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

Abstract

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