/10.4314/bcse.v39i3.14