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One-step fabrication of ordered Pt–Cu alloy nanotube arrays for ethanol electrooxidation
Materials Letters 64 (2010) 1169–1172
Contents lists available at ScienceDirect
Materials Letters j o u r n a l h o m e p a g e : w w w. e l s e v i e r. c o m / l o c a t e / m a t l e t
One-step fabrication of ordered Pt–Cu alloy nanotube arrays for ethanol electrooxidation Xinyi Zhang ⁎, Dan Li, Dehua Dong, Huanting Wang, Paul A. Webley ⁎ Department of Chemical Engineering, Monash University, Clayton, VIC3800, Australia
a r t i c l e
i n f o
Article history: Received 21 January 2010 Accepted 16 February 2010 Available online 26 February 2010 Keywords: Direct alcohol fuel cells Pt–Cu alloy nanotubes Electron microscopes Electrooxidation
a b s t r a c t Novel one dimensional (1D) nanostructured metallic electrodes have received much attention in the area of the fuel cell because of their extremely high surface-to-volume ratios and excellent activities. Here, we report the one-step fabrication of Pt–Cu alloy nanotube arrays. As determined by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy, ordered Pt–Cu alloy nanotubes have been successfully fabricated utilizing a nanochannel alumina template. The electrocatalytic activities of the Pt–Cu alloy nanotubes for the oxidation of ethanol in acidic medium were investigated by cyclic voltammetry. The results show that the Pt–Cu alloy nanotubes can be used as effective electrocatalysts for ethanol oxidation in direct alcohol fuel cells. © 2010 Elsevier B.V. All rights reserved.
1. Introduction The direct alcohol fuel cell (DAFC) is a promising candidate for portable power sources, electric vehicles and transportation applications [1–4]. Among the fuels, ethanol is one of the potential fuels and it can be easily produced in great quantity by fermentation of biomass. However, ethanol oxidation to CO2 is associated with the cleavage of the C–C bond, which requires higher activation energy than C–H bond breaking [5]. Pt and Pt-based catalysts have been extensively investigated as electrocatalysts for the electrooxidation of liquid fuels such as methanol and ethanol [6,7]. However, Pt itself is known to be rapidly poisoned on its surface by strongly adsorbed species coming from the dissociative adsorption of ethanol [8,9]. In this regard, the development of more efficient electrocatalysts for ethanol oxidation is highly desirable. One of the strategies is to develop binary or ternary alloy electrocatalysts because alloying of metals may result in important changes in their activity and poison tolerance in DAFCs [10,11]. Recently, novel one dimensional (1D) nanostructured metallic electrodes have received much attention in the area of fuel cell because of their extremely high surface-to-volume ratios and excellent activities. For example, Pd nanowire arrays exhibit high activity for ethanol oxidation [12]. Pt nanotubes have been used as electrocatalysts for the oxygen reduction [13]. These unsupported electrocatalysts have the potential to combine the advantages of carbon supported Pt catalysts while overcoming their drawbacks and possess high surface area, high utilization, high activity, and high ⁎ Corresponding authors. Tel.: + 61 3 9905 1959; fax: + 61 3 9905 5686. E-mail addresses: [email protected] (X. Zhang), [email protected] (P.A. Webley). 0167-577X/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2010.02.041
durability [14]. Here, we report the fabrication of ordered Pt–Cu alloy nanotubes (PCNTs) utilizing a nanochannel alumina template by a one-step electrodeposition method. We demonstrate that the PCNTs can be used as effective electrocatalysts for ethanol oxidation in direct alcohol fuel cells. 2. Experimental Nanochannel alumina (NCA) templates were prepared by anodizing high purity aluminum foils. In order to electrodeposit Pt–Cu alloy, a gold film with about 5 nm thickness was deposited on one side of the NCA template as electrode by using a vacuum evaporation apparatus. PCNTs were deposited from a 0.5 M H2SO4 solution containing 5 g/l K2PtCl4 and 12 g/l CuSO4 by using a galvanostatic method. The cathode current density was kept at 100μAcm− 2. All electrochemical deposition and electrochemical measurement were carried out on an electroanalytical instrument (autolab II) at room temperature. The electrocatalytic activities of the PCNTs with Pt–Cu alloy loading of 0.21 mgcm− 2 was tested for the oxidation of ethanol. The morphology, composition, and microstructure of the PCNTs were investigated by using a scanning electron microscope (SEM, JEOL JSM7001F) with energy-dispersed X-ray spectrometry (EDS) and a transmission electron microscope (TEM, JEOL-2011). 3. Results and discussion Fig. 1a shows the SEM image of the NCA template with a pore diameter of about 250 nm. Fig. 1b shows the SEM image of the surface view of the free-standing PCNTs with a length of about 800 nm after completely dissolving the NCA template. The inset shows the enlarged image of the PCNTs. It can be seen that the PCNTs replicate the pore
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X. Zhang et al. / Materials Letters 64 (2010) 1169–1172
Fig. 1. (a) SEM image of alumina template with 250 nm pore diameter. (b) SEM image of Pt–Cu alloy nanotube array. (c) XRD pattern of the Pt–Cu alloy nanotube array. (d) EDS spectrum of the Pt–Cu alloy nanotube array.
sizes and shapes. The diameter and wall thickness of the PCNTs are about 250 nm and 45 nm, respectively. The XRD spectrum of PCNTs is shown in the inset of Fig. 1c. The reflection peaks of a face-centered cubic Pt–Cu structure are distinguishable, and no obvious impurity phases are observed. Fig. 1d shows the EDS taken from the PCNTs composed of 29 at.% Pt and 71 at.% Cu. The microstructure of the PCNTs was further investigated by TEM. Fig. 2a shows a bright field
image of a bundle of PCNTs. The corresponding electron diffraction pattern taken from the PCNTs in Fig. 2b can be indexed as facecentered cubic Pt–Cu crystalline structure, which is consistent with the XRD spectrum. Fig. 2c shows the high magnification image of a single Pt–Cu alloy nanotube. Rough surface of the nanotube can be observed. A high resolution TEM image taken from a Pt–Cu alloy nanotube is shown in Fig. 2d. It can be seen that the Pt–Cu alloy
Fig. 2. (a) TEM image of a bundle of Pt–Cu alloy nanotubes. (b) The electron diffraction pattern of Pt–Cu alloy nanotubes. (c) High magnification TEM image of a single Pt–Cu alloy nanotube. (d) High resolution TEM image of a Pt–Cu alloy nanotube.
X. Zhang et al. / Materials Letters 64 (2010) 1169–1172
nanotube is composed of nanocrystals with sizes ranging from 2 nm to 5 nm, where the well-recognized lattice spacing of 0.21 corresponds to the {111} atomic planes of a faced-centered cubic Pt–Cu alloy. The electrocatalytic activities of the PCNTs for the oxidation of ethanol were tested in 0.5 M H2SO4 solution by using cyclic voltammetry. Fig. 3a shows the cyclic voltammograms (CVs) for PCNTs in 0.5 M H2SO4 solution at different scan cycles. It can be clearly seen that the shape of the CVs changes remarkably with the increase of the scan cycles. At the first scan, the anodic current increases during the forward sweep, a peak current at 0.68 V can be observed. Then a current plateau appears, which is due to the formation of a less active PtO monolayer. No typical hump for hydrogen adsorption and desorption appears on the PCNT electrode, which can be attributed to high Cu content on the surface of the PCNTs [15]. At the 100th scan, the peak current appears at 0.6 V. It can be inferred that the dissolution of Cu stunts the formation of PtO during the anodization. Such effect becomes less pronounced with the increase of the cycles, resulting in the shift of the current peak from 0.68 V to 0.6 V. A hump for the hydrogen adsorption and desorption appears between about 0.1 V and −0.2 V. After the 100th scan, the cathode current peaks can be observed at about 0.31 V during the backward sweep, which can be attributed to the reduction of the platinum oxide formed during the positive-going sweep. It is worth noting that the hump area increases with the increase of the scan cycles and reaches the maximum at the 200th cycle. The electrochemical active surface area (EAS) of the electrode is proportional to the coulombic charge for hydrogen de-
1171
sorption [16,17]. It can be deduced that the EAS of the PCNTs increases with the increase of the scan cycles and reaches the maximum value at the 200th cycle. After 300 cycles, no obvious decrease in the hydrogen ad/desorption area occurs, suggesting a good durability of the PCNTs. Fig. 3b shows the CVs for PCNT electrodes in 0.5 M H2SO4 solution in the presence of 1 M ethanol. At the first scan, the current from ethanol oxidation becomes apparent as the potential rises in the forward scan. Usually, ethanol oxidation produces a prominent anodic peak in the forward scan (If), and then a current decline appears. This can be attributed to the formation of a less active PtO monolayer, which blocks the supply of the active oxygen atoms and hence further oxidation of ethanol is suppressed [18]. No current peak is observed in the forward scan. The anodic peak at 0.65 V can be observed in the reverse scan, which results from the oxidation of intermediate organic species, such as Pt C O [19,20]. The voltammetric cycling is continued in order to investigate the durability of the PCNTs for ethanol oxidation. Usually the anodic current of Pt electrode decreases gradually with the successive scans, which can be explained in terms of the poisoning mechanism of the intermediate species during the ethanol oxidation reaction on the Pt electrodes. Interestingly, the anodic current of the PCNT electrode increases with the increase of the scan cycles, after 60 scan cycles the anodic current reaches the maximum value about 32 mAcm− 2 at 1.0 V, about 1.5 times of the value at the first scan. After 80th cycles, the anodic current still remains at 30 mAcm− 2 at 1.0 V. This result reveals the good stability of the PCNTs as electrocatalysts for the ethanol oxidation. The PCNTs have several interesting features. First, the anodic current for ethanol oxidation on the PCNT electrode increases with the increase of the scan cycle until the anodic current reaches the maximum value. This can be explained in term of voltammetric dissolution of Cu from Pt–Cu alloy [15]. The electrochemical dealloying of Cu from the PCNTs during the cyclic scan increases the active sites, which leads to the increase of the anodic current for ethanol oxidation. Second, the disappearance of If reveals that the formation of PtO monolayer is prevented. It can be inferred that the preferential dissolution of Cu in the Pt–Cu alloy not only increases the active surface area of the Pt–Cu electrode but also freshens the surface of the PCNT electrode to prevent the formation of PtO. It was suggested that the oxidation of ethanol increases with increase of the lattice parameter [21]. The lattice parameter of Pt–Cu alloy is larger than that of Pt, which could favor the cleavage of the C–C bond. Besides, the large surface area and high void volume on the PCNT array electrodes can allow efficient mass and electron transport to and from the catalyst sites, which should also enhance the supply of the active oxygen atoms for the oxidation of ethanol. 4. Conclusions In conclusion, PCNTs with diameters of 250 nm have been successfully fabricated by one-step direct electrodeposition. The PCNTs exhibit good stability and catalytic activity for ethanol oxidation and show promise to be a new type of supportless electrocatalyst in direct alcohol fuel cells. References [1] [2] [3] [4] [5] [6] [7] [8] [9]
Fig. 3. (a) Cyclic voltammograms on Pt–Cu alloy nanotube array electrode in 0.5 M H2SO4. (b) Cyclic voltammograms on Pt–Cu nanotube array electrode in 0.5 M H2SO4+ 1 M CH3CH2OH. Scan rate: 50 mVs− 1.
Long JW, Stroud RM, Swider-Lyons KE, Rolison DR. J Phys Chem B 2000;104:9772. Joo SH, Choi SJ, Oh I, Kwak J, Liu Z, Terasaki O, Ryoo R. Nature 2001;412:169. Qi Z, Kaufman A. J Power sources 2003;113:37. Lamy C, Belgsir EM, Léger J-M. J Appl Electrochem 2001;31:799. Antolini E. J Power Sources 2007;170:1. Bao SJ, Bao QL, Li CM, Dong ZL. Electrochim Commun 2007;9:1233. Prabhuram J, Manoharan R. J Power sources 1998;74:54. Sen Gupta S, Mahapatra SS, Datta J. J Power sources 2004;131:169. Spătaru N, Zhang X, Spătaru T, Tryk DA, Fujishima A. J Electrochem Soc 2008;155: B264. [10] Zhou W, Zhou Z, Song S, Li W, Sun G, Tsiakaras P, Xin Q. Appl Catal B 2003;46:273. [11] Spinacé EV, Linardi M, Oliveira Neto A. Electrochim Commun 2005;7:365.
1172 [12] [13] [14] [15] [16]
X. Zhang et al. / Materials Letters 64 (2010) 1169–1172 Xu C, Wang H, Shen PK, Jiang SP. Adv Mater 2007;19:4256. Chen ZW, Waje M, Li WZ, Yan YS. Angew Chem Int Ed 2007;46:4060. Zhang X, Dong D, Li D, Wang H, Webley PA. Electrochim Commun 2009;11:190. Strasser P, Koh S, Greeley J. Phys Chem Chem Phys 2008;10:3670. Lee SJ, Mukerjee S, Mcbreen J, Rho YW, Kho YT, Lee TH. Electrochim Acta 1998;43: 3693.
[17] Pozio A, Francesco MD, Cemmi A, Cardellini F, Giorgi L. J Power Sources 2002;105: 13. [18] Manoharan R, Prabhuram J. J Power Sources 2000;96:220. [19] Planes GA, García G, Pastor E. Electrochim Commun 2007;9:839. [20] Morallón E, Rodes A, Vázquez JL, Pérez JM. J Electrochem Soc 1995;391:149. [21] Colmati F, Antolini E, Gonzalez ER. J Electrochem Soc 2007;154:B39.
Contents lists available at ScienceDirect
Materials Letters j o u r n a l h o m e p a g e : w w w. e l s e v i e r. c o m / l o c a t e / m a t l e t
One-step fabrication of ordered Pt–Cu alloy nanotube arrays for ethanol electrooxidation Xinyi Zhang ⁎, Dan Li, Dehua Dong, Huanting Wang, Paul A. Webley ⁎ Department of Chemical Engineering, Monash University, Clayton, VIC3800, Australia
a r t i c l e
i n f o
Article history: Received 21 January 2010 Accepted 16 February 2010 Available online 26 February 2010 Keywords: Direct alcohol fuel cells Pt–Cu alloy nanotubes Electron microscopes Electrooxidation
a b s t r a c t Novel one dimensional (1D) nanostructured metallic electrodes have received much attention in the area of the fuel cell because of their extremely high surface-to-volume ratios and excellent activities. Here, we report the one-step fabrication of Pt–Cu alloy nanotube arrays. As determined by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy, ordered Pt–Cu alloy nanotubes have been successfully fabricated utilizing a nanochannel alumina template. The electrocatalytic activities of the Pt–Cu alloy nanotubes for the oxidation of ethanol in acidic medium were investigated by cyclic voltammetry. The results show that the Pt–Cu alloy nanotubes can be used as effective electrocatalysts for ethanol oxidation in direct alcohol fuel cells. © 2010 Elsevier B.V. All rights reserved.
1. Introduction The direct alcohol fuel cell (DAFC) is a promising candidate for portable power sources, electric vehicles and transportation applications [1–4]. Among the fuels, ethanol is one of the potential fuels and it can be easily produced in great quantity by fermentation of biomass. However, ethanol oxidation to CO2 is associated with the cleavage of the C–C bond, which requires higher activation energy than C–H bond breaking [5]. Pt and Pt-based catalysts have been extensively investigated as electrocatalysts for the electrooxidation of liquid fuels such as methanol and ethanol [6,7]. However, Pt itself is known to be rapidly poisoned on its surface by strongly adsorbed species coming from the dissociative adsorption of ethanol [8,9]. In this regard, the development of more efficient electrocatalysts for ethanol oxidation is highly desirable. One of the strategies is to develop binary or ternary alloy electrocatalysts because alloying of metals may result in important changes in their activity and poison tolerance in DAFCs [10,11]. Recently, novel one dimensional (1D) nanostructured metallic electrodes have received much attention in the area of fuel cell because of their extremely high surface-to-volume ratios and excellent activities. For example, Pd nanowire arrays exhibit high activity for ethanol oxidation [12]. Pt nanotubes have been used as electrocatalysts for the oxygen reduction [13]. These unsupported electrocatalysts have the potential to combine the advantages of carbon supported Pt catalysts while overcoming their drawbacks and possess high surface area, high utilization, high activity, and high ⁎ Corresponding authors. Tel.: + 61 3 9905 1959; fax: + 61 3 9905 5686. E-mail addresses: [email protected] (X. Zhang), [email protected] (P.A. Webley). 0167-577X/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2010.02.041
durability [14]. Here, we report the fabrication of ordered Pt–Cu alloy nanotubes (PCNTs) utilizing a nanochannel alumina template by a one-step electrodeposition method. We demonstrate that the PCNTs can be used as effective electrocatalysts for ethanol oxidation in direct alcohol fuel cells. 2. Experimental Nanochannel alumina (NCA) templates were prepared by anodizing high purity aluminum foils. In order to electrodeposit Pt–Cu alloy, a gold film with about 5 nm thickness was deposited on one side of the NCA template as electrode by using a vacuum evaporation apparatus. PCNTs were deposited from a 0.5 M H2SO4 solution containing 5 g/l K2PtCl4 and 12 g/l CuSO4 by using a galvanostatic method. The cathode current density was kept at 100μAcm− 2. All electrochemical deposition and electrochemical measurement were carried out on an electroanalytical instrument (autolab II) at room temperature. The electrocatalytic activities of the PCNTs with Pt–Cu alloy loading of 0.21 mgcm− 2 was tested for the oxidation of ethanol. The morphology, composition, and microstructure of the PCNTs were investigated by using a scanning electron microscope (SEM, JEOL JSM7001F) with energy-dispersed X-ray spectrometry (EDS) and a transmission electron microscope (TEM, JEOL-2011). 3. Results and discussion Fig. 1a shows the SEM image of the NCA template with a pore diameter of about 250 nm. Fig. 1b shows the SEM image of the surface view of the free-standing PCNTs with a length of about 800 nm after completely dissolving the NCA template. The inset shows the enlarged image of the PCNTs. It can be seen that the PCNTs replicate the pore
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X. Zhang et al. / Materials Letters 64 (2010) 1169–1172
Fig. 1. (a) SEM image of alumina template with 250 nm pore diameter. (b) SEM image of Pt–Cu alloy nanotube array. (c) XRD pattern of the Pt–Cu alloy nanotube array. (d) EDS spectrum of the Pt–Cu alloy nanotube array.
sizes and shapes. The diameter and wall thickness of the PCNTs are about 250 nm and 45 nm, respectively. The XRD spectrum of PCNTs is shown in the inset of Fig. 1c. The reflection peaks of a face-centered cubic Pt–Cu structure are distinguishable, and no obvious impurity phases are observed. Fig. 1d shows the EDS taken from the PCNTs composed of 29 at.% Pt and 71 at.% Cu. The microstructure of the PCNTs was further investigated by TEM. Fig. 2a shows a bright field
image of a bundle of PCNTs. The corresponding electron diffraction pattern taken from the PCNTs in Fig. 2b can be indexed as facecentered cubic Pt–Cu crystalline structure, which is consistent with the XRD spectrum. Fig. 2c shows the high magnification image of a single Pt–Cu alloy nanotube. Rough surface of the nanotube can be observed. A high resolution TEM image taken from a Pt–Cu alloy nanotube is shown in Fig. 2d. It can be seen that the Pt–Cu alloy
Fig. 2. (a) TEM image of a bundle of Pt–Cu alloy nanotubes. (b) The electron diffraction pattern of Pt–Cu alloy nanotubes. (c) High magnification TEM image of a single Pt–Cu alloy nanotube. (d) High resolution TEM image of a Pt–Cu alloy nanotube.
X. Zhang et al. / Materials Letters 64 (2010) 1169–1172
nanotube is composed of nanocrystals with sizes ranging from 2 nm to 5 nm, where the well-recognized lattice spacing of 0.21 corresponds to the {111} atomic planes of a faced-centered cubic Pt–Cu alloy. The electrocatalytic activities of the PCNTs for the oxidation of ethanol were tested in 0.5 M H2SO4 solution by using cyclic voltammetry. Fig. 3a shows the cyclic voltammograms (CVs) for PCNTs in 0.5 M H2SO4 solution at different scan cycles. It can be clearly seen that the shape of the CVs changes remarkably with the increase of the scan cycles. At the first scan, the anodic current increases during the forward sweep, a peak current at 0.68 V can be observed. Then a current plateau appears, which is due to the formation of a less active PtO monolayer. No typical hump for hydrogen adsorption and desorption appears on the PCNT electrode, which can be attributed to high Cu content on the surface of the PCNTs [15]. At the 100th scan, the peak current appears at 0.6 V. It can be inferred that the dissolution of Cu stunts the formation of PtO during the anodization. Such effect becomes less pronounced with the increase of the cycles, resulting in the shift of the current peak from 0.68 V to 0.6 V. A hump for the hydrogen adsorption and desorption appears between about 0.1 V and −0.2 V. After the 100th scan, the cathode current peaks can be observed at about 0.31 V during the backward sweep, which can be attributed to the reduction of the platinum oxide formed during the positive-going sweep. It is worth noting that the hump area increases with the increase of the scan cycles and reaches the maximum at the 200th cycle. The electrochemical active surface area (EAS) of the electrode is proportional to the coulombic charge for hydrogen de-
1171
sorption [16,17]. It can be deduced that the EAS of the PCNTs increases with the increase of the scan cycles and reaches the maximum value at the 200th cycle. After 300 cycles, no obvious decrease in the hydrogen ad/desorption area occurs, suggesting a good durability of the PCNTs. Fig. 3b shows the CVs for PCNT electrodes in 0.5 M H2SO4 solution in the presence of 1 M ethanol. At the first scan, the current from ethanol oxidation becomes apparent as the potential rises in the forward scan. Usually, ethanol oxidation produces a prominent anodic peak in the forward scan (If), and then a current decline appears. This can be attributed to the formation of a less active PtO monolayer, which blocks the supply of the active oxygen atoms and hence further oxidation of ethanol is suppressed [18]. No current peak is observed in the forward scan. The anodic peak at 0.65 V can be observed in the reverse scan, which results from the oxidation of intermediate organic species, such as Pt C O [19,20]. The voltammetric cycling is continued in order to investigate the durability of the PCNTs for ethanol oxidation. Usually the anodic current of Pt electrode decreases gradually with the successive scans, which can be explained in terms of the poisoning mechanism of the intermediate species during the ethanol oxidation reaction on the Pt electrodes. Interestingly, the anodic current of the PCNT electrode increases with the increase of the scan cycles, after 60 scan cycles the anodic current reaches the maximum value about 32 mAcm− 2 at 1.0 V, about 1.5 times of the value at the first scan. After 80th cycles, the anodic current still remains at 30 mAcm− 2 at 1.0 V. This result reveals the good stability of the PCNTs as electrocatalysts for the ethanol oxidation. The PCNTs have several interesting features. First, the anodic current for ethanol oxidation on the PCNT electrode increases with the increase of the scan cycle until the anodic current reaches the maximum value. This can be explained in term of voltammetric dissolution of Cu from Pt–Cu alloy [15]. The electrochemical dealloying of Cu from the PCNTs during the cyclic scan increases the active sites, which leads to the increase of the anodic current for ethanol oxidation. Second, the disappearance of If reveals that the formation of PtO monolayer is prevented. It can be inferred that the preferential dissolution of Cu in the Pt–Cu alloy not only increases the active surface area of the Pt–Cu electrode but also freshens the surface of the PCNT electrode to prevent the formation of PtO. It was suggested that the oxidation of ethanol increases with increase of the lattice parameter [21]. The lattice parameter of Pt–Cu alloy is larger than that of Pt, which could favor the cleavage of the C–C bond. Besides, the large surface area and high void volume on the PCNT array electrodes can allow efficient mass and electron transport to and from the catalyst sites, which should also enhance the supply of the active oxygen atoms for the oxidation of ethanol. 4. Conclusions In conclusion, PCNTs with diameters of 250 nm have been successfully fabricated by one-step direct electrodeposition. The PCNTs exhibit good stability and catalytic activity for ethanol oxidation and show promise to be a new type of supportless electrocatalyst in direct alcohol fuel cells. References [1] [2] [3] [4] [5] [6] [7] [8] [9]
Fig. 3. (a) Cyclic voltammograms on Pt–Cu alloy nanotube array electrode in 0.5 M H2SO4. (b) Cyclic voltammograms on Pt–Cu nanotube array electrode in 0.5 M H2SO4+ 1 M CH3CH2OH. Scan rate: 50 mVs− 1.
Long JW, Stroud RM, Swider-Lyons KE, Rolison DR. J Phys Chem B 2000;104:9772. Joo SH, Choi SJ, Oh I, Kwak J, Liu Z, Terasaki O, Ryoo R. Nature 2001;412:169. Qi Z, Kaufman A. J Power sources 2003;113:37. Lamy C, Belgsir EM, Léger J-M. J Appl Electrochem 2001;31:799. Antolini E. J Power Sources 2007;170:1. Bao SJ, Bao QL, Li CM, Dong ZL. Electrochim Commun 2007;9:1233. Prabhuram J, Manoharan R. J Power sources 1998;74:54. Sen Gupta S, Mahapatra SS, Datta J. J Power sources 2004;131:169. Spătaru N, Zhang X, Spătaru T, Tryk DA, Fujishima A. J Electrochem Soc 2008;155: B264. [10] Zhou W, Zhou Z, Song S, Li W, Sun G, Tsiakaras P, Xin Q. Appl Catal B 2003;46:273. [11] Spinacé EV, Linardi M, Oliveira Neto A. Electrochim Commun 2005;7:365.
1172 [12] [13] [14] [15] [16]
X. Zhang et al. / Materials Letters 64 (2010) 1169–1172 Xu C, Wang H, Shen PK, Jiang SP. Adv Mater 2007;19:4256. Chen ZW, Waje M, Li WZ, Yan YS. Angew Chem Int Ed 2007;46:4060. Zhang X, Dong D, Li D, Wang H, Webley PA. Electrochim Commun 2009;11:190. Strasser P, Koh S, Greeley J. Phys Chem Chem Phys 2008;10:3670. Lee SJ, Mukerjee S, Mcbreen J, Rho YW, Kho YT, Lee TH. Electrochim Acta 1998;43: 3693.
[17] Pozio A, Francesco MD, Cemmi A, Cardellini F, Giorgi L. J Power Sources 2002;105: 13. [18] Manoharan R, Prabhuram J. J Power Sources 2000;96:220. [19] Planes GA, García G, Pastor E. Electrochim Commun 2007;9:839. [20] Morallón E, Rodes A, Vázquez JL, Pérez JM. J Electrochem Soc 1995;391:149. [21] Colmati F, Antolini E, Gonzalez ER. J Electrochem Soc 2007;154:B39.