Preparation of hierarchical hollow CoFe Prussian blue analogues and its heat-treatment derivatives for the electrocatalyst of oxygen evolution reaction.

The microstructure of materials importantly affects their performance. As electrocatalyst materials, the performance of hollow-structure materials is usually better than that of solid materials because of the larger specific surface area, lower density, and more exposed active sites of hollow structure. Bimetallic catalysts usually exhibit better catalytic activity than monometallic catalysts because of the synergistic effects between different metal elements. Prussian blue and its analogues (PB/PBAs) are ideal precursors for preparing hollow-structure bimetallic catalysts due to their structure and composition characteristics. In this study, ZIF-67 hollow sphere (HS) was used as the template to prepare hierarchical hollow CoFePBA (H-SCP) through anion-exchange method. The oxygen evolution reaction (OER) catalytic performance of H-SCP was further improved by low-temperature heat treatment in N atmosphere. The H-SCP-350 sample, which was obtained at a heat-treatment temperature of 350 ℃, was a bimetallic nanocomposite. Part of H-SCP was converted into metallic cobalt and cobalt-iron alloy during heat treatment. The synergistic effect among the different components effectively improved the electrocatalytic activity of the material. Therefore, H-SCP-350 showed the best OER catalytic performance among all samples. The overpotential was only 291mV at a current density of 10 mA cm when tested in 1 M KOH electrolyte.