Electrocatalytic hydrogen evolution over micro and mesoporous cobalt metal-organic frameworks

The development of water electrolysis devices is crucial for the sustainable production of green hydrogen fuel. However, the slow kinetics and high overpotential are key shortfalls for hydrogen production during the half-cell hydrogen evolution reaction (HER) and significantly reduce the overall efficiency. Here we fabricated two micro- and mesoprorous cobalt MOFs [Co(BDC)(DMSO)(DMF)](n) and [Co(NH2-BDC)(DMSO)(DMF)](n) (labeled Co-1 and Co-2, respectively) by using a benezenedicarboxylic acid (H2BDC) linker and its amine-derivative (H2N-BDC). The chemical functionalization of organic linkers in MOFs enhances catalytic activity by providing Lewis acidity or basicity, potentially enhancing electrocatalytic activity. Co-1 MOF ([Co(BDC)(DMSO)](n)) had a rod-like morphology, while Co-2 MOF ([Co(NH2-BDC)(DMSO)](n)) was in the form of two-dimensional sheets. After characterizing the materials using PXRD, SEM-EDX, XPS, TGA, FTIR, and gas sorption, we explored the electrocatalytic activity of the MOFs for hydrogen evolution reaction (HER). The presence of surface amino functions slightly improved HER activity of cobalt MOFs in terms of overpotential (eta from 0.217 V to 0.215 V @ 25mAcm(-2)) and Tafel slope (from 95mVdec(-1) to 91mVdec(-1)). However, Co-2 showed better stability and high Faradaic efficiency (97 %), which we attribute to morphological features, mesoporosity, and the presence of basic surface functionalities.