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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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Cyclic voltammograms (CV) of samples on glassy carbon (GC) electrodes in N2- and O2-saturated 0.1 M aq. KOH solution with a scan rate of 10 mV s−1.(a) the pristine graphite; (b) ClGnP; (c) BrGnP; (d) IGnP; (e) Pt/C. Pink arrows indicate the contributions of hydrogen evolution at around −0.7 V and out of limiting potential (−0.8 V). (f) Linear sweep voltammograms (LSV) at a rotation rate of 1600 rpm and a scan rate of 10 mV s−1, showing a gradual increase in current and a positive shift in the onset potential along the order of the pristine graphite < ClGnP < BrGnP < IGnP < Pt/C (pink arrow).
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f3: Cyclic voltammograms (CV) of samples on glassy carbon (GC) electrodes in N2- and O2-saturated 0.1 M aq. KOH solution with a scan rate of 10 mV s−1.(a) the pristine graphite; (b) ClGnP; (c) BrGnP; (d) IGnP; (e) Pt/C. Pink arrows indicate the contributions of hydrogen evolution at around −0.7 V and out of limiting potential (−0.8 V). (f) Linear sweep voltammograms (LSV) at a rotation rate of 1600 rpm and a scan rate of 10 mV s−1, showing a gradual increase in current and a positive shift in the onset potential along the order of the pristine graphite < ClGnP < BrGnP < IGnP < Pt/C (pink arrow).

Mentions: Having characterized the morphological and the chemical structures for XGnPs, we further investigated their electrocatalytic activities in N2- and O2-saturated 0.1 M aq. KOH solutions using the pristine graphite and commercial Pt/C electrocatalysts with the same mass loadings as reference. Cyclic voltammograms (CV) in Figures 3a–3d show the obvious oxygen reduction peaks for all the four carbon-based electrodes in the O2-saturated 0.1 M aq. KOH solution, while they displayed featureless CVs in the corresponding N2-satureted medium. Figure 3a shows a single cathodic reduction peak at −0.37 V with a current density of −0.28 mA cm−2 for the pristine graphite electrode in the O2-saturated 0.1 M aq. KOH solution. The corresponding cathodic reduction peaks for the ClGnP, BrGnP and IGnP were positively shifted to −0.24, −0.22 and −0.22 V, respectively. The corresponding peak currents for oxygen reduction were determined to be −0.39, −0.60 and −0.78 mA cm−2 for the ClGnP, BrGnP and IGnP, respectively. These values are over 1.4, 2.1 and 2.8 times that of the pristine graphite (−0.28 mA cm−2). Thus, the reduction currents of XGnPs gradually increased while their onset potentials positively shifted along the order of ClGnP < BrGnP < IGnP. As shown in Figures S8–S10 and Table S5, the capacitances of XGnPs gradually increased in the order of the pristine graphite < ClGnP < BrGnP < IGnP. Among all the electrodes tested in this study, the IGnP electrode has the highest capacitances of 127.6 and 139.5 F g−1 in both N2- and O2-saturated electrolytes with a high cycle stability. Clearly, therefore, the edge-halogenations, particularly Br and I, play an important role to significantly improve the ORR activity of graphite, while edge-hydrogenated GnPs (HGnPs), prepared by ball-milling under the same conditions in the absence of halogen, showed marginally improved ORR activity45.


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)

Cyclic voltammograms (CV) of samples on glassy carbon (GC) electrodes in N2- and O2-saturated 0.1 M aq. KOH solution with a scan rate of 10 mV s−1.(a) the pristine graphite; (b) ClGnP; (c) BrGnP; (d) IGnP; (e) Pt/C. Pink arrows indicate the contributions of hydrogen evolution at around −0.7 V and out of limiting potential (−0.8 V). (f) Linear sweep voltammograms (LSV) at a rotation rate of 1600 rpm and a scan rate of 10 mV s−1, showing a gradual increase in current and a positive shift in the onset potential along the order of the pristine graphite < ClGnP < BrGnP < IGnP < Pt/C (pink arrow).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f3: Cyclic voltammograms (CV) of samples on glassy carbon (GC) electrodes in N2- and O2-saturated 0.1 M aq. KOH solution with a scan rate of 10 mV s−1.(a) the pristine graphite; (b) ClGnP; (c) BrGnP; (d) IGnP; (e) Pt/C. Pink arrows indicate the contributions of hydrogen evolution at around −0.7 V and out of limiting potential (−0.8 V). (f) Linear sweep voltammograms (LSV) at a rotation rate of 1600 rpm and a scan rate of 10 mV s−1, showing a gradual increase in current and a positive shift in the onset potential along the order of the pristine graphite < ClGnP < BrGnP < IGnP < Pt/C (pink arrow).
Mentions: Having characterized the morphological and the chemical structures for XGnPs, we further investigated their electrocatalytic activities in N2- and O2-saturated 0.1 M aq. KOH solutions using the pristine graphite and commercial Pt/C electrocatalysts with the same mass loadings as reference. Cyclic voltammograms (CV) in Figures 3a–3d show the obvious oxygen reduction peaks for all the four carbon-based electrodes in the O2-saturated 0.1 M aq. KOH solution, while they displayed featureless CVs in the corresponding N2-satureted medium. Figure 3a shows a single cathodic reduction peak at −0.37 V with a current density of −0.28 mA cm−2 for the pristine graphite electrode in the O2-saturated 0.1 M aq. KOH solution. The corresponding cathodic reduction peaks for the ClGnP, BrGnP and IGnP were positively shifted to −0.24, −0.22 and −0.22 V, respectively. The corresponding peak currents for oxygen reduction were determined to be −0.39, −0.60 and −0.78 mA cm−2 for the ClGnP, BrGnP and IGnP, respectively. These values are over 1.4, 2.1 and 2.8 times that of the pristine graphite (−0.28 mA cm−2). Thus, the reduction currents of XGnPs gradually increased while their onset potentials positively shifted along the order of ClGnP < BrGnP < IGnP. As shown in Figures S8–S10 and Table S5, the capacitances of XGnPs gradually increased in the order of the pristine graphite < ClGnP < BrGnP < IGnP. Among all the electrodes tested in this study, the IGnP electrode has the highest capacitances of 127.6 and 139.5 F g−1 in both N2- and O2-saturated electrolytes with a high cycle stability. Clearly, therefore, the edge-halogenations, particularly Br and I, play an important role to significantly improve the ORR activity of graphite, while edge-hydrogenated GnPs (HGnPs), prepared by ball-milling under the same conditions in the absence of halogen, showed marginally improved ORR activity45.

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