Size-controlled engineering of cobalt metal catalysts through a coordination effect for oxygen electrocatalysis

In the preparation process of carbon-based transition metal catalysts, the transition metal atoms usually seriously agglomerate, thus reducing the catalytic activity. To slow down the agglomeration of transition metal atoms during high-temperature treatments, herein, organics with coordination functions are proposed to regulate the typical metal-organic framework compound ZIF-67 with rich Co atoms. Electron microscopy structural characterization proves that ZIF-67 modified by coordinated organic compounds, including ascorbic acid (AA), citric acid (CA) and ethylenediaminetetraacetic acid disodium salt (EA), greatly improves the dispersibility of cobalt in the final product. All the adjusted ZIF-67 can derive cobalt-based bifunctional oxygen catalysts with higher activity. Among them, EA-MOF-Co shows the best ORR performance, with a half-wave potential comparable to commercial Pt/C in alkaline solutions and an obviously reduced oxygen evolution overpotential. This suggests that it is an effective method for use of coordination organics to tether metal ions and prevent their further agglomeration during carbonation.