Applications of metal–organic framework-derived materials in fuel cells and metal-air batteries

Oxygen reduction reaction (ORR) is the core of energy conversion and storage devices such as fuel cells and metal-air batteries. Development of highly active and stable electrocatalysts (e.g. metal-free carbonous materials, single-atom catalysts, and nanocomposites) has been a rigorous challenge for the clean energy technologies. In recent years, metal–organic frameworks (MOFs) with a unique flexible structure and uniformly dispersed active sites have become novel and attractive precursors for preparation of carbon-based composite materials, which show wide applications in many fields, especially in electrochemistry. Herein, we summarize the applications of various MOF-derived electrocatalysts (including MOF-derived single atom electrocatalysts, MOF-derived metal-free electrocatalysts, and MOF-derived nanocomposite electrocatalysts) in fuel cells and metal-air batteries. The influences of active sites (including metal central ions and heteroatoms), electronic structure, chemical composition and porosity of MOF-derived materials on the ORR performance are commented by combination of experimental results and theoretical calculations. The dispersity and coordination environment of the active sites in MOF-derived single-atom electrocatalysts are significantly influenced by the structure of the MOF precusuror and pyrolysis conditions. How to increase mass density of effective active sites and protect the active sites from damage and corrosion is discussed. The applications of MOF-derived electrocatalysts in the field of fuel cells and metal-air batteries are highlighted.