The oxygen reduction reaction (ORR) is one of the most important reactions in both life processes and energy conversion systems. The replacement of noble-metal Pt-based ORR electrocatalysts by nonprecious-metal catalysts is crucial for the large-scale commercialization of automotive fuel cells. Inspired by the mechanisms of dioxygen activation by metalloenzymes, herein we report a structurally well-defined, bio-inspired ORR catalyst that consists of a biomimetic model compound-an axial imidazole-coordinated porphyrin-covalently attached to multiwalled carbon nanotubes. Without pyrolysis, this bio-inspired electrocatalyst demonstrates superior ORR activity and stability compared to those of the state-of-the-art Pt/C catalyst in both acidic and alkaline solutions, thus making it a promising alternative as an ORR electrocatalyst for application in fuel-cell technology.

There is an urgent need for developing nonprecious metal catalysts to replace Pt-based electrocatalysts for oxygen reduction reaction (ORR) in fuel cells. Atomically dispersed M−N x /C catalysts have shown promising ORR activity; however, enhancing their performance through modulating their active site structure is still a challenge. In this study, a simple approach was proposed for preparing atomically dispersed iron catalysts embedded in nitrogen-and fluorine-doped porous carbon materials with fivecoordinated Fe−N 5 sites. The C@PVI-(DFTPP)Fe-800 catalyst, obtained through pyrolysis of a bio-inspired iron porphyrin precursor coordinated with an axial imidazole from the surface of polyvinylimidazole-grafted carbon black at 800 °C under an Ar atmosphere, exhibited a high electrocatalytic activity with a half-wave potential of 0.88 V versus the reversible hydrogen electrode for ORR through a four-electron reduction pathway in alkaline media. In addition, an anion-exchange membrane electrode assembly (MEA) with C@PVI-(DFTPP)Fe-800 as the cathode electrocatalyst generated a maximum power density of 0.104 W cm −2 and a current density of 0.317 mA cm −2 . X-ray absorption spectroscopy demonstrated that a single-atom catalyst (Fe−N x /C) with an Fe−N 5 active site can selectively be obtained; furthermore, the catalyst ORR activity can be tuned using fluorine atom doping through appropriate preassembling of the molecular catalyst on a carbon support followed by pyrolysis. This provides an effective strategy to prepare structure-performance-correlated electrocatalysts at the molecular level with a large number of M−N x active sites for ORR. This method can also be utilized for designing other catalysts.

The oxygen reduction reaction (ORR) is one of the most important reactions in life processes and energy conversion systems. To alleviate global warming and the energy crisis, the development of high-performance electrocatalysts for ORR for their application in energy conversion and storage devices such as metal-air batteries and fuel cells is highly desirable. Inspired by the biological oxygen activation/reduction process associated with heme- and multicopper-containing metalloenzymes, iron and copper-based transition metal complexes have been extensively explored as ORR electrocatalysts. This review outlines recent progress on non-precious-metal electrocatalysts for ORR that do not require pyrolysis treatment, which is regarded as desirable from the viewpoint of bio-inspired molecular catalyst design, focusing on iron/cobalt macrocycles (porphyrins, phthalocyanines, and corroles) and copper complexes in which the ORR activity is tuned by ligand variation/substitution, the method of catalyst immobilization, and the underlying supporting materials. Current challenges and exciting imminent developments in bio-inspired ORR electrocatalysts are summarized and proposed.

Inspired by the multicopper active site of laccase, which efficiently catalyzes the oxygen reduction reaction (ORR), herein we report a novel bio-inspired ORR catalyst composed of a multinuclear copper complex that was immobilized on the surface of reduced graphene oxide (rGO) via the covalently grafted triazole-dipyridine (TADPy) dinucleating ligand. This rGO-TADPyCu catalyst exhibited high ORR activity and superior long-term stability compared to Pt/C in alkaline media.

The oxygen reduction reaction (ORR) is one of the most important reactions in both life processes and energy conversion systems. The replacement of noble‐metal Pt‐based ORR electrocatalysts by nonprecious‐metal catalysts is crucial for the large‐scale commercialization of automotive fuel cells. Inspired by the mechanisms of dioxygen activation by metalloenzymes, herein we report a structurally well‐defined, bio‐inspired ORR catalyst that consists of a biomimetic model compound—an axial imidazole‐coordinated porphyrin—covalently attached to multiwalled carbon nanotubes. Without pyrolysis, this bio‐inspired electrocatalyst demonstrates superior ORR activity and stability compared to those of the state‐of‐the‐art Pt/C catalyst in both acidic and alkaline solutions, thus making it a promising alternative as an ORR electrocatalyst for application in fuel‐cell technology.