Molecular Control of Carbon-Based Oxygen Reduction Electrocatalysts through Metal Macrocyclic Complexes Functionalization

Owing to their zero pollution and high efficiency, fuel cells and metal-air batteries show great potential for broad application to sustainable energy technologies. However, the use of expensive and scarce Pt-based materials as cathode catalysts to overcome the slow kinetics of oxygen-reduction reaction (ORR) limits the scalability of such devices. Recently, considerable progress has been made in the development of nonprecious-metal ORR catalysts. Although metal macrocyclic complexes (MMC) exhibiting a well-defined M-N-4 (M = Fe, Co, Mn, Cu, etc.) structure (which can provide open sites to combine with oxygen and catalyze ORR) have attracted widespread attention, the MMC ORR performance is usually unsatisfactory because MCCs exhibit poor conductivity, symmetric electron distribution, inferior O-2 adsorption, and low activation. However, MMC-modified conductive-carbon materials effectively solve such problems and simultaneously boost the ORR catalytic activity. In this review, the recent achievements in MMC-functionalized carbon materials as ORR catalysts are summarized, and the current challenges and prospects of MMC-functionalized carbon-based ORR catalysts are discussed based on recent experimental and theoretical studies.

Automated summary

Fuel cells and metal-air batteries have great potential for sustainable energy technologies due to their zero pollution and high efficiency. However, the high cost and scarcity of Pt-based materials as cathode catalysts limit their scalability. Recent progress in nonprecious-metal catalysts has addressed some of these challenges.