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

Abstract

The 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 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, Raman, x-ray diffraction, Fourier transform infrared and thermogravimetric analysis. 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, scan rate-dependence analyses, electrochemical impedance spectroscopy, linear sweep voltammetry, turnover frequency (TOF), and Tafel measurements. The Zn-MOF/AC composite exhibits the lowest overpotential (0.32 V 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 × 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.