Metal-organic framework decorated with black tea-derived activated carbon as electrocatalyst for alkaline-based hydrogen evolution reaction

Abstract

TThe hydrogen evolution reaction (HER) from water-splitting electrolysis in a non-acidic medium produces pure hydrogen gas on a large scale. Therefore, exploring highly abundant electrocatalysts free from precious group metals (PGMs) is significant because it addresses the critical issues of high cost. Hence, this study examines the effect of a zinc-based metal-organic framework (Zn-MOF) decorated with black tea-derived activated carbon (AC) as a suitable electrocatalyst for hydrogen production. The structural composition and properties of the synthesised Zn-MOF/AC composite and its precursors (i.e., carbon (C), AC, and Zn-MOF) were characterised using scanning electron microscopy (SEM), Raman, X-ray diffraction (XRD), Fourier transform infrared (FTIR) and thermogravimetric analysis (TGA). The electrochemical performance of the screen-printed electrodes fabricated with active materials (i.e., C, AC, Zn-MOF, and Zn-MOF/AC composite) for HER applications was investigated using cyclic voltammetry (CV), scan rate-dependence analyses, electrochemical impedance spectroscopy (EIS), linear sweep voltammetry (LSV), turnover frequency (TOF), and Tafel measurements. The Zn-MOF/AC composite exhibits the lowest overpotential (0.32V at 6 mAcm-2) and the largest electrochemically active surface area (ECSA = 31.81 cm²), indicating abundant accessible active sites and improved charge transfer. The composite shows a lower Tafel slope (113.3 mV·dec⁻¹) than that of Zn-MOF (135.9 mV·dec⁻¹) with a TOF of 10.14 x 10-4 mol H₂·s⁻¹. Taken together, these results show that Zn-MOF/AC offers the best balance of low overpotential and high active-surface exposure, demonstrating synergistic enhancement for practical hydrogen evolution.