Engineering the structure of ZIF-derived catalysts by revealing the critical role of temperature for enhanced oxygen reduction reaction

Zeolitic imidazolate frameworks (ZIF)-derived catalysts are being extensively investigated for the oxygen reduction reaction (ORR) due to its low cost, high tunability, and facile fabrication. However, an understanding of the critical role of temperature during pyrolysis remains lacking, which makes the design of catalysts by thermal activation rely on empirical engineering. In this work, we use ZIF-67 as a model material to study the impact of temperature on microstructural evolution by in situ transmission electron microscopy. Microstructural features of cobalt precipitation, nitrogen loss, and porous carbon support formation were investigated and semi-quantified. A tradeoff between the microstructural features is revealed and confirmed by the ORR performance. By understanding the temperature-microstructure-ORR performance relationship, we further design a simple low-temperature pyrolysis strategy and achieve outstanding ORR activity. Although demonstrated on ZIF-67, the critical role of temperature as disclosed by this work is beneficial for all ZIF-related materials to further boost ORR performance. Meanwhile, our one-step strategy is easy to implement and allows for scaling up for industrial application.