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Facile, scalable synthesis of edge-halogenated graphene nanoplatelets as efficient metal-free eletrocatalysts for oxygen reduction reaction.

Jeon IY, Choi HJ, Choi M, Seo JM, Jung SM, Kim MJ, Zhang S, Zhang L, Xia Z, Dai L, Park N, Baek JB - Sci Rep (2013)

Bottom Line: A series of edge-selectively halogenated (X = Cl, Br, I) graphene nanoplatelets (XGnPs = ClGnP, BrGnP, IGnP) were prepared simply by ball-milling graphite in the presence of Cl2, Br2 and I2, respectively.The newly-developed XGnPs can be well dispersed in various solvents, and hence are solution processable.First-principle density-functional calculations revealed that halogenated graphene edges could provide decent adsorption sites for oxygen molecules, in a good agreement with the experimental observations.

View Article: PubMed Central - PubMed

Affiliation: Interdisciplinary School of Green Energy, Low-Dimensional Carbon Materials Center, Ulsan National Institute of Science and Technology (UNIST), 100 Banyeon, Ulsan, South Korea.

ABSTRACT
A series of edge-selectively halogenated (X = Cl, Br, I) graphene nanoplatelets (XGnPs = ClGnP, BrGnP, IGnP) were prepared simply by ball-milling graphite in the presence of Cl2, Br2 and I2, respectively. High BET surface areas of 471, 579 and 662 m(2)/g were observed for ClGnP, BrGnP and IGnP, respectively, indicating a significant extent of delamination during the ball-milling and subsequent workup processes. The newly-developed XGnPs can be well dispersed in various solvents, and hence are solution processable. Furthermore, XGnPs showed remarkable electrocatalytic activities toward oxygen reduction reaction (ORR) with a high selectivity, good tolerance to methanol crossover/CO poisoning effects, and excellent long-term cycle stability. First-principle density-functional calculations revealed that halogenated graphene edges could provide decent adsorption sites for oxygen molecules, in a good agreement with the experimental observations.

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(a) A schematic representation for mechanochemically driven edge-halogenation reaction between the in-situ generated active carbon species (gold balls) and reactant halogens (twin green balls). Active carbon species were generated by homolytic bond cleavages of graphitic C-C bonds and reacted with halogen molecules to produce edge-halogenated graphene nanoplatelets (XGnPs) in a sealed ball-mill capsule and the remnant active carbon species are terminated upon subsequent exposure to air moisture. Red and gray balls stand for oxygen and hydrogen, respectively; (b) ball-mill capsule containing the pristine graphite and stainless steel balls (diameter 5 mm); (c) violent sparkling (red spots) occurred when the reaction mixture was exposed to ambient air moisture and excess purple I2 was sublimated in the air (arrow); (d) continued sparkling from residual IGnP at the bottom of a ball-mill capsule even after most of the IGnPs and stainless balls were taken out. The images were captured from supporting video clip in ESI.
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f1: (a) A schematic representation for mechanochemically driven edge-halogenation reaction between the in-situ generated active carbon species (gold balls) and reactant halogens (twin green balls). Active carbon species were generated by homolytic bond cleavages of graphitic C-C bonds and reacted with halogen molecules to produce edge-halogenated graphene nanoplatelets (XGnPs) in a sealed ball-mill capsule and the remnant active carbon species are terminated upon subsequent exposure to air moisture. Red and gray balls stand for oxygen and hydrogen, respectively; (b) ball-mill capsule containing the pristine graphite and stainless steel balls (diameter 5 mm); (c) violent sparkling (red spots) occurred when the reaction mixture was exposed to ambient air moisture and excess purple I2 was sublimated in the air (arrow); (d) continued sparkling from residual IGnP at the bottom of a ball-mill capsule even after most of the IGnPs and stainless balls were taken out. The images were captured from supporting video clip in ESI.

Mentions: The ball-milling-driven mechanochemical reaction between active carbon species and halogens is schematically shown in Figure 1a. Briefly, the high speed rotation (500 rpm) of the stainless steel balls during ball milling generated sufficient kinetic energy to cause bond cleavages for the graphitic C-C framework (Figure 1b). As a result, active carbon species (mostly carboradicals, carbocations and carbanions)36 formed at the broken edges of graphite, which were sufficiently reactive to pick up halogens (e.g., Cl2, Br2, I2) in the sealed ball-mill capsule. The detailed mechanism is proposed in Figure S1 in the Electronic Supporting Information (ESI). The high reactivity of the active carbon species was indicated by violent sparkling observed when capsule lid was opened (Figures 1c, 1d and supporting video clip in ESI), presumably due to the termination reaction for the remnants of the active carbon species with air moisture.


Facile, scalable synthesis of edge-halogenated graphene nanoplatelets as efficient metal-free eletrocatalysts for oxygen reduction reaction.

Jeon IY, Choi HJ, Choi M, Seo JM, Jung SM, Kim MJ, Zhang S, Zhang L, Xia Z, Dai L, Park N, Baek JB - Sci Rep (2013)

(a) A schematic representation for mechanochemically driven edge-halogenation reaction between the in-situ generated active carbon species (gold balls) and reactant halogens (twin green balls). Active carbon species were generated by homolytic bond cleavages of graphitic C-C bonds and reacted with halogen molecules to produce edge-halogenated graphene nanoplatelets (XGnPs) in a sealed ball-mill capsule and the remnant active carbon species are terminated upon subsequent exposure to air moisture. Red and gray balls stand for oxygen and hydrogen, respectively; (b) ball-mill capsule containing the pristine graphite and stainless steel balls (diameter 5 mm); (c) violent sparkling (red spots) occurred when the reaction mixture was exposed to ambient air moisture and excess purple I2 was sublimated in the air (arrow); (d) continued sparkling from residual IGnP at the bottom of a ball-mill capsule even after most of the IGnPs and stainless balls were taken out. The images were captured from supporting video clip in ESI.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3672906&req=5

f1: (a) A schematic representation for mechanochemically driven edge-halogenation reaction between the in-situ generated active carbon species (gold balls) and reactant halogens (twin green balls). Active carbon species were generated by homolytic bond cleavages of graphitic C-C bonds and reacted with halogen molecules to produce edge-halogenated graphene nanoplatelets (XGnPs) in a sealed ball-mill capsule and the remnant active carbon species are terminated upon subsequent exposure to air moisture. Red and gray balls stand for oxygen and hydrogen, respectively; (b) ball-mill capsule containing the pristine graphite and stainless steel balls (diameter 5 mm); (c) violent sparkling (red spots) occurred when the reaction mixture was exposed to ambient air moisture and excess purple I2 was sublimated in the air (arrow); (d) continued sparkling from residual IGnP at the bottom of a ball-mill capsule even after most of the IGnPs and stainless balls were taken out. The images were captured from supporting video clip in ESI.
Mentions: The ball-milling-driven mechanochemical reaction between active carbon species and halogens is schematically shown in Figure 1a. Briefly, the high speed rotation (500 rpm) of the stainless steel balls during ball milling generated sufficient kinetic energy to cause bond cleavages for the graphitic C-C framework (Figure 1b). As a result, active carbon species (mostly carboradicals, carbocations and carbanions)36 formed at the broken edges of graphite, which were sufficiently reactive to pick up halogens (e.g., Cl2, Br2, I2) in the sealed ball-mill capsule. The detailed mechanism is proposed in Figure S1 in the Electronic Supporting Information (ESI). The high reactivity of the active carbon species was indicated by violent sparkling observed when capsule lid was opened (Figures 1c, 1d and supporting video clip in ESI), presumably due to the termination reaction for the remnants of the active carbon species with air moisture.

Bottom Line: A series of edge-selectively halogenated (X = Cl, Br, I) graphene nanoplatelets (XGnPs = ClGnP, BrGnP, IGnP) were prepared simply by ball-milling graphite in the presence of Cl2, Br2 and I2, respectively.The newly-developed XGnPs can be well dispersed in various solvents, and hence are solution processable.First-principle density-functional calculations revealed that halogenated graphene edges could provide decent adsorption sites for oxygen molecules, in a good agreement with the experimental observations.

View Article: PubMed Central - PubMed

Affiliation: Interdisciplinary School of Green Energy, Low-Dimensional Carbon Materials Center, Ulsan National Institute of Science and Technology (UNIST), 100 Banyeon, Ulsan, South Korea.

ABSTRACT
A series of edge-selectively halogenated (X = Cl, Br, I) graphene nanoplatelets (XGnPs = ClGnP, BrGnP, IGnP) were prepared simply by ball-milling graphite in the presence of Cl2, Br2 and I2, respectively. High BET surface areas of 471, 579 and 662 m(2)/g were observed for ClGnP, BrGnP and IGnP, respectively, indicating a significant extent of delamination during the ball-milling and subsequent workup processes. The newly-developed XGnPs can be well dispersed in various solvents, and hence are solution processable. Furthermore, XGnPs showed remarkable electrocatalytic activities toward oxygen reduction reaction (ORR) with a high selectivity, good tolerance to methanol crossover/CO poisoning effects, and excellent long-term cycle stability. First-principle density-functional calculations revealed that halogenated graphene edges could provide decent adsorption sites for oxygen molecules, in a good agreement with the experimental observations.

Show MeSH
Related in: MedlinePlus