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.

Novel N, S co-doped graphene (NSG) was prepared by annealing graphene oxide with thiourea as the single N and S precursor. The NSG electrodes, as efficient metal-free electrocatalysts, show a direct four-electron reaction pathway, high onset potential, high current density and high stability for the oxygen reduction reaction.

Heteroatom-doped carbon materials have been extensively investigated as metal-free electrocatalysts to replace commercial Pt/C catalysts in oxygen reduction reactions in fuel cells and Li-air batteries. However, the synthesis of such materials usually involves high temperature or complicated equipment. Graphene-based sulfur composites have been recently developed to prolong the cycling life of Li-S batteries, one of the most attractive energy-storage devices. Given the high cost of graphene, there is significant demand to recycle and reuse graphene from Li-S batteries. Herein, we report a green and cost-effective method to prepare sulfur-doped graphene, achieved by the continuous charge/discharge cycling of graphene-sulfur composites in Li-S batteries. This material was used as a metal-free electrocatalyst for the oxygen reduction reaction and shows better electrocatalytic activity than pristine graphene and better methanol tolerance durability than Pt/C.

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 mm), 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.

In this work, we successfully, for the first time, perform the molecular doping of graphene as metal-free electrocatalysts for oxygen reduction reaction. The doped small molecule onto graphene could induce the charge transfer between graphene and the molecules, which leads to significantly enhanced electrocatalytic activity for oxygen reduction reaction.

Heteroatom‐doped carbon materials have been extensively investigated as metal‐free electrocatalysts to replace commercial Pt/C catalysts in oxygen reduction reactions in fuel cells and Li–air batteries. However, the synthesis of such materials usually involves high temperature or complicated equipment. Graphene‐based sulfur composites have been recently developed to prolong the cycling life of Li–S batteries, one of the most attractive energy‐storage devices. Given the high cost of graphene, there is significant demand to recycle and reuse graphene from Li–S batteries. Herein, we report a green and cost‐effective method to prepare sulfur‐doped graphene, achieved by the continuous charge/discharge cycling of graphene–sulfur composites in Li–S batteries. This material was used as a metal‐free electrocatalyst for the oxygen reduction reaction and shows better electrocatalytic activity than pristine graphene and better methanol tolerance durability than Pt/C.

In this work, for the first time, we have developed a one-step hydrothermal method to synthesize a hybrid material consisting of NiCo 2 S 4 nanocrystals grown on reduced graphene oxide as an efficient nonprecious electrocatalyst for oxygen reduction reaction (ORR) in alkaline medium. Our synthetic process here is quite simple, straightforward and environment benign. In comparison with rGO, NiCo 2 O 4 -rGO, and commercial Pt/C, NiCo 2 S 4 -rGO shows significantly enhanced catalytic activity over rGO and NiCo 2 O 4 -rGO, and close reduction activity but much superior methanol tolerance and better durability to commercial Pt/C catalyst. The half wave potential (E 1/2 ) for NiCo 2 S 4 -rGO hybrid is only about 62 mV more negative than that of the commercial Pt/C catalyst but 81 mV more positive than NiCo 2 O 4 -rGO, 116 mV than rGO. The superior performance for NiCo 2 S 4 -rGO is presumably attributed to a combination effect of mixed valence in transition metals composites favorable for O 2 to be absorbed/reduced and a synergetic effect resulted from NiCo 2 S 4 and rGO. The advantages over NiCo 2 O 4 -rGO might be ascribed to the inverse spinel crystal structure of NiCo 2 S 4 , its relative higher conductivity, and that Na 2 S serves both as S source and reducing agent facilitating increasing the hybrid catalytic activity.

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