Well-defined Co-N-C catalyst based on ZIF-67 in mixed solvents with low amount of ligands for efficient oxygen reduction reaction

Non-precious metal nitrogen-carbon composites (M-N-C) derived from ZIFs are an excellent non-precious metal catalyst for use in energy conversion and storage devices such as fuel cells and metal-air batteries. Herein ZIF-67 precursor with good dispersion, perfect crystal structure and size of below 270 nm was synthesized by consuming low amount of 2-methylimidazole ligand using a mixture of ethanol (EA) and methanol (MT) as the reaction medium. Compared with the traditional method of reducing the size of ZIF-67 by increasing the amount of ligands in methanol, this method avoids the waste of raw materials and saves the cost. The Co-N-C-MT/EA catalysts derived from ZIF-67 exhibits good ORR activity in alkaline media (0.1 M KOH) with a half-wave potential of 0.81 V vs RHE. After 5000 cycles, the initial potential and half-wave potential basically remain no change, showing excellent long-term stability. And remarkable methanol resistance is also displayed comparing with commercial Pt/C. The present experimental result shows that the improved synthesis method of ZIF-67 precursors has far-reaching implications for the field of catalyst research.