2D metal–organic framework: harnessing π–d conjugation in bimetallic synergy for electrocatalytic hydrogen evolution reaction

Abstract

Hydrogen evolution reaction (HER) is a key process for green hydrogen production, but designing efficient, cost-effective catalysts free of noble metals is challenging. Two-dimensional (2D) metal–organic frameworks (MOFs) offer a promising platform for the development of catalysts for water electrolysis. In this study, a bimetallic 2D MOF, CuCo-THQ (THQ = tetrahydroxy-1,4-benzoquinone) is synthesized and evaluated for HER in alkaline media. CuCo-THQ (1 : 1) exhibited a low overpotential of 144 (±1) mV at 10 mA cm⁻² and a favorable Tafel slope of ∼89 mV dec⁻¹, outperforming the monometallic counterparts Cu-THQ and Co-THQ. The current density (j) normalized by electrochemically active surface area (ECSA) for the bimetallic CuCo-THQ (1 : 1) demonstrates superior HER activity, indicating that the enhanced catalytic performance arises from the intrinsic activity of the electrocatalyst rather than solely from an increased density of active sites. The bimetallic CuCo-THQ (1 : 1) also demonstrated excellent durability over 1000 cyclic voltammetry (CV) cycles and prolonged chronoamperometry, with minimal structural degradation. X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR) studies, coupled with density functional theory (DFT) and Bader charge analysis, revealed strong cooperative Cu–Co electronic interactions via redox-active THQ linkers (π–d conjugation), which facilitated the HER process. These findings establish CuCo-THQ as a scalable, cost-effective, and robust electrocatalyst, highlighting the potential of THQ-based 2D MOFs for practical alkaline water-splitting applications.