Synthesis of Porous Carbon-coated Cobalt Catalyst through Pyrolyzing Metal–Organic Framework and their Bifunctional OER/ORR Catalytic Activity for Zn-Air Rechargeable Batteries

A metal–organic framework (MOF) was synthesized using 4,4′-stilbenedicarboxylic acid (H₂SDA) in dimethylformamide (DMF). Carbon-coated Co (C@Co) catalysts were prepared by the direct calcination of Co₃(SDA)₃(DMF)₂ MOF crystals at various temperatures. The highest surface area of the C@Co catalyst is obtained at 600 °C which can further be increased by the ball mill operation. The X-ray photon spectroscopy and X-ray diffraction analysis proved the formation of metallic Co in the carbon matrix at temperatures over 500 °C, while Co₃O₄ formation was observed at 500 °C. Furthermore, the graphitic properties of the Co particles were analyzed by Raman spectroscopy. The durability of the carbon-coated Co catalysts derived from MOFs (C@Co catalysts) was analyzed by the cycle test (charge/discharge at 20 mA/cm² per 2 h) and was retained over 350 h. These catalysts showed remarkable stability for both ORR (oxygen reduction reaction) and OER (oxygen evolution reaction), comparable to that of Co₃O₄ and Co metal powder in alkaline solution.