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Electrodeposited Ni–S intermetallic compound film electrodes for hydrogen evolution reaction in alkaline solutions
Materials Letters 64 (2010) 261–263
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 ev i e r. c o m / l o c a t e / m a t l e t
Electrodeposited Ni–S intermetallic compound film electrodes for hydrogen evolution reaction in alkaline solutions Yinliang Cao a,b, Jingjun Liu a,b, Feng Wang a,b,⁎, Jing Ji a,b, Jianjun Wang c, Shiyong Qin c, Lianghu Zhang c a b c
State Key Laboratory of Chemical Resource Engineering, Beijing University of Chemical Technology, Beijing 100029, PR China Institute of Carbon Fibers and Composites, Beijing University of Chemical Technology, Beijing 100029, PR China Blue Star (Beijing) Chemical Machinery Co., Ltd., Beijing 100176, PR China
a r t i c l e
i n f o
Article history: Received 15 September 2009 Accepted 26 October 2009 Available online 10 November 2009 Keywords: Electrodeposition Nickel–sulfur Intermetallic compound Electro-catalytic activity Hydrogen evolution reaction
a b s t r a c t Tailoring of nickel–sulfur (Ni–S) intermetallic compound film electrodes for hydrogen evolution reaction in alkaline solutions was attempted by electrodeposition from a typical Watts bath containing sodium thiosulfate as sulfur source and sulfosalicylic acid as additive. The XRD analysis shows that the as-deposited Ni–S film electrode with fine morphological features comprised of intermetallic compound phase structure and amorphous phase structure. The intermetallic compound film electrodes generate a higher catalytic activity for the hydrogen evolution reaction in alkaline solution in comparison with Ni–S film electrodes comprised of amorphous phase structures, even with commercial Ni mesh or Ni/RuO2 composite electrode. © 2009 Elsevier B.V. All rights reserved.
1. Introduction One motivation to prepare novel film electrodes with low overpotential for the hydrogen evolution reaction (HER) in alkaline solutions is to meet the demand of energy saving for the electrolytic production of hydrogen in chlor-alkali industry, because the cost of power from those cathode materials with high cathode overpotential is one of the major obstacles to produce sodium hydroxide at low cost, considering the constant growth of power source price worldwide [1]. In the past few years, as reported in the literatures, there has been a great deal of effort to develop new materials with high electrocatalytic activity towards HER in alkaline solutions [2–6]. Nickel and nickel-based alloy electrodes are well known to be promising electrode materials because of their low cost and high electro-catalytic activity towards HER in aqueous solution. Among these, nickel–sulfur (Ni–S) binary alloy electrodes exhibit different electro-catalytic activity towards HER in alkaline solutions with different phase structures (typical phases: super-saturated solid solution, amorphous and intermetallic compound) in dependence on the sulfur content in alloys [7]. Recent attempts [8,9] to grow Ni–S thin films have demonstrated that this material is an ideal candidate for large area thin film electrodes for HER. As for now, however, the wider application of Ni–S alloy films in the chlor-alkali industry is still blocked by their weak mechanical properties and weak adhesion on the substrates probably due to the brittle microstructures and the ⁎ Corresponding author. Institute of Carbon Fibers and Composites, Beijing University of Chemical Technology, Beijing 100029, PR China. Tel./fax: +86 10 6441 1301. E-mail address: [email protected] (F. Wang). 0167-577X/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2009.10.056
micro-cracks occurring throughout the surfaces of films [9]. In general, one way to get rid of these difficulties is by adding certain additive to the plating baths so as to promote the morphological features of as-deposited Ni–S film electrodes. It is well known that the use of additives is essential to produce films that have good characteristics like adhesion, aspect, low stress or to shift the reduction potential of the metallic ion to less negative values. In this study, we used sulfosalicylic acid as additive to modify the typical Watts baths containing sodium thiosulfate as sulfur source. Based on the modified plating baths, we have succeeded in preparation of the Ni–S intermetallic compound film electrodes with fine morphological performances by an electrodeposition process. The electro-catalytic activities towards HER in alkaline solution of Ni–S thin film electrodes with different phase structures were characterized by measuring the overpotential of hydrogen evolution reaction (HER) in the 1.0 mol/L NaOH aqueous solution determined by the cathodic polarization measurements. 2. Experimental procedure The Ni–S film electrodes were fabricated by an electrodeposition process in the modified Watts bath system consisted of six nickel sulfate hydrate (1.0 mol/L), hexahydrated nickel chloride (0.2 mol/L), boric acid (0.5 mol/L), sodium thiosulfate (0.6 mol/L) as sulfur source and sulfosalicylic acid as additive. The used electrolyzer was a beaker of 500 cm3 with a magnetic stirrer agitation system. The Ni–S film was electrodeposited on copper foil which was electrochemically polished to a mirror finished surface. The anode was a commercial platinum electrode.
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Y. Cao et al. / Materials Letters 64 (2010) 261–263
The chemical composition and surface morphologies of the fabricated Ni–S film electrodes were determined by the energy dispersive X-ray spectrometry (EDS) (ESCALAB250) and scanning electron microscope (SEM) (S-4700, Hitachi). The crystalline structures of the film electrodes were determined by X-ray diffraction (XRD) (Dmax2 III, Rigaku). Investigations of electrolytic hydrogen evolution on the prepared Ni–S film electrodes were conducted in a three-electrode cell with a saturated calomel electrode (SCE) as the reference electrode, and a platinum sheet as the counter electrode. These measurements were carried out in 1.0 mol/L NaOH aqueous solution using EG&G Potentiostat/Galvanostat consisting of a M273 PARC Potentiostat. Electrochemical measurements were recorded after approximately 30 min of galvanostatic polarization at a constant current density, j = 100 mA/cm2, at room temperature (25 °C). The overpotential of Ni–S film electrodes for hydrogen evolution in the tested electrolyte can be calculated as following equation: η = Ф−E
ð1Þ
where, η is the overpotential of hydrogen evolution reaction; Ф is the reversible electrode potential for hydrogen evolution reaction vs. the reference electrode; E is the measured potential for hydrogen evolution under the testing condition. The reversible electrode potential for hydrogen compared with the reference electrode is calculated by the following equation available in the literature [10]. Φ = −925:82 + 0:278 ðT−298Þ
ð2Þ
3. Results and discussion 3.1. Fabrication of Ni–S alloy film electrodes Fig. 1 shows the current density-dependence of S content in the Ni–S films. The increase in current densities caused the rapid reduction of sulfur content in the alloy composition, even though at a constant sodium thiosulfate concentration. This suggests that the composition of Ni–S thin films can be controlled by adjusting the cathodic current density, showing a controllable electrochemical feature. The surface morphologies of Ni–S film electrodes electrochemically deposited from the baths with or without sulfosalicylic acid as additive observed by SEM are presented in Fig. 2. As can be observed from Fig. 2a, many micro-cracks occur throughout the surfaces of films deposited from the bath without sulfosalicylic acid as additive. Compared above, however, the micro-cracks existed on the surface
Fig. 1. Influence of cathodic current density on the S content in the Ni–S thin films.
Fig. 2. SEM images of Ni–S alloy deposited from modified Watts bath with and without the additive at 25 °C, (a) without the additive, (b) with the additive.
almost disappear, and some dendrite-like nano-grains clearly appear on the surfaces of films deposited from the bath with sulfosalicylic acid as additive (Fig. 2b). It is evidence that the addition of sulfosalicylic acid in plating bath could endow film electrodes better surface performance during the electrodeposition process for the film electrodes. In this case, sulfosalicylic acid used as additive lowers the surface tension, and apparently helps to reduce the micro-cracks throughout the surface, thus improving the mechanical properties of the as-deposited Ni–S films [11,12].
Fig. 3. XRD patterns of Ni–S alloy films: (a) 20.1 at.%; (b) 29.6 at.%; (c) 37.5 at.%.
Y. Cao et al. / Materials Letters 64 (2010) 261–263
Fig. 4. Electrochemical cathodic polarization curves at the scan rate of 2 mV/s in 1.0 mol/L NaOH solution: (a) Ni mesh; (b) Ni–S amorphous film electrode (c) Ni/RuO2; (d) Ni–S intermetallic compound film electrode.
263
determined by the cathodic polarization measurements. Fig. 4 shows cathodic polarization curves of the Ni–S intermetallic compound film electrode, Ni–S amorphous film electrode and commercial Ni mesh or Ni/RuO2 electrodes in practical use. It is found from Fig. 4 that the measured overpotential of hydrogen evolution for the Ni–S intermetallic compound electrodes is lower than those of Ni–S amorphous film electrode and the commercial nickel mesh and Ni/RuO2 electrodes in practical use. The overpotential of hydrogen evolution for the Ni–S intermetallic compound electrode is only 130 mV, showing the very high electro-catalytic activity toward HER. Those findings confirmed the fact that the phase structure characteristics of Ni–S electrodes are closely relative to the electro-catalytic activity toward hydrogen evolution in alkaline solutions. These results suggest that the Ni–S intermetallic compound film electrode exhibits high electro-catalytic activity towards HER and would be a promising electrode material for the chlor-alkali industry. The high electro-catalytic of the Ni–S intermetallic compound film electrode towards HER on alkaline solution may be directly related to the strong adsorption of hydrogen on the surface of Ni3S2 intermetallic compound phase [13].
3.2. X-ray diffraction characterizations
4. Conclusion
The phase structures of the Ni–S film electrodes were characterized by means of wide-angle X-ray diffraction analysis. Fig. 3 illustrates the typical X-ray diffraction patterns for the film electrodes with different sulfur content. As the sulfur content in the deposited film is 20.1 at.%, a broad diffraction peak recorded at 44° (Fig. 3a), representing the typical structure of the amorphous phase. This indicates that the as-deposited Ni–S film electrode is an amorphous phase structure in this case. However, as the sulfur content increase to 29.6 at.%, the broad peak disappears, meanwhile, some sharp diffraction peaks appear, almost similar to those of Ni3S2 (JCPDS: 44-1418) (Fig. 3b). After sulfur content up to 37.5 at.%, these diffraction peaks become sharper (Fig. 3c), owing to the higher quantity of Ni3S2 in the matrix. In this case, the Ni–S thin film has almost changed into Ni3S2 intermetallic compound since S content is almost similar to the proportion of Ni to S for forming Ni3S2 = 40 at.%. It is obvious that the crystallographic structures of Ni–S thin films strongly depend on the sulfur content in alloy films, and we can easily tailor the Ni–S intermetallic compound electrodes by increasing applied cathodic current density during electrodeposition process.
A novel Ni–S intermetallic compound film electrode has been successfully prepared by an electrodeposition process from a typical Watts bath containing sodium thiosulfate as sulfur source and sulfosalicylic acid as additive. Results indicate that the measured overpotential of hydrogen evolution reaction for the Ni–S intermetallic compound film electrode is only 130 mV, which is lower than those of the Ni–S amorphous film electrode and the commercial Ni mesh or nickel/RuO2 electrodes, showing higher HER electro-catalytic activity. The combination of high electro-catalytic activity towards HER and fine morphological performance provides a considerable applied value of the Ni–S intermetallic compound film electrode to the chlor-alkali industry.
3.3. Electro-catalytic activity toward HER The electro-catalytic activity of the as-deposited Ni–S film electrodes was characterized by measuring the overpotential of hydrogen evolution reaction (HER) in the 1.0 mol/L NaOH aqueous solution
References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13]
Fundo AM, Abrantes LM. J Electroananl Chem 2007;600:63. Jeong YU, Manthiram A. Inorg Chem 2001;40:73. Correia Adriana N, Sergio AS, Luis AA. Electrochem Commun 1999;1:600. Sulitanu Nicolae. J Magn Magn Mater 2000;214:176. Paseka Ivo. Electrochim Acta 2001;47:921. Popczyka M, Budnioka A, Lasiab A. Int J Hydrogen Energy 2005;30:265. Zhu X, Wen Z, Gu Z, Huang S. J Electrochem Soc 2006;153:A504. Han Q, Liu K, Chen J, Wei X. Int J Hydrogen Energy 2003;28:1207. Sabela R, Paseka I. J Appl Electrochem 1990;20:500. Zhang X, Zhao L, Zhang J, Ji C. Chem Henan 2004;8:13. Donten M, Cesiulis H, Stojek Z. Electrochim Acta 2005;50:1405. He HW, Liu HJ, Zhou KC. J Nonferrous Metals 2005;15:1780. Vandenborre H, Vermeiren PH, Leysen R. Elecrtrochim Acta 1984;29:297.
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 ev i e r. c o m / l o c a t e / m a t l e t
Electrodeposited Ni–S intermetallic compound film electrodes for hydrogen evolution reaction in alkaline solutions Yinliang Cao a,b, Jingjun Liu a,b, Feng Wang a,b,⁎, Jing Ji a,b, Jianjun Wang c, Shiyong Qin c, Lianghu Zhang c a b c
State Key Laboratory of Chemical Resource Engineering, Beijing University of Chemical Technology, Beijing 100029, PR China Institute of Carbon Fibers and Composites, Beijing University of Chemical Technology, Beijing 100029, PR China Blue Star (Beijing) Chemical Machinery Co., Ltd., Beijing 100176, PR China
a r t i c l e
i n f o
Article history: Received 15 September 2009 Accepted 26 October 2009 Available online 10 November 2009 Keywords: Electrodeposition Nickel–sulfur Intermetallic compound Electro-catalytic activity Hydrogen evolution reaction
a b s t r a c t Tailoring of nickel–sulfur (Ni–S) intermetallic compound film electrodes for hydrogen evolution reaction in alkaline solutions was attempted by electrodeposition from a typical Watts bath containing sodium thiosulfate as sulfur source and sulfosalicylic acid as additive. The XRD analysis shows that the as-deposited Ni–S film electrode with fine morphological features comprised of intermetallic compound phase structure and amorphous phase structure. The intermetallic compound film electrodes generate a higher catalytic activity for the hydrogen evolution reaction in alkaline solution in comparison with Ni–S film electrodes comprised of amorphous phase structures, even with commercial Ni mesh or Ni/RuO2 composite electrode. © 2009 Elsevier B.V. All rights reserved.
1. Introduction One motivation to prepare novel film electrodes with low overpotential for the hydrogen evolution reaction (HER) in alkaline solutions is to meet the demand of energy saving for the electrolytic production of hydrogen in chlor-alkali industry, because the cost of power from those cathode materials with high cathode overpotential is one of the major obstacles to produce sodium hydroxide at low cost, considering the constant growth of power source price worldwide [1]. In the past few years, as reported in the literatures, there has been a great deal of effort to develop new materials with high electrocatalytic activity towards HER in alkaline solutions [2–6]. Nickel and nickel-based alloy electrodes are well known to be promising electrode materials because of their low cost and high electro-catalytic activity towards HER in aqueous solution. Among these, nickel–sulfur (Ni–S) binary alloy electrodes exhibit different electro-catalytic activity towards HER in alkaline solutions with different phase structures (typical phases: super-saturated solid solution, amorphous and intermetallic compound) in dependence on the sulfur content in alloys [7]. Recent attempts [8,9] to grow Ni–S thin films have demonstrated that this material is an ideal candidate for large area thin film electrodes for HER. As for now, however, the wider application of Ni–S alloy films in the chlor-alkali industry is still blocked by their weak mechanical properties and weak adhesion on the substrates probably due to the brittle microstructures and the ⁎ Corresponding author. Institute of Carbon Fibers and Composites, Beijing University of Chemical Technology, Beijing 100029, PR China. Tel./fax: +86 10 6441 1301. E-mail address: [email protected] (F. Wang). 0167-577X/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2009.10.056
micro-cracks occurring throughout the surfaces of films [9]. In general, one way to get rid of these difficulties is by adding certain additive to the plating baths so as to promote the morphological features of as-deposited Ni–S film electrodes. It is well known that the use of additives is essential to produce films that have good characteristics like adhesion, aspect, low stress or to shift the reduction potential of the metallic ion to less negative values. In this study, we used sulfosalicylic acid as additive to modify the typical Watts baths containing sodium thiosulfate as sulfur source. Based on the modified plating baths, we have succeeded in preparation of the Ni–S intermetallic compound film electrodes with fine morphological performances by an electrodeposition process. The electro-catalytic activities towards HER in alkaline solution of Ni–S thin film electrodes with different phase structures were characterized by measuring the overpotential of hydrogen evolution reaction (HER) in the 1.0 mol/L NaOH aqueous solution determined by the cathodic polarization measurements. 2. Experimental procedure The Ni–S film electrodes were fabricated by an electrodeposition process in the modified Watts bath system consisted of six nickel sulfate hydrate (1.0 mol/L), hexahydrated nickel chloride (0.2 mol/L), boric acid (0.5 mol/L), sodium thiosulfate (0.6 mol/L) as sulfur source and sulfosalicylic acid as additive. The used electrolyzer was a beaker of 500 cm3 with a magnetic stirrer agitation system. The Ni–S film was electrodeposited on copper foil which was electrochemically polished to a mirror finished surface. The anode was a commercial platinum electrode.
262
Y. Cao et al. / Materials Letters 64 (2010) 261–263
The chemical composition and surface morphologies of the fabricated Ni–S film electrodes were determined by the energy dispersive X-ray spectrometry (EDS) (ESCALAB250) and scanning electron microscope (SEM) (S-4700, Hitachi). The crystalline structures of the film electrodes were determined by X-ray diffraction (XRD) (Dmax2 III, Rigaku). Investigations of electrolytic hydrogen evolution on the prepared Ni–S film electrodes were conducted in a three-electrode cell with a saturated calomel electrode (SCE) as the reference electrode, and a platinum sheet as the counter electrode. These measurements were carried out in 1.0 mol/L NaOH aqueous solution using EG&G Potentiostat/Galvanostat consisting of a M273 PARC Potentiostat. Electrochemical measurements were recorded after approximately 30 min of galvanostatic polarization at a constant current density, j = 100 mA/cm2, at room temperature (25 °C). The overpotential of Ni–S film electrodes for hydrogen evolution in the tested electrolyte can be calculated as following equation: η = Ф−E
ð1Þ
where, η is the overpotential of hydrogen evolution reaction; Ф is the reversible electrode potential for hydrogen evolution reaction vs. the reference electrode; E is the measured potential for hydrogen evolution under the testing condition. The reversible electrode potential for hydrogen compared with the reference electrode is calculated by the following equation available in the literature [10]. Φ = −925:82 + 0:278 ðT−298Þ
ð2Þ
3. Results and discussion 3.1. Fabrication of Ni–S alloy film electrodes Fig. 1 shows the current density-dependence of S content in the Ni–S films. The increase in current densities caused the rapid reduction of sulfur content in the alloy composition, even though at a constant sodium thiosulfate concentration. This suggests that the composition of Ni–S thin films can be controlled by adjusting the cathodic current density, showing a controllable electrochemical feature. The surface morphologies of Ni–S film electrodes electrochemically deposited from the baths with or without sulfosalicylic acid as additive observed by SEM are presented in Fig. 2. As can be observed from Fig. 2a, many micro-cracks occur throughout the surfaces of films deposited from the bath without sulfosalicylic acid as additive. Compared above, however, the micro-cracks existed on the surface
Fig. 1. Influence of cathodic current density on the S content in the Ni–S thin films.
Fig. 2. SEM images of Ni–S alloy deposited from modified Watts bath with and without the additive at 25 °C, (a) without the additive, (b) with the additive.
almost disappear, and some dendrite-like nano-grains clearly appear on the surfaces of films deposited from the bath with sulfosalicylic acid as additive (Fig. 2b). It is evidence that the addition of sulfosalicylic acid in plating bath could endow film electrodes better surface performance during the electrodeposition process for the film electrodes. In this case, sulfosalicylic acid used as additive lowers the surface tension, and apparently helps to reduce the micro-cracks throughout the surface, thus improving the mechanical properties of the as-deposited Ni–S films [11,12].
Fig. 3. XRD patterns of Ni–S alloy films: (a) 20.1 at.%; (b) 29.6 at.%; (c) 37.5 at.%.
Y. Cao et al. / Materials Letters 64 (2010) 261–263
Fig. 4. Electrochemical cathodic polarization curves at the scan rate of 2 mV/s in 1.0 mol/L NaOH solution: (a) Ni mesh; (b) Ni–S amorphous film electrode (c) Ni/RuO2; (d) Ni–S intermetallic compound film electrode.
263
determined by the cathodic polarization measurements. Fig. 4 shows cathodic polarization curves of the Ni–S intermetallic compound film electrode, Ni–S amorphous film electrode and commercial Ni mesh or Ni/RuO2 electrodes in practical use. It is found from Fig. 4 that the measured overpotential of hydrogen evolution for the Ni–S intermetallic compound electrodes is lower than those of Ni–S amorphous film electrode and the commercial nickel mesh and Ni/RuO2 electrodes in practical use. The overpotential of hydrogen evolution for the Ni–S intermetallic compound electrode is only 130 mV, showing the very high electro-catalytic activity toward HER. Those findings confirmed the fact that the phase structure characteristics of Ni–S electrodes are closely relative to the electro-catalytic activity toward hydrogen evolution in alkaline solutions. These results suggest that the Ni–S intermetallic compound film electrode exhibits high electro-catalytic activity towards HER and would be a promising electrode material for the chlor-alkali industry. The high electro-catalytic of the Ni–S intermetallic compound film electrode towards HER on alkaline solution may be directly related to the strong adsorption of hydrogen on the surface of Ni3S2 intermetallic compound phase [13].
3.2. X-ray diffraction characterizations
4. Conclusion
The phase structures of the Ni–S film electrodes were characterized by means of wide-angle X-ray diffraction analysis. Fig. 3 illustrates the typical X-ray diffraction patterns for the film electrodes with different sulfur content. As the sulfur content in the deposited film is 20.1 at.%, a broad diffraction peak recorded at 44° (Fig. 3a), representing the typical structure of the amorphous phase. This indicates that the as-deposited Ni–S film electrode is an amorphous phase structure in this case. However, as the sulfur content increase to 29.6 at.%, the broad peak disappears, meanwhile, some sharp diffraction peaks appear, almost similar to those of Ni3S2 (JCPDS: 44-1418) (Fig. 3b). After sulfur content up to 37.5 at.%, these diffraction peaks become sharper (Fig. 3c), owing to the higher quantity of Ni3S2 in the matrix. In this case, the Ni–S thin film has almost changed into Ni3S2 intermetallic compound since S content is almost similar to the proportion of Ni to S for forming Ni3S2 = 40 at.%. It is obvious that the crystallographic structures of Ni–S thin films strongly depend on the sulfur content in alloy films, and we can easily tailor the Ni–S intermetallic compound electrodes by increasing applied cathodic current density during electrodeposition process.
A novel Ni–S intermetallic compound film electrode has been successfully prepared by an electrodeposition process from a typical Watts bath containing sodium thiosulfate as sulfur source and sulfosalicylic acid as additive. Results indicate that the measured overpotential of hydrogen evolution reaction for the Ni–S intermetallic compound film electrode is only 130 mV, which is lower than those of the Ni–S amorphous film electrode and the commercial Ni mesh or nickel/RuO2 electrodes, showing higher HER electro-catalytic activity. The combination of high electro-catalytic activity towards HER and fine morphological performance provides a considerable applied value of the Ni–S intermetallic compound film electrode to the chlor-alkali industry.
3.3. Electro-catalytic activity toward HER The electro-catalytic activity of the as-deposited Ni–S film electrodes was characterized by measuring the overpotential of hydrogen evolution reaction (HER) in the 1.0 mol/L NaOH aqueous solution
References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13]
Fundo AM, Abrantes LM. J Electroananl Chem 2007;600:63. Jeong YU, Manthiram A. Inorg Chem 2001;40:73. Correia Adriana N, Sergio AS, Luis AA. Electrochem Commun 1999;1:600. Sulitanu Nicolae. J Magn Magn Mater 2000;214:176. Paseka Ivo. Electrochim Acta 2001;47:921. Popczyka M, Budnioka A, Lasiab A. Int J Hydrogen Energy 2005;30:265. Zhu X, Wen Z, Gu Z, Huang S. J Electrochem Soc 2006;153:A504. Han Q, Liu K, Chen J, Wei X. Int J Hydrogen Energy 2003;28:1207. Sabela R, Paseka I. J Appl Electrochem 1990;20:500. Zhang X, Zhao L, Zhang J, Ji C. Chem Henan 2004;8:13. Donten M, Cesiulis H, Stojek Z. Electrochim Acta 2005;50:1405. He HW, Liu HJ, Zhou KC. J Nonferrous Metals 2005;15:1780. Vandenborre H, Vermeiren PH, Leysen R. Elecrtrochim Acta 1984;29:297.