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Potential application of anion-exchange membrane for hydrazine fuel cell electrolyte
Electrochemistry Communications 5 (2003) 892–896 www.elsevier.com/locate/elecom
Potential application of anion-exchange membrane for hydrazine fuel cell electrolyte Koji Yamada a, Kazuaki Yasuda b,*, Naoko Fujiwara b, Zyun Siroma b, Hirohisa Tanaka a, Yoshinori Miyazaki b, Tetsuhiko Kobayashi b a
b
Materials R&D Department, Materials Engineering Division, Daihatsu Motor Co., Ltd., 3000 Yamanoue, Ryuo-cho, Gamo-gun, Shiga 520-2593, Japan Special Division for Green Life Technology, National Institute of Advanced Industrial Science and Technology, 1-8-31 Midorigaoka, Ikeda, Osaka 563-8577, Japan Received 18 August 2003; accepted 22 August 2003 Published online: 11 September 2003
Abstract A platinum electrocatalyst layer was directly bound to a perfluorinated anion-exchange membrane (AEM) by the electroless plating method and used for the characterization of AEM as a polymer electrolyte membrane for a direct hydrazine fuel cell. The crossover amount of hydrazine through AEM was much lower than that through the cation-exchange membrane (CEM) that did not depend on the applied current density. The fuel cell performance was far superior when using AEM than when using CEM. Ó 2003 Elsevier B.V. All rights reserved. Keywords: Anion-exchange membrane; Direct-fueled fuel cell; Hydrazine; Electroless plating; Crossover
1. Introduction Direct-fueled fuel cells are a suitable power source especially for mobile electric appliances. A direct methanol fuel cell (DMFC) based on proton-exchange membrane fuel cell (PEMFC) technology is expected as a prospective candidate for this application [1–3]. However, the efficiency and power output of DMFCs are low because of severe poisoning of the anode catalyst by reaction intermediates such as CO and methanol crossover through the electrolyte membrane [1]. Hydrazine (N2 H4 ) is an ideal fuel for a direct fuel cell system from the viewpoint that the fuel electro-oxidation process does not suffer from any poisoning effects [4,5]. Recently, we reported that a direct hydrazine fuel cell (DHFC) using a perfluorinated proton-exchange
*
Corresponding author. Tel.: +81-727-51-9653; fax: +81-727-519629. E-mail address: [email protected] (K. Yasuda). 1388-2481/$ - see front matter Ó 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.elecom.2003.08.015
membrane (PEM) showed a much higher cell voltage than DMFC especially in the low-current density region [6]. However, rapid lowering of the cell voltage with an increase of current density was observed, revealing that the reduction of fuel crossover was an important task. Since hydrazine is an alkaline liquid, using the anion-exchange membrane (AEM) as an electrolyte is expected as an effective method to improve cell performance. However, PEMFC using AEM has not been developed yet, because of low-ionic conductivity, heat-resistance and the durability of present AEMs: there is little particular merit in being superior to the cation-exchange membrane (CEM). Another reason is the difficulty in binding electrodes onto the membrane since polymer electrolyte solution, such as NafionÒ solution, is unavailable. In this report, the platinum electrode was bound directly to the chemically stable perfluorinated AEM by electroless plating and the permeation of hydrazine through the membrane was measured to investigate the potential of AEM as an electrolyte membrane for DHFC using a polymer electrolyte membrane.
K. Yamada et al. / Electrochemistry Communications 5 (2003) 892–896
2. Experimental To prepare the membrane-electrode assembly (MEA), platinum electrocatalyst was chemically plated onto two perfluorinated polymer electrolyte membranes, NafionÒ 117 (E.I. DuPont de Nemours and Company, EW: 1100, 0.175 mm thick) and TosflexÒ SF-17 (Tosoh, EW: 1100, 0.220 mm thick, now commercially unavailable) by electroless plating (Takenaka–Torikai method) developed by the National Institute of Advanced Industrial Science and Technology [7,8]. A solution of H2 PtCl6 and a reducing solution, NaBH4 , were placed on both sides of the membrane, respectively, for plating NafionÒ 117. A solution of Pt(NH4 )6 Cl4 was used for plating TosflexÒ . The amount of deposited platinum was 1 mg cm2 at each side. A sintered titanium fiber was used for the current collector on the anode side. A carbon cloth with a thin gas diffusion layer was used on the cathode side. The prepared MEA, with an electrode area of 10 cm2 , was inserted into a single cell to measure the cell performance. A sufficient amount of 2 mol l1 aqueous solution of hydrazine hydrate (N2 H4 H2 O) was supplied to the anode at a flow rate of 2 ml min1 and argon gas humidified at 60 °C was supplied to the cathode at a flow rate of 200 ml min1 . The cell temperature was controlled at 60 °C. DC current was applied to the cell with a current pulse generator (HC-115, Hokuto Denko Ltd.). Hydrazine is oxidized at the anode and hydrogen evolution occurs at the cathode. To make the data easier to follow, the experimental configuration for the reactions at the cell using each membrane is depicted in Fig. 1, which shows the ideal case without crossover. To examine the degree of hydrazine permeation during operation, compositions of the exhaust from both electrodes were analyzed under a different current flow condition. The gas composition (hydrogen, oxygen, nitrogen) was measured by gas chromatography. The water-soluble
893
components (ammonia and hydrazine) were measured by ion chromatography and absorption spectrophotometry, respectively. Results are given in 106 mol min1 units. For the experiment to compare fuel cell performance, oxygen gas humidified at 60 °C was supplied to the cathode at a flow rate of 400 ml min1 instead of argon. Before measuring DHFC performance, the cell was operated for 1 h with pure hydrogen, following 1-h operation by 2 mol l1 N2 H4 H2 O solutions as fuel. The cell temperature was controlled at 60 °C.
3. Results and discussion Binding of the membrane with electrodes is a key issue for electrochemical systems using solid polymer electrolyte. For PEMFC, NafionÒ solution plays an important role in adhesion between the polymer electrolyte membrane and electrodes, and increase in the three-phase region [9]. Since the TosflexÒ solution was unavailable, electroless plating was applied as a method for the MEA preparation to study the potential of this membrane. Fig. 2 shows a scanning electron micrograph of a cross-section of electroless plated AEM. As is evident, the platinum layer was tightly bound on the surfaces of the membrane. This method gave strong adhesion with small contact resistance by a low-temperature process without even drying the membrane. On the other hand, the conventional hot press method without using the polymer electrolyte solution gave poor adhesion and resulted in high contact resistance especially for the TosflexÒ membrane. The electroless plating method is also appropriate for evaluating the properties of membranes, which have low tolerance to heat, pressure or dry conditions, such as hydrocarbon polymer electrolyte membranes.
Fig. 1. Schematic diagram of the cell reaction under exhaust material measurement using: (a) CEM and (b) AEM.
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K. Yamada et al. / Electrochemistry Communications 5 (2003) 892–896
Fig. 2. Scanning electron micrograph image of cross-section of the electroless plated membrane.
The DC current was applied to the cell fed with 2 mol l1 liquid aqueous solution of hydrazine hydrate at the anode side and argon at the cathode side. Fig. 3 exhibits the results of the measurement of the exhaust composition from the cell using CEM with applied current. The increases in the nitrogen evolution from
the anode and the hydrogen evolution from the cathode with the increase of current density agreed with the theoretical values. Hydrogen and ammonia detected in the anode exhaust were products of side reaction (catalytic decomposition) on the anode. A large amount of hydrazine, which permeated through the membrane from the anode to the cathode, appeared in the cathode exhaust as shown in Fig. 3(b). It should be noted that the hydrazine crossover remarkably increased with the increase of current density. According to the reports related to DMFC, the methanol crossover rate decreases with the increasing current density due to an increased utilization of methanol at the anode [10,11]. But the crossover rate at high methanol concentrations increases with current density as a consequence of the electro-osmotic drag [12]. Although no reports in the literature exist regarding the electro-osmotic drag of hydrazine, like water or methanol, across polymer electrolyte membranes, a transport phenomenon like the electro-osmotic drag appeared in Fig. 3(b). Such crossover of hydrazine in this case does not necessarily occur in quite the same way as that of methanol in DMFC. Hydrazine solution is alkaline liquid and parts of hydrazine exist as hydrazinium ion (N2 Hþ 5 ) especially in the acid membrane. As hydrazinium ion generated from unreacted hydrazine penetrates easily into the CEM by ion-exchange, a large part of the proton can be transported through the CEM in the form of hydrazinium ion because the proton concentration is probably low in the CEM exposed to the supplied alkaline solution at the anode side. This mechanism may accelerate hydrazine crossover with the increase of current density. Ammonia, a product of catalytic de-
Fig. 3. The exhaust composition in DHFC from the cell using CEM: (a) anode content and (b) cathode content. Anode/cathode pressures ¼ 0.1/0.1 MPa.
K. Yamada et al. / Electrochemistry Communications 5 (2003) 892–896
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Fig. 4. The exhaust composition in DHFC from the cell using AEM: (a) anode content and (b) cathode content. Anode/cathode pressures ¼ 0.1/0.1 MPa.
composition at the anode, was also detected from the cathode exhaust. Ammonia can also transport easily through the membrane in the form of NHþ 4. Fig. 4 exhibits the results of the measurement of exhaust composition from the cell using AEM. Due to the higher resistance of AEM, the applied voltage was higher than in the case using CEM. Contrary to the previous observations, it is obvious that there is little crossover of hydrazine or ammonia without dependency on the current density over the tested range of the current density as shown in Fig. 4(b). The cathode hydrazine amount in the open circuit state without applied current reflects the amount of the hydrazine permeation by a concentration gradient. The cathode hydrazine amount from the cell using AEM in the open circuit was almost the detection limit in contrast to 5 106 mol min1 for the one using CEM. The cathode ammonia amount for the AEM cell in the same condition was 9.4 106 mol min1 , about half of 17.4 106 mol min1 for the CEM cell. These results show that the permeation rate of hydrazine and ammonia through AEM was much lower than that through CEM. Oxygen gas was supplied to the cathode side of the cell and the current–voltage relation of DHFC was measured as shown in Fig. 5. Since the specific surface area of deposited platinum is not as high and the electrode composition is unsuitable for oxygen reduction, the cathode performance of this electrode is very susceptible to hydrazine crossover and high cell performance as a fuel cell cannot be expected. However, this experiment clearly indicates the effectiveness of using AEM in DHFCs. As shown in Fig. 5, the cell using
Fig. 5. The DHFC performances with different types of membrane. Anode/cathode pressures ¼ 0.1/0.15 MPa.
CEM gave a much poorer performance than that using AEM. The cathode performance of the cell using CEM was severely lowered by the crossover hydrazine and the cell using AEM suffered a much lower effect of hydrazine crossover. Although improvement of cell performance is necessary by the development of a membrane solution such as NafionÒ solution or a method for MEA preparation, these results indicate that the crossover rate will be significantly improved using AEM for PEM type DHFC. To the authorsÕ knowledge, this is the first report on operating PEMFC based on the perfluorinated anionexchange membrane, although solid polymer electrolyte water electrolysis using the TosflexÒ membrane was
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K. Yamada et al. / Electrochemistry Communications 5 (2003) 892–896
studied at our former institute [13,14]. Fuel cells using AEM make it possible to use cheaper electrocatalysts such as Ag or Ni, while the one using CEM allows only expensive Pt group metals as the electrocatalyst because of the high acidity of CEM. Although the resistance of the OH ion conductor is higher than the proton conductor, AEM has many advantages as an electrolyte membrane for the direct-fueled PEMFC using hydrazine as a fuel. 4. Conclusion Membrane-electrode assembly using AEM was prepared by the electroless plating method and used for the characterization of AEM as a polymer electrolyte membrane for DHFC. The experimental results found in the literature show that there was little permeation of hydrazine through AEM in contrast to CEM, which tends to permeate hydrazine with the increase of current density. The hydrazine fuel cell performance was far superior in when using AEM than when using CEM. If a polymer solution of AEM is developed, AEM can be expected as a suitable polymer electrolyte membrane for PEM type DHFCs. Acknowledgements The authors thank Mrs. Y. Murai for conducting the experiment on the preparation of MEA. The au-
thor is greatly indebted to Mr. A. Taniguchi of the Graduate School of Materials Science, the Nara Institute of Science and Technology for his kind help in this work.
References [1] C. Lamy, J.M. Leger, The First International Symposium on New Materials Fuel Cell Systems, 1995, p. 296. [2] R.G. Hockaday, M. DeJohn, C. Navas, P.S. Turner, H.L. Vaz, L.L. Vazul, Abstracts of Fuel Cell Seminar 2000, 2000, p. 791. [3] C.K. Dyer, J. Power Sources 106 (2002) 31. [4] A.J. Bard, Anal. Chem. 35 (1963) 1602. [5] L.D. Burke, K.J. OÕDwyer, Electrochim. Acta 34 (1989) 1659. [6] K. Yamada, K. Asazawa, K. Yasuda, T. Ioroi, H. Tanaka, Y. Miyazaki, T. Kobayashi, J. Power Sources 115 (2003) 236. [7] H. Takenaka, E. Torikai, Y. Kawami, N. Wakabayashi, Int. J. Hydrogen Energy 7 (1982) 397. [8] N. Fujiwara, K. Yasuda, T. Ioroi, Z. Siroma, Y. Miyazaki, Electrochim. Acta 47 (2002) 4079. [9] R.A. Lemons, J. Power Sources 29 (1990) 251. [10] A. Heinzel, V.M. Barragan, J. Power Sources 84 (1999) 70. [11] S.R. Narayanan, A. Kindler, B. Jeffries-Nakamura, W. Chun, H. Frank, M. Smart, T.I. Valdez, S. Surampdi, G. Halpert, J. Kosek, C. Cropley, Annu. Battery Conf. Appl. Adv. 11 (1996) 113. [12] H. Dohle, J. Divisek, R. Jung, J. Power Sources 86 (2000) 469. [13] M. Motone, Y. Kawami, Y. Nishimura, M. Mizuhata, K. Oguro, H. Takenaka, Denki Kagaku 62 (1994) 71. [14] M. Motone, Y. Nishimura, M. Mizuhata, K. Oguro, Denki Kagaku 62 (1994) 425.
Potential application of anion-exchange membrane for hydrazine fuel cell electrolyte Koji Yamada a, Kazuaki Yasuda b,*, Naoko Fujiwara b, Zyun Siroma b, Hirohisa Tanaka a, Yoshinori Miyazaki b, Tetsuhiko Kobayashi b a
b
Materials R&D Department, Materials Engineering Division, Daihatsu Motor Co., Ltd., 3000 Yamanoue, Ryuo-cho, Gamo-gun, Shiga 520-2593, Japan Special Division for Green Life Technology, National Institute of Advanced Industrial Science and Technology, 1-8-31 Midorigaoka, Ikeda, Osaka 563-8577, Japan Received 18 August 2003; accepted 22 August 2003 Published online: 11 September 2003
Abstract A platinum electrocatalyst layer was directly bound to a perfluorinated anion-exchange membrane (AEM) by the electroless plating method and used for the characterization of AEM as a polymer electrolyte membrane for a direct hydrazine fuel cell. The crossover amount of hydrazine through AEM was much lower than that through the cation-exchange membrane (CEM) that did not depend on the applied current density. The fuel cell performance was far superior when using AEM than when using CEM. Ó 2003 Elsevier B.V. All rights reserved. Keywords: Anion-exchange membrane; Direct-fueled fuel cell; Hydrazine; Electroless plating; Crossover
1. Introduction Direct-fueled fuel cells are a suitable power source especially for mobile electric appliances. A direct methanol fuel cell (DMFC) based on proton-exchange membrane fuel cell (PEMFC) technology is expected as a prospective candidate for this application [1–3]. However, the efficiency and power output of DMFCs are low because of severe poisoning of the anode catalyst by reaction intermediates such as CO and methanol crossover through the electrolyte membrane [1]. Hydrazine (N2 H4 ) is an ideal fuel for a direct fuel cell system from the viewpoint that the fuel electro-oxidation process does not suffer from any poisoning effects [4,5]. Recently, we reported that a direct hydrazine fuel cell (DHFC) using a perfluorinated proton-exchange
*
Corresponding author. Tel.: +81-727-51-9653; fax: +81-727-519629. E-mail address: [email protected] (K. Yasuda). 1388-2481/$ - see front matter Ó 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.elecom.2003.08.015
membrane (PEM) showed a much higher cell voltage than DMFC especially in the low-current density region [6]. However, rapid lowering of the cell voltage with an increase of current density was observed, revealing that the reduction of fuel crossover was an important task. Since hydrazine is an alkaline liquid, using the anion-exchange membrane (AEM) as an electrolyte is expected as an effective method to improve cell performance. However, PEMFC using AEM has not been developed yet, because of low-ionic conductivity, heat-resistance and the durability of present AEMs: there is little particular merit in being superior to the cation-exchange membrane (CEM). Another reason is the difficulty in binding electrodes onto the membrane since polymer electrolyte solution, such as NafionÒ solution, is unavailable. In this report, the platinum electrode was bound directly to the chemically stable perfluorinated AEM by electroless plating and the permeation of hydrazine through the membrane was measured to investigate the potential of AEM as an electrolyte membrane for DHFC using a polymer electrolyte membrane.
K. Yamada et al. / Electrochemistry Communications 5 (2003) 892–896
2. Experimental To prepare the membrane-electrode assembly (MEA), platinum electrocatalyst was chemically plated onto two perfluorinated polymer electrolyte membranes, NafionÒ 117 (E.I. DuPont de Nemours and Company, EW: 1100, 0.175 mm thick) and TosflexÒ SF-17 (Tosoh, EW: 1100, 0.220 mm thick, now commercially unavailable) by electroless plating (Takenaka–Torikai method) developed by the National Institute of Advanced Industrial Science and Technology [7,8]. A solution of H2 PtCl6 and a reducing solution, NaBH4 , were placed on both sides of the membrane, respectively, for plating NafionÒ 117. A solution of Pt(NH4 )6 Cl4 was used for plating TosflexÒ . The amount of deposited platinum was 1 mg cm2 at each side. A sintered titanium fiber was used for the current collector on the anode side. A carbon cloth with a thin gas diffusion layer was used on the cathode side. The prepared MEA, with an electrode area of 10 cm2 , was inserted into a single cell to measure the cell performance. A sufficient amount of 2 mol l1 aqueous solution of hydrazine hydrate (N2 H4 H2 O) was supplied to the anode at a flow rate of 2 ml min1 and argon gas humidified at 60 °C was supplied to the cathode at a flow rate of 200 ml min1 . The cell temperature was controlled at 60 °C. DC current was applied to the cell with a current pulse generator (HC-115, Hokuto Denko Ltd.). Hydrazine is oxidized at the anode and hydrogen evolution occurs at the cathode. To make the data easier to follow, the experimental configuration for the reactions at the cell using each membrane is depicted in Fig. 1, which shows the ideal case without crossover. To examine the degree of hydrazine permeation during operation, compositions of the exhaust from both electrodes were analyzed under a different current flow condition. The gas composition (hydrogen, oxygen, nitrogen) was measured by gas chromatography. The water-soluble
893
components (ammonia and hydrazine) were measured by ion chromatography and absorption spectrophotometry, respectively. Results are given in 106 mol min1 units. For the experiment to compare fuel cell performance, oxygen gas humidified at 60 °C was supplied to the cathode at a flow rate of 400 ml min1 instead of argon. Before measuring DHFC performance, the cell was operated for 1 h with pure hydrogen, following 1-h operation by 2 mol l1 N2 H4 H2 O solutions as fuel. The cell temperature was controlled at 60 °C.
3. Results and discussion Binding of the membrane with electrodes is a key issue for electrochemical systems using solid polymer electrolyte. For PEMFC, NafionÒ solution plays an important role in adhesion between the polymer electrolyte membrane and electrodes, and increase in the three-phase region [9]. Since the TosflexÒ solution was unavailable, electroless plating was applied as a method for the MEA preparation to study the potential of this membrane. Fig. 2 shows a scanning electron micrograph of a cross-section of electroless plated AEM. As is evident, the platinum layer was tightly bound on the surfaces of the membrane. This method gave strong adhesion with small contact resistance by a low-temperature process without even drying the membrane. On the other hand, the conventional hot press method without using the polymer electrolyte solution gave poor adhesion and resulted in high contact resistance especially for the TosflexÒ membrane. The electroless plating method is also appropriate for evaluating the properties of membranes, which have low tolerance to heat, pressure or dry conditions, such as hydrocarbon polymer electrolyte membranes.
Fig. 1. Schematic diagram of the cell reaction under exhaust material measurement using: (a) CEM and (b) AEM.
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K. Yamada et al. / Electrochemistry Communications 5 (2003) 892–896
Fig. 2. Scanning electron micrograph image of cross-section of the electroless plated membrane.
The DC current was applied to the cell fed with 2 mol l1 liquid aqueous solution of hydrazine hydrate at the anode side and argon at the cathode side. Fig. 3 exhibits the results of the measurement of the exhaust composition from the cell using CEM with applied current. The increases in the nitrogen evolution from
the anode and the hydrogen evolution from the cathode with the increase of current density agreed with the theoretical values. Hydrogen and ammonia detected in the anode exhaust were products of side reaction (catalytic decomposition) on the anode. A large amount of hydrazine, which permeated through the membrane from the anode to the cathode, appeared in the cathode exhaust as shown in Fig. 3(b). It should be noted that the hydrazine crossover remarkably increased with the increase of current density. According to the reports related to DMFC, the methanol crossover rate decreases with the increasing current density due to an increased utilization of methanol at the anode [10,11]. But the crossover rate at high methanol concentrations increases with current density as a consequence of the electro-osmotic drag [12]. Although no reports in the literature exist regarding the electro-osmotic drag of hydrazine, like water or methanol, across polymer electrolyte membranes, a transport phenomenon like the electro-osmotic drag appeared in Fig. 3(b). Such crossover of hydrazine in this case does not necessarily occur in quite the same way as that of methanol in DMFC. Hydrazine solution is alkaline liquid and parts of hydrazine exist as hydrazinium ion (N2 Hþ 5 ) especially in the acid membrane. As hydrazinium ion generated from unreacted hydrazine penetrates easily into the CEM by ion-exchange, a large part of the proton can be transported through the CEM in the form of hydrazinium ion because the proton concentration is probably low in the CEM exposed to the supplied alkaline solution at the anode side. This mechanism may accelerate hydrazine crossover with the increase of current density. Ammonia, a product of catalytic de-
Fig. 3. The exhaust composition in DHFC from the cell using CEM: (a) anode content and (b) cathode content. Anode/cathode pressures ¼ 0.1/0.1 MPa.
K. Yamada et al. / Electrochemistry Communications 5 (2003) 892–896
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Fig. 4. The exhaust composition in DHFC from the cell using AEM: (a) anode content and (b) cathode content. Anode/cathode pressures ¼ 0.1/0.1 MPa.
composition at the anode, was also detected from the cathode exhaust. Ammonia can also transport easily through the membrane in the form of NHþ 4. Fig. 4 exhibits the results of the measurement of exhaust composition from the cell using AEM. Due to the higher resistance of AEM, the applied voltage was higher than in the case using CEM. Contrary to the previous observations, it is obvious that there is little crossover of hydrazine or ammonia without dependency on the current density over the tested range of the current density as shown in Fig. 4(b). The cathode hydrazine amount in the open circuit state without applied current reflects the amount of the hydrazine permeation by a concentration gradient. The cathode hydrazine amount from the cell using AEM in the open circuit was almost the detection limit in contrast to 5 106 mol min1 for the one using CEM. The cathode ammonia amount for the AEM cell in the same condition was 9.4 106 mol min1 , about half of 17.4 106 mol min1 for the CEM cell. These results show that the permeation rate of hydrazine and ammonia through AEM was much lower than that through CEM. Oxygen gas was supplied to the cathode side of the cell and the current–voltage relation of DHFC was measured as shown in Fig. 5. Since the specific surface area of deposited platinum is not as high and the electrode composition is unsuitable for oxygen reduction, the cathode performance of this electrode is very susceptible to hydrazine crossover and high cell performance as a fuel cell cannot be expected. However, this experiment clearly indicates the effectiveness of using AEM in DHFCs. As shown in Fig. 5, the cell using
Fig. 5. The DHFC performances with different types of membrane. Anode/cathode pressures ¼ 0.1/0.15 MPa.
CEM gave a much poorer performance than that using AEM. The cathode performance of the cell using CEM was severely lowered by the crossover hydrazine and the cell using AEM suffered a much lower effect of hydrazine crossover. Although improvement of cell performance is necessary by the development of a membrane solution such as NafionÒ solution or a method for MEA preparation, these results indicate that the crossover rate will be significantly improved using AEM for PEM type DHFC. To the authorsÕ knowledge, this is the first report on operating PEMFC based on the perfluorinated anionexchange membrane, although solid polymer electrolyte water electrolysis using the TosflexÒ membrane was
896
K. Yamada et al. / Electrochemistry Communications 5 (2003) 892–896
studied at our former institute [13,14]. Fuel cells using AEM make it possible to use cheaper electrocatalysts such as Ag or Ni, while the one using CEM allows only expensive Pt group metals as the electrocatalyst because of the high acidity of CEM. Although the resistance of the OH ion conductor is higher than the proton conductor, AEM has many advantages as an electrolyte membrane for the direct-fueled PEMFC using hydrazine as a fuel. 4. Conclusion Membrane-electrode assembly using AEM was prepared by the electroless plating method and used for the characterization of AEM as a polymer electrolyte membrane for DHFC. The experimental results found in the literature show that there was little permeation of hydrazine through AEM in contrast to CEM, which tends to permeate hydrazine with the increase of current density. The hydrazine fuel cell performance was far superior in when using AEM than when using CEM. If a polymer solution of AEM is developed, AEM can be expected as a suitable polymer electrolyte membrane for PEM type DHFCs. Acknowledgements The authors thank Mrs. Y. Murai for conducting the experiment on the preparation of MEA. The au-
thor is greatly indebted to Mr. A. Taniguchi of the Graduate School of Materials Science, the Nara Institute of Science and Technology for his kind help in this work.
References [1] C. Lamy, J.M. Leger, The First International Symposium on New Materials Fuel Cell Systems, 1995, p. 296. [2] R.G. Hockaday, M. DeJohn, C. Navas, P.S. Turner, H.L. Vaz, L.L. Vazul, Abstracts of Fuel Cell Seminar 2000, 2000, p. 791. [3] C.K. Dyer, J. Power Sources 106 (2002) 31. [4] A.J. Bard, Anal. Chem. 35 (1963) 1602. [5] L.D. Burke, K.J. OÕDwyer, Electrochim. Acta 34 (1989) 1659. [6] K. Yamada, K. Asazawa, K. Yasuda, T. Ioroi, H. Tanaka, Y. Miyazaki, T. Kobayashi, J. Power Sources 115 (2003) 236. [7] H. Takenaka, E. Torikai, Y. Kawami, N. Wakabayashi, Int. J. Hydrogen Energy 7 (1982) 397. [8] N. Fujiwara, K. Yasuda, T. Ioroi, Z. Siroma, Y. Miyazaki, Electrochim. Acta 47 (2002) 4079. [9] R.A. Lemons, J. Power Sources 29 (1990) 251. [10] A. Heinzel, V.M. Barragan, J. Power Sources 84 (1999) 70. [11] S.R. Narayanan, A. Kindler, B. Jeffries-Nakamura, W. Chun, H. Frank, M. Smart, T.I. Valdez, S. Surampdi, G. Halpert, J. Kosek, C. Cropley, Annu. Battery Conf. Appl. Adv. 11 (1996) 113. [12] H. Dohle, J. Divisek, R. Jung, J. Power Sources 86 (2000) 469. [13] M. Motone, Y. Kawami, Y. Nishimura, M. Mizuhata, K. Oguro, H. Takenaka, Denki Kagaku 62 (1994) 71. [14] M. Motone, Y. Nishimura, M. Mizuhata, K. Oguro, Denki Kagaku 62 (1994) 425.