Kinetic and thermodynamic studies of hydrogen ...

Kinetic and thermodynamic studies of hydrogen storage alloys as negative electrode materials for Ni/MH batteries: a review M. Tliha, C. Khaldi, S. Boussami, N. Fenineche, O. El-Kedim, H. Mathlouthi & J. Lamloumi Journal of Solid State Electrochemistry Current Research and Development in Science and Technology ISSN 1432-8488 Volume 18 Number 3 J Solid State Electrochem (2014) 18:577-593 DOI 10.1007/s10008-013-2300-3

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Author's personal copy J Solid State Electrochem (2014) 18:577–593 DOI 10.1007/s10008-013-2300-3

REVIEW

Kinetic and thermodynamic studies of hydrogen storage alloys as negative electrode materials for Ni/MH batteries: a review M. Tliha & C. Khaldi & S. Boussami & N. Fenineche & O. El-Kedim & H. Mathlouthi & J. Lamloumi

Received: 7 February 2013 / Revised: 8 October 2013 / Accepted: 14 October 2013 / Published online: 19 November 2013 # Springer-Verlag Berlin Heidelberg 2013

Abstract This paper reviews the present performances of intermetallic compound families as materials for negative electrodes of rechargeable Ni/MH batteries. The performance of the metal-hydride electrode is determined by both the kinetics of the processes occurring at the metal/solution interface and the rate of hydrogen diffusion within the bulk of the alloy. Thermodynamic and electrochemical properties for each hydride compound family will be reported. The steps of hydrogen absorption/desorption such as charge-transfer and hydrogen diffusion for evaluating the electrochemical properties of hydrogen storage alloys are discussed. Exchange current density (I 0) and hydrogen diffusion coefficient (D H) are the two most important parameters for evaluating the electrochemical properties of metal hydride electrode. The values of the two parameters for a number of hydrogen storage alloys are compared. The relationship between alloy composition and electrochemical properties is noted and evaluated. M. Tliha (*) : C. Khaldi : S. Boussami : H. Mathlouthi : J. Lamloumi Laboratoire de Mécanique, Matériaux et Procédés, ESSTT, Université de Tunis, 5 Avenue Taha Hussein, 1008 Tunis, Tunisia e-mail: [email protected] M. Tliha Department of Physics, University College, Umm-Alqura University, Al-Qunfudah, Saudi Arabia N. Fenineche IRTES-LERMPS/FR FCLAB, UTBM, Site de Sévenans, 90010 Belfort Cedex, France O. El-Kedim FEMTO-ST, MN2S, UTBM, Site de Sévenans, 90010 Belfort Cedex, France

Keywords Intermetallic compounds . Thermodynamic properties . Electrochemical kinetics . Diffusion coefficient of hydrogen . Exchange current density

Introduction It is very important to develop electric vehicles for protecting environment, saving energy, and improving energy structure. With enhancement of consciousness of environment protection and increasing exhaustion of oil resources, countries and groups all over the world have drawn up development projects of electric vehicles (EV) and hybrid electric vehicles [1]. However, the final acceptance of electric vehicles will depend strongly on the electrochemical performances of the battery and on its acquisition price and maintenance costs [2]. The nickel–metal hydride (Ni/MH) is presently the most promising battery system for electric vehicles in the short and mid-term, which has many advantages, such as high energy density, high rate capacity, good overcharge and overdischarge capability, and containing no poisonous heavy metals and no electrolyte consumption during charge/discharge cycling [3–9]. The rechargeable nickel–metal hydride battery has a similar design to that of nickel–cadmium system (Ni/Cd). The principal difference is that the former uses hydrogen absorbed in a metal alloy for the active negative material in place of cadmium in the latter design. The active material of the positive electrode of the Ni/MH battery is nickel oxy-hydroxide (NiOOH), in the charged state. The negative active material in the charged state is hydrogen, in the form of a metal hydride. The high-energy density, excellent power density, and long cycle life of Ni/MH batteries also make them a leading technology as the battery power source for EVs, especially in bipolar designs.

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Therefore, the development of Ni/MH batteries is one of the most important areas of study on high-energy density batteries today. Metal hydrides are regarded as promising candidates for the negative materials of nickel/metal-hydride (Ni/MH) batteries due to their high-energy density, favorable charge and discharge ability, long charge–discharge cyclic life, and environmental compatibility [5, 6, 10–16]. The most important electrochemical characteristics of the hydrogen storage compounds used in these batteries include capacity, cycle life time, exchange current density, and equilibrium potential. The electrochemical behavior of such intermetallics depends on the types of intermetallics, microstructure, the nature and amount of each element in the intermetallic compound, and the electrochemical process (es) taking place. These electrochemical characteristics can be altered by designing the composition of the hydrogen storage alloy to provide optimum performance of the Ni-MH batteries. Different methods have been used to study the kinetics of metal hydrides [17–27]. Electrochemical impedance spectroscopy (EIS) has been a standard tool for investigation of electrochemical systems for quite some time. The major advantage of the method lies within the fact that the frequency of the signal can be varied over a large range, enabling resolution of phenomena with different time constants, such as diffusion and charge transfer. Usually the measurement is performed with a low-amplitude signal around an equilibrium state. This makes the method useful for evaluating the parameters, in a battery electrode, for different state of charge (SOC) whereas other measurement techniques usually give an average over a range of SOC. On Nyquist plots for AC impedance measurements, two semicircles were observed for all the MH electrodes under study, i.e., a small semicircle in the high-frequency region and a large semicircle in the lower frequency region. However, the interpretations of the AC impedance for MH electrodes have been controversial up to now. The assignment of the small arc in the high-frequency region is not very clear at the moment and is still a matter of controversy. Kuriyama et al. [28] ascribed the measured high-frequency arc to the contact resistance between the current collector and the alloy pellet. Other researchers [29, 30] also assigned the semicircle in the high of frequency region to the contact resistance between the current collector and the active material and/or particle-to particle resistance. Ticianelli et al. [31] assigned the observed arc in the high-frequency region to the contact resistance between the current collector and the active material. Züttel et al. [32] specified that this contact resistance depends on the chemical states of the contact surface and also on the thickness of the oxide layer. Yuan and Xu [33] reported that such a semicircle was also observed for hydrogen storage alloy ingots, making the assignment to contact resistance questionable. Khaldi et al. [34] attributed the high-frequency arc to the behavior of corrosion layer formed on the electrode

J Solid State Electrochem (2014) 18:577–593

surface, but evidence was lacking. However recently, some researchers [35–39] attributed the features at high frequency to the charge-transfer reaction. Several authors [28, 29, 35, 40–46] have modeled different metal hydride systems. Most of the authors have been using different equivalent circuits to analyze the mechanism of hydrogenation/dehydrogenation reactions of the hydride electrodes, although the impedance diagrams of the metal hydride electrode are relatively similar. Sometimes, the same data may be represented by different equivalent circuits. In this case, it is difficult to find a suitable equivalent circuit. Mathematical modeling of impedance response has been performed along two main paths. One approach is to try to fit impedance data to equivalent circuits, and assign the various subprocesses to the circuit elements, an approach which has been taken by many authors [28, 42, 47–49]. Based on an equivalent circuit model, Kuriyama et al. [28, 47] suggested that the following parameters need to be taken into account: hydrogen content, rates of the electrode reactions on alloy particles, double-layer capacitance, and contact resistance and capacitance between alloy particles in the electrode. The limitations of this approach are obviously related to the difficulties in relating the elements of the equivalent circuit to the physical processes. The other approach is to develop physical models describing the processes believed to be determining for the response. An overview of mathematical models describing impedance response related to various processes (chemical/ electrochemical reaction as well as transport processes) is provided by Lasia [50]. Most of the circuit elements in the model are common electrical elements such as resistance, capacity, inductance, constant-phase element, Warburg impedance (semi-infinite linear diffusion), Warburg impedance (finite-length diffusion), impedance of porous electrodes, and impedance for the case of rate control by a homogeneous chemical reaction. To be useful, the elements in the model should have a basis in the physical electrochemistry of the system. Constant-phase elements (CPE) are widely used in equivalent electrical circuits due to the existence of commercial software for the fitting of AC impedance experimental data [51, 52]. The physical meaning of CPE is still a matter of controversy [53–56]. The CPE behavior is generally attributed to double-layer capacitance, adsorption, surface inhomogeneity, roughness, electrode porosity, nonuniform current and/or potential distributions, etc. In the literature, different equations for CPE were proposed. In the following equations, j is the imaginary number pffiffiffiffiffiffi j ¼ −1 and ω is the angular frequency (ω =2πf,f being the frequency). Lasia [50] gives the impedance of the CPE as: Z CPE ¼ 1=T ð jωÞϕ

ð1Þ

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Where T is a constant in F cm−2sΦ−1 and ∅ is related the angle to the rotation of a purely capacitive line on the complex plane plots. Brug et al. [57] proposed:

type multicomponent metal hydride alloys are extensively being studied for their commercial use in Ni-MH batteries.

Z CPE ¼ Q=ðjωÞ1−α

The AB2 hydrogen storage intermetallic compounds have been investigated extensively because of their potential application in high-capacity negative electrodes for Ni=MH batteries. The AB2-type alloys mainly form one of two structures, either the cubic C15 structure or the hexagonal C14 structure [70, 71]. The potential AB2 types are obtained with Mg, Ti, and Zr on the A site. The B elements are represented mainly by different combinations of 3d atoms, V, Cr, Mn, and Ni. Previously, we have investigated the structural and electrochemical properties of C14-based AB2 materials having various combinations of A site elements (Ti and Zr) [72], and B site elements such as vanadium [73], tin [74], manganese [75], aluminum [76], chromium [77, 78], nickel [77], and iron [79]. Co-substitution has also been investigated extensively in AB2 alloys as a path to improving performance for both hydrogen storage and battery applications [80–84]. The earliest studies were done by Shaltiel et al. on Zr(Cox M1−x )2 (M = V, Cr, Mn) alloys, which found that as the Co-content increased, the PCT plateau pressure increased, and the absolute value of heat of formation (|ΔH |) decreased [80]. Honda et al. substituted Co for Mn in C14 Zr(Mn1−x Cox )Alz and found that as the cobalt content increased the plateau pressure/hydrogen absorption speed increased but the storage capacity decreased [81]. Given their excellent hydrogen absorption ability and ease of activation, Zr-based intermetallic compounds with C14/C15-laves structure have potential application in the fields of hydrogen storage and separation and have been the subject of many studies over the past few decades. The hydrogen absorption capacity of ZrV2 can be as high as 4.8 H/M at 1 atm hydrogen partial pressure without any change in crystal structure [85]. However, ZrV2 hydrides are too stable to release hydrogen easily which makes it for ZrV 2 difficult to meet the requirements of rechargeable batteries and applications in the nuclear industry [85]. In addition, the high cost of vanadium and high pyrophoricity of ZrV2 are also obstacles for practical applications. Hyper-stoichiometric AB2 alloys are advocated for the higher Ni-content resulting in better high-rate dischargeability [86–88], higher hydrogen plateau pressure which contributes to a higher reversible capacity [86, 89], an easier activation [83, 90], an increased amount of C15 phase for a higher capacity [89, 91, 92], a reduction of nonstorage secondary phases such as Zr7Ni10 and Zr9Ni11 [91, 92], creation of BCC phase with higher storage capability [93], and an increase in cycle stability [94]. The Laves phase series of compounds has attracted large attention in the last decade due to their good hydrogen storage capacity. However, AB2-type alloys suffer from poor activation.

ð2Þ

where Q is a constant (with dimensions Ω cm2 s−(1−α)) and 1−α has the same meaning as ϕ in Eq. (1). Zoltowski [53] proposed two definitions, i.e., Z CPE ¼ 1=Qa ðjωÞα

ð3Þ

and Z CPE ¼ 1=ðQb jωÞα

ð4Þ

The definition according to Eq. (3) was recommended in ref. [53] because Q a is directly proportional to the active area. The dimensions of Q a and Q b are Ω−1 m−2 sα or (Ω m2)−1/α sα , respectively. A combination of these expressions can be also found. Depending on the formula used, the CPE parameter is Q, 1/Q , or Q α and, for capacitive dispersions, the CPE exponent is α or (1−α) with α close to 1 or close to zero, respectively. The exponent α may acquire different values that characterize the nature of CPE; at α equal to 0, 0.5, 1, and −1, CPE transforms into the resistance R , Warburg impedance W, capacitance C, and inductance L, respectively [50, 53, 58]. In this case, the CPE becomes an extremely flexible fitting parameter, but its meaning in terms of a distribution of time constants is lost. The different expressions given for the CPE underline that the physical meaning of this element is not clear. The equivalent circuit has the character of a model, which more or less precisely reflects the reality. The equivalent circuit should not involve too many elements because then the standard errors of the corresponding parameters become too large, and the model considered has to be assessed as not determined, i.e., it is not valid. In this paper, the thermodynamic and electrochemical properties of metallic hydrides will be reviewed.

Intermetallic hydride families The classes of hydrogen storage alloys can be principally or conventionally classified as AB5-type alloys, AB2-type alloys, AB3-type alloys, AB-type alloys, Mg-based alloys, and Vbased solid solution alloys. Their performances differ greatly in terms of specific capacity, activation, rate dischargeability, and cyclic lifetime. Few archetype materials of these classes are shown in Table 1. The details of these materials can be seen in the references given therein. Today, AB5- and AB2-

AB2 compounds



Table 1 Classification of intermetallic system for hydrogen storage Properties

AB5

A2B

AB

AB2

AB3

Specific example Structure Hydrides Temperature Storage capacity (wt%) References

LaNi5 Hexagonal LaNi5H6 Room temp 1.43 [59–61]

Mg2Ni Cubic Mg2NiH4 ~300 °C 3.8 [62–64]

TiFe Cubic TiFeH2 Near room temp 1.75 [65, 66]

TiMn2 Hexagonal or cubic TiMn2H2 Near room temp 1.7 [67, 68]

LaNi3 Rhombohedral LaNi3H5 Near room temp 1.2 [69]

AB5 compounds Among the various types of hydrogen storage alloys, the AB5-type alloys were the first generation to be used as electrode materials. The AB5-based compounds have a hexagonal or orthorhombic structure with the CaCu5-type lattice [95]. In the beginning, the LaNi5 parent compound of AB5-type alloys was systematically investigated as an active negative electrode material for Ni-MH batteries [4]. The discharge capacity of LaNi5 alloy, however, decreased rapidly with the increase of the charge/discharge cycles because the alloy pulverized and oxidizing La into La(OH)3 in the alkali solution on cycling [4]. The surface layer of the LaNi5 alloy is formed of Ni and La2O3. The oxidation layer has a thickness of about 40 to 50 nm (see Fig. 1. [96]). Willems and coworkers [4, 5] have discovered that the partial substitution of Ni by Co was an effective way to enhance the charge/ discharge life cycle of LaNi5 alloy due to the decrease of the volume expansion and hence pulverization during the charge–discharge cycling. Since then, the electrochemical properties of the RENi5-based hydride electrode alloys have been investigated extensively for the further improvement of the overall properties and the reduction in price of this type of alloy. The most popular ways are the multialloying, namely the partial substitution of Ni (B side) by Co, Mn, Cr, Fe, Zr, Al, Ti, Ca, Cu, and Si, and the replacement of La (A side) by a Mischmetal (cerium-rich mischmetal Mm or lanthanum-rich mischmetal ML) [7, 97–101]. Capacities for various substituted

compounds are given in Table 2 [102]. In all cases, the pseudobinary compounds show smaller capacity than the corresponding parent compound. The AB5-type hydrogen storage alloy Mm (Ni, Mn, Co, Al)5 is one of an alloy series which are being extensively used now. The alloy of composition MmNi3.55Mn0.4Al0.3Co0.75 was shown to meet the minimum requirements for a practical battery with respect to cost, cycle life, and storage capacity [103, 104]. Cobalt, a key element to keep long cycling life, is the most expensive element in the commercial hydrogen storage alloys and 10 wt% Co constitutes about 40–50 % of the total cost of the raw materials [105–115]. Therefore, it is interesting to investigate low-Co and/or Co-free AB5type alloys. Many works have demonstrated the possibility and application of the partial replacement of Cu, Zn, Mn, Al, Fe, Si, Cr, Sn, etc. for Co. Copper was used to substitute Co in the alloys MlNi3.5Co0.7−7x Cu8x Al0.8−x (x =0–0.1) [116, 117] and it is found that the electrochemical properties of the alloys is not affected when 50 % of Co content was substituted by Cu and the cycle life for the alloys would decrease with the increase of Cu content. Ma et al. [118] researched the electrochemical properties of the Co-free MlNi 4.45 − x Mn0.4Al0.15Snx alloys and found that the cycle life of the alloy x =0.4 is the best for those of all the alloys; however, its discharge capacity is only 269.1 mAh g−1. Cr, Cu, and Si of three elements were used to substitute Co in a united way in the alloy system of MmNi3.65Co0.22Mn0.36Cr0.2Cu0.2Si0.1 by

Fig. 1 Representation of the surface of LaNi5. The surface layer is formed of Ni and La2O3 [96]

40-50 nm

La2O3

Ni

LaNi5


581

Table 2 Hydrogen capacity for various pseudo-binary AB5-type alloys at the pressure indicated between brackets Composition

Csg (H/f.u.), (PH2 (bar))

Cel (mAh g−1)

LaNi5 LaNi4.7Al0.3 LaNi4.25Co0.75 LaNi4Cu

6.24 (25) 5.85 (10) 6.23 (10) 5.45 (10)

387 370 386 334

LaNi4Fe LaNi4.5Sn0.5 LaNi4Mn LaNi3.55Mn0.4Al0.3Co0.75 MnNi3.55Mn0.4Al0.3Co0.75

5.45 (10) 5.25 (10) 5.82 (10) 5.60 (10) 5.30 (10)

327 304 364 334 332

Hu [106] and it was found that the capacity decay was 25.6 % after 300 full cycles. But the discharge capacity of the alloy above was only 273 mAh g−1. Recently, it is reported that the electrochemical performances were improved through the additive of some active elements. Tang et al. [119] developed a low-cobalt alloy through addition of Mg, the discharge capacity of the alloy was 320 mAh g−1 and the capacity decay was 12 % after 300 charging/discharging cycles. Wei et al. [120] found that through the addition of trace of Ca element, the cycle life of the low-cobalt alloys can be improved. Zhang et al. [121] found that when a trace of B element was added in the low-Co AB5-type alloy, the cycle life of the as-cast and quenched alloys could be enhanced dramatically. Iron is one of the relevant candidates for cobalt substitution in AB5 MH alloys due to its atomic radius, number of electrons, and electronegativity being similar to those of Ni and Co. Zuttel et al. [122] replaced a part of the cobalt by iron in the LmNi3.8Al0.4Mn0.3Co0.3Fe0.2 compound. They found a long electrochemical cycle life. At 40 °C, there is a loss of only 0.15 % of the capacity after 200 cycles. Hasegawa et al. [123] found that iron has a beneficial effect on cyclic stability. Cocciantelli et al. [124] also found a beneficial effect of Fe substitution in MmNi3.8−x Mn0.33Al0.4Co0.51Fex (x =0, 0.16) compounds and scanning electron microscopy observations showed that the addition of iron reduced their decrepitation. It has been shown that alloys in which cobalt is partially substituted by iron, which is relatively inexpensive, maintain a good cycling stability [22, 125–135]. AB3 compounds However, none of the available electrode alloys including AB5 and AB2 types can meet the specification of the power battery because of the limitation of their properties, such as the low discharge capacity of the AB5-type electrode alloy and the poor activation capability of the AB2-type Laves phase electrode alloy. Therefore, the research in this area has been focused on finding new type electrode alloys with higher

capacity and longer cycle life. Recently, some of the new series of R-Mg-Nin ( R = rare earth, 2 Co > Cr > Ti, V > Cu. In MmNi5−x Mx (M = Mn, Al, and Sn; x =0.4 and 0.8), the partial substitution of Ni with Al, Mn, and Sn in MmNi5 resulted in the lowering of hysteresis loss upon hydrogenation [208]. Gamo et al. [209, 210] investigated the Ti–Mn alloys in detail. They showed that TiMn2-based pseudo-binary alloys, such as Ti0.9Zr0.1Mn1.4Cr0.4 V0.2, exhibit good properties for hydrogen storage. However, the hysteresis of this alloy is still large and the hydrogen absorption pressure is as high as ≈ 20 atm. Hagstrom and his coworkers measured the PCT

absorption

H2

Hystérésis désorption

α max

β min

X (H/mole) Fig. 4 Generalized illustration of pressure-composition hysteresis in metal–hydrogen systems

Fig. 5 PCI isotherms for LaNi5 and MmNi3.55 Co0.75Mn0.4 Al0.3 (ref. [203])



Fig. 6 PCI isotherms of the as cast Ml0.7 Mg0.3Ni3.2 alloy measured at the first and second hydrogen absorption/desorption cycles (ref. [204])

characteristics of some Ti-based AB2 and CeLaNi-based AB5 materials and found that substitutions of V and Co considerably reduce the hysteresis effect [185].

Electrochemical kinetics of metal hydrides Generally, the electrochemical kinetics of hydrogen storage alloy electrodes is mainly determined by both charge-transfer process on the alloy surface and hydrogen atom diffusion within the bulk of the alloy. The former can be characterized by charge-transfer resistance (R ct) or the surface exchange current (I 0), while the latter can be determined by hydrogen diffusion coefficient. The exchange current density reflects a charge transfer capability in an electronic transformation from adsorbed hydrogen to hydrogen ion at the discharge process and from hydrogen ion to adsorbed hydrogen at charge process. The increase in the exchange current density leads to an improvement in the high-rate discharge capability. Previous efforts have investigated the dependence of the exchange current density upon hydrogen content in the alloy. Using linear polarization (LP), Tafel polarization, and electrochemical impedance spectroscopy techniques, Popović et al. [211] found that the exchange current density of the LaNi4.15Co0.43Mn0.40Fe0.02 alloy electrode increases with increasing hydrogen concentration in the alloy electrode and the values of the exchange current determined by AC impedance are in good agreement with values obtained by micropolarization and Tafel polarization (see Fig. 7). Ratnakumar et al. [23] and Witham et al. [212] found that exchange current densities estimated from linear polarization for LaNi5−x Gex and LaNi5−x Snx alloys were in agreement with those from AC impedance, but were quite different from the values obtained from Tafel polarization. Wang et al. [213] proposed that this discrepancy may be caused by a neglect of the effect of hydrogen transfer between the absorbed and

Fig. 7 Variation of the exchange current with state of charge determined by DC anodic (filled triangle) and cathodic (filled square) micropolarization measurements, AC impedance (empty square) and the anodic Tafel polarization measurements (filled circle) (ref. [211])

adsorbed states. Conventional Tafel polarization method cannot be applied to estimate the exchange current density for porous metal hydride system due to presence of internal mass transfer effects and internal ohmic voltage drop of the electrode [214]. Ramya et al. [38] have studied the effect of nickel substitution on the electrochemical properties of TiMn2−x Nix alloys and determined the exchange current density of the alloys using AC impedance. They found that the exchange current density of the TiMn2 − x Nix alloys increases with increasing SOC. Popov et al. [215] determined the exchange current density of La0.65Ce0.35Ni3.55Co0.75Mn0.4A10.3 alloy electrode from linear polarization at different states of charge. They reported that the exchange current density increases with decreasing the hydrogen content in the alloy and reaches a maximum value at approximately 15 % of SOC. Then, the exchange current density starts to decrease with decreasing the hydrogen content in the α phase region of the alloy. Using AC impedance impedance, Muruganantham et al. [39] found that the exchange current density of the MnFe2 alloy electrode increases significantly on charging the electrode: this indicates that the electrocatalytic activity on the surface of the alloy is greatly improved which, thereby, reduces the overpotential during the charge–discharge process. The exchange current density of the electrode varies from 18.5 mA g−1 at 16.66 % SOC to 25.5 mA g−1 at 100 % SOC. In our previous studies [216, 217], we have shown a similar dependence of the exchange current density upon hydrogen content in the LaNi3.55Mn0.4Al0.3Co0.4Fe0.35 metal hydride alloy electrode using linear polarization and AC impedance. When the SOC of the electrode is less than about 50 %, the exchange current density increases rapidly with hydrogen content and then remains almost constant; however, as the


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hydrogen content increases the exchange current density also increases due to the changes from the α to the β phases and also due to variations in the alloy electroactive area. Recently [216], in our work, we have demonstrated that the values of the real surface area increases from 3.74 to 4.2 cm2 with the increase in SOC of the metal hydride electrode from 0 to 100 %. Comparing the values of I 0 calculated from LP and AC impedance measurement, it can be found that the values of I 0 estimated from AC impedance are slightly higher than the values obtained from LP. The difference in the values of I 0 may be due to the magnitudes of the polarization resistance R p and the charge transfer resistance R tc estimated from LP and AC impedance, respectively. In generally, the polarization resistance is composed of ohmic resistance, charge transfer resistance, and diffusion resistance. Zheng et al. [49] found that, for LaNi4.25Al0.75, the resistance measured from linear micropolarization is approximately equal to the sum: the charge-transfer, hydrogen-transfer, and hydrogen-diffusion resistances, all three measurable from AC impedance spectroscopy. Similarly, Wang et al. [213] found that the resistance measured from the linear micropolarization gives the total resistance of the hydriding–dehydriding reactions, and it reduces to the exchange current only when the electrochemical reaction is rate determining. The resistance measured from linear micro polarization is approximately equal to the sum of three resistances measured from AC impedance, namely charge-transfer, hydrogen transfer, and hydrogen-diffusion resistances; however, when the SOD is high, the resistance measured from linear micro polarization is higher than total resistances measured from AC impedance [213]. The values of exchange current density I 0 for a number of alloys, found in the literature, are compiled in Table 3. The Table 3 Values of exchange current density for a number of hydrogen storage alloys Alloys

SOC (%) I 0 (mA g−1) Method References

LaNi3.55Mn0.4Al0.3Co0.4Fe0.35 0 40

211.60 307.00

100

322.18

12 50

33.50 54.52

EIS

our work [216]

LP

our work [217]

[33]

100

53.60

0 50

29.10 21.12

EIS

0 50

26.84 20.03

LP

MmFe2

16.66 50

18.5 18

EIS

[39]

100

25.5

Zr0.5Ti0.5 V0 .5Ni1.3Cr0.2

100

104

LP

[218]

PrNi3 LaNi3

50 50

208.71 209.46

LP

[219]

YaNi3

50

215.27

MmNi3.6Co0.8Mn0.4Al0.2

differences in the results can be attributed to differences in composition and in real surface area. The kinetics of the charge transfer reaction is hardly influenced by the composition of the bulk electrode material. The electrocatalytic activity, which is reflected by the exchange current density, is mainly determined by the chemical composition and the surface properties of the electrode such as oxide thickness, electrical conductivity, surface porosity and topology, surface area, and degree of catalytic activity. The hydrogen diffusion in a charge–discharge reaction is influenced by both the micro- and the macro-structure of the alloy. The diffusion coefficient of atomic hydrogen in the solid phase was shown to depend on the strength of the metal– hydrogen interaction and the hydrogen concentration in the bulk since this is a characteristic of mass transport in metal hydride electrodes [24]. The hydrogen diffusion coefficient, D H, is one of the most important kinetic parameters for MH alloy because the hydrogen diffusion process limits the rate of battery reactions in many cases. Till now, there have been a large number of reports for determining the diffusion coefficient of hydrogen in various metal hydride electrodes using various electrochemical techniques, including currentstep method [24], potential-step method [220], cyclic voltammetry [221], electrochemical impedance spectroscopy [222], and galvanostatic intermittent titration technique [223]. The potential-step method, a simple and convenient technology, is widely used to study the hydrogen diffusion coefficient. In our recent studies [216, 224], the constant-potential discharge and AC impedance measurements are used to evaluate the diffusion coefficient of hydrogen in the LaNi3.55Mn0.4Al0.3Co0.4Fe0.35 metal hydride electrode at various SOC. We have shown that the diffusion coefficient increases with the increase of hydrogen concentration in the alloy (see Figs. 8 and 9). The value of D H estimated from constant-potential discharge in is around 2.99×10−11 cm2 s−1 at 60 % SOC [224] and then obtained from AC impedance is around 1.34×10−11 cm2 s−1 at the same SOC [216]. A similar concentration dependence where the diffusion coefficient increases with hydrogen concentration has been seen previously [211, 225–227]. The transport of hydrogen in MH takes place by a hopping mechanism involving two types of hydrogen motion [228, 229]. Hydriding of the metal begins with a rapid diffusion of a small amount of H into the interior of the alloy to produce a dilute solid solution denoted as the α phase [230]. As the hydrogen dissolution proceeds, the α phase is gradually supersaturated with hydrogen in its surface region and the β hydride starts to deposit [231]. At the end of the charging, the entire α solid solution is converted and the alloy particle has hydride in the β phase [232]. Wicke and Brodovsky [233] reported that the apparent diffusion coefficient is dependent on the hydrogen content in the alloy. It may also be mentioned that for microcrystalline


J Solid State Electrochem (2014) 18:577–593 1.6

1.2

1

H

D (*10

-11

2 -1

cm s )

1.4

0.8

0.6

0

20

40

60

80

100

SOC (100%)

Fig. 8 Variation of the hydrogen diffusion coefficient of the LaNi3.55Mn0.4Al0.3Co0.4Fe0.35 alloy with state of charge determined by AC impedance measurements (our work [216])

LaNi3.94Si0.54 films and also for LaNi4.15Co0.43Mn0.40Fe0.02, the diffusivity was reported to increase with increasing hydrogen concentration (expanded lattice) in the alloy [211, 225]. Using the galvanostatic intermittent titration technique (GITT), Yang et al. [226] found that the diffusion coefficient increases substantially as the SOC increases. The average value of that the diffusion coefficient is around 2.2×10−11 cm2 s−1 above 20 % SOC. Ciureanu et al. [227] made electrochemical studies on Ni64 Zr36 and determined the diffusion coefficient of hydrogen using the chronopotentiometric method. They found a strong dependence of the diffusion coefficient on the hydrogen concentration. The values increased from 2.2× 10−10 to 4.5×10−10 cm2 s−1 for H/M ratios of 2.65 to 6.36, respectively. Using AC impedance, Haran et al. [27] found that the diffusion coefficient of hydrogen in LaNi4.27S0.24 increases with increasing SOC. The diffusion coefficient varies from 1.671×10−10 cm2 s−1 at 45 % SOC to 3.851×10−11 cm2 s−1 at 0 % SOC. However, some authors show results to the contrary. Using constant potential discharge (CPD), constant current discharge (CCD), galvanostatic intermittent titration (GIT), cyclic voltammetry (CV) and AC impedance techniques, Yang

Fig. 9 Variation of the hydrogen diffusion coefficient of the LaNi3.55Mn0.4Al0.3Co0.4Fe0.35 alloy with different state of charge determined by constant-potential discharge technique (our work [224])

et al. [221, 223, 234] reported that the hydrogen diffusion coefficient of the MlNi3.75Co0.65Mn0.4Al0.2 alloy electrode increases with the increase of depth of discharge. The value of hydrogen coefficient diffusion determined by CPDT, CCDT, GITT, and AC impedance differ. Using potential step method, Iwakura et al. [220] found that the hydrogen diffusion coefficient of the MmNi4.2Al0.5 M0.3 (M = Cr, Mn, Fe, Co, Ni) alloy decreased with the increase of hydrogen concentration in it. Using potential intermittent titration and potentiostatic methods, Feng et al. [235, 236] reported that the hydrogen diffusion coefficient in a LaNi4.7Al0.3 metal hydride electrode increases with the increase of depth of discharge. The same dependence of the diffusion coefficient upon hydrogen cotenant was also reported by Kum et al. [237] using potential-step technique. Despite this diversity, there is a point upon which various authors agree; the existing decrease of the hydrogen diffusion coefficient, during the discharge of the MH electrode, with an increasing concentration of hydrogen initially absorbed into the alloy electrode [24, 220–223, 235–238]. This phenomenon is attributed to the existence of hydrogen– hydrogen and/or hydrogen–constitutive intermetallic host interactions [220, 237]. The values of the diffusion coefficient of hydrogen D H for a number of alloys, found in the literature, are compiled in Table 4. However, the values of the hydrogen diffusion coefficient in rare-earth systems vary over 8 orders of magnitude at room temperature (from 10−6 to 10−14 cm2 s−1). These widely varying values of D H may be due to differences in the microstructure, metal stoichiometry and composition of the alloys, differences in experimental methods, and also differences in the hydrogen concentrations in the various alloys. The microstructure of the alloys depends on their preparation and hydrogenation. The hydrogen diffusion coefficient can also vary with the type of hydrogenation process, i.e., gas-phase hydrogenation/electrochemical hydrogenation [222]. The values of hydrogen diffusion coefficient of the alloy electrodes determined by various electrochemical techniques are not exactly the same. In addition to the uncertainty or inaccuracy of some parameters used in these techniques as a cause, this is mainly due to the fact that each technique has its own essential conditions and proper application conditions, and different implications were made during the deduction of the formulae for calculation of the D H value in individual technique. This makes some difference between these techniques. Sometimes, even the results for the same alloy determined using same method are quite different. The electrochemical behavior of such intermetallics depends on their structure, the nature and amount of each element in the intermetallic compound, and the electrochemical process(es) taking place. High exchange current density and high hydrogen diffusivity in the bulk of

Author's personal copy J Solid State Electrochem (2014) 18:577–593 Table 4 Values of hydrogen diffusion coefficient for a number of hydrogen storage alloys

589

Alloys

SOC (%)

D H (cm2 s−1)

Method

References

LaNi3.55Mn0.4Al0.3Co0.4Fe0.35

0 40

0.57×10−11 1.38×10−11

EIS

our work [216]

100

1.33×10−11

7 60

0.639×10−11 2.999×10−11

CPD

our work [224]

100

3.069×10−11

LaNi4.27S0.24

0 45

3.851×10−11 1.671×10−10

CPD

[27]

MlNi3.65Co0.75Mn0.4Al0.2

10 60

1.97×10−7 1.09×10−8

CV

[221]

100

5.75×10−9

LaNi4.15Co0.43Mn0.40Fe0.02

100

2.53×10−11

CPD

[211]

Mn0.95Ti0.05Ni3.85Co0.45Mn0.35Al0.35

100

1.2×10−11

A. polarization

[239]

LaNi5

–

5×10−6

NMR

[240]

PrNi3 LaNi3

100 100

4.51×10−10 6.27×10−10

CPD

[219]

YNi3

100

14.69×10−10

Ti0.9Zr0.2Mn1.5Cr0.3 V0.3–x wt%La0.7 Mg0.25Zr0.05Ni2.975Co0.525

100

CPD

[241]

CPD

[142]

La2Mg(Ni0.95Al0.05)9 La2Mg(Ni0.95Sn0.05)9

100 100

0.62×10−14 (x =0), 1.58×10−14 (x =5), 2.70×10−14 (x =10) 1.18×10−10 7.57×10−10

Ti0.9Zr0.2Mn1.5Cr0.3 V0.3

100

0.62×10−14

CPD

[242]

TiCr1.85

–

3.1×10-8

QNS

[243]

–

3.4×10−8

NMR

100 100

4.3×10−11 4.3×10−11

CPD

(x =0, 5, 10)

Ti0.9Zr0.1Mn1.6Ni0.4 Ti0.8Zr0.2Mn1.6Ni0.4

the alloy are needed for improved performance of a metal hydride electrode. These characteristics can be changed by designing the composition of the hydrogen storage alloy to provide optimum performance of the Ni=MH. Hydrogen diffusivity in the alloy and exchange current density should be high to ensure the high discharge rate of the Ni=MH battery, especially at high discharge current densities. These parameters are related to the mass transfer and charge transfer processes, and the dischargeability of the battery depends critically on these processes. Hydrogen diffusivity in the bulk of alloys and exchange current density affect the rate at which energy can be stored in, and also removed from, the Ni=MH battery. The electrocatalytic activity, which is reflected by the exchange current density, is hardly influenced by the chemical composition and the surface properties of the electrode such as oxide thickness, electrical conductivity, surface porosity and topology, surface area, and degree of catalytic activity.

Conclusions A large number of hydrogen storage alloys have been developed as negative electrode materials for Ni/MH batteries.

[244]

Their performances differ greatly in terms of specific capacity, activation, rate dischargeability, and cyclic lifetime. There is an apparent trend to concentrate on low cost, light weight, and excellent charge–discharge properties. These characteristics can be changed by designing the composition of the hydrogen storage alloy to provide optimum performance of the Ni/MH batteries. The electrochemical behavior of such intermetallics depends on the types of intermetallics, microstructure, the nature and amount of each element in the intermetallic compound, and the electrochemical process(es) taking place. In this review, we present some recent results on the electrochemical behavior of such compounds and the mechanisms of the electrochemical reactions. At the present time, Co-free hydrogen storage alloy has got attention and there are some studies on it in recent years. Until now, AB5type hydrogen storage alloys are still one of the main choices in commercial Ni/MH battery industry and lots of efforts are made on cutting off their raw materials costs. Besides the cost issue, Fe is an interesting substitution element inAB5 MH alloys due to its atomic radius, number of electrons, and electronegativity being similar to those of Ni and Co. Recently, most of the Fe substitution in rare-earth-based AB5 MH alloys are for the purpose of replacing expensive Co.


In the search for new metal hydrides, recent attention has been dedicated to the family of AB3- or A2B7-type rare earth– magnesium-based alloys because their electrochemical discharge capacities (about 400 mAh g−1) are higher than AB5-type alloys. Now, the main problem for this series of alloys to be used for industrialization is the poor cyclic stability. It is well known that element substitution is one of the effective methods for improving the overall properties of the hydrogen storage alloys. At present, LaMgNiCo-based alloys showed promising future for practical applications. But the high cost is still an obstacle to their wide applications. To reduce the alloy's cost, Co-free hydrogen storage alloy has got attention and there are some studies on it. The results are still quite incomplete. The performance of a metal hydride electrode is determined by the kinetics of the processes occurring at the metal–electrolyte interface and the rate of hydrogen diffusion within the bulk of the alloy. The exchange current density and hydrogen diffusion coefficient are the most important kinetic parameters that could significantly affect the performance of Ni–MH rechargeable batteries. Their values for a number of hydrogen storage alloys are compared. The differences in the results can be attributed to differences in composition and in the characteristics of the electrode reactions such as state of charge, cycle, temperature, and surface modification. Acknowledgments The authors wish to thank the reviewers for the helpful comments and careful revision of the manuscript.

References 1. Zhan F, Jiang LJ, Wu BR, Xia ZH, Wei XY, Qin GR (1999) J Alloys Compd 293:804–808 2. Yang XG, Liaw BY (2001) J Power Sources 101:158–166 3. Tliha M, Mathlouthi H, Khaldi C, Lamloumi J, Percheron-guegan A (2006) J Power Sources 160:1391–1394 4. Jurczyk M, Rajewski W, Majchrzycki W, Wojcik G (1999) J Alloys Compd 290:262–266 5. Willems JJG, Buschow KHJ (1987) J Less-Common Met 129:13–30 6. Sakai T, Miyamura H, Kuriyama N, Kato A, Oguro K, Ishikawa H (1990) J Electrochem Soc 137:795–799 7. Pan HG, Ma JX, Wang CS, Chen CP, Wang QD (1999) Electrochim Acta 44:3977–3987 8. Latroche M, Chabre Y, Percheron-Guegan A, Isnard O, Knop B (2002) J Alloys Compd 330:787–791 9. Anani A, Visintin A, Srinivasan S, Appleby AJ, Lim HS (1992) J Electrochem Soc 139:985–988 10. Pan HG, Chen Y, Wang CS, Ma JX, Chen CP, Wang QD (1999) Electrochim Acta 44:2263–2269 11. Ovshinsky SR, Fetcenko MA (1993) J Ross Science 260:176–181 12. Zhang Y, Chen LX, Lei YQ, Wang QD (2002) Electrochim Acta 47: 1739–1746 13. Tian QF, Zhang Y, Sun LX, Xu F, Tan ZC, Yuan HT, Zhang T (2006) J Power Sources 158:1463–1471 14. Tsukahara M, Kamiya T, Takahashi K, Kawabata A, Sakurai S, Shi J, Takeshita N, Kuriyama HT, Sakai T (2000) J Electrochem Soc 147:2941–2944

J Solid State Electrochem (2014) 18:577–593 15. Lei YQ, Wu YM, Yang QM, Wu J, Wang QD (1994) Z Phys Chem 183:379–384 16. Iwakura C, Nohara S, Inoue H, Fukumoto Y (1996) Chem Commun 15:1831–1832 17. Bai T, Han S, Zh X, Zhang Y, Li Y, Zhang W (2009) Mater Chem Phys 117:173–177 18. Li Y, Han S, Li J, Zhu X, Hu L (2008) J Alloys Compd 458:357–362 19. Ma J, Pan H, Zhu Y, Li S, Chen C, Wang Q (2001) Electrochem Acta 46:2427–2434 20. Ye H, Huang YX, Huang TS, Zhang H (2002) J Alloys Compd 330: 866–870 21. Wang MH, Zhang Y, Zhang LZ, Sun LX, Tan ZC, Xu F, Yuan HT, Zhang T (2006) J Power Sources 159:159–162 22. Khaldi C, Mathlouthi H, Lamloumi J, Percheron-Guegan J (2004) J Int J Hydrogen Energy 29:307–311 23. Ratnakumar BV, Withan C, Bowman RC, Hightower A, Fultz B (1996) J Electrochem Soc 143:2578–2584 24. Zheng G, Popov BN, White RE (1996) J Electrochem Soc 143(3): 834–839 25. Ciureanu M, Moroz D, Ducharme R et al (1994) Z Phys Chem Bd 183:365–370 26. Strom-Olsen JO, Zhao Y, Ryan DH (1991) J Less-Common Met 172:922–927 27. Haran BS, Popov BN, White RE (1998) J Power Sources 75:56–63 28. Kuriyama N, Sakai T, Miyamura H, Uehara I, Ishikawa H, Iwasaki H (1992) J Electrochem Soc 139:L72–L73 29. Zhang W, Kumar MP, Srinivasan S, Ploehn HJ (1995) J Electrochem Soc 142:2935–2943 30. Koura N, Takeda N, Kawashima K, Idemoto Y (1998) Denki Kagaku Oyobi Kogyo Butsuri Kagaku 66:1135–1140 31. Ticianelli EA, Mukerjee S, McBreen J, Adzic GD, Johnson JR, Reilly JJ (1999) J Electrochem Soc 146:3582–3590 32. Züttel A, Güther V, Otto A, Bärtsch M, Kötz R, Chartouni D, Nützenadel CH, Schlapbach L (1999) J Alloys Compd 293:663–669 33. Yuan A, Xu N (2001) J Alloys Compd 322:269–275 34. Khaldi C, Mathlouthi H, Lamloumi J (2009) J Alloys Compd 479: 284–289 35. Wang C (1998) J Electrochem Soc 145(6):1801–1812 36. Yang H, Zhang Y, Zhou Z, Wei J, Wang G, Song D, Cao X, Wang C (1995) J Alloys Compd 231:625–630 37. Baddour-Hadjean R, Mathlouthi H, Pereira-Ramos JP, Lamloumi J, Latroche M, Percheron-Guegan A (2003) J Alloys Compd 356: 750–754 38. Ramya K, Rajalakshmi N, Sridhar P, Sivasankar B (2003) J Alloys Compd 352:315–324 39. Muruganantham R, Rajalakshmi N, Dhathathreyan KS, Ramaprabhu S (2003) J Power Sources 114:352–356 40. Lim C, Pyun SI (1993) Electrochim Acta 38:2645–2652 41. Zheng G, Haran BS, Popov BN, White RE (1999) J Appl Electrochem 29:361–369 42. Li X, Dong H, Zhang A, Wie Y (2006) J Alloys Compd 426:93–96 43. Deng C, Shi P, Zhang P (2006) Mater Chem Phys 98:514–518 44. Wang Y, Lu ZW, Wang YL, Yan TY, Qu JQ, Gao XP, Shen PW (2006) J Alloys Compd 421:236–239 45. Gao X, Liu J, Ye S, Song D, Zhang Y (1997) J Alloys Compd 253: 515–519 46. Gao XP, Zhang W, Yang HB, Song DY, Zhang YS, Zhou ZX, Shen PW (1996) J Alloys Compd 235:225–231 47. Kuriyama N, Sakai T, Miyamura H, Uehara I, Ishikawa H (1993) J Alloys Compd 192:161–163 48. Zheng G, Popov BN, White RE (1997) J Appl Electrochem 27: 1328–1332 49. Zheng G, Popov BN, White RE (1998) J Appl Electrochem 28:381–385 50. Lasia A, In: White RE, Conway BE, Bockris JOM (eds) (1999) Modern aspects of electrochemistry 32. Kluwer Academic/Plenum, New York, p 143

Author's personal copy J Solid State Electrochem (2014) 18:577–593 51. Boukamp BA (1990) Equivalent circuits. Twente University of Technology, Enschede 52. ZVIEW (1993) Impedance/gain phase graphics and analysis software. Scribner Associates, Charlottesville 53. Zoltowski P (1998) J Electroanal Chem 443:149–154 54. Sadkowski A (2000) J Electroanal Chem 481:222–226 55. Láng G, Heusler KE (2000) J Electroanal Chem 481:227–229 56. Zoltowski P (2000) J Electroanal Chem 481:230–231 57. Brug GJ, Van Den Eeden ALG, Sluyters-Rehbach M, Sluyters JH (1984) J Electroanal Chem 176:275–295 58. Ross Macdonald J (1987) Impedance spectroscopy: emphasizing solid materials and analysis. Wiley, New York 59. Singh SK, Ramakrishna K, Singh AK, Srivastava ON (1989) Int J Hydrogen Energy 14:573–577 60. Pandey SK, Srivastava A, Srivastava ON (2007) Int J Hydrogen Energy 32:2461–2465 61. Singh RK, Lototsky MV, Srivastava ON (2007) Int J Hydrogen Energy 32:2971–2976 62. Zhang J, Zhou DW, He LP, Peng P, Liu JS (2009) J Phys Chem Solids 70:32–39 63. Zhang XZ, Yang R, Qu JL, Zhao W, Xie L, Tian WH, Li X (2010) Nanotechnology 21:095706 64. Bernauer O, Topler J, Noreus D, Hempelmann R, Richter D (1989) Int J Hydrogen Energy 14:187–200 65. Reilly JJ Jr, Wiswall RH (1974) Inorg Chem 13:218–222 66. Gennari FC, Urretavizcaya G, Gamboa JJA, Meyer GJ (2003) Alloys Compd 354:187–192 67. Yoshida M, Akiba E (1995) J Alloys Compd 224:121–126 68. Bobet JL, Chevalier B, Darriet B (2000) Intermetallics 8:359–363 69. Chen J, Takeshita TH, Tanaka H, Kuriyama N, Sakai T, Uehara I, Haruta M (2000) J Alloys Compd 302:304–313 70. Ivey DG, Northwood DO (1983) J Mater Sci 18:321–347 71. Shaltiel D (1978) J Less-Common Met 62:407–416 72. Young K, Fetcenko MA, Li F, Ouchi T (2008) J Alloys Compd 464: 238–247 73. Young K, Fetcenko MA, Li F, Ouchi T, Koch J (2009) J Alloys Compd 468:482–492 74. Young K, Fetcenko MA, Ouchi T, Li F, Koch J (2009) J Alloys Compd 469:406–416 75. Young K, Ouchi T, Koch J, Fetcenko MA (2009) J Alloys Compd 477:749–758 76. Yu JS, Lee SM, Cho K, Lee JY (2000) J Electrochem Soc 147: 2013–2017 77. Young K, Ouchi T, Fetcenko MA (2009) J Alloys Compd 476:774–781 78. Young K, Ouchi T, Mays W, Reichman B, Fetcenko MA (2009) J Alloys Compd 480:434–439 79. Yong K, Fetcenko MA, Khoch J, Morii K, Shimizu T (2009) J Alloys Compd 486:559–569 80. Shaltiel D, Jacob I, Davidov D (1977) J Less-Common Met 53:117–131 81. Honda N, Furukawa N, Fujitani S, Yonezu I (1990) US Patent 4913879 82. Kim S, Lee J (1994) J Alloys Compd 210:109–113 83. Nakano H, Wakao S (1995) J Alloy Compd 231:587–593 84. Chen J, Dou SX, Liu HK (1997) J Alloys Compd 256:40–44 85. Pebler A, Gulbransen EA (1966) Electrochem Technol 4:211–215 86. Kim D, Jang K, Lee J (1999) J Alloys Compd 293:583–592 87. Zuttel A, Fischer P, Fauth F, Otto A, Guther V (2002) J Alloys Compd 333:99–102 88. Lupu D, Biris AR, Biris AS, Indrea E, Misan I, Zuttel A, Schlapbach L (2003) J Alloys Compd 350:319–323 89. Gao X, Song D, Zhang Y, Wang G, Shen P (1995) J Alloys Compd 223:77–80 90. Cui X, Li Q, Chou K, Chen S, Lin G, Xu K (2008) Intermetallics 16: 662–667

591 91. Gao XP, Ye SH, Liu J, Song DY, Zhang YS (1998) Int J Hydrogen Energy 23:781–786 92. Shu K, Zhang S, Lei Y, Lu G, Wang Q (2003) J Alloys Compd 349: 237–241 93. Pan H, Zhu Y, Gao M, Wang Q (2002) J Electrochem Soc 149: A829–A833 94. Zhu Y, Pan H, Gao M, Liu Y, Wang Q (2003) J Alloys Compd 348: 301–308 95. Lakner JF, Uribe FS, Steward SA (1980) J Less-Common Met 72: 87–105 96. Wallace WE, Kalicek RF, Imamura H (1979) J Phys Chem 83: 1708–1712 97. Sakai T, Miyamura H, Kuriyama N, Kato A, Oguro K, Ishikawa H (1990) J Less-Common Met 159:127–139 98. Sakai T, Yoshinaga H, Miyamura H, Kuriyama N, Ishikawa H (1992) J Alloy Compd 180:37–54 99. Pan HG, Ma JX, Wang CS, Cheng SA, Wang XH, Chen CP, Wang QD (1999) J Alloys Compd 293:648–652 100. Hu WK, Le H, Kim DM, Jeon SW, Lee JY (1998) J Alloys Compd 268:261–265 101. Notten PHL, Latroche M, Percheron-Guegan A (1999) J Electrochem Soc 146:3181–3189 102. D Maziére (2002) J Phys IV France 12 :Pr2-III 103. Ogawa H, Ikoma M, Kawano H, Matsumoto I (1988) J Power Sources 12:393–410 104. Ikoma M, Kawano H, Matsumoto I, Yanagihara N (1987) Eur Pat No. 0271043 105. Huang YX, Zhang H (2000) J Alloys Compd 305:76–81 106. Hu WK (1999) J Alloys Compd 289:299–305 107. Hu WK (2000) J Alloys Compd 297:206–210 108. Wang Y, Yuan H, Wang G, Zhang Y (2002) Solid State Ionics 148: 509–512 109. Tang R, Zhang ZH, Liu LQ, Liu YN, Zhu JW, Yu G (2004) Int J Hydrogen Energy 29:851–858 110. Yuexiang H, Hong Z (2000) J Alloys Compd 305:76–81 111. Tang R, Liu L, Liu Y, Yu G (2003) Int J Hydrogen Energy 28:815–819 112. Chartouni D, Meli F, Züttel A, Gross K, Schlapbach L (1996) J Alloys Compd 241:160–166 113. Mao LC, Shan ZQ, Yin SH, Liu B, Wu F (1999) J Alloys Compd 293:825–828 114. Sakai T, Oguro K, Miyamura H, Kuriyama N, Kato A, Ishikawa H (1990) J Less-Common Met 161:193–202 115. Adzic GD, Johnson JR, Mukerjee S, Breen JM, Reilly JJ (1997) J Alloys Comp 253:579–582 116. Tang W, Gai Y, Zheng H (1995) J Alloys Compd 224:292–298 117. Weizhong T, Yinxin G, Haoyu Z (1995) J Appl Electrochem 25: 874–880 118. Ma JX, Pan HG, Yu G, Chen CP, Wang QD (2002) J Alloys Compd 343:164–169 119. Tang R, Zhang Z, Liu L, Liu Y, Zhu J, Yu G (2004) Int J Hydrogen Energy 29:851–858 120. Wei XD, Liu YN, Yu G, Zhu JW (2006) J Alloys Compd 414:253–258 121. Zhang YH, Chen MY, Wang XL, Wang GQ, Lin YF, Qi Y (2004) J Power Sources 125:273–279 122. Zuttel A, Chartouni D, Gross K et al (1997) J Alloys Compd 253: 626–628 123. Hasegawa K, Ohnishi M, Oshitani M, Takeshima K, Matsumaru Y (1994) Z Phys Chem Bd 183:325–331 124. Cocciantelli JM, Bernard P, Fernandez S, Atkin J (1997) J Alloys Compd 253:642–647 125. Iwakura C, Ohkawa K, Senoh H, Inoue H (2001) Electrochim Acta 46:4383–4388 126. Chen XL, Lei YQ, Liao B, Wei FS, Chen LX (2004) Chin J Nonferrous Metals 14:1862–1868

Author's personal copy 592 127. Vivet S, Jouber JM, Knosp B, Percheron-Guegan A (2003) J Alloys Compd 356:779–783 128. Zhang YH, Wang GQ, Dong XP, Guo SH, Ren JY, Wang XL (2005) J Power Sources 148:105–111 129. Zhang Y, Dong X, Wang G, Guo S, Wang X (2005) J Power Sources 140:381–387 130. Zhao Y, Zhang Y, Wang G, Dong X, Guo S, Wang X (2005) J Alloys Compd 388:284–292 131. Tliha M, Mathlouthi H, Khaldi C, Lamloumi J, Percheron-Guégan A (2006) J Power Sources 160:1391–1394 132. Moussa MB, Abedellaoui M, Mathlouthi H, Lamloumi J, Percheron-Guégan A (2006) J Alloys Compd 407:256–262 133. Ayari M, Paul-Boncour V, Lamloumi J, Percheron-Guégan A (2002) J Magn Magn Mater 242:850–853 134. Ayari M, Paul-Boncour V, Lamloumi J, Percheron-Guégan A, Guillot M (2005) J Magn Magn Mater 288:374–383 135. Moussa MB, Abedellaoui M, Mathlouthi H, Lamloumi J, Percheron-Guégan A (2008) J Alloys Compd 458:410–414 136. Kadir K, Sakai T, Uehara I (1997) J Alloys Compd 257: 115–121 137. Kadir K, Kuriyama N, Sakai T, Uehara I, Eriksson L (1999) J Alloys Compd 284:145–154 138. Kadir K, Sakai T, Uehara I (1999) J Alloys Compd 287: 264–270 139. Kadir K, Sakai T, Uehara I (2000) J Alloys Compd 302:112–117 140. Liu YF, Pan HG, Gao MX, Li R, Lei YQ (2004) J Alloys Compd 376:304–313 141. Zhang YH, Li BW, Ren HP, Cai Y, Dong XP, Wang XL (2008) J Alloys Compd 458:340–345 142. Liao B, Lei YQ, Chen LX, Lu GL, Pan HG, Wang QD (2004) J Alloys Compd 376:186–195 143. Zhang YH, Li BW, Ren HP, Wu ZW, Dong XP, Wang XL (2008) J Alloys Compd 461:591–597 144. Zhang YH, Li BW, Ren HP, Guo SH, Qi Y, Wang XL (2009) J Alloys Compd 485:333–339 145. Shen X, Chen Y, Tao M, Wu C, Deng G, Kang Z (2009) Int J Hydrogen Energy 34:2661–2669 146. Zhang YH, Li BW, Ren HP, Cai Y, Dong XP, Wang XL (2007) Int J Hydrogen Energy 32:4627–4634 147. Zhang YH, Li BW, Ren HP, Wu ZW, Dong XP, Wang XL (2008) J Alloys Compd 460:414–420 148. Bai TY, Han SM, Zhu XL, Zhang Y, Li Y, Zhang WC (2009) Mater Chem Phys 117:173–177 149. Zhang YH, Dong XP, Zhao DL, Guo SH, Qi Y, Wang XL (2008) Trans Nonferrous Metals Soc China 18:857–864 150. Kohno T, Yoshida H, Kawashima F, Inaba T, Sakai I, Yamamoto M, Kanda M (2000) J Alloys Compd 311:L5–L7 151. Zhnag XB, Sun DZ, Yin WY, Chai YJ, Zhao MS (2005) Electrochim Acta 50:1957–1964 152. Zhang YH, Wang GQ, Dong XP, Guo SH, Ren JY, Wang XL (2006) Rare Metal Mater Eng 35:277–282 153. Cheng LF, Wang RB, Pu CH, Wang BG, Li ZL, Luo YW, He DN, Yang CZ (2009) Rare Metal Mater Eng 38:451–455 154. Wei XD, Zhang P, Dong H, Liu YN, Zhu JW, Yu G (2008) J Alloys Compd 458:583–587 155. Wei XD, Liu SS, Dong H, Zhang P, Liu YN, Zhu JW, Yu G (2007) J Electrochim Acta 52:2423–2428 156. Guo J, Yang K, Xu LQ, Liu YX, Zhou KW (2007) J Hydrogen Energy 32:2412–2416 157. Shao H, Asano K, Enoki H, Akiba E (2009) J Alloys Compd 479: 409–413 158. Zhao X, Ma L (2009) Int J Hydrogen Energy 34:4788–4796 159. Bououdina M, Grant D, Walker G (2006) Int J Hydrogen Energy 31: 177–182 160. Buschow KHJ, Bouten PCP, Miedema AR (1982) Rep Prog Phys 45:937–1039

J Solid State Electrochem (2014) 18:577–593 161. Kleperis J, Wojcik G, Czerwinski A, Skowronski J, Kopczyk M, Beltowska-Brzezinska M (2001) J Solid State Electrochem 5: 229–249 162. Abrashev B, Spassov T, Bliznakov S, Popov A (2010) Int J Hydrogen Energy 35:6332–6337 163. Schlapbach L, Riesterer T (1983) Appl Phys A 32:169–182 164. Sandrock GD, Goodell PD (1984) J Less-Common Metals 104: 159–173 165. Schlapbach L (1992) Hydrogen in intermetallic compounds II. In: Schlapbach L (ed) Topics in Appl. Phys. 67. Springer, Berlin, p 76 166. Sandrock G (1999) J Alloys Compd 293:877–888 167. Lee HH, Lee KY, Lee JY (1996) J Alloys Compd 239:63–70 168. Xu YH, Chen CP, Wang XL, Wang QD (2002) J Alloys Compd 335:262–265 169. Jurczyk M, Jankowska E, Nowak M, Jakubowicz J (2002) J Alloys Compd 336:265–269 170. Cuevas F, Latroche M, Percheron-Guegan A (2005) J Alloys Compd 404:545–549 171. Drenchev B, Spassov T (2007) J Alloys Compd 441:197–201 172. Szajek A, Jurczyk M, Jankowska E (2003) J AlloysCompd 348: 285–292 173. Cuevas F, Latroche M, Ochin P, Dezellus A, Fernandez JF, Sanchez C et al (2002) J Alloys Compd 330:250–255 174. Drenchev B, Spassov T, Radev D (2008) J Appl Electrochem 38: 437–444 175. Wang CS, Lei YQ, Wang QD (1998) Electrochim Acta 43: 3193–3207 176. Wang CS, Lei YQ, Wang QD (1998) J Power Sources 70:222–227 177. Westlake DG (1983) J Less-Common Met 90:251–273 178. Stetson NT, Yvon K, Fischer P (1994) Inorg Chem 33:4598–4599 179. Joubert JM, Cerny R, Latroche M, Percheron-Guegan A, Yvon K (2005) Intermetallics 13:227–231 180. Bliznakov S, Lefterova E, Bozukov L, Popov A, Andreev P (2004) Proceedings of the International Workshop “Advanced Techniques for Energy Sources Investigation and Testing”, September 4–9, Sofia, Bulgaria 181. Zhang RJ, Lu MQ, Chen DM, Yang K (2005) Acta Metall Sinica 41:427–432 182. Hong k (1991) Method for preparing materials for hydrogen storage and for hydride electrode applications, US patent 5,006,328 183. Sastri MVC (ed) (1998) Metal hydrides: Fundamentals and applications. Narosa, New Delhi 184. Hagstrom MT, Vanhanen JP, Lund PD (1998) J Alloys Compds 269:288–293 185. Hagstrom MT, Klyamkin SN, Lund PD (1999) J Alloys Compds 293:67–73 186. Kapischke J, Hapke J (1998) Exp Therm Fluid Sci 18:70–81 187. Puszkiel JA, Arneodo Larochette P, Gennari FC (2008) Int J Hydrogen Energy 33:3555–3560 188. Singh RK, Lototsky MV, Srivastava ON (2007) Int J Hydrogen Energy 32:2971–2976 189. Feng F, Geng M, Northwood DO (2002) Comput Mater Sci 23: 291–299 190. Giza K, Iwasieczko W, Pavlyuk VV, Bala H, Drulis H (2008) J Power Sources 181:38–40 191. Laurencelle F, Dehouche Z, Goyette J (2006) J Alloys Compds 424: 266–271 192. Kandavel M, Bhat VV, Rougier A, Aymard L, Nazri GA, Tarascon JM (2008) Int J Hydrogen Energy 33:3754–3761 193. Anil Kumar E, Prakash Maiya M, Srinivasa Murthy S (2007) Int J Hydrogen Energy 32:2382–2389 194. Yamaguchi M, Akiba E (1994) Ternary hydrides. In: Buschow KHJ (ed) Electronic and magnetic properties of metals andceramics part II. Wiley, New York, pp 334–398 195. Bliznakov S, Lefterova E, Bozukov L, Popov A, Andreev P (2004) Proceedings of the International Workshop “Advanced Techniques


196. 197. 198. 199. 200. 201. 202. 203.

204. 205. 206. 207. 208. 209. 210. 211. 212. 213. 214. 215. 216. 217. 218. 219.

for Energy Sources Investigation and Testing”, September 4–9, Sofia, Bulgaria Schlapbach L (1988) Hydrogen in intermetallic compounds I 63: 350. Springer, Berlin Jordy C, Percheron-Guegan A, Bouet J, Sanchez P, Chanson C, Leonardi J (1991) J Less-Common Met 172:1236–1245 Young K, Chao B, Bendersky LA, Wang K (2012) J Power Sources 218:487–494 Balasubramaniam R (1997) J Alloys Compd 253:203–206 Inui H, Yamamoto T, Hirota M, Yamaguchi M (2002) J Alloys Compd 330:117–124 Kisi EH, Buckley CE, Gray EM (1992) J Alloys Compd 185:369–384 Wu E, Kisi EH, Maca Gray E (1998) J Appl Crystallogr 31:363–368 Adzic G, Johnson JR, Reilly JJ, McBreen J, Mukerjee S, Kumar MPS, Zhang W, Srinivasan S (1995) J Electrochem Soc 142:3429–3433 Peng CH, Zhu M (2004) J Alloys Compd 375:324–329 Young K, Ouchi T, Fetcenko MA (2009) J Alloys Compd 480:428–433 Young K, Ouchi T, Fetcenko MA (2009) J Alloys Compd 480:440–448 Osumi Y, Suzuki H, Kato A, Oguro K, Kawai S, Kaneko M (1983) J Less-Common Met 89:287–292 Mungole MN, Balasubramaniam R, Rai KN (1995) Int J Hydrogen Energy 20:151–157 Gamo T, Moriwaki Y, Yanagihara N, Yamashita T, Iwaki T (1985) Int J Hydrogen Energy 10:39–47 Moriwaki Y, Gamo T, Iwaki T (1991) J Less-Comm Met 172:1028–1035 Popović MM, Grgur BN, Vojnović MV, Rakin P, Krstajić NV (2000) J Alloys Compd 298:107–113 Witham C, Fultz B, Ratnakumar BV, Bowman RC, Hightower A (1997) J Electrochem Soc 144:3758–3764 Wang CS, Soriaga MP, Srinivasan S (2000) J Power Sources 85: 212–223 Zheng G, Popov BN, White RE (1996) J Electrochem Soc 143:435–441 Popov BN, Zheng G, White RE (1996) J Appl Electrochem 26:603–611 Tliha M, Boussami S, Mathlouthi H, Lamloumi J, PercheronGuégan A (2010) J Alloys Compd 506:559–564 Tliha M, Mathlouthi H, Lamloumi J, Percheron-Guégan (2007) Int J Hydrogen Energy 32:611–614 Verbetsky VN, Petrii OA, Vasina SY, Bespalov AP (1999) Int J Hydrogen Energy 24:247–249 Zhang X, Yin W, Chai Y, Zhao M (2005) Mater Sci Eng B 117:123–128

593 220. Iwakura C, Oura T, Inoue H, Matsuoka M, Yamamoto Y (1995) J Electroanal Chem 398:37–41 221. Yuan X, Xu N (2001) J Alloys Compd 316:113–117 222. Yuan X, Xu N (2001) J Alloys Compd 329:115–120 223. Yuan X, Ma ZF, Nuli Y, Xu N (2004) J Alloys Compd 385:90–95 224. Tliha M, Mathlouthi H, Lamloumi J, Percheron-Guégan (2007) J Alloys Compd 436:221–225 225. Zhou ZX, Huang JS, Hu WK, Yao FY, Zhang YS (1995) J Alloys Compounds 231:297–301 226. Yang XG, Liaw BY (2001) J Power Sources 102:186–197 227. Ciureanu M, Ryan DH, Strom-Olsen JO, Trudeau ML (1993) J Electrochem Soc 140:579–584 228. Karlicek RF Jr, Lowe IJ (1980) J Less-Common Met 73:219–225 229. Zuchner H, Hempelmann TR (1991) J Less-Common Met 172: 611–617 230. Wang XL, Suda S (1992) Int J Hydrogen Energy 17:139–147 231. Wang CS, Wang XH, Lei YQ, Chen CP, Wang QD (1996) Int J Hydrogen Energy 21:471–478 232. Zhang W, Srinivasan S, Ploehn HJ (1996) J Electrochem Soc 143: 4039–4047 233. Wicke E, Brodowsky H (1978) Hydrogen in palladium alloys (chapter 3). In: Alefeld G, Volkl J (eds) Hydrogen in metals II, application oriented properties, topics in applied physics (vol. 29). Springer, Berlin 234. Yuan X, Xu N (2001) J Appl Electrochem 31:1033–1039 235. Feng F, Han J, Geng M, Northwood DO (2000) J Electroanal Chem 487:111–119 236. Feng F, Northwood DO (2004) J Power Sources 136:346–350 237. Kim HS, Nishizawa M, Uchida I (1999) Electrochim Acta 45:483–488 238. Iwakura C, Fukuda K, Senoh H, Inoue H, Matsuoka M, Yamamoto Y (1998) Electrochim Acta 43:2041–2046 239. Geng M, Han J, Feng F, Matchett AJ, Northwood DO (1999) J New Mat Electrochem Systems 2:261–265 240. Khodosov E, Linnik A, Kobsenko G, Ivanchenko V (1977) In: Proceedings of the 2nd international congress on ‘Hydorgen in metals’, (Paris). Pergamon, Oxford, paper 1D10 241. Chu HL, Zhang Y, Sun LX, Qiu SJ, Xu F, Yuan HT (2007) Int J Hydrogen Energy 32:1898–1904 242. Chu H, Zhang Y, Sun L, Qiu S, Qi Y, Xu F, Yuan H (2007) J Alloys Compd 446:614–619 243. Campbell SI, Kemali M, Ross DK, Bull DJ, Fernandez JF, Johnson MR (1999) J Alloys Compd 293:351–355 244. Ramya K, Rajalakshmi N, Sridhar P, Sivasankar B (2004) J Alloys Compd 373:252–259