electrocatalytic oxygen reduction performance of silver nanoparticle

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ELECTROCATALYTIC OXYGEN REDUCTION
PERFORMANCE OF SILVER NANOPARTICLE
DECORATED ELECTROCHEMICALLY
EXFOLIATED GRAPHENE
Joao Henrique Lopes, Siyu Ye, Jeff T Gostick, Jake E Barralet‡* and Geraldine Merle‡
J. H. Lopes
Faculty of Dentistry, McGill University, Montreal, H3A 2B2, (Canada)
E-mail: ([email protected])
Dr. S. Ye
Ballard Power Systems, 9000 Glenlyon Parkway, Burnaby, V5J 5J8 (Canada)
E-mail: ([email protected])
Prof. J. T. Gostick
Department of Chemical Engineering, McGill University, Montreal, H3A 0C5, (Canada)
E-mail : ([email protected])
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Prof. J. E. Barralet
Faculty of Dentistry, McGill University, Montreal, H3A 2B2, (Canada)
Department of Surgery, Faculty of Medicine, McGill University, Montreal, (Canada)
E-mail: ([email protected])
Dr. G. Merle
Faculty of Dentistry, McGill University, Montreal, H3A 2B2, (Canada)
E-mail: ([email protected])
SUPPORTING INFORMATION
SI. I. Discussion on the TGA data
The thermal stability of the as-prepared GRn was investigated by thermal gravimetric analysis
(TGA) under air and compared to GRp and GO (Figure 3f). Graphite exhibited one clear step of
weight loss at 750 ºC, related to the decomposition of the carbon, while Grn and GO decompose
in several steps. GRn curve exhibited a four-step thermal decomposition profile: initially a very
small mass loss (< 1%) started before 150 ºC attributable to the loss of residual solvent, followed
by a continuous decomposition (~8%) between 150 to 450 ºC related to the pyrolysis of PSS and
of the labile oxygen-containing groups. Between 450 to 750 ºC, a substantial weight loss of ~
21% occurs due to the decomposition of more stable oxygen-containing functional groups and
finally the decomposition of the carbon skeleton (> 750 ºC).1, 2, 3, 4 Although GO exhibited the
same thermal decomposition profile, the recorded weight losses were considerably higher than
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GRn (39 and 34%). The absence of an event related to the decomposition carbon skeleton for
GO is in agreement with a carbonaceous matrix being throughout being oxidized.2
SI. II. Characterization of graphite and graphene – FTIR spectra
Figure S1 shows FTIR absorption spectra of graphite and graphene electrochemically
exfoliated. The spectrum of the graphite exhibits two absorption bands at 2928 and 2865 cm-1
representing the C-H stretch vibrations.5 The absence of –OH, C=O, C-OH or C-O bands5,
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confirms the low oxidation degree of the graphene samples.
Figure SI. FTIR spectra of graphite and graphene samples.
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SI. III. Heterogeneous electron-transfer (HET)
The heterogeneous electron-transfer (HET) rate was investigated with cyclic voltammetry in
presence of 𝐾! [𝐹𝑒(𝐢𝑁)! ]/𝐾! [𝐹𝑒(𝐢𝑁)! ] (1:1 molar ratio) (Figure SII).
Figure SII. Cyclic voltammograms for (a) bare (b) graphite, (c) SDS +6V, (d) PSS +6V, and
(e) PSS +10V in N2-saturated 1 M KCl solution containing a total 10 mM concentration of
[𝑭𝒆(π‘ͺ𝑡)πŸ” ]πŸ‘!/πŸ’! (1:1 molar ratio). Scans start at +0.7 V. Scan rate, 50 mVs-1.
The current density generated at the GRn was greater than the graphite and bare electrodes,
indicating a higher electric conductivity for the GRn electrode due to its low defects density and
low oxidation degree. The redox peaks (E!/! ) were close to 0.21 V (Table 1) for each electrodes
at low potential scan rate (10 mVs-1) and the I! anodic / I! cathodic ratio approaches 1,
confirming the reversible redox reaction. The peak-to-peak potential separation (βˆ†E! ) for GRn
was quite low (68 mV) close to the ideal value of 59mV. In comparison the βˆ†E! value at the bare
and graphite were 103 mV and 85 mV respectively. The βˆ†E! value is related to the electron
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transfer coefficient and the low value for GRn indicates a fast electron transfer. Note that βˆ†E! for
all electrodes were substantially higher than 60/n mV (n=1, 25 ºC), suggesting a type of quasireversible behavior.7, 8, 9 Enhanced electron-transfer kinetics (𝐾!"" ) values were determined from
the anodic/cathodic peak separation and the dimensionless parameters πœ“ and 𝐾!"" .10 We first
!!
assumed 𝛼 = 0.5 and used the following diffusion coefficients: 𝐹𝑒(𝐢𝑁)!!
! /𝐹𝑒(𝐢𝑁)! ,
𝐷! = 7.63π‘₯10!! π‘π‘š! βˆ™ 𝑠 !! , 𝐷! = 6.32π‘₯10!! π‘π‘š! βˆ™ 𝑠 !! .7 The apparent electron-transfer rate
constants, 𝐾!"" , are summarized in Table 1. Having the lowest βˆ†πΈ! of 68 mV, GRn electrode
showed the fastest HET at 8.31 x 10-3 cm s-1. This value was substantially higher than GRp (βˆ†πΈ!
= 85 mV and 𝐾!"" = 2.77x 10-3 cm.s-1) and the bare GC (βˆ†πΈ! = 103 mV and 𝐾!"" = 1.38x 10-3
cm.s-1) electrodes.
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