Metal-organic framework derived carbon materials for electrocatalytic oxygen reactions: Recent progress and future perspectives

The electrocatalytic oxygen reactions, i.e. oxygen reduction/evolution reactions (ORR/OER), play a key role in electrochemical energy conversion and storage devices, including fuel cells, electrolyzers, and metal-air batteries, and have attracted significant attention in the past decades. Platinum-group metal (PGM)-free materials have been intensively investigated as alternatives to replace the well-accepted but costly PGM-based catalysts such as Pt for ORR and Ir/Ru (oxides) for OER. Particularly, metal-organic framework (MOF)-derived carbon materials are emerging PGM-free catalysts for ORR/OER. So far, excellent works have been achieved to enhance the activity and durability of the MOF-derived PGM-free catalysts. It is the occasion to promote the PGM-free catalysts to the next level of application, i.e. in real devices. However, ORR/OER in real devices are potentially subject to the porosity related challenges, e.g. electron/mass transfer issue and active site isolation in organic Li-air batteries. To address these challenges, the rational design of porous electrocatalyst for devices is required. In this review, we summarize the most recent progress of MOF-derived carbon materials for ORR/OER with the focus on not only the active site engineering but also the design of porous structure. We also provide perspectives on the rational design of PGM-free catalysts using MOF as precursors.