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FexC–C hybrid material as a support for Pt anode catalyst in direct formic acid fuel cell
Electrochemistry Communications 11 (2009) 28–30
Contents lists available at ScienceDirect
Electrochemistry Communications journal homepage: www.elsevier.com/locate/elecom
FexC–C hybrid material as a support for Pt anode catalyst in direct formic acid fuel cell Xiao-Ming Wang, Yong-Yao Xia * Department of Chemistry, Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, Fudan University, Shanghai 200433, China
a r t i c l e
i n f o
Article history: Received 13 September 2008 Received in revised form 6 October 2008 Accepted 7 October 2008 Available online 14 October 2008 Keywords: Pt FexC–C Hybrid material Formic acid
a b s t r a c t FexC–C hybrid material as a support for Pt anode catalyst in direct formic acid fuel cell was investigated for the first time. The resultant Pt/FexC–C catalysts were prepared by using a simple reduction reaction to load Pt on FexC–C hybrid material, which was synthesized through the carbonization of sucrose and Fe(NO3)3. It was found that the Pt/FexC–C catalysts exhibited excellent catalytic activity for formic acid electrooxidation. The great improvement in the catalytic performance is attributed to the fact that FexC–C hybrid material ameliorated the tolerance to CO adsorption of Pt and facilitated the uniform dispersion of Pt. Ó 2008 Elsevier B.V. All rights reserved.
1. Introduction During the last decade, great progress has been made in direct formic acid fuel cell (DFAFC) science and technology. However, the commercialization of DFAFC is still hindered by some technical challenges, especially the unsatisfactory catalytic activity of anode catalysts. Currently, in order to improve the catalytic activity of catalysts, considerable research has focus on seeking new support materials that can provide the structure effect and the synergistic electronic effect. Conventionally, highly conductive carbon material, such as XC72, expanded graphite [1], graphite nanofiber [2], ordered porous carbon [3–8] and carbon nanotube [9,10], provides a high dispersion of metal nanoparticles and facilitates electron transfer, resulting in better catalytic activity. Besides, a kind of ‘‘active support materials” has been revealed that they could have a catalytic role that contributed to the observed enhancement in the methanol or formic acid electrooxidation. For example, nitrogen containing carbon nanotube [11], ruthenium oxides/Vulcan XC-72 mixed supports [12], carbon–silica composite [13] and WO3/C hybrid material [14] could bring about the strong metal-support interaction that would greatly affect the electrochemical properties of the fuel cell catalysts. The appearance of ‘‘active support material” delivers us an idea to settle the corrosion of active metal promoter. As we know, FexC is a very stable compound in acidic solution comparing with Fe, * Corresponding author. Tel./fax: +86 21 55664177. E-mail address: [email protected] (Y.Y. Xia). 1388-2481/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.elecom.2008.10.008
which has been reported as a cheap and useful promoter [15]. In this work, FexC–C hybrid material as a support for Pt anode catalyst in direct formic acid fuel cell was investigated for the first time. Experiments proved that FexC–C hybrid material could improve the catalytic activity of Pt for formic acid electrooxidation, shunning the problem of the Fe corrosion. 2. Experiment FexC–C hybrid material containing various FexC contents, varying from 8 wt% to 60 wt%, was prepared as follows. The sucrose, Fe(NO3)3 and HNO3 were dissolved in 20 mL water. Then the solution was dried and heat-treated at 300 and 900 °C for 2 h under the protection of nitrogen, respectively. Finally, the obtained hybrid material was treated in a high energy ball mill for 30 min. The FexC content in FexC–C hybrid material was calculated on basis of the residue after 500 °C heat-treatment in presence of oxygen. The 20 wt% Pt nanoparticles were deposited onto the FexC–C hybrid material by a NaBH4 reduction method. First, 7.5 mL 0.02 M H2PtCl6 was added in 20 mL water. Then, 120 mg FexC–C hybrid material was added into the above solution. After the suspension was sonicated for 30 min at room temperature, it was slowly added into 20 mL NaBH4 solution with stirring. The resulting suspension was further sonicated for 30 min. Finally, it was filtered, washed and dried in vacuum oven at 60 °C for 12 h. For comparison, Pt/XC-72 catalyst was prepared by the same method. Powder XRD measurement was performed on a Rigaku D/MAXIIA X-ray diffractometer using Cu-Ka radiation. The electrochemical measurements were tested on CHI600 electrochemical analyzer
X.M. Wang, Y.Y. Xia / Electrochemistry Communications 11 (2009) 28–30
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trodes. All potentials were quoted with respect to SCE. Each working electrode contained ca. 42 lg/cm2 of Pt. In the electrochemical measurements, the current densities are normalized to apparent surface area of the GC electrode. 3. Results and discussion The XRD patterns of the catalysts were shown in Fig. 1. In all catalysts, the five characteristic diffraction peaks at ca. 40°, 46°, 68°, 82° and 86° can be observed and belong to the face-centered cubic (fcc) phase of Pt. From the smaller diffraction intensity, it can be concluded that FexC–C hybrid material is in favor of the uniform dispersion of Pt. And, the more FexC is introduced into FexC–C hybrid material, the smaller dimension of Pt nanoparticle will be gained. The average sizes of the particles can be calculated using Debye–Scherrer formula
Þ ¼ 0:89k=b cos h dðA Fig. 1. XRD patterns of Pt/XC-72 (a) and Pt/FexC–C catalysts containing 7.4% (b), 10.6% (c), 14.3% (d), 24.6% (e), 35.7% (f), 44.0% (g) and 60.1% (h) FexC.
where b is the width of half peak, k is the incident wavelength, d is the particle diameter and h is the diffraction angle. The average particle size is 8.2 nm for Pt/XC-72, 7.6 nm for Pt/FexC–C (7.4%), 6.9 nm for Pt/FexC–C (10.6%), 6.5 nm for Pt/FexC–C (14.3%), 6.3 nm for Pt/ FexC–C (24.6%), 6.0 nm for Pt/FexC–C (35.7%), 5.8 nm for Pt/FexC–C (44.0%) and 5.3 nm for Pt/FexC–C (60.1%), respectively. Except the diffraction peaks of Pt, the composition of support materials are clearly displayed in XRD patterns. FexC is composed of Fe3C (main diffraction peaks at ca. 26° and 36°) and Fe2C (main diffraction peak at ca. 43°). And, the ratio of Fe3C and Fe2C regularly decreases with the increase of FexC content. Besides, a small quantity of Fe3O4 can be observed in support materials.
Fig. 2. (A) Cyclic voltammetry of Pt/XC-72 (a), Pt/FexC–C (24.6%) (b) and FexC–C (24.6%) (c) electrodes in the 0.5 M H2SO4 + 0.5 M HCOOH solution at a scan rate of 50 mV/s. (B) The relationship between the specific activity and FexC content.
and a conventional three-electrode electrochemical cell, in which a plate and saturated calomel electrode (SCE, 0.242 V vs. normal hydrogen electrode) were used as the counter and reference elec-
Fig. 3. CO-stripping voltammograms of Pt/XC-72 (A) and Pt/FexC–C (24.6%) (B) electrodes in the 0.5 M H2SO4 solution at a scan rate of 50 mV/s.
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X.M. Wang, Y.Y. Xia / Electrochemistry Communications 11 (2009) 28–30
Fig. 2A displays the cyclic voltammetry on Pt/XC-72, Pt/FexC–C (24.6%) and FexC–C (24.6%) electrodes in the solution of 0.5 M HCOOH and 0.5 M H2SO4 at a scan rate of 50 mV/s. Three pieces of important information are presented. First, there is a lower catalytic activity for formic acid electrooxidation on Pt/XC-72 electrode. In detail, two anodic peaks near 0.40 and 0.73 V and one cathodic peak near 0.50 V are observed. The current densities reach 2.99, 8.49 and 8.55 mA/cm2, respectively. Second, FexC–C (24.6%) electrode has no obvious catalytic activity for formic acid electrooxidation in the examined potential range. Third, compared with Pt/XC-72 electrode, Pt/FexC–C (24.6%) shows remarkable catalytic activity for formic acid electrooxidation. For Pt/FexC–C (24.6%) electrode, two anodic peaks and the cathodic peak almost locate the same potential. However, the corresponding current densities arrive to 6.41, 10.12 and 10.12 mA/cm2. The influence of the FexC content on catalytic activity for formic acid is investigated and revealed in Fig. 2B. The specific catalytic activity is obtained from the current density of forward peaks for formic acid electrooxidation on Pt/FexC–C electrodes. The ‘‘volcano-type” relationship between the specific catalytic activity and FexC content can be observed. It is found that FexC, with a varying content from 8% to 60%, can improve the catalytic activity of Pt/ C. The Pt/FexC–C catalysts containing FexC near 24.6% have the best catalytic performance among all catalysts. In order to test the poisoning effect of CO, ultra-high purity CO was admitted to adsorb on the working electrode at 0.1 V vs. SCE for 15 min, followed by purging CO out of the electrochemical cell at 0.1 V vs. SCE for 10 min. The typical results are exhibited in Fig. 3. The most notable difference between CO-stripping on Pt/XC-72 and that on Pt/FexC–C (24.6%) is the negative shift of the CO oxidation peak in the latter. The onset of CO oxidation
on Pt/FexC–C (24.6%) electrode is shifted negatively by about 100 mV, and the peak potential by about 50 mV, compared with Pt/XC-72 electrode. This is indication that FexC is helpful to weakening the CO adsorptive bond on Pt active sites. It is known to all that formic acid decomposition on Pt is mainly via the CO pathway. Thus, for Pt/XC-72 and Pt/FexC–C (24.6%) electrodes, Ja/Jc ratio implies extensive poisoning of the catalyst surface by CO adsorption [16]. According to the results of cyclic voltammetry (Fig. 2A), the ratio of Pt/XC-72 and Pt/FexC–C (24.6%) electrodes is 0.34 and 0.63, respectively. Pt/FexC–C (24.6%) electrode shows the excellent tolerance to CO adsorption, which is the primary reason for the improvement of catalytic activity. The result of CO-stripping measurement is in good agreement with the result of CV. However, which is the better support material between Fe3C and Fe2C is not clear. It should be further studied. Besides, XRD measurement proves that Pt on FexC–C is smaller than that on XC-72. Smaller particle size can provide more active sites, indicating that smaller particle size is another reason of better catalytic activity for Pt/FexC–C (24.6%). The chronoamperometry curves further prove that Pt/FexC–C (24.6%) electrode has better catalytic activity for formic acid than Pt/XC-72 electrode. In Fig. 4, it can be observed that the current densities on Pt/XC-72 and Pt/FexC–C (24.6%) electrodes after 1000 s are 0.19 and 0.48 mA/cm2 at 0.2 V, 0.44 and 0.84 mA/cm2 at 0.3 V, 0.62 and 0.91 mA/cm2 at 0.4 V, respectively. The current density on Pt/FexC–C (24.6%) electrode has an obvious improvement than that on Pt/XC-72 electrode. 4. Conclusion FexC–C hybrid material as the support for Pt anode catalyst in direct formic acid fuel cell has been proved to have obvious accelerating effect on formic acid electrooxidation. The great improvement in the catalytic performance attributes to the fact that FexC–C hybrid material ameliorates the tolerance to CO adsorption of Pt and facilitates the uniform dispersion of Pt. Importantly, compared with alloy catalysts, Pt loaded on this kind of active support materials can be controlled easily in the particle dimension and surface morphology. Thus, it is certain that catalytic activity of Pt/FexC–C catalyst for formic acid electrooxidation can be further improved in future research. References [1] A. Bhattacharya, A. Hazra, S. Chatterjee, P. Sen, S. Laha, I. Basumallick, J. Power Sources 136 (2004) 208. [2] E.S. Steigerwalt, G.A. Deluga, D.E. Cliffel, C.M. Lukehart, J. Phys. Chem. B 105 (2001) 8097–8101. [3] G. Chai, S.B. Yoon, S. Kang, J.H. Choi, Y.E. Sung, Y.S. Ahn, H.S. Kim, J.S. Yu, Electrochim. Acta 50 (2004) 823–826. [4] F.B. Su, J.H. Zeng, Y.S. Yu, L. Lv, J.Y. Lee, X.S. Zhao, Carbon 43 (2005) 2366. [5] J. Ding, K.Y. Chan, J.W. Ren, F.S. Xiao, Electrochim. Acta 50 (2005) 3131. [6] G.S. Chai, S.B. Yoon, J.S. Yu, J.H. Choi, Y.E. Sung, J. Phys. Chem. B 108 (2004) 7074. [7] M.C. Gutierrez, M.J. Hortigulela, J.M. Amarilla, R. Jimenez, M.L. Ferrer, F.D. Monte, J. Phys. Chem. C 111 (2007) 5557. [8] M.L. Anderson, R.M. Stroud, D.R. Rolison, Nano. Lett. 2 (2002) 235. [9] W.Z. Li, C.H. Liang, J.S. Qiu, W.J. Zhou, H.M. Han, Z.B. Wei, G.Q. Sun, Qin Xin, Carbon 40 (2002) 787. [10] C. Kim, Y.J. Kim, Y.A. Kim, T. Yanagisawa, K.C. Park, M. Endo, J. Appl. Phys. 96 (2004) 5904. [11] T. Maiyalagan, B. Viswanathan, U.V. Varadaraju, Electrochem. Commun. 7 (2005) 905. [12] K. Lasch, G. Hayn, L. Jorissen, J. Garche, O. Besenhardt, J. Power Sources 105 (2002) 305–310. [13] M. Kim, S. Hwang, J.S. Yu, J. Mater. Chem. 17 (2007) 1656. [14] Z.H. Zhang, Y.J. Huang, J.J. Ge, C.P. Liu, T.H. Lu, W. Xing, Electrochem. Commun. 10 (2008) 999. [15] W. Chen, J.M. Kim, S.H. Sun, S.W. Chen, Phys. Chem. Chem. Phys. 8 (2006) 2779. [16] W. Chen, J.M. Kim, S.H. Sun, S.W. Chen, Langmuir 23 (2007) 11303.
Fig. 4. Chronoamperometry curves of Pt/XC-72 (A) and Pt/FexC-C (24.6%) (B) electrodes in the 0.5 M H2SO4 + 0.5 M HCOOH solution at 0.2, 0.3 and 0.4 V vs. SCE.
Contents lists available at ScienceDirect
Electrochemistry Communications journal homepage: www.elsevier.com/locate/elecom
FexC–C hybrid material as a support for Pt anode catalyst in direct formic acid fuel cell Xiao-Ming Wang, Yong-Yao Xia * Department of Chemistry, Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, Fudan University, Shanghai 200433, China
a r t i c l e
i n f o
Article history: Received 13 September 2008 Received in revised form 6 October 2008 Accepted 7 October 2008 Available online 14 October 2008 Keywords: Pt FexC–C Hybrid material Formic acid
a b s t r a c t FexC–C hybrid material as a support for Pt anode catalyst in direct formic acid fuel cell was investigated for the first time. The resultant Pt/FexC–C catalysts were prepared by using a simple reduction reaction to load Pt on FexC–C hybrid material, which was synthesized through the carbonization of sucrose and Fe(NO3)3. It was found that the Pt/FexC–C catalysts exhibited excellent catalytic activity for formic acid electrooxidation. The great improvement in the catalytic performance is attributed to the fact that FexC–C hybrid material ameliorated the tolerance to CO adsorption of Pt and facilitated the uniform dispersion of Pt. Ó 2008 Elsevier B.V. All rights reserved.
1. Introduction During the last decade, great progress has been made in direct formic acid fuel cell (DFAFC) science and technology. However, the commercialization of DFAFC is still hindered by some technical challenges, especially the unsatisfactory catalytic activity of anode catalysts. Currently, in order to improve the catalytic activity of catalysts, considerable research has focus on seeking new support materials that can provide the structure effect and the synergistic electronic effect. Conventionally, highly conductive carbon material, such as XC72, expanded graphite [1], graphite nanofiber [2], ordered porous carbon [3–8] and carbon nanotube [9,10], provides a high dispersion of metal nanoparticles and facilitates electron transfer, resulting in better catalytic activity. Besides, a kind of ‘‘active support materials” has been revealed that they could have a catalytic role that contributed to the observed enhancement in the methanol or formic acid electrooxidation. For example, nitrogen containing carbon nanotube [11], ruthenium oxides/Vulcan XC-72 mixed supports [12], carbon–silica composite [13] and WO3/C hybrid material [14] could bring about the strong metal-support interaction that would greatly affect the electrochemical properties of the fuel cell catalysts. The appearance of ‘‘active support material” delivers us an idea to settle the corrosion of active metal promoter. As we know, FexC is a very stable compound in acidic solution comparing with Fe, * Corresponding author. Tel./fax: +86 21 55664177. E-mail address: [email protected] (Y.Y. Xia). 1388-2481/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.elecom.2008.10.008
which has been reported as a cheap and useful promoter [15]. In this work, FexC–C hybrid material as a support for Pt anode catalyst in direct formic acid fuel cell was investigated for the first time. Experiments proved that FexC–C hybrid material could improve the catalytic activity of Pt for formic acid electrooxidation, shunning the problem of the Fe corrosion. 2. Experiment FexC–C hybrid material containing various FexC contents, varying from 8 wt% to 60 wt%, was prepared as follows. The sucrose, Fe(NO3)3 and HNO3 were dissolved in 20 mL water. Then the solution was dried and heat-treated at 300 and 900 °C for 2 h under the protection of nitrogen, respectively. Finally, the obtained hybrid material was treated in a high energy ball mill for 30 min. The FexC content in FexC–C hybrid material was calculated on basis of the residue after 500 °C heat-treatment in presence of oxygen. The 20 wt% Pt nanoparticles were deposited onto the FexC–C hybrid material by a NaBH4 reduction method. First, 7.5 mL 0.02 M H2PtCl6 was added in 20 mL water. Then, 120 mg FexC–C hybrid material was added into the above solution. After the suspension was sonicated for 30 min at room temperature, it was slowly added into 20 mL NaBH4 solution with stirring. The resulting suspension was further sonicated for 30 min. Finally, it was filtered, washed and dried in vacuum oven at 60 °C for 12 h. For comparison, Pt/XC-72 catalyst was prepared by the same method. Powder XRD measurement was performed on a Rigaku D/MAXIIA X-ray diffractometer using Cu-Ka radiation. The electrochemical measurements were tested on CHI600 electrochemical analyzer
X.M. Wang, Y.Y. Xia / Electrochemistry Communications 11 (2009) 28–30
29
trodes. All potentials were quoted with respect to SCE. Each working electrode contained ca. 42 lg/cm2 of Pt. In the electrochemical measurements, the current densities are normalized to apparent surface area of the GC electrode. 3. Results and discussion The XRD patterns of the catalysts were shown in Fig. 1. In all catalysts, the five characteristic diffraction peaks at ca. 40°, 46°, 68°, 82° and 86° can be observed and belong to the face-centered cubic (fcc) phase of Pt. From the smaller diffraction intensity, it can be concluded that FexC–C hybrid material is in favor of the uniform dispersion of Pt. And, the more FexC is introduced into FexC–C hybrid material, the smaller dimension of Pt nanoparticle will be gained. The average sizes of the particles can be calculated using Debye–Scherrer formula
Þ ¼ 0:89k=b cos h dðA Fig. 1. XRD patterns of Pt/XC-72 (a) and Pt/FexC–C catalysts containing 7.4% (b), 10.6% (c), 14.3% (d), 24.6% (e), 35.7% (f), 44.0% (g) and 60.1% (h) FexC.
where b is the width of half peak, k is the incident wavelength, d is the particle diameter and h is the diffraction angle. The average particle size is 8.2 nm for Pt/XC-72, 7.6 nm for Pt/FexC–C (7.4%), 6.9 nm for Pt/FexC–C (10.6%), 6.5 nm for Pt/FexC–C (14.3%), 6.3 nm for Pt/ FexC–C (24.6%), 6.0 nm for Pt/FexC–C (35.7%), 5.8 nm for Pt/FexC–C (44.0%) and 5.3 nm for Pt/FexC–C (60.1%), respectively. Except the diffraction peaks of Pt, the composition of support materials are clearly displayed in XRD patterns. FexC is composed of Fe3C (main diffraction peaks at ca. 26° and 36°) and Fe2C (main diffraction peak at ca. 43°). And, the ratio of Fe3C and Fe2C regularly decreases with the increase of FexC content. Besides, a small quantity of Fe3O4 can be observed in support materials.
Fig. 2. (A) Cyclic voltammetry of Pt/XC-72 (a), Pt/FexC–C (24.6%) (b) and FexC–C (24.6%) (c) electrodes in the 0.5 M H2SO4 + 0.5 M HCOOH solution at a scan rate of 50 mV/s. (B) The relationship between the specific activity and FexC content.
and a conventional three-electrode electrochemical cell, in which a plate and saturated calomel electrode (SCE, 0.242 V vs. normal hydrogen electrode) were used as the counter and reference elec-
Fig. 3. CO-stripping voltammograms of Pt/XC-72 (A) and Pt/FexC–C (24.6%) (B) electrodes in the 0.5 M H2SO4 solution at a scan rate of 50 mV/s.
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X.M. Wang, Y.Y. Xia / Electrochemistry Communications 11 (2009) 28–30
Fig. 2A displays the cyclic voltammetry on Pt/XC-72, Pt/FexC–C (24.6%) and FexC–C (24.6%) electrodes in the solution of 0.5 M HCOOH and 0.5 M H2SO4 at a scan rate of 50 mV/s. Three pieces of important information are presented. First, there is a lower catalytic activity for formic acid electrooxidation on Pt/XC-72 electrode. In detail, two anodic peaks near 0.40 and 0.73 V and one cathodic peak near 0.50 V are observed. The current densities reach 2.99, 8.49 and 8.55 mA/cm2, respectively. Second, FexC–C (24.6%) electrode has no obvious catalytic activity for formic acid electrooxidation in the examined potential range. Third, compared with Pt/XC-72 electrode, Pt/FexC–C (24.6%) shows remarkable catalytic activity for formic acid electrooxidation. For Pt/FexC–C (24.6%) electrode, two anodic peaks and the cathodic peak almost locate the same potential. However, the corresponding current densities arrive to 6.41, 10.12 and 10.12 mA/cm2. The influence of the FexC content on catalytic activity for formic acid is investigated and revealed in Fig. 2B. The specific catalytic activity is obtained from the current density of forward peaks for formic acid electrooxidation on Pt/FexC–C electrodes. The ‘‘volcano-type” relationship between the specific catalytic activity and FexC content can be observed. It is found that FexC, with a varying content from 8% to 60%, can improve the catalytic activity of Pt/ C. The Pt/FexC–C catalysts containing FexC near 24.6% have the best catalytic performance among all catalysts. In order to test the poisoning effect of CO, ultra-high purity CO was admitted to adsorb on the working electrode at 0.1 V vs. SCE for 15 min, followed by purging CO out of the electrochemical cell at 0.1 V vs. SCE for 10 min. The typical results are exhibited in Fig. 3. The most notable difference between CO-stripping on Pt/XC-72 and that on Pt/FexC–C (24.6%) is the negative shift of the CO oxidation peak in the latter. The onset of CO oxidation
on Pt/FexC–C (24.6%) electrode is shifted negatively by about 100 mV, and the peak potential by about 50 mV, compared with Pt/XC-72 electrode. This is indication that FexC is helpful to weakening the CO adsorptive bond on Pt active sites. It is known to all that formic acid decomposition on Pt is mainly via the CO pathway. Thus, for Pt/XC-72 and Pt/FexC–C (24.6%) electrodes, Ja/Jc ratio implies extensive poisoning of the catalyst surface by CO adsorption [16]. According to the results of cyclic voltammetry (Fig. 2A), the ratio of Pt/XC-72 and Pt/FexC–C (24.6%) electrodes is 0.34 and 0.63, respectively. Pt/FexC–C (24.6%) electrode shows the excellent tolerance to CO adsorption, which is the primary reason for the improvement of catalytic activity. The result of CO-stripping measurement is in good agreement with the result of CV. However, which is the better support material between Fe3C and Fe2C is not clear. It should be further studied. Besides, XRD measurement proves that Pt on FexC–C is smaller than that on XC-72. Smaller particle size can provide more active sites, indicating that smaller particle size is another reason of better catalytic activity for Pt/FexC–C (24.6%). The chronoamperometry curves further prove that Pt/FexC–C (24.6%) electrode has better catalytic activity for formic acid than Pt/XC-72 electrode. In Fig. 4, it can be observed that the current densities on Pt/XC-72 and Pt/FexC–C (24.6%) electrodes after 1000 s are 0.19 and 0.48 mA/cm2 at 0.2 V, 0.44 and 0.84 mA/cm2 at 0.3 V, 0.62 and 0.91 mA/cm2 at 0.4 V, respectively. The current density on Pt/FexC–C (24.6%) electrode has an obvious improvement than that on Pt/XC-72 electrode. 4. Conclusion FexC–C hybrid material as the support for Pt anode catalyst in direct formic acid fuel cell has been proved to have obvious accelerating effect on formic acid electrooxidation. The great improvement in the catalytic performance attributes to the fact that FexC–C hybrid material ameliorates the tolerance to CO adsorption of Pt and facilitates the uniform dispersion of Pt. Importantly, compared with alloy catalysts, Pt loaded on this kind of active support materials can be controlled easily in the particle dimension and surface morphology. Thus, it is certain that catalytic activity of Pt/FexC–C catalyst for formic acid electrooxidation can be further improved in future research. References [1] A. Bhattacharya, A. Hazra, S. Chatterjee, P. Sen, S. Laha, I. Basumallick, J. Power Sources 136 (2004) 208. [2] E.S. Steigerwalt, G.A. Deluga, D.E. Cliffel, C.M. Lukehart, J. Phys. Chem. B 105 (2001) 8097–8101. [3] G. Chai, S.B. Yoon, S. Kang, J.H. Choi, Y.E. Sung, Y.S. Ahn, H.S. Kim, J.S. Yu, Electrochim. Acta 50 (2004) 823–826. [4] F.B. Su, J.H. Zeng, Y.S. Yu, L. Lv, J.Y. Lee, X.S. Zhao, Carbon 43 (2005) 2366. [5] J. Ding, K.Y. Chan, J.W. Ren, F.S. Xiao, Electrochim. Acta 50 (2005) 3131. [6] G.S. Chai, S.B. Yoon, J.S. Yu, J.H. Choi, Y.E. Sung, J. Phys. Chem. B 108 (2004) 7074. [7] M.C. Gutierrez, M.J. Hortigulela, J.M. Amarilla, R. Jimenez, M.L. Ferrer, F.D. Monte, J. Phys. Chem. C 111 (2007) 5557. [8] M.L. Anderson, R.M. Stroud, D.R. Rolison, Nano. Lett. 2 (2002) 235. [9] W.Z. Li, C.H. Liang, J.S. Qiu, W.J. Zhou, H.M. Han, Z.B. Wei, G.Q. Sun, Qin Xin, Carbon 40 (2002) 787. [10] C. Kim, Y.J. Kim, Y.A. Kim, T. Yanagisawa, K.C. Park, M. Endo, J. Appl. Phys. 96 (2004) 5904. [11] T. Maiyalagan, B. Viswanathan, U.V. Varadaraju, Electrochem. Commun. 7 (2005) 905. [12] K. Lasch, G. Hayn, L. Jorissen, J. Garche, O. Besenhardt, J. Power Sources 105 (2002) 305–310. [13] M. Kim, S. Hwang, J.S. Yu, J. Mater. Chem. 17 (2007) 1656. [14] Z.H. Zhang, Y.J. Huang, J.J. Ge, C.P. Liu, T.H. Lu, W. Xing, Electrochem. Commun. 10 (2008) 999. [15] W. Chen, J.M. Kim, S.H. Sun, S.W. Chen, Phys. Chem. Chem. Phys. 8 (2006) 2779. [16] W. Chen, J.M. Kim, S.H. Sun, S.W. Chen, Langmuir 23 (2007) 11303.
Fig. 4. Chronoamperometry curves of Pt/XC-72 (A) and Pt/FexC-C (24.6%) (B) electrodes in the 0.5 M H2SO4 + 0.5 M HCOOH solution at 0.2, 0.3 and 0.4 V vs. SCE.