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Low-temperature route to dispersed manganese dioxide nanorods
Materials Letters 78 (2012) 202–204
Contents lists available at SciVerse ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Low-temperature route to dispersed manganese dioxide nanorods K. Huang a, b, M. Lei a, b,⁎, R. Zhang a, b, H.J. Yang b, Y.G. Yang b a b
State Key Laboratory of Information Photonics and Optical Communications, Beijing University of Posts and Telecommunications, Beijing 100876, China School of Science, Beijing University of Posts and Telecommunications, Beijing 100876, China
a r t i c l e
i n f o
Article history: Received 14 February 2012 Accepted 16 March 2012 Available online 23 March 2012 Keywords: Nanocrystalline materials Microstructure Electrical properties
a b s t r a c t A facile hydrothermal route was developed to fabricate a large amount of dispersed MnO2 nanorods in the presence of poly (sodium 4-styrene-sulfonate). The XRD pattern indicates that these well crystalline nanorods are tetragonal α-MnO2 and have smooth surface. It is deduced that electronegative poly (sodium 4-styrenesulfonate) can prevent aggregation of α-MnO2 nanorods. The curves of discharge capacity vs cycle number indicate that the discharge capacities of dispersed nanorods are much larger than those of the aggregated nanorices and commercial powders. It is suggested that both the one-dimensional morphology and excellent dispersity are the main reasons for the higher discharge capacity of the dispersed nanorods. © 2012 Elsevier B.V. All rights reserved.
1. Introduction
2. Experimental
One-dimensional (1D) metal oxide nanostructures have attracted numerous attentions due to their excellent physical and chemical properties and potential application in electronics, optoelectronics, solar energy storage and transmission, catalysis, detectors, sensors etc. [1–9]. As one of the most important metal oxides, 1D manganese dioxide (MnO2) had been demonstrated to be of enhanced catalytic and electrochemical properties compared with their bulk counterparts [10–14]. Several additives-free methods including refluxing route [15], wet chemical method [16], thermal decomposition [17] and hydrothermal synthesis [18–20] had been developed to fabricate various 1D nanostructures. Nevertheless, the as-prepared 1D nanostructures are difficult to be dispersed, which limits their catalytic and electrochemical applications due to their relative low surface areas. Recently, some organic additives and/or templates were found to successfully control the nucleation, growth and alignment of inorganic materials. The mechanism may be extended to synthesize metal oxide nanostructures. In this work, a mediate hydrothermal method was developed to fabricate well crystalline and dispersed MnO2 nanorods. An electronegative polymer poly (sodium 4-styrene-sulfonate) (PSSS) [21–22] was added to modulate the growth process of MnO2 nanorods. The microstructure, probable reaction mechanism and discharge capacity cycle properties of the MnO2 nanorods are investigated.
In the experiment, 0.005 mol MnSO4, 0.002 mol KMnO4, 0.1 g (PSSS) and 150 ml mixed solution of distilled water and ethanol (the volume ratio of water and ethanol is 4:1) were added into Teflon-lined stainless steel autoclaves and stirred for an hour. Then, 30 ml H2SO4 (1 M) were slowly added into the mixed solution under vigorous stirring. Finally, autoclaves were sealed and further put into a furnace with temperature of 110 °C for 24 h. The obtained black precipitates were washed with distilled water for several times and dried in air for further characterization. Powder X-ray diffraction (XRD) data of the nanowires were collected on a MAC-M18XHF diffractometer. Morphology and microstructure of the products were characterized by field-emission scanning electron microscopy (FE-SEM; Hitachi S-5200) and transmission electron microscopy (TEM; Philips CM200) equipped with energy-dispersive X-ray spectroscopy (EDS), respectively. The electrochemical properties of the MnO2 nanorods as cathodes used in rechargeable lithium-ion batteries were measured at room temperature. The fabrication of the laboratory cells and electrodes are conducted according to the reported works [18].
⁎ Corresponding author at: State Key Laboratory of Information Photonics and Optical Communications, Beijing University of Posts and Telecommunications, Beijing 100876, China. Tel./fax: +86 10 62282242. E-mail address: [email protected] (M. Lei). 0167-577X/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2012.03.071
3. Results and discussion Fig. 1 shows the XRD patterns of the products obtained by the PSSSassisted hydrothermal method. The diffraction peaks in Fig. 1a can be indexed as pure tetragonal α-MnO2 of (310), (121), (301), (411), (521), (002) and (451), respectively, agreeing well with the standard card (ICDD-PDF No: 72-1982). The products are composed of well dispersed nanorods with average diameter of 15 nm, as revealed by Fig. 2a. TEM image of an individual nanorod (inset of Fig. 2b) indicates smooth surface and uniform diameter along the direction. The corresponding EDS spectrum (Fig. 2b) reveals the nanorod is mainly consist of Mn and O elements, and the atomic ratio of Mn and O is ca. 1:1.912,
K. Huang et al. / Materials Letters 78 (2012) 202–204
Fig. 1. XRD pattern of the products obtained by PSSS-assisted hydrothermal method.
close to chemical formation of MnO2, further confirming MnO2 formation of the product. The HRTEM image (Fig. 2c) shows that interplanar spacing of the lattice planes is ca. 0.692 nm, agreeing well with that of (110) lattice planes of the tetragonal α-MnO2. It can be seen from Fig. 2d that thin amorphous layer with thickness of 4 nm cover over the whole nanorod, and no obvious bulk defects in the nanorod. We further investigate the structure and morphology of the MnO2 products in the absence of PSSS. Though the structure of the as-prepared is not changed, the morphology of the final MnO2 products is completely changed (Fig. 3a and b). The products exhibit irregular micro-sized shape. The enlarged TEM image shows that the irregular microparticles are composed of a large number of nanorices. These nanorices (Fig. 3b) exhibit sharp tip and the average diameter is ca. 12 nm. These nanorices are easily cumulated, which is different from the as-prepared dispersed nanorods. The corresponding HRTEM image (Fig. 3c) clearly reveals the poor crystalline nature of the nanorices. It can be concluded from the experimental results that PSSS plays an important role in the growth process of MnO2. PSSS is an electronegative polymer and is able to initiate nucleation of some inorganic compounds through binding of some alkaline earth metal ions including Mg2+, Ca2+, Sr 2+ Ba 2+, etc., and stabilizing the corresponding crystal growth. We deduce that PSSS may play a similar role for the
203
nucleation and growth of MnO2. In the electronegative environment, PSSS first binds Mn2+ to form intermediate chelate complex. Then, the chelate complex and KMnO4 are reduced and oxidized into 1D MnO2 by the hydrogen ions, respectively. The PSSS finally covers with the as-prepared MnO2 to prevent from aggregating in the 1D MnO2. Fig. 4a and b show the discharge capacity versus cycle number of dispersed and aggregated MnO2 nanorods-based electrodes, respectively. The first discharge capacity of dispersed MnO2 nanorods reaches 211 mA h g− 1, while the aggregated MnO2 nanorices exhibit a lower capacity of 172 mA h g − 1. The first discharge capacity of dispersed MnO2 nanorods is higher than 180 mA h g− 1 of commercial α-MnO2 powders, although they show a similar discharge curve to that of the commercial powders. Both the dispersed nanorods and aggregated nanorices exhibit a steady and continuous capacity drop during repeated charge–discharge process. After 40 cycles, a relatively large discharge capacity of 139 and 112 mA h g− 1, respectively, are still retained. The discharge capacity gradually decreases owing to the isolated metallic nanocrystallite (Mn) aggregation during cycling. The improved electrode properties of the dispersed α-MnO2 nanorods may be the results of the 1D morphology and excellent dispersity. The 1D property minimizes the distance over which protons or Li+ diffuses, and accelerates diffusion kinetics and decrease electrode polarization during the electrode process [23]. Moreover, compared with the aggregated nanorices, the dispersed MnO2 nanorods possess high surface areas that provide more active sites for the contact between electrode materials and electrolyte [24]. So, the discharge capacity of dispersed nanorods is higher than that of aggregated nanorices. 4. Conclusions Tetragonal α-MnO2 nanorods were fabricated by a facile PSSSassisted hydrothermal method. The nanorods are well crystalline and are of excellent dispersity. A novel α-MnO2 nanorices were obtained without polymer PSSS. These poor crystalline nanorices are of sharp tip and are easily cumulated. Electronegative PSSS plays an important role in the formation of MnO2 nanorods. PSSS can first bind Mn2+ ions to form chelate complex. Then, both the chelate complex and KMnO4 are reduced and oxidized into 1D MnO2 nanorods by the
Fig. 2. (a) TEM image, (b) EDS spectrum, (c) HRTEM and (d) enlarged HRTEM images of the MnO2 nanorods obtained by PSSS-assisted hydrothermal method.
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K. Huang et al. / Materials Letters 78 (2012) 202–204
Fig. 4. Discharge capacities of (a) dispersed MnO2 nanorods and (b) aggregated MnO2 nanorods over the 40 cycles.
hydrogen ions. The PSSS finally covers with the as-prepared MnO2 to prevent from aggregating in the MnO2 nanorods. The first discharge capacity of dispersed MnO2 nanorods reaches 211 mA h g− 1, while the aggregated MnO2 nanorods exhibit a lower capacity of 172 mA h g− 1. After 40 cycles, a relatively large discharge capacity of 139 and 112 mA h g− 1, respectively, are still retained. The improved electrode properties of the dispersed α-MnO2 nanorods are the results of the 1D morphology and excellent dispersity. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24]
Fig. 3. (a) TEM, (b) enlarged TEM and (c) HRTEM images of the MnO2 nanorices without PSSS.
Hochbaum AI, Yang PD. Chem Rev 2010;110:527–46. Wang XD, Song JH, Liu J, Wang ZL. Science 2007;316:102–5. Chen KJ, Hung FY, Chang SJ, Young SJ. J Alloys Compd 2009;479:674–7. Lei M, Hu QR, Wang SL, Tang WH. Mater Lett 2010;64:19–21. Teng X, Han W, Ku W, Hücker M. Angew Chem Int Ed 2008;47:2055–8. Carlson J, Maccagnano SE, Zheng M, Silcox J, Krauss TD. Nano Lett 2007;7:3698–703. Li SZ, Ding XD, Li J, Ren XB, Sun J, Ma E. Nano Lett 2010;10:1774–9. Lei M, Hu QR, Wang X, Wang SL, Tang WH. J Alloys Compd 2010;489:663–6. Dong YJ, Tian BZ, Kempa TJ, Lieber CM. Nano Lett 2009;9:2183–7. Winter M, Brodd R. Chem Rev 2004;104:4245–69. Wang YM, Liu HF, Bao M, Li BJ, Su HH, Wen YX, et al. J Alloys Compd 2011;509: 8306–12. Reddy AL, Shaijumon MM, Gowda SR, Ajayan PM. Nano Lett 2009;9:1002–6. Hao Q, Xu LQ, Li GD, Ju ZC, Sun CH, Ma HY, et al. J Alloys Compd 2011;509:6217–21. Cheng F, Tao Z, Liang J, Chen J. Chem Mater 2008;20:667–81. Cui HJ, Huang HZ, Fu ML, Yuan BL, Pearl W. Catal Commun 2011;12:1339–43. Wang HE, Lu Z, Qian D, Fang S, Zhang J. J Alloys Compd 2008;466:250–7. Kuratani K, Tatsumi K, Kuriyama N. Cryst Growth Des 2007;7:1375–7. Cheng FY, Zhao JZ, Song WN, Li CS, Ma H, Chen J, et al. Inorg Chem 2006;45:2038–44. Abdelazez K, Ahmed M, Peng H, Wu KB, Huang KX. Chem Eng J 2011;172:531–9. Li F, Wu JF, Qin QH, Li Z, Huang XT. J Alloys Compd 2010;492:339–46. Lei M, Tang WH, Cao LZ, Li PG, Yu JG. J Cryst Growth 2006;294:358–66. Lei M, Tang WH, Yu JG. Mater Res Bull 2005;40:656–64. Nishizawa M, Mukai K, Kuwabata S, Martin CR, Yoneyama H. J Electrochem Soc 1997;144:1923–7. Sugantha M, Ramakrishnan PA, Hermann AM, Warmsingh CP, Ginley DS. Int J Hydrogen Energy 2003;28:597–600.
Contents lists available at SciVerse ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Low-temperature route to dispersed manganese dioxide nanorods K. Huang a, b, M. Lei a, b,⁎, R. Zhang a, b, H.J. Yang b, Y.G. Yang b a b
State Key Laboratory of Information Photonics and Optical Communications, Beijing University of Posts and Telecommunications, Beijing 100876, China School of Science, Beijing University of Posts and Telecommunications, Beijing 100876, China
a r t i c l e
i n f o
Article history: Received 14 February 2012 Accepted 16 March 2012 Available online 23 March 2012 Keywords: Nanocrystalline materials Microstructure Electrical properties
a b s t r a c t A facile hydrothermal route was developed to fabricate a large amount of dispersed MnO2 nanorods in the presence of poly (sodium 4-styrene-sulfonate). The XRD pattern indicates that these well crystalline nanorods are tetragonal α-MnO2 and have smooth surface. It is deduced that electronegative poly (sodium 4-styrenesulfonate) can prevent aggregation of α-MnO2 nanorods. The curves of discharge capacity vs cycle number indicate that the discharge capacities of dispersed nanorods are much larger than those of the aggregated nanorices and commercial powders. It is suggested that both the one-dimensional morphology and excellent dispersity are the main reasons for the higher discharge capacity of the dispersed nanorods. © 2012 Elsevier B.V. All rights reserved.
1. Introduction
2. Experimental
One-dimensional (1D) metal oxide nanostructures have attracted numerous attentions due to their excellent physical and chemical properties and potential application in electronics, optoelectronics, solar energy storage and transmission, catalysis, detectors, sensors etc. [1–9]. As one of the most important metal oxides, 1D manganese dioxide (MnO2) had been demonstrated to be of enhanced catalytic and electrochemical properties compared with their bulk counterparts [10–14]. Several additives-free methods including refluxing route [15], wet chemical method [16], thermal decomposition [17] and hydrothermal synthesis [18–20] had been developed to fabricate various 1D nanostructures. Nevertheless, the as-prepared 1D nanostructures are difficult to be dispersed, which limits their catalytic and electrochemical applications due to their relative low surface areas. Recently, some organic additives and/or templates were found to successfully control the nucleation, growth and alignment of inorganic materials. The mechanism may be extended to synthesize metal oxide nanostructures. In this work, a mediate hydrothermal method was developed to fabricate well crystalline and dispersed MnO2 nanorods. An electronegative polymer poly (sodium 4-styrene-sulfonate) (PSSS) [21–22] was added to modulate the growth process of MnO2 nanorods. The microstructure, probable reaction mechanism and discharge capacity cycle properties of the MnO2 nanorods are investigated.
In the experiment, 0.005 mol MnSO4, 0.002 mol KMnO4, 0.1 g (PSSS) and 150 ml mixed solution of distilled water and ethanol (the volume ratio of water and ethanol is 4:1) were added into Teflon-lined stainless steel autoclaves and stirred for an hour. Then, 30 ml H2SO4 (1 M) were slowly added into the mixed solution under vigorous stirring. Finally, autoclaves were sealed and further put into a furnace with temperature of 110 °C for 24 h. The obtained black precipitates were washed with distilled water for several times and dried in air for further characterization. Powder X-ray diffraction (XRD) data of the nanowires were collected on a MAC-M18XHF diffractometer. Morphology and microstructure of the products were characterized by field-emission scanning electron microscopy (FE-SEM; Hitachi S-5200) and transmission electron microscopy (TEM; Philips CM200) equipped with energy-dispersive X-ray spectroscopy (EDS), respectively. The electrochemical properties of the MnO2 nanorods as cathodes used in rechargeable lithium-ion batteries were measured at room temperature. The fabrication of the laboratory cells and electrodes are conducted according to the reported works [18].
⁎ Corresponding author at: State Key Laboratory of Information Photonics and Optical Communications, Beijing University of Posts and Telecommunications, Beijing 100876, China. Tel./fax: +86 10 62282242. E-mail address: [email protected] (M. Lei). 0167-577X/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2012.03.071
3. Results and discussion Fig. 1 shows the XRD patterns of the products obtained by the PSSSassisted hydrothermal method. The diffraction peaks in Fig. 1a can be indexed as pure tetragonal α-MnO2 of (310), (121), (301), (411), (521), (002) and (451), respectively, agreeing well with the standard card (ICDD-PDF No: 72-1982). The products are composed of well dispersed nanorods with average diameter of 15 nm, as revealed by Fig. 2a. TEM image of an individual nanorod (inset of Fig. 2b) indicates smooth surface and uniform diameter along the direction. The corresponding EDS spectrum (Fig. 2b) reveals the nanorod is mainly consist of Mn and O elements, and the atomic ratio of Mn and O is ca. 1:1.912,
K. Huang et al. / Materials Letters 78 (2012) 202–204
Fig. 1. XRD pattern of the products obtained by PSSS-assisted hydrothermal method.
close to chemical formation of MnO2, further confirming MnO2 formation of the product. The HRTEM image (Fig. 2c) shows that interplanar spacing of the lattice planes is ca. 0.692 nm, agreeing well with that of (110) lattice planes of the tetragonal α-MnO2. It can be seen from Fig. 2d that thin amorphous layer with thickness of 4 nm cover over the whole nanorod, and no obvious bulk defects in the nanorod. We further investigate the structure and morphology of the MnO2 products in the absence of PSSS. Though the structure of the as-prepared is not changed, the morphology of the final MnO2 products is completely changed (Fig. 3a and b). The products exhibit irregular micro-sized shape. The enlarged TEM image shows that the irregular microparticles are composed of a large number of nanorices. These nanorices (Fig. 3b) exhibit sharp tip and the average diameter is ca. 12 nm. These nanorices are easily cumulated, which is different from the as-prepared dispersed nanorods. The corresponding HRTEM image (Fig. 3c) clearly reveals the poor crystalline nature of the nanorices. It can be concluded from the experimental results that PSSS plays an important role in the growth process of MnO2. PSSS is an electronegative polymer and is able to initiate nucleation of some inorganic compounds through binding of some alkaline earth metal ions including Mg2+, Ca2+, Sr 2+ Ba 2+, etc., and stabilizing the corresponding crystal growth. We deduce that PSSS may play a similar role for the
203
nucleation and growth of MnO2. In the electronegative environment, PSSS first binds Mn2+ to form intermediate chelate complex. Then, the chelate complex and KMnO4 are reduced and oxidized into 1D MnO2 by the hydrogen ions, respectively. The PSSS finally covers with the as-prepared MnO2 to prevent from aggregating in the 1D MnO2. Fig. 4a and b show the discharge capacity versus cycle number of dispersed and aggregated MnO2 nanorods-based electrodes, respectively. The first discharge capacity of dispersed MnO2 nanorods reaches 211 mA h g− 1, while the aggregated MnO2 nanorices exhibit a lower capacity of 172 mA h g − 1. The first discharge capacity of dispersed MnO2 nanorods is higher than 180 mA h g− 1 of commercial α-MnO2 powders, although they show a similar discharge curve to that of the commercial powders. Both the dispersed nanorods and aggregated nanorices exhibit a steady and continuous capacity drop during repeated charge–discharge process. After 40 cycles, a relatively large discharge capacity of 139 and 112 mA h g− 1, respectively, are still retained. The discharge capacity gradually decreases owing to the isolated metallic nanocrystallite (Mn) aggregation during cycling. The improved electrode properties of the dispersed α-MnO2 nanorods may be the results of the 1D morphology and excellent dispersity. The 1D property minimizes the distance over which protons or Li+ diffuses, and accelerates diffusion kinetics and decrease electrode polarization during the electrode process [23]. Moreover, compared with the aggregated nanorices, the dispersed MnO2 nanorods possess high surface areas that provide more active sites for the contact between electrode materials and electrolyte [24]. So, the discharge capacity of dispersed nanorods is higher than that of aggregated nanorices. 4. Conclusions Tetragonal α-MnO2 nanorods were fabricated by a facile PSSSassisted hydrothermal method. The nanorods are well crystalline and are of excellent dispersity. A novel α-MnO2 nanorices were obtained without polymer PSSS. These poor crystalline nanorices are of sharp tip and are easily cumulated. Electronegative PSSS plays an important role in the formation of MnO2 nanorods. PSSS can first bind Mn2+ ions to form chelate complex. Then, both the chelate complex and KMnO4 are reduced and oxidized into 1D MnO2 nanorods by the
Fig. 2. (a) TEM image, (b) EDS spectrum, (c) HRTEM and (d) enlarged HRTEM images of the MnO2 nanorods obtained by PSSS-assisted hydrothermal method.
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K. Huang et al. / Materials Letters 78 (2012) 202–204
Fig. 4. Discharge capacities of (a) dispersed MnO2 nanorods and (b) aggregated MnO2 nanorods over the 40 cycles.
hydrogen ions. The PSSS finally covers with the as-prepared MnO2 to prevent from aggregating in the MnO2 nanorods. The first discharge capacity of dispersed MnO2 nanorods reaches 211 mA h g− 1, while the aggregated MnO2 nanorods exhibit a lower capacity of 172 mA h g− 1. After 40 cycles, a relatively large discharge capacity of 139 and 112 mA h g− 1, respectively, are still retained. The improved electrode properties of the dispersed α-MnO2 nanorods are the results of the 1D morphology and excellent dispersity. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24]
Fig. 3. (a) TEM, (b) enlarged TEM and (c) HRTEM images of the MnO2 nanorices without PSSS.
Hochbaum AI, Yang PD. Chem Rev 2010;110:527–46. Wang XD, Song JH, Liu J, Wang ZL. Science 2007;316:102–5. Chen KJ, Hung FY, Chang SJ, Young SJ. J Alloys Compd 2009;479:674–7. Lei M, Hu QR, Wang SL, Tang WH. Mater Lett 2010;64:19–21. Teng X, Han W, Ku W, Hücker M. Angew Chem Int Ed 2008;47:2055–8. Carlson J, Maccagnano SE, Zheng M, Silcox J, Krauss TD. Nano Lett 2007;7:3698–703. Li SZ, Ding XD, Li J, Ren XB, Sun J, Ma E. Nano Lett 2010;10:1774–9. Lei M, Hu QR, Wang X, Wang SL, Tang WH. J Alloys Compd 2010;489:663–6. Dong YJ, Tian BZ, Kempa TJ, Lieber CM. Nano Lett 2009;9:2183–7. Winter M, Brodd R. Chem Rev 2004;104:4245–69. Wang YM, Liu HF, Bao M, Li BJ, Su HH, Wen YX, et al. J Alloys Compd 2011;509: 8306–12. Reddy AL, Shaijumon MM, Gowda SR, Ajayan PM. Nano Lett 2009;9:1002–6. Hao Q, Xu LQ, Li GD, Ju ZC, Sun CH, Ma HY, et al. J Alloys Compd 2011;509:6217–21. Cheng F, Tao Z, Liang J, Chen J. Chem Mater 2008;20:667–81. Cui HJ, Huang HZ, Fu ML, Yuan BL, Pearl W. Catal Commun 2011;12:1339–43. Wang HE, Lu Z, Qian D, Fang S, Zhang J. J Alloys Compd 2008;466:250–7. Kuratani K, Tatsumi K, Kuriyama N. Cryst Growth Des 2007;7:1375–7. Cheng FY, Zhao JZ, Song WN, Li CS, Ma H, Chen J, et al. Inorg Chem 2006;45:2038–44. Abdelazez K, Ahmed M, Peng H, Wu KB, Huang KX. Chem Eng J 2011;172:531–9. Li F, Wu JF, Qin QH, Li Z, Huang XT. J Alloys Compd 2010;492:339–46. Lei M, Tang WH, Cao LZ, Li PG, Yu JG. J Cryst Growth 2006;294:358–66. Lei M, Tang WH, Yu JG. Mater Res Bull 2005;40:656–64. Nishizawa M, Mukai K, Kuwabata S, Martin CR, Yoneyama H. J Electrochem Soc 1997;144:1923–7. Sugantha M, Ramakrishnan PA, Hermann AM, Warmsingh CP, Ginley DS. Int J Hydrogen Energy 2003;28:597–600.