Green synthesis of <i>Mentha Spicata</i> -derived ZnO/Cu ₂ O hybrid nanomaterials as efficient and stable electrocatalysts for oxygen evolution reaction

Abstract This study presents the green synthesis of ZnO/Cu 2 O hybrid nanomaterials derived from Mentha Spicata (Mint) leaf aqueous extract, employed as an eco-friendly reducing agent, targeting electrocatalytic oxygen evolution reaction (OER) applications. The crystalline nature of the synthesized Mentha Spicata leaf of ZnO/Cu 2 O (MCZ) hybrid nanomaterials was systematically analyzed using X-ray diffraction (XRD). Detailed structural and morphological characterizations, including XRD, Attenuated Total Reflectance Fourier-transform infrared spectroscopy (ATR-FTIR), Raman spectroscopy, and Field Emission Scanning Electron Microscopy with Energy-Dispersive X-ray spectroscopy (FESEM-EDX), confirmed the successful fabrication of well-defined crystalline hybrid nanostructures. When implemented as electrocatalysts on carbon paper electrodes in alkaline medium (1 M KOH), the biogenically synthesized MCZ hybrid nanomaterials exhibited superior OER catalytic activity, achieving a low overpotential of 263.4 mV to reach a current density of 10 mA cm −2 at a scan rate of 10 mV s −1 , compared to ZnO, Cu 2 O and benchmark catalyst IrO 2. The catalysts demonstrated a turnover frequency (TOF) of 0.022 s −1 at 1.55 V versus the reversible hydrogen electrode (RHE), coupled with outstanding long-term operational stability. These findings underscore the efficacy of the bio-assisted synthetic methodology for fabricating sustainable, high-performance electrocatalysts suitable for efficient overall water splitting.