In Situ Transformed Cobalt Metal–Organic Framework Electrocatalysts\nfor the Electrochemical Oxygen Evolution Reaction

Abstract

The\ndevelopment of an active and efficient electrocatalyst for\nthe oxygen evolution reaction remains indispensable for the smooth\nrunning of an electrolyzer. Herein, we have synthesized two cobalt\nmetal–organic frameworks (Co-MOFs) with the formulas [C₆H₆CoN₂O₄] (compound <b>1</b>) and [C₁₂H₁₀CoN₂O₄] (compound <b>2</b>) using pyrazine and 4,4′-bipyridine\nas linkers in dimethylformamide medium by a solvothermal method. Both\nCo-MOFs shows strong antiferromagnetic interactions with Θ_p = −70 and −61 K for compounds <b>1</b> and <b>2</b>, respectively. The in situ transformation of\nboth compounds catalyzes the OER efficiently in alkaline medium, affording\na current density of 10 mA/cm² at overpotentials of 276\n± 3 and 302 ± 3 mV by compounds <b>1</b> and <b>2</b>, respectively. Moreover, compound <b>1</b> shows a\nvery high turnover frequency (15.087 s^–1), lower\nTafel slope (56 mV/dec), and greater Faradaic efficiency of 95.42%\nin comparison to compound <b>2</b>. The transformations of the\nCo-MOFs have been accessed by employing powder X-ray diffraction (PXRD),\nhigh-resolution transmission electron microscopic (HRTEM) analysis,\nand X-ray photoelectron spectroscopy, which reveal the formation of\nuniform hexagonal Co­(OH)₂ plates. Therefore, the as-developed\nCo-MOF is found to be an efficient pre-electrocatalyst for the OER\nin alkaline medium. These results not only reveal the preparation\nof OER electrocatalysts from a Co-MOF but also establish a method\nto derive a potentially active electrocatalyst to substitute for the\ntraditional noble-metal-based materials.