Poly(3-hexylthiophene)/multi-walled carbon nanotube composites: electrochemical and optical characterization
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Poly(3-hexylthiophene)/multi-walled carbon nanotube composites: electrochemical and optical characterization Hállen D. R. Calado1, Marcelo Valadares3, Anthony W. Musumeci2, Eric R. Waclawik2, Luiz A. Cury3, Glaura G. Silva1
1
Departamento de Química e 3Departamento de Física - Universidade Federal de Minas Gerais, Pampulha, 31270 901, Belo Horizonte, Minas Gerais, Brazil 2 School of Physical and Chemical Sciences, Queensland University of Technology, Brisbane, Queensland 4001, GPO Box 2434, Australia
ABSTRACT Carbon nanotubes (CNT) / conjugated polymer composites have been used for the preparation of thin film-modified electrodes. Thin, short, multi-walled CNT (MWNT) (purity > 95%) was completely coated by regioregular poly(3-hexylthiophene) (P3HT) through precipitation of a mixture of both in the non-solvent methanol. This work reports the electrochemical and optical characterization of P3HT and composites after dissolution in xylene and spin casting of films with thickness 95% carbon purity, ~10nm diameter, 1, where ipa is the intensity of the anodic peak current and ipc is the intensity of the cathodic peak current. The anodic peak appears rather broad with a full width at half-height larger than 90 mV, what is expected for a surface reaction with Nernstian behavior [18], this has been attributed to interactions among charged sites or the distribution of various conjugation lengths in the polymer [19, 20]. 1,0
10.00 -4
inormalized (A)
0,6 0,4
ipa / mA
0,8
-5
ipa = 1.466x10 + 7.066x10 v
8.00
R = 0.9979
6.00 4.00
(b)
2.00 0.00 0
0,2
20
40
60 -1 v / mV s
80
100
0,0 -0,2 -0,4
(a) -1,0
-0,5
0,0 E (V)
0,5
1,0
Figure 2. a) Cyclic voltammograms for the P3HT/MWNT composite’s films, electrolyte LiClO4 in CH3CN 10-1 mol L-1. (•) 0%, (---) 0.25%, (__) 2%, (….) 17% of MWNT. Scan rate: 100 mV/s, vs. Ag/AgNO3. Inside: b) anodic current of peak versus scan rate for sample P3HT/MWNT 2%. c) Cyclic voltammograms for the P3HT/MWNT composite film with 17% of MWNT at two different scan rates. vs. Ag/AgNO3.
Table 1 shows the main CV parameters extracted from figure 2a. Both anodic and cathodic current peaks presented a linear behavior as a function of scan rate (figure 2b), as expected for an electrode with surface-bound electroactive sites where the reactions occur with negligible mass transport [18]. Table 1: Cyclic voltammetric data for P3HT/MWNT films at 100 mV/s.[a] Composite 0%
Epa / V 0.67
Epc / V 0.47
E0 ´ / V 0.57
0.25%
0.68
0.47
0.58
2%
0.69
0.42
0.56
0.68
0.45
0.57
17% [a]
-1
-1
10 mol L LiClO4/CH3CN; Pt electrodes, vs. Ag/AgNO3 Epa: Anodic peak potential, Epc: Cathodic peak potential, E0’: Formal potential of an electrode ½ (Epa + Epc).
The very small variations observed in the values of the anodic peak potentials (Epa) as a function of MWNT content (Table 1 - data confirmed with analysis in duplicate) indicate that the electrons in these films are available to be oxidized in a similar way as compared to P3HT. The literature [21] describes the doping of regiorre
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