Metal-free carbonaceous materials, including nitrogen-doped graphene and carbon nanotubes, are emerging as alternative catalysts for peroxymonosulfate (PMS) activation to avoid drawbacks of conventional transition metal-containing catalysts, such as the leaching of toxic metal ions. However, these novel carbocatalysts face relatively high cost and complex syntheses, and their activation mechanisms have not been well-understood. Herein, we developed a novel nitrogen-doped carbonaceous nanosphere catalyst by carbonization of polypyrrole, which was prepared through a scalable chemical oxidative polymerization. The defective degree of carbon substrate and amount of nitrogen dopants (i.e., graphitic nitrogen) were modulated by the calcination temperature. The product carbonized at 800 °C (CPPy-F-8) exhibited the best catalytic performance for PMS activation, with 97% phenol degradation efficiency in 120 min. The catalytic system was efficient over a wide pH range (2-9), and the reaction of phenol degradation had a relatively low activation energy (18.4 ± 2.7 kJ mol). The nitrogen-doped carbocatalyst activated PMS through a nonradical pathway. A two-step catalytic mechanism was extrapolated: the catalyst transfers electrons to PMS through active nitrogen species and becomes a metastable state of the catalyst (State I); next, organic substrates are oxidized and degraded by serving as electron donors to reduce State I. The catalytic process was selective toward degradation of various aromatic compounds with different substituents, probably depending on the oxidation state of State I and the ionization potential (IP) of the organics; that is, only those organics with an IP value lower than ca. 9.0 eV can be oxidized in the CPPy-F-8/PMS system.

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The unique chemical and physical properties of graphene and its derivatives (graphene oxide, heteroatom‐doped graphene, and functionalized graphene) have stimulated tremendous efforts and made significant progress in fuel cell applications. This review focuses on the latest advances in the use of graphene‐based materials in electrodes, electrolytes, and bipolar plates for fuel cells. The understanding of structure‐activity relationships of metal‐free heteroatom‐doped graphene and graphene‐supported catalysts was highlighted. The performances and advantages of graphene‐based materials in membranes and bipolar plates were summarized. We also outlined the challenges and perspectives in using graphene‐based materials for fuel cell applications.

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