cb pasta de C e polioxometalato, Notas de estudo de Engenharia Elétrica
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cb pasta de C e polioxometalato, Notas de estudo de Engenharia Elétrica

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A novel bacterial cellulose-based carbon paste electrode and its polyoxometalate-modified properties

Electrochemistry Communications 11 (2009) 1018–1021

Contents lists available at ScienceDirect

Electrochemistry Communications

journal homepage: www.elsevier .com/locate /e lecom

A novel bacterial cellulose-based carbon paste electrode and its polyoxometalate-modified properties

Yan Liang a, Ping He a,*, Yongjun Ma a, Yong Zhou b, Chonghua Pei a,*, Xiaobing Li c

a School of Materials Science and Engineering, Southwest University of Science and Technology, Mianyang 621010, PR China b School of Chemistry and Chemical Engineering, Huazhong University of Science and Technology, Wuhan 430074, PR China c Institute of Electronic Engineering, China Academy of Engineering Physics, Mianyang 621900, PR China

a r t i c l e i n f o a b s t r a c t

Article history: Received 18 February 2009 Received in revised form 2 March 2009 Accepted 3 March 2009 Available online 10 March 2009

Keywords: Bacterial cellulose Carbon paste electrode Polyoxometalate Modified electrode Electrocatalysis

1388-2481/$ - see front matter  2009 Elsevier B.V. A doi:10.1016/j.elecom.2009.03.001

* Corresponding authors. Tel.: +86 816 6088350. E-mail addresses: heping@swust.edu.cn, heping1

peichonghua@swust.edu.cn (C.H. Pei).

A novel bacterial cellulose nanofiber-based carbon paste electrode (BCPE) was fabricated. It was charac- terized by scanning electron microscopy, cyclic voltammetry and electrochemical impedance spectros- copy. Compared with traditional carbon paste electrode, BCPE exhibited better electrochemical reversibility with the enhancement of the redox currents and decrease of peak potential separation as well as lower charge transfer resistance in Fe(CN)63/4 redox system. Keggin-type sodium phospho- polyoxomolybdate, PMo12, was successfully assembled on BCPE via cyclic voltametric scan, and the obtained PMo12/BCPE possessed not only a good electrochemical behavior but also an excellent electro- catalytic activity toward the reduction of nitrite. Because of its nano-dimension, lower cost and promi- nent electrochemical properties, bacterial cellulose-based carbonaceous materials would be a candidate of graphite for the preparation of novel carbon paste electrode.

 2009 Elsevier B.V. All rights reserved.

1. Introduction

Bacterial cellulose (BC) produced by bacteria is an unbranched macromolecular compound composed of b-1,4-linked glucopyra- nose unit [1,2]. With so many unique properties such as high chemical purity, ultrafine network structure, good mechanical strength, biocompatibility and the controllability in the prepara- tion process, BC and its derivatives could be widely applicable in paper, medical materials, permeable membrane and thermotropic liquid crystalline, etc. [3–9]. In our recent experiments, BC was pre- pared according to our former work [2]. Furthermore, it was found that, upon carbonizing at temperature up to 900 C under nitrogen atmosphere, BC was converted into a kind of carbon nanofiber, and the corresponding SEM image was shown in Fig. 1.

Carbon paste electrode (CPE) consisting of carbon powder and water-immiscible liquid binder is one of the most commonly used electrodes in electrochemical investigations. It is characteristic of many properties such as low background current, easy renewal of its surface, facile fabrication and modification with desired prop- erties via incorporating different substances during the paste prep- aration [10–16]. However, its application was limited because of the low sensitivity and selectivity. To our knowledge, there have been some researches on the modification of CPEs with carbon nanotube, mesoporous materials carbon nanofiber and other car-

ll rights reserved.

971@yahoo.com.cn (P. He),

bonaceous materials for the purpose of enhancing the sensitivity and selectivity [17–22]. Nevertheless, the modification of CPE with carbonized nanofiber BC has never been studied.

In this paper, a novel nano-dimension carbonized BC based CPE (BCPE) was developed and its electrochemical behavior was studied by cyclic voltammetry, electrochemical impedance spec- troscopy, etc. Furthermore, Keggin-type sodium phosphopolyoxo- molybdate (Mo12Na3O40P, PMo12) was assembled on BCPE via cyclic voltametric scan method [23], and the PMo12/BCPE modi- fied electrode possesses excellent electrocatalytic activity to the reduction of nitrite.

2. Experimental

BCPE was prepared by hand-mixing of 40.0 mg carbonized BC [2] with 70 ll Silicone oil in an agate mortar and ground to uniform paste. The paste was firmly packed into a cavity (U 3 mm) at the end of a Teflon tube. The electrical contact was achieved by a cop- per wire connected to the paste in the inner hole of the tube. The fabrication procedure of a traditional carbon paste electrode was similar to BCPE just replacing bacterial cellulose with 200 mg graphite powder. All the surfaces of BCPE and CPE were smoothed on a piece of weighing paper just prior to use. PMo12 was assem- bled on the obtained electrode surfaces via cyclic voltametric scan for 100 segments in 0.1 M H2SO4 + 50 mM PMo12 solution in the potential range of 0.55 to 0.25 V for BCPE and 0.45 to 0.20 V for CPE, respectively.

16000

18000

2000

2500 BCPE (measured) BCPE (fitted ) a

Fig. 1. SEM image of carbonized BC.

Y. Liang et al. / Electrochemistry Communications 11 (2009) 1018–1021 1019

Cyclic voltammetry and electrochemical impedance spectros- copy (EIS) were performed on PARSTAT 2273 Electrochemical Sys- tem (Princeton Applied Research, USA). Three-electrode system was utilized including a home-made BCPE or traditional CPE as working electrode, a saturated calomel electrode (SCE) as reference electrode and a platinum wire as auxiliary electrode. EIS was per- formed in 0.1 M KCl + 1 mM K3Fe(CN)6 solution with the perturba- tion amplitude 5 mV (versus open circuit potential), and the frequencies swept from 105 to 5  103 Hz. The data were ana- lyzed and fitted with the aid of Zview software (Scribner Associates Inc.). Scanning electron microscopy (Hitachi S4800, Japan) was uti- lized to study the morphology of bacterial cellulose.

3. Results and discussion

Shown in Fig. 1 was SEM image of carbonized BC treated at 900 C. It was obvious that carbonized BC is a kind of nanofiber with three-dimensional network-like structure, which could sig- nificantly increase the effective electrode surface and facilitate the diffusion of analytes into the film.

Potassium ferricyanide was chosen as a probe to evaluate the performance of the proposed electrodes. Fig. 2 exhibited typical electrochemical responses of CPE and BCPE in 0.1 M KCl + 1 mM K3Fe(CN)6 solution, respectively. Good linear relationships be-

0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 -0.1 -0.2 -0.3 -10

-8

-6

-4

-2

0

2

4

6

8

10 b

a

C ur

re nt

/ uA

Potential / V (vs. SCE)

Fig. 2. CVs of CPE (a) and BCPE (b) in 0.1 M KCl + 1 mM K3Fe(CN)6 at scan rate of 10 mV s1.

tween the redox currents and the square root of scan rates were observed for the two electrodes over 0.01–0.25 V s1 range, reveal- ing a solution control mechanism and a faster charge transfer kinetics. On the other hand, the peak-to-peak potential separations (DEp) of 0.131 and 0.078 V were observed at CPE (curve a) and BCPE (curve b), respectively, and a pair of more well-defined redox peaks appeared on BCPE with larger peak current. The decrease in peak separation and enhanced currents observed on BCPE reflected a change in diffusional regime [24]. Furthermore, the results indi- cated that better reversibility was obtained on BCPE than that on CPE in terms of improved reversibility and enhanced sensitivity. All these could be attributed to the use of nano-dimension carbon- ized BC with higher active surface area as carbonaceous materials as well as its cross-linked structure, which was propitious to a fas- ter electron transfer. As for the slightly bigger capacitive current of BCPE compared with traditional CPE, it was possibly related to the nano-dimension net structure of carbonized BC.

Illustrated in Fig. 3 are Nyquist plots of the two well-fabricated electrodes. The depressed arcs in mid-high frequency section pre- sented typical constant phase element (CPE) characteristics con- taining information of kinetics of the faradic process, and they could be fitted using (RctCPE) circuit. The approximately linear curves in low-frequency section were related to capacitance and diffusion resistance, and thus could be fitted using (CW) circuit, in which Warburg impedance (W) responded to diffusion and capacitance(C) was contained in CPE mentioned above. Thus, an equivalent circuit as shown in the inset (a) of Fig. 3 was designed, by which the fitted plots were quite well in agreement with the measured plots. Shown in Table 1 was the data of kinetics param- eters of the two electrodes. The value of charge transfer resistance (Rct) of BCPE was much smaller than that of CPE, indicating a faster electron transfer process on BCPE than that on CPE [25], which could be attributed to that the carbonized BC has a higher real sur- face area.

Shown in Fig. 4a were the CVs of the PMo12 film growth on BCPE by potential cycling in 0.1 M H2SO4 solution containing PMo12 at the scan rate of 100 mV s1. Three redox couples corresponding to PMo12 redox reaction appeared in the potential range from 0.55 to 0.25 V, and all the reduction and oxidation peak currents

0 2500 5000 7500 1000 0 12500 15000 17500 20000 0

2000

4000

6000

8000

10000

12000

14000

2

1

Rs CPE

Rct W

0 500 1000 1500 2000 2500 3000 0

500

1000

1500

-Z ''/

o hm

Z' / ohm

-Z ''

/ o hm

Z' / ohm

CPE (measured) BCPE (measured) BCPE (fitted)

Fig. 3. Nyquist plots of BCPE (1) and CPE (2) in 0.1 M KCl + 1 mM K3Fe(CN)6. The applied perturbation amplitude was 5 mV (versus open circuit potential) and the frequencies were swept from 105 to 5  103 Hz. Equivalent circuit (b). Rs: solution resistance; Rct: charge transfer resistance; CPE: constant phase element, which is a complex of various elements; W: Warburg resistance, which reflects diffuse barrier at low-frequency part.

Table 1 Values for the parameters Rct, CPE-T, CPE-P, W-R, W-T, W-P and the associated error% computed by fitting of the experimental EIS data (Fig. 3).

Electrode Rct (X) CPE-T (mF) CPE-P (F) W-R (X) W-T (X) W-P (X)

Value Error Value Error Value Error Value Error Value Error Value Error

CPE 6548 0.7% 5.0E-4 1.8% 0.90 0.2% 53138 0.2% 264 0.3% 0.45 0.4% BCPE 84.44 1.1% 1.5E-7 1.3% 0.50 0.5% 63300 0.1% 505 0.2% 0.47 0.2%

1.2 1.0 0.8 0.6 0.4 0.2 0.0 -0.2

-0.30

-0.15

0.00

0.15

0.30

0.45

0.60

0.60 0.45 0.30 0.15 0.00 -0.15 -0.30

-0.2

-0.1

0.0

0.1

0.2

0.3

0.5 0.4 0.3 0.2 0.1 0.0 -0.1 -0.2 -0.3

-80

-60

-40

-20

0

20

40

60

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100

500 mV s-1

10 mV s-1

C ur

re nt

/ uA

Potential / V (vs. SCE)

b

3'

2'1'

32

1

800 mV s-1

10 mV s-1

C ur

re nt

/ m

A

Potential / V (vs. SCE)

a

C ur

re nt

/ m

A

Potential / V (vs. SCE)

Fig. 4. CVs of a BCPE during continuous growth by cycling potential scan in 0.1 M H2SO4 + 5 mM PMo12 (a) and those of PMo12-modified BCPE and CPE (the inset) in 0.5 M H2SO4 + 0.5 M Na2SO4 with various scan rates (b).

0.6 0.5 0.4 0.3 0.2 0.1 0.0 -0.1 -0.2 -0.3 -0.1

0.0

0.1

0.2

0.3

0.4

0.5

-2 0 2 4 6 8 10 12 14 16

50

55

60

65

70

75

C ur

re nt

/ uA

Concentration / mM

C ur

re nt

/ m

A

Potential / V (vs. SCE)

Fig. 5. CVs of PMo12/BCPE in 0.5 M H2SO4 + 0.5 M Na2SO4 solution containing 0, 0.249, 0.495, 0.98, 2.38, 4.54, 8.33, 14.28 mM nitrite at the scan rate of 100 mV s1.

1020 Y. Liang et al. / Electrochemistry Communications 11 (2009) 1018–1021

increased gradually with increasing cycling time until they reached a stabled state. CVs of PMo12 growing on CPE were also obtained in 0.1 M H2SO4 solution in the presence of PMo12 (not shown), and the redox peak currents were lower than those on BCPE. It could be attributed to the higher real active surface area and more sur- face defects of carbonized BC due to its nano-structure [20], result- ing in larger number of activated sites than that on CPE.

As shown in Fig. 4b, there are three pairs of well-defined redox peaks corresponding to 2-, 4-, 6-electron transfer of PMo12 on PMo12/BCPE in the potential range from 0.55 to 0.25 V and on PMo12/CPE from 0.45 to 0.2 V. Its electrochemical behavior was similar to that of PMo12 in aqueous solution, showing that the sur- face of electrodes were modified successfully, and the structure and character of PMo12 on the two electrodes surface were not var- ied through the assembled process. There was a linear relationship between the redox peak currents and scan rates for PMo12/CPE (not shown), showing that the redox process was controlled by surface reaction on PMo12/CPE. While the redox peak currents were pro- portional to the square root of scan rates up to 800 mV s1 for PMo12/BCPE, indicating that a solution controlled reaction process happened on PMo12/BCPE with faster electron transfer kinetics in wide scan rate ranges. Moreover, the peak currents of PMo12/BCPE were much higher than those of PMo12/CPE, which was possibly relevant to the nano-structure and more surface defects of carbon- ized BC and therefore more PMo12O403 anions were absorbed on the surface of BCPE.

It was well known that polyoxomalates (POMs) have been em- ployed extensively in electrocatalytic reduction of nitrite since re- duced POMs can serve as powerful electron reservoirs and are capable of delivering electrons to other species [26–30]. Therefore, the electrocatalytic activity to the reduction of nitrite on PMo12/ BCPE was investigated in this work. As shown in Fig. 5, addition of nitrite ions to the cell produced a dramatic change in the cyclic voltammogram with an increase of the cathodic currents and a concomitant decrease of the anodic currents, indicating that an electrocatalytic process occurred on the electrode surface. More- over, all the three redox couples presented the same feature, revealing that all the three cathodic waves of PMo12O403 anions indeed possessed a good electrocatalytic activity toward the reduc- tion of nitrite, which was in agreement with the reported literature [26]. As illustrated in the inset of Fig. 5, the calibration curve was obtained according to the relationship between current response of the second cathodic peak and nitrite concentrations, which fol- lowed a regression equation from 2.5  104 to 1.5  102 M: ip/ lA = 51.70 + 1.50 Cnitrite/mM (r = 0.9998, n = 8). The detection limit was calculated to be 1.0  104 M in accordance with 3r. The reproducibility and stability of PMo12/BCPE were assessed by suc- cessive cyclic scanning from 0.55 to 0.25 V over 100 times, and it was observed that the redox currents of PMo12 on PMo12/BCPE had no apparent change. Therefore, the PMo12-modified BCPE exhibited a good stability for the electrocatalytic application.

4. Conclusions

BCPE was fabricated with nano-dimension carbonized BC fiber and studied by SEM, cyclic voltammetry and electrochemical impedance spectroscopy. Compared with traditional CPE, a faster

Y. Liang et al. / Electrochemistry Communications 11 (2009) 1018–1021 1021

electron transfer kinetics process happened on BCPE in wide scan rate ranges. Moreover, PMo12 was successfully assembled on BCPE surface by cyclic voltametric scanning method. Good stability and catalytic activity to the reduction of nitrite were observed on PMo12/BCPE. This novel carbonaceous materials is prospected to be used in electrocatalysis and other fields due to its mentioned advantages.

Acknowledgements

This work was supported by the Talent Introduction Fund from Southwest University of Science and Technology (No. 053116) and the Natural Science Foundation from the Ministry of Education of Sichuan Province (No. 06ZD1105) and the Nature Science Founda- tion for Youths from Sichuan Province (No. 08ZK026-062).

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