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Simultaneous etching and doping of cobalt sulfides–graphene hybrid with NH3-plasma effectively enhances the oxygen electrocatalytic activity.

Metal-free electrocatalysts have been extensively developed to replace noble metal Pt and RuO catalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in fuel cells or metal-air batteries. These electrocatalysts are usually deposited on a 3D conductive support (e.g., carbon paper or carbon cloth (CC)) to facilitate mass and electron transport. For practical applications, it is desirable to create in situ catalysts on the carbon fiber support to simplify the fabrication process for catalytic electrodes. In this study, the first example of in situ exfoliated, edge-rich, oxygen-functionalized graphene on the surface of carbon fibers using Ar plasma treatment is successfully prepared. Compared to pristine CC, the plasma-etched carbon cloth (P-CC) has a higher specific surface area and an increased number of active sites for OER and ORR. P-CC also displays good intrinsic electron conductivity and excellent mass transport. Theoretical studies show that P-CC has a low overpotential that is comparable to Pt-based catalysts, as a result of both defects and oxygen doping. This study provides a simple and effective approach for producing highly active in situ catalysts on a carbon support for OER and ORR.

For the first time, we developed edge-rich and dopant-free graphene as a highly efficient ORR electrocatalyst. Electrochemical analysis revealed that the as-obtained edge-rich graphene showed excellent ORR activity through a one-step and four-electron pathway. With a similar strategy, edge-rich carbon nanotubes and graphite can also be obtained with enhanced ORR activity. This work confirms the important role of edge carbon in efficient ORR electrocatalysis without interruption by any other dopants.

Renewable energy technology has been considered as a "MUST" option to lower the use of fossil fuels for industry and daily life. Designing critical and sophisticated materials is of great importance in order to realize high-performance energy technology. Typically, efficient synthesis and soft surface modification of nanomaterials are important for energy technology. Therefore, there are increasing demands on the rational design of efficient electrocatalysts or electrode materials, which are the key for scalable and practical electrochemical energy devices. Nevertheless, the development of versatile and cheap strategies is one of the main challenges to achieve the aforementioned goals. Accordingly, plasma technology has recently appeared as an extremely promising alternative for the synthesis and surface modification of nanomaterials for electrochemical devices. Here, the recent progress on the development of nonthermal plasma technology is highlighted for the synthesis and surface modification of advanced electrode materials for renewable energy technology including electrocatalysts for fuel cells, water splitting, metal-air batteries, and electrode materials for batteries and supercapacitors, etc.

The vision of a hydrogen economy relies on efficient utilization and production of hydrogen in a hydrogen fuel cell and a water electrolyzer. In both technologies, the sluggish kinetics of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) account for the most efficiency loss because the reactions on catalytic sites are constrained by adsorption-energy scaling relations involving intermediates of *OOH, *O, and *OH (where * denotes the active site). Therefore, a novel paradigm for catalyst design is required by overcoming or circumventing the adsorption-energy scaling relations. In this Review, the fundamentals of oxygen electrocatalysis, including reaction of the mechanism and origin of the adsorption-energy scaling relationship, are first introduced. Crucial strategies to overcome the scaling relations are then summarized. Finally, future research directions in this area are proposed. This work provides guidelines for the rational design of efficient catalysts for oxygen electrocatalysis beyond the limitation posed by scaling relations.

Carbon-based metal-free electrocatalysts for the oxygen reduction reaction (ORR) in alkaline medium have been extensively investigated with the aim of replacing the commercially available, but precious platinum-based catalysts. For the proper design of carbon-based metal-free electrocatalysts for the ORR, it would be interesting to identify the active sites of the electrocatalyst. The ORR was now studied with an air-saturated electrolyte solution droplet (diameter ca. 15 μm), which was deposited at a specified position either on the edge or on the basal plane of highly oriented pyrolytic graphite. Electrochemical measurements suggest that the edge carbon atoms are more active than the basal-plane ones for the ORR. This provides a direct way to identify the active sites of carbon materials for the ORR. Ball-milled graphite and carbon nanotubes with more exposed edges were also prepared and showed significantly enhanced ORR activity. DFT calculations elucidated the mechanism by which the charged edge carbon atoms result in the higher ORR activity.

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