Electrochemistry Communications 22 (2012) 170–173
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Porous screen-printed carbon electrode Xiangheng Niu a, 1, Chen Chen a, 1, Hongli Zhao a, b,⁎, Jie Tang a, Yuxiu Li a, Minbo Lan a, c,⁎ a b c
Shanghai Key Laboratory of Functional Materials Chemistry, and Research Centre of Analysis and Test, East China University of Science and Technology, Shanghai 200237, PR China Institute of Applied Chemistry, East China University of Science and Technology, Shanghai 200237, PR China Key Laboratory for Ultrafine Materials of Ministry of Education, East China University of Science and Technology, Shanghai 200237, PR China
a r t i c l e
i n f o
Article history: Received 18 May 2012 Received in revised form 6 June 2012 Accepted 12 June 2012 Available online 19 June 2012 Keywords: Porous screen-printed carbon electrode CaCO3 powder Ink doping
a b s t r a c t A new screen-printed carbon electrode with porous architectures prepared using an extremely facile and low-cost approach is introduced. The preparation mainly involved a printing procedure of a graphite-based layer doped with CaCO3 powders and a subsequent dissolution of these powders. The resulting porous screen-printed carbon electrode (P-SPCE) can offer large surface, broad potential window, low background current and high electrochemical reactivity. Moreover, the proposed P-SPCE provides enhanced performance for enzyme-free H2O2 sensing compared to conventional glassy carbon electrodes and screen-printed carbon electrodes. These attractive properties of the P-SPCE are expected to be of wider applications. © 2012 Elsevier B.V. All rights reserved.
1. Introduction Electrodes with porous structures have always attracted intense interest because they can provide large surfaces, which are beneficial for enhancing homogeneous electrocatalysis (e.g., promoting the formic acid oxidation reaction for flue cells [1]) and improving analytical performance of electrochemical sensors and biosensors (e.g., facilitating the enzyme immobilization for H2O2 biosensing [2]). In the past decades, several strategies such as template-assisted synthesis [3], dealloying [4] and thermal decomposition [5] have been proposed to prepare various porous electrodes. Among these methods, templateassisted synthesis, which involves chemical hydrolysis [6] or electrochemical deposition [7] of corresponding precursors in the interstitial spaces of close packed arrays assembled by polystyrene colloidal crystals [8], latex beads [9] or silica spheres [10] etc., is the most commonly used approach to fabricate metal-based electrodes with porous frameworks. As a typical thick film technique, the screen printing technology is capable of mass-producing disposable electrodes with advantages including low cost, miniaturization, flexibility and replicability, and screen-printed electrodes (SPEs) are receiving wide applications in electrochemical sensors (e.g., Bi2O3-modified SPEs for heavy metal detection) and biosensors (e.g., mediator-modified SPEs for physiological species analysis) [11]. It is believed that porous SPEs will not only retain the attractive properties of porous electrodes but also possess the
⁎ Corresponding authors at: Shanghai Key Laboratory of Functional Materials Chemistry, and Research Centre of Analysis and Test, East China University of Science and Technology, Shanghai 200237, PR China. Tel.: +86 21 64253574; fax: +86 21 64252947. E-mail addresses:
[email protected] (H. Zhao),
[email protected] (M. Lan). 1 Authors who have made equal contributions to this work. 1388-2481/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.elecom.2012.06.020
superiorities of SPEs. However, as far as we know, there is very few information about the preparation of porous SPEs mainly due to the limit of applicable inks available commercially. Herein, we report for the first time a porous screen-printed carbon electrode (P-SPCE) prepared in a facile and low-cost method. The preparation process mainly involved the printing of a carbon layer using a CaCO3-doped graphite-based ink, followed by dissolving these CaCO3 powders in acidic media. This strategy combining the screen printing technology with the ink doping approach can massproduce P-SPCEs conveniently and inexpensively. Besides, the structural features of P-SPCEs can be rationally adjusted, e.g., changing the porosity through doping different amounts of CaCO3. The resulting P-SPCE with large surface, broad potential window, low background current and high electrochemical reactivity can provide enhanced performance for nonenzymatic H2O2 sensing. 2. Experimental 2.1. Electrode preparation The proposed P-SPCE was prepared as follows: firstly, 0.72 g spherical CaCO3 powders (Aladdin Reagent Co., approximately 0.8 μm in diameter) well-dispersed in 5 mL volatile thinner were uniformly hand-mixed with 1.80 g graphite-based ink (Electrodag423SS, Acheson Co.); then, a silver paste layer (BY2100, Shanghai Baoyin Electronic Material Co.), a carbon layer (using the CaCO3doped graphite-based ink) and an insulating layer (AC-3G, Jujo Chemical Co.) were successively printed on a PET substrate [12]; after drying, the doped CaCO3 was dissolved using 1 M HCl under vigorous stirring conditions for 1 h; finally, the electrode was rinsed with adequate ultrapure water and dried in air for further measurements.
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For comparison, conventional screen-printed carbon electrodes (SPCEs) were also prepared using the original graphite-based ink with similar processes. 2.2. Procedures Scanning electron microscopy (SEM JSM-6360LV, JEOL) was used to observe the surface morphologies of electrodes. All electrochemical measurements were carried out on a CHI workstation equipped with a P-SPCE (or GCE or SPCE) working electrode, a Pt wire counter electrode and a KCl-saturated Ag/AgCl reference electrode. Linear sweep voltammetry (LSV) was employed to evaluate the potential window and background current in 0.1 M H2SO4, PBS (pH = 7.4) and NaOH, respectively. Cyclic voltammetric (CV) measurements in 2 mM K3 [Fe(CN)6] solutions containing 0.5 M KCl were performed to study the electrochemical reactivity. Electrochemical impedance spectroscopy (EIS) in the ferricyanide system was carried out at open-circuit potentials with a frequency range from 100 kHz to 0.1 Hz. All measurements for nonenzymatic H2O2 analysis were performed in 0.1 M PBS (pH = 7.4) deoxygenated by bubbling highly pure argon. Chronoamperometric responses upon successive addition of H2O2 were recorded at an applied potential of −0.4 V under a constant stir (100 rpm). 3. Results and discussion 3.1. Properties of the P-SPCE 3.1.1. Surfacing imaging Fig. 1(A) illustrates the configuration of the resulting P-SPCE, with the same diameter (3 mm) of the carbon working area as the GCE and SPCE. SEM images reveal significant differences in the surface morphology between SPCEs (B) and P-SPCEs (C). One can see that the SPCE exhibits a relatively flat surface comprising numerous graphite flakes. The small particles on these graphite surfaces are assigned to the crosslinking agents in the original ink. As for the P-SPCE, graphite sheets and small particles are also observed clearly. Furthermore, a great number of pores are obtained on the P-SPCE surface, attributing to the dissolution of CaCO3 powders doped in the graphite-based ink. Moreover, many pores link together because of the high doping ratio (almost 30 wt.%) and form three-dimensional networks with a large amount of channels stretching to depths. Based on the observed SEM image, this porous structure exposes a large surface, which is supposed to be beneficial for enhancing performance of the electrode for many utilities.
Fig. 1. (A) Illustrations of the configuration of the P-SPCE; SEM images of the SPCE (B) and P-SPCE (C).
3.1.2. Potential window and background current Generally, the potential window and background contribution of carbon-based electrodes have great effects upon their potential applications. Fig. 2 shows LSVs of the P-SPCE in 0.1 M H2SO4, PBS (pH=7.4) and NaOH. A substantial oxygen evolution signal starts at +1.4, +1.7 and +0.9 V vs. Ag/AgCl in acidic, neutral and alkaline electrolytes, respectively. The cathodic limit resulting from hydrogen evolution is extended to −0.8, −1.1 and −0.9 V, respectively. Overall, the potential window of the P-SPCE obtained in H2SO4 (2.2 V) and PBS (2.8 V) is comparable or even wider than that obtained on the GCE (2.2 V and 2.5 V, respectively). As expected, a relatively narrow potential window (around 1.8 V) due to the low potential for oxygen evolution is observed in the strongly alkaline medium, slightly narrower than that of the GCE (2.1 V). During these windows, small background currents are obtained for the P-SPCE. All residual currents are tens of nA, indicating that the background contribution will make negligible influence on routine electroanalysis. 3.1.3. Electrochemical reactivity A typical drawback of conventional SPEs, compared to GCEs, is the relatively slow electrochemical kinetics in relation to the ferricyanide system [11]. Fig. 3(A) represents CVs of the GCE, SPCE and P-SPCE in
Fig. 2. Linear sweep voltammograms of the P-SPCE in 0.1 M H2SO4, PBS (pH = 7.4) and NaOH.
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Fig. 3. (A) Cyclic voltammograms of the GCE, SPCE and P-SPCE in 2 mM K3[Fe(CN)6] solutions containing 0.5 M KCl at a scan rate of 20 mV/s; (B) EIS plots of the GCE, SPCE and PSPCE in the ferricyanide system.
2 mM K3[Fe(CN)6] solutions containing 0.5 M KCl. Different from the well-defined reversible signals of [Fe(CN)6] 3 −/[Fe(CN)6]4 − observed on the GCE, the P-SPCE provides a pair of quasi-reversible peaks for the electrochemical reaction. The equilibrium potential (E′) observed on the P-SPCE slightly shifts to negative values mainly due to the porosity. On the one hand, the porous structure can change the diffusion regime of analytes in an analytically useful manner [13,14]; on the other hand, porous frameworks not only allow fast transport of analytes through the electrolyte/electrode interface due to short diffusion length but also make analytes contact with more surfaces due to high surface area, thus facilitating the electrochemical reactions [15]. The peak potential differences (△Ep) are calculated as 63, 205 and 143 mV for the GCE, SPCE and P-SPCE, respectively. Accordingly, the peak current (ip) increases in the following order: SPCEb P-SPCEb GCE. These parameters consisting of △Ep, ip and SC ipc/ipa, as listed in Fig. 3(A), reveal that although the P-SPCE cannot provide the electrochemical reactivity level as high as the GCE in connection to the ferricyanide system, significant enhancement has been obtained compared to the SPCE. In addition, the homemade P-SPCE exhibits a good uniformity. Eight electrodes from four batches were used for measurements in the ferricyanide system, providing a relative standard deviation (RSD) of 7.4% and 6.5% based on △Ep and ip, respectively. Fig. 3(B) represents EIS plots of the GCE, SPCE and P-SPCE. All the three electrodes exhibit a similar impedance behavior. Parameters of the equivalent circuit (inset in Fig. 3(B)) indicate that the solution resistance ranges from 15 to 17 Ω·cm2. The double-layer capacitance value of the P-SPCE (3.4 μF cm− 2) is found to be similar with that of the SPCE (3.2 μF cm− 2), much lower than that of the GCE (14.0 μF cm− 2). In general, the disposable P-SPCE can provide greatly enhanced electrochemical reactivity compared to conventional SPEs.
electrocatalytic activity towards H2O2 reduction in comparison with common GCEs and SPCEs, ascribing to the porous structure and large active surface. Fig. 4 displays chronoamperometric responses of the GCE, SPCE and P-SPCE in 0.1 M PBS (pH = 7.4) upon successive addition of H2O2 at −0.4 V. Apparently, the current signals obtained on the three electrodes increase accordingly upon the H2O2 levels, and the analytical sensitivity towards H2O2 detection increases in the order of P-SPCE> GCE > SPCE. The relationships between steady-state currents (obtained at the step terminal) and H2O2 concentrations, as depicted in the inset, indicate that all the three electrodes provide linear responses for H2O2 levels in the range from 0 to 2 mM. The corresponding correlation coefficients (R2) are 0.9985, 0.9966 and 0.9990 for the GCE, SPCE and P-SPCE, respectively. Overall, the resulting P-SPCE exhibits favorable performance for nonenzymatic H2O2 sensing.
3.2. Utility in nonenzymatic H2O2 sensing The aforementioned attractive properties make the P-SPCE a great promising platform for various electroanalytical utilities. In this research, we evaluated the application potential of the P-SPCE for enzymatic-free H2O2 detection. CV experiments reveal that H2O2 in neutral media can be markedly electro-reduced on carbon-based electrodes. The reduction of H2O2 starts at −0.18, −0.20 and −0.29 V on the P-SPCE, GCE and SPCE, respectively. The P-SPCE provides enhanced
Fig. 4. Chronoamperometric responses of the GCE, SPCE and P-SPCE in 0.1 M PBS (pH = 7.4) upon successive addition of H2O2 at − 0.4 V; the inset represents the relationships between obtained steady-state currents and H2O2 levels.
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4. Conclusions In summary, we have successfully prepared a new carbon electrode with porous structures combining the screen printing technology with the ink doping approach. This strategy offers an extremely facile and low-cost route to mass-produce porous SPEs. The resulting P-SPCE exhibits beneficial large surfaces and electrochemical behaviors. These attractive properties will make the P-SPCE find broader applications. Acknowledgments Research grants from the Science and Technology Commission of Shanghai Municipality (Nos. 10dz2220500, 10391901600) and the Ministry of Education of the People's Republic of China (No. WK1014051) are acknowledged. References [1] R.Y. Wang, C. Wang, W.B. Cai, Y. Ding, Advanced Materials 22 (2010) 1845. [2] D.L. Lu, J. Cardiel, G.Z. Cao, A.Q. Shen, Advanced Materials 22 (2010) 2809. [3] P. Jiang, J. Cizeron, J.F. Bertone, V.L. Colvin, Journal of the American Chemical Society 121 (1999) 7957.
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