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Electrochemical performance of porous Ni3Al electrodes for hydrogen evolution reaction
Hongxing Dong
a , b , Ting Lei a, Yuehui He a,*, Nanping Xu c , Baiyun Huang a, C.T. Liu d
a State Key Laboratory for Powder Metallurgy, Central South University, Changsha, Hunan 410083, China b Institute of Electro-Mechanical, Hangzhou Polytech, Hangzhou, Zhejiang 311402, China c Membrane Science and Technology Research Center, Nanjing University of Technology, Nanjing 210009, China d Department of Mechanical Engineering, The Hong Kong Polytechnic University, Hong Kong, China
a r t i c l e i n f o
Article history:
Received 23 March 2011 Received in revised form 2 June 2011 Accepted 8 June 2011 Available online 18 July 2011
Keywords:
Porous Ni3Al intermetallics Reactive synthesis Hydrogen evolution reaction Electrocatalytic activity Electrolysis
a b s t r a c t
Porous Ni3Al intermetallic material with a mean pore diameter of around 1
mm was
prepared by step sintering Ni and Al powder pressed compacts in vacuum furnace at 900 C. The electrocatalytic activity of the as-fabricated porous Ni3Al material as an elec- trode for hydrogen evolution reaction (HER) in alkaline solutions was investigated by cyclic voltammetry (CV), linear sweep voltammetry (LSV) and electrochemical impedance spec- troscopy (EIS) techniques. It is found that the onset potential of porous Ni3Al for HER shifted in the positive direction favoring hydrogen generation with lower overpotential, compared with foam Ni and dense Ni electrodes. Effects of electrolyte concentration and temperature on HER as well as the electrochemical stability in alkaline solution were investigated and the electrochemical activation energy was determined for the porous Ni3Al. The increased activity for HER was attributed to the high porosity, an increased electrochemical surface area and the nanostructure of porous Ni3Al electrode. The corro- sion tests showed that the corrosion resistance of porous Ni3Al electrode changed during the immersion process due to the formation of passive film layers. Copyright
ª 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights
reserved.
1.
Introduction
Hydrogen, as a high-quality clean and renewable energy resource, is increasingly considered as one of the most promising candidates for the fuel of the future [1,2]. The production of hydrogen by water electrolysis is a simple, mature, large-scale industrial method, but the key problems of this technology mainly related to relatively low production rates and high energy consumption, restrain its commercial application at the present [3] . Optimizing structural design and developing advanced electrodes have been crucial to reduce the electrical consumption and improve the efficiency of water electrolysis [4,5] . Therefore, considerable research
efforts have been conducted to enhance the electrocatalytic activity of electrodes to reduce the overpotentials for the hydrogen evolution reaction (HER) [6
e9] .
The increase of electrode surface area is one of the effec-
tive means of improving the activity of electrodes. Porous materials as electrodes for water electrolysis with larger surface area have been usually obtained through leaching active elements (such as Al, Zn, Cu, etc. [11
e16]) out of the
precursor, among which, porous Raney Ni [10] is a typical representative. However, the instability of Raney Ni limited its practical application due to the dissolution of active elements in working. Moreover, the electrocatalytic properties were reduced due to hydrogen bubble trapping in the small holes
* Corresponding author. Tel.:
þ86 731 88836144; fax: þ86 731 88710855.
E-mail address: yuehui@mail.csu.edu.cn (Y. He).
A v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m
j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / h e
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 3 6 ( 2 0 1 1 ) 1 2 1 1 2
e1 2 1 2 0
0360-3199/$
e see front matter Copyright ª 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
doi:10.1016/j.ijhydene.2011.06.115

pageNum = 2

(usually
[4]. Therefore, in
order to make water electrolysis more efficient and econom- ical, there is a high demand to decrease the overpotentials of electrode reactions and to improve its catalytic performance as well as to select inexpensive electrode materials with good electrocatalytic activity.
Ni3Al intermetallic compound has shown good alkaline
corrosion resistance and special mechanical properties [17,18]. Therefore, it is possible for electrically conductive porous Ni3Al materials to be used as electrodes in water electrolysis. In this paper, we presented a way to fabricate the novel porous Ni3Al electrode by a combination of elemental reaction synthesis and step sintering process. The electro- chemical behavior of hydrogen evolution and the electro- catalytic activity toward HER as well as the HER stability and corrosion behavior of the porous Ni3Al electrode in alkaline solution were investigated.
2.
Experimental
2.1.
Preparation of porous Ni3Al electrode
Commercially pure carbonyl Ni (3
e5 mm) and gas atomizing Al
(3
e5 mm) powders were mixed in the ratio of Nie14 wt%Al.
The Ni and Al powders were ball-mixed for 10 h using a mixer, and
pressed
to
compacts
with
a
dimension
of
5 mm
45 mm 1 mm under a pressure of 200 MPa. The
specimens were then sintered in a vacuum furnace under 1
103 Pa at temperatures of 480, 580, and 900 C for dura-
tions of 1 h followed by furnace cooling to room temperature. The heating rate was 2 C min
1 during the whole process in
order to avoid the possible self-propagating high-temperature synthesis (SHS) procedure and to realize near net-shape of porous Ni3Al materials. The as-obtained porous Ni3Al mate- rials were examined by X-ray diffraction to identify the phase composition and corresponding crystalline structures.
2.2.
Characterization of porous Ni3Al
The morphology and composition as well as crystalline structures of the fabricated porous Ni3Al were characterized by a field-emission scanning electron microscope (NOVA NANOSEM 230) equipped with EDX and X-ray diffractometry (XRD: D/MAX-255). The pore size distribution for porous Ni3Al was measured by the mercury porosimeter method (Pore- master GT-60).
Electrochemical characterizations of porous Ni3Al elec-
trode for hydrogen evolution in 6 M KOH solution were carried out by cyclic voltammetry, cathodic polarization, and elec- trochemical
impedance
spectroscopy
(EIS)
techniques,
respectively. The electrochemical measurements were carried out in a conventional three-electrode system, using 6 M KOH solution as electrolyte. The alkaline solutions were prepared with triple-distilled water. The working electrode was fixed in a Teflon holder, leaving a geometric surface area of 1 cm
2
exposed. The counter electrode was large Pt foil and the reference was a Hg/HgO electrode. All potentials are given vs the Hg/HgO electrode in 6 M KOH. The working electrode was reduced at
1.5 V for 600 s prior to each measurement.
Steady-state CV curves and Tafel curve were recorded in
alkaline solution at a scan rate of 10 mV s
1 and 2 mV s1,
respectively. The EIS measurements at different cathodic overpotentials were performed at the steady-state in the frequency range of 10 kHz to 0.1 Hz, and with the perturbation amplitude of 5 mV. For comparison, commercial foam Ni (porosity: 90%) and pure compact Ni electrodes were also tested.
3.
Results and discussion
3.1.
Morphology characterization of porous Ni3Al
The scanning electron micrographs of porous Ni3Al and green compacts are shown in Fig. 1 . As could be seen in Fig. 1(a) , the green compacts consist of Ni and Al particles. Fig. 1(b) shows the porous micrograph of the fabricated porous Ni3Al, indi- cating a high open porosity up to 40%. The cross-section of sintered compact presented in Fig. 1(c) shows that the thick- ness of porous Ni3Al is about 1 mm. Zooming in, a large number of interconnected pores are significant as shown by inset in Fig. 1(c). The pore formation mechanism during the elemental powder synthesis has been documented in other works [19] .
Fig. 2 presents the typical pore size distribution diagram of
porous Ni3Al, indicating a relatively narrow pore size distri- bution with a mean pore diameter of around 1
mm. Further-
more, the electrical resistance measured by twin bridged technique is about 1
104 U cm, which resembles that of
foam Ni (4.6
104 U cm), suggesting that the electrical
conductivity of porous Ni3Al is excellent.
3.2.
XRD analyses of phase transformation during
sintering process
The fabricated porous Ni3Al was examined by X-ray diffrac- tion to identify its phase composition and crystalline struc- ture. Fig. 3 shows the XRD patterns of powder compacts at different temperatures. The green compact consists of only Ni and Al phases. As the temperature rises, peaks related to Ni2Al3 and Ni3Al phases appear, while the Al peaks become weakened. The formation of intermediate phase during the sintering procedure results from the interdiffusion reaction between Ni and Al atoms in compacts. When the temperature reaches 900 C, single Ni3Al phase appears on the entire compact. Six peaks in the diffraction spectrum at 25, 37.5, 44, 51, 57.5 and 75 can be assigned to (100), (110), (111), (200), (210) and (220) planes of Ni3Al, respectively. The grain size of Ni3Al was estimated to be 14.9 nm, from the full width at half maximum of the most intense diffraction line of Ni3Al (111) by Scherrer’s equation [20] .
3.3.
Electrocatalytic evolution of hydrogen on porous
Ni3Al electrode
The electrocatalytic activity of porous Ni3Al as an electrode for HER in alkaline solution was investigated. For comparison, foam Ni and bulk Ni electrodes are also measured. Cyclic voltammogram is employed to determine the double layer
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capacity of the porous Ni3Al and the typical CV recorded at different sweep rates is displayed in Fig. 4(a) . Stationary double layer currents are seen between the potential ranging from 
 0.28 to 0.18 V vs Hg/HgO. In this region, the average of 
 capacitive current is proportional to the double layer capaci- tance, and the variation of the average of double layer current 
 densities jdl,ave 
 ¼ (jjcj þ jjaj)/2 as a function of potential sweep 
 rate is described as following [21] : 
 jdl;ave ¼ 
  
 jc 
 j þ jja 
  
 2 
 ¼ Cd1 
  
 dE=dt 
  
 (1) 
 where Cd1 is the double layer capacitance of electrode, and jc and ja are cathodic and anodic current density, respectively. Plots of current density against sweep rate for all the three studied electrodes exhibit good linear relationship, as pre- sented in Fig. 4(b) . Therefore, the capacitances of three elec- trodes can be estimated from the slopes. The relative magnitude of the respective roughness factor, Rf, is calculated by assuming the value of 20 
 mF cm2 for the capacitance of 
 smooth mercury electrode, and the results are summarized in Table 1 . The results indicate that both the capacitance order and roughness factor order are: porous Ni3Al 
 > foam Ni > bulk 
 Ni, indicating that porous Ni3Al has the largest active surface area. 
 The linear sweep cathodic polarization for HER in 6 M KOH 
 is illustrated in Fig. 4(c). It shows that the cathodic current densities of the three electrodes increase as the overpotential increases. Moreover, the onset potential of porous Ni3Al for 
 Fig. 1 
 e SEM morphology of porous NieAl: (a) green 
 compacts; (b) sintered porous Ni 
 eAl; (c) cross-section 
 morphology, and the inset is a magnification of (c). 
 Fig. 2 
 e Pore distribution of porous Ni3Al. 
 Fig. 3 
 e Phase transformation of porous NieAl during the 
 sintering procedure. 
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HER is much more positive, favoring hydrogen generation with lower overpotential, as compared to foam Ni and pure compact Ni electrodes, which indicates that porous Ni3Al has the higher hydrogen evolution activity and better electro- catalytic performance. The current density on porous Ni3Al
electrode is higher than 90 mA cm
2
at the potential of
1.35 V, which is 3 times higher than that on foam Ni elec- trode (26.9 mA cm
2). The high electrocatalytic activity of the
porous Ni3Al electrode is likely attributed to the large elec- trochemical surface area.
Tafel slopes of the three electrodes for HER on the linear
sweep curve at the lower overpotential region are summa- rized in Table 1. The exchange current density, j0, a critical kinetic parameter in the dynamic electrochemistry, is derived directly from the intercept by the extrapolation of Tafel slope to equilibrium potential. As shown in Table 1 , the Tafel slopes for porous Ni3Al, foam Ni and pure compact Ni are 219, 130 and 107 mV, respectively. Generally, the lower Tafel slope indicates a favoring hydrogen generation. However, porous Ni3Al exhibits a high Tafel slope. Interestingly, the increase of Tafel slope during HER has also been reported on other porous materials [22
e25], the reason of which is likely due to the limit
diffusion with respect to the complex and disordered porous structures [22]. Mathematical models also confirmed the high Tafel slope of porous materials during the HER process [26]. In addition, the exchange current density j0 with respect to the effective
electrode
area
is
3.4
103, 6.15 104 and
5.9
104 mA cm2 for porous Ni3Al, foam Ni and pure
compact Ni, respectively. Clearly, the j0 on the porous Ni3Al is 10 times larger, indicating that porous Ni3Al has better cata- lytic properties for hydrogen evolution.
To further study the HER behavior on the interface of
porous electrode and electrolyte, the electrochemical imped- ance spectra of porous Ni3Al are recorded within the linear part of the potential region of Tafel plots, in which the steady- state conditions are ensured as shown in Fig. 4(c) . The repre- sentative Nyquist plots of the porous Ni3Al electrode at three different overpotentials are presented in Fig. 5 . It shows that the entire complex plane plots displayed two depressed semicircles, where a small semicircle in the high frequency domains was almost independent of the potential, whereas the semicircle in the low frequency domain decreased with the increase in negative overpotential. Since the features in the complex impedance plane plots are consistent with that for the HER on porous electrodes in alkaline medium reported in literature [27,28], it is reasonable to suggest that the hydrogen evolution mechanism on porous Ni3Al electrode is not modified during electrolysis and the hydrogen evolution should follow the same processes. Therefore, the high frequency semicircle was related to the electrode material and was independent of the kinetics of the faradic process, and the low frequency semicircle was attributed to the charge transfer resistance (Rct) of the HER and was dependent on the kinetics of reaction. Consequently, the impedance data can be inter- preted by an often used 2-CPE model containing a series connection of two parallel R-constant phase element (CPE) in series with uncompensated resistance due to the electrode configuration, which is well demonstrated in literature [5,29]. When the overpotentials increased, the Rct decreased from 0.347
U cm2 at h ¼ 75 mV to 0.259 U cm2 at h ¼ 135 mV,
indicating that Rct is dependent on the overpotential (where the Eequi is 0.902 V vs Hg/HgO obtained from the experiment). On the other hand, the value of Rct for porous Ni3Al is lower than those of porous Ni electrode prepared by leaching Al out from Ni/Al and Ni/Zn precursors [26]. The lowest charge
Fig. 4
e Electrochemistry properties of different cathode
electrode: (a) cyclic voltammograms in the double layer region of the porous Ni
eAl electrode at scan rates ranging
from 1 to 40 mV sL
1; (b) mean current density as a function
of scan rate for the electrodes; (c) the cathodic linear sweep for the electrodes at a scan rate of 10 mV sL
1.
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transfer resistance (Rct) as well as highest value of the esti- mated exchange current density ( j0) confirms that the porous Ni3Al electrode exhibits higher electrocatalytic activity toward hydrogen evolution than those foam Ni and pure compact Ni electrodes. 
 3.4. 
 Effect of parameters on the electrocatalytic 
 properties 
 3.4.1. 
 Effect of electrolyte concentration 
 The effect of electrolyte concentration on HER is investigated and the results are illustrated in Fig. 6 . Fig. 6(a) is the LSV curve recorded in KOH solution with concentrations ranging from 0.1 M to 8 M at a scan rate of 10 mV s 
 1. Fig. 6(b) shows the 
 variation of current density for HER as a function of KOH concentration ( j 
 eC ) on porous Ni3Al electrode at the potential 
 of 
 1.3 V. The current densities increase with the increase of 
 KOH concentration up to 6 M, and decrease thereafter. Apparently, porous Ni3Al electrode exhibits the best electro- catalytic activity for HER in 6 M KOH solution. 
 It is generally accepted that the HER mechanism in alkaline 
 solution is a combination of reaction steps involving the formation of adsorbed hydrogen [22,23]: 
 M 
 þ H2O þ e.K1 
 EK 
 1 
 MHads 
 þ OH ðVolmerÞ 
 (2) 
 MHads 
 þ H2O þ e.K2 
 EK 
 2 
 H2 
 þ M þ OH ðHeyrovskyÞ 
 (3) 
 where the subscript ads represents the adsorbed status, ki and ki (i ¼ 1, 2) are the rate constants of the forward and backward 
 reactions, which are influenced by the concentration of OH and H2O. It is well known that an appropriate increase of the electrolyte concentration will increase solution conductivity and ion activity, which are advantageous to ionic transfer in the solution. During the HER process, H2O and OH are competitively adsorbed on the electrode surface. When the electrolyte concentration is higher than 6 M, the increase of the concentration of electrolyte may result in an increase in the viscosity and a decrease in the ion activity, which in turn influences the departure of the bubbles and electron transfer. 
 Table 1 
 e Electrochemical properties of porous Ni3Al electrode observed at potentials close to the limits of the studied 
 domain. 
 Electrocatalysts 
 Tafel slope 
 (mV/dec) 
 i0 (mA/cm 
 2) 
 Cd ( 
 mF/cm2) 
 Rf 
 i0/Srealf 
 a (mA/cm2) 
 Onset potential 
 (V vs Hg/HgO) 
 I1.35V (mA/cm 
 2) 
 Pure flake Ni 
 107 
 0.007 
 234 
 11.7 
 5.9 
  104 
 1.25 
 10.1 
 Foam Ni 
 130 
 0.03 
 1007 
 50.4 
 6.15 
  104 
 1.15 
 26.9 
 Porous Ni3Al 
 219 
 1.9 
 10,930 
 546.5 
 3.4 
  103 
 0.95 
 90.1 
 a Note: the exchange current of real surface area. 
 Fig. 5 
 e Nyquist plots for porous Ni3Al electrode at different 
 overpotentials. 
 Fig. 6 
 e Influence of KOH concentration on the catalytic 
 activity of porous Ni3Al electrode for hydrogen evolution: 1: 0.1 mol LL 
 1; 2: 0.5 mol LL1; 3: 2 mol LL1; 4: 4 mol LL1; 5: 
 6 mol LL 
 1; 6: 8 mol LL1. 
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Meanwhile, higher concentration favors the adsorption of OH on the electrode surface, resulting in fewer sites for H2O adsorption. As a result, the overall reaction rates for hydrogen evolution, corresponding to the forward reactions of Volmer and Heyrovsky steps, were reduced. Therefore, it is important to maintain a constant electrolyte concentration during the water electrolysis process.
3.4.2.
Effect of electrolyte temperature
The Tafel plots recorded at different temperatures for the porous Ni3Al electrodes are presented in Fig. 7(a). The inset in Fig. 7(a) indicates the linear part from which the kinetic parameters are derived. In order to ensure good reproduc- ibility, the linear sweep voltammetry is swept from negative to positive potential direction. As could be seen in Fig. 7 a, Tafel slope is very similar for all temperatures. However, the increase of temperature leads to a significant reduction of the overpotential and an increase of the exchange current density. For comparison, the HER behaviors are also charac- terized on foam Ni electrode at temperatures ranging from 25 to 55 C, which displays the same increase trend with the
increase of temperature. However, it is worthy to note that at temperature of 65 C or higher, the foam Ni electrode exhibits decreased activity or even no activity for hydrogen evolution, and likely, serious passivation occurred on foam Ni at high temperature. Therefore, on this point of view, porous Ni3Al shows relatively better stability for temperature.
From the cathodic polarization curves in 6 M KOH solution
obtained at different temperatures, the exchange current densities are derived by extrapolation of Tafel slopes to zero overpotential, and the Arrhenius plot is present in Fig. 7(b). The curve of log j0 against T
1 exhibits a linear relationship
and thus electrochemical activation energies for the HER could be calculated according to the following equation [30]:
log j0
¼ logðFKcÞ DG0=2:303RT
(4)
where R is the gas constant and
DG0 is the apparent activation
energy. The calculated value of apparent activation energy for porous Ni3Al is 30.1 kJ mol
1, lower than those obtained on Ni
(35 kJ mol
1), NieMoeCd (32 kJ mol1), Fe (39 kJ mol1), and
Ni
eFe (31 kJ mol1) [31]. Apparently, porous Ni3Al shows
higher catalytic activity for HER by reducing the activation energy of the reaction, which is also confirmed by the reduced overpotential for hydrogen evolution as shown in Fig. 4(c). The
Fig. 7
e Influence of temperature on the catalytic activity of
porous Ni3Al electrode for hydrogen evolution.
Fig. 8
e Cyclic voltammograms at a scan rate of 10 mV sL1
on porous electrodes in 6 mol LL
1 KOH solution at different
cycles: (a) foam Ni, (b) porous Ni3Al.
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enhanced electrocatalytic activity of porous Ni3Al is attributed to its specific characteristic and porous structure.
3.5.
The electrochemical stability of porous Ni3Al
The stability of porous electrode in alkaline solution is vital for its practical application. CV is employed to investigate the stability of porous Ni3Al and foam Ni electrodes. Fig. 8 shows the cyclic voltammograms on foam Ni and porous Ni3Al recorded in 6 M KOH solution at 298 K at a scan rate of 10 mV s
1 for 100e500 cycles in the potential range of 1.4 to
0.75 V. The hydrogen evolution current densities at 1.395 V for porous Ni3Al at 100th, 200th, 300th, 400th, and 500th cycle are 113.8, 112.4, 109.8, 111.1 and 111.9 mA cm
2, respectively.
At the same potential, the hydrogen evolution current density for foam Ni at 100th, 200th, 300th, 400th and 500th cycle are 21.2, 17.7, 16.4, 15.7 and 15.9 mA cm
2, respectively. Compared
to the cathodic current density in the first cycle in alkaline
solution shown in Fig. 3, the current decays for porous Ni3Al after 100 and 500 cycles under the same conditions are about 1.6 and 7%, respectively, whereas the current decays for foam Ni after 100 and 500 cycles are 25 and 70%, respectively. It has also been reported a 37% current decay for foam Ni after 100 cycles in 6 M KOH among the potential region of
1.45 to
1.0 V [32] . These results suggest that porous Ni3Al has higher electrochemical stability for hydrogen evolution than foam Ni.
3.6.
The corrosion resistance of porous Ni3Al
The open circuit potential (Eocp) of porous Ni3Al electrode as a function of immersion time was also measured, which can give important results about porosity and corrosion behavior of metals [28]. The data obtained are given in Fig. 9 . It shows that the Eocp of porous Ni3Al electrode started from an active value (
0.65 V) and shifted to a nobler direction with the
immersion time, and then became stabilized after 50 h, indi- cating a good electrochemical stability. The change of the open circuit potential with time suggests the formation of passive film on porous Ni3Al surface in alkaline solution.
Fig. 10 is the Tafel curves of porous Ni3Al electrode after 1,
24 and 124 h exposure at open circuit conditions in 6 M KOH solution. It is speculated based on literature [11,33] that there probably exists NiO, NiOH and/or NiOOH between the poten- tial range of
0.8 V to þ0.5 V. Such a claim is supported by the
results reported on NiCoZn electrode [28]. Furthermore, the anodic current densities decrease with increasing exposure time due to intensified surface passivity, indicating the better corrosion resistance of porous Ni3Al in long-term immersion in alkaline solution. However, the cathodic current density of HER seems to be less influenced by the immersion time, implying an easy removal of any existing corrosion products from the porous Ni3Al during hydrogen gas evolution. It also indicates that the formation of passive layer reduces oxygen evolution reaction (see Fig. 10 from
þ0.5 to þ1.2 V).
The surface morphology and EDX analysis of porous Ni3Al
electrode after soaking in 6 M KOH solution for 124 h are dis- played in Fig. 11 . The EDX analysis suggested the formation of oxide or hydrated oxide on the porous Ni3Al surface, which is in good agreement with the anodic passivation as depicted in
0
20
40
60
80
100
120
140
-0.7
-0.6
-0.5
-0.4
-0.3
-0.2
-0.1
E
ocp
/
V v
s.
Hg
/Hg
O
t / Hours
Fig. 9
e Change of open circuit potential with immersion
time.
Fig. 10
e Tafel curves of porous Ni3Al electrode after
different exposure time in 6 mol LL
1 KOH.
Fig. 11
e SEM micrograph and EDS analysis of porous Ni3Al
after 124 h exposure in 6 mol LL
1 KOH.
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Fig. 10. No significant changes are observed on the surface morphology of porous Ni3Al after immersion in 6 M KOH solution in comparison with that of as-prepared porous Ni3Al specimen shown in Fig. 1(b). Moreover, the ion concentration of Al and Ni in the alkaline solution after soaking for 124 h is about 4.32 
  106 g mL1 and 1  108 g mL1, respectively, suggest- 
 ing that the dissolution of Al and Ni is neglectable. Accordingly, the passive film may function as a barrier to improve the corrosion resistance of porous Ni3Al in alkaline solution. 
 4. 
 Conclusions 
 Ni3Al intermetallic compound with porous structure was prepared through elemental powders reaction synthesis. The fabricated porous Ni3Al had a narrow pore size distribution with a mean pore diameter of around 1 
 mm. The onset 
 potential of hydrogen evolution on porous Ni3Al is higher than that of foam Ni and dense Ni materials. The best catalytic performance was found for HER in 6 M alkaline solution. The apparent activation energy of porous Ni3Al was 30.1 kJ mol 
 1. 
 Polarization measurements suggested that the formation of a passive film on porous Ni3Al surface increased its corrosion resistance, but had little influence on its catalytic activity for the HER in alkaline medium. The excellent performance of hydrogen evolution of porous Ni3Al may be ascribed to its specific characteristic and porous structure. Porous Ni3Al exhibits better electrocatalytic activity toward hydrogen evolution reaction and electrochemical stability in alkaline solution, which is of important for practical application in water electrolysis for hydrogen generation. 
 Acknowledgments 
 This research was financially supported by the National Natural Science Foundation of China (No. 20476106, No. 50721003 and No. 20636020) and by the National Natural Science 
 Funds 
 for 
 Distinguished 
 Young 
 Scholar 
 (No. 
 50825102), “973” program (No. 2009B623400), “863” program (2006AA03Z511). 
 r e f e r e n c e s 
 [1] Ramachandran R, Raghu KM. An overview of industrial uses 
 of hydrogen. International Journal of Hydrogen Energy 1998; 23(7):593 
 e8. 
 [2] Armor JN. Catalysis and the hydrogen economy. Catalysis 
 Letters 2005;101(3 
 e4):131e5. 
 [3] Holladay JD, Hu J, King DL, Wang Y. Review: an overview of 
 hydrogen production technologies. Catalysis Today 2009; 139(4):244 
 e60. 
 [4] Marozzi CA, Chialvo AC. Development of electrode 
 morphologies of interest in electrocatalysis: part 2: hydrogen evolution reaction on macroporous nickel electrodes. Electrochimica Acta 2001;46(6):861 
 e6. 
 [5] Losiewicza B, Budnioka A, Ro´wi 
 nskia E, Giewkaa E, Lasia A. 
 The structure, morphology and electrochemical impedance study of the hydrogen evolution reaction on the modified 
 nickel electrodes. International Journal of Hydrogen Energy 2004;29(2):145 
 e57. 
 [6] Kibria MF, Mridha MS, Khan AH. Electrochemical studies of 
 a nickel electrode for the hydrogen evolution reaction. International Journal of Hydrogen Energy 1995;20(6):435 
 e40. 
 [7] Zheng Haitao, Mathe Mkhulu. Hydrogen evolution reaction 
 on single crystal WO3/C nanoparticles supported on carbon in acid and alkaline solution. International Journal of Hydrogen Energy 2011;36(3):1960 
 e4. 
 [8] Rosalbino F, Maccio` D, Saccone A, Angelini E, Delfino S. 
 Fe 
 eMoeR (R ¼ rare earth metal) crystalline alloys as 
 a cathode material for hydrogen evolution reaction in alkaline solution. International Journal of Hydrogen Energy 2011;36(3):1965 
 e73. 
 [9] Adriana NC, Sergio ASM, Luis AA. Studies of the hydrogen 
 evolution reaction on smooth Co and electrodeposited Ni 
 eCo 
 ultramicroelectrode. Electrochemistry Communications 1999;1(12):600 
 e4. 
 [10] Tanaka S, Hirose N, Tanaki T. Evaluation of Raney-nickel 
 cathodes prepared with aluminum powder and tin powder. International Journal of Hydrogen Energy 2000;25(5):481 
 e5. 
 [11] Ramazan S, G 
 }ufe´za K. Hydrogen evolution and corrosion 
 performance of NiZn coatings. Energy Conversion and Management 2007;48(2):583 
 e91. 
 [12] Chen LL, Andrzei L. Ni 
 eAl Powder electrocatalyst for 
 hydrogen evolution: effect of Heat-treatment on morphology, composition, and kinetics. Journal of the Electrochemical Society 1993;140(9):2464 
 e72. 
 [13] Miao HJ, Piron DL. Composite-coating electrodes for hydrogen 
 evolution reaction. Electrochimica Acta 1993;38(8):1079 
 e85. 
 [14] Endoh E, Otouma H, Morimoto T. Advanced low hydrogen 
 overvoltage cathode for chlor-alkali electrolysis cells. International Journal of Hydrogen Energy 1988;13(4):207 
 e13. 
 [15] Xu CX, Wang LQ, Wang RY, Wang K, Zhang Y, Tian F, et al. 
 Nanotubular mesoporous bimetallic nanostructures with enchanced electrocatalytic performance. Advanced Materials 2009;21(21):2165 
 e9. 
 [16] Tanaka Sh, Hirose N, Tanaki T, Ogata YH. Effect of Ni 
 eAl 
 precursor alloy on the catalytic activity for a Raney-Ni cathode. Journal of the Electrochemical Society 2000;147(6): 2242 
 e5. 
 [17] Wu L, Dong HX, He YH. Preparation and corrosion resistance 
 in KOH solution of porous Ni3Al. Chinese Journal of Materials Research 2011;25(2):118 
 e23. 
 [18] Dong HX, He YH, Jiang Y, Wu L, Zou J, Xu NP, et al. Effect of Al 
 content on porous Ni 
 eAl alloys. Materials Science and 
 Engineering A 2011;528(13 
 e14):4849e55. 
 [19] He YH, Jiang Y, Xu NP, Zou J, Huang BY, Liu CT, et al. 
 Fabrication of Ti 
 eAl micro/nanometer-sized porous alloys 
 through Kirkendall effect. Advanced Materials 2007;19(16): 2102 
 e6. 
 [20] Crabb EM, Ravikumar MK. Synthesis and characterisation of 
 carbonsupported PtGe electrocatalysts for CO oxidation. Electrochimica Acta 2001;46(7):1033 
 e41. 
 [21] Bai C, Hong L, Li JB, Li X, Yang J, Tao J. Core-ring structured 
 NiCo2O4 nanoplatelets: synthesis, characterization, and electrocatalytic applications. Advanced Functional Materials 2008;18(9):1440 
 e7. 
 [22] Andrea K, Nicolae V, Waltraut B, Narcis D. Kinetics of 
 hydrogen evolution reaction on skeleton nickel and nickel 
 etitanium electrodes obtained by thermal arc spraying 
 technique. International Journal of Hydrogen Energy 2007; 32(15):3258 
 e65. 
 [23] Rami A, Lasia A. Kinetics of hydrogen evolution on Ni 
 eAl 
 alloy electrodes. Journal of Applied Electrochemistry 1992; 22(4):376 
 e82. 
 [24] Lasia A. Hydrogen evolution/oxidation reactions on porous 
 electrodes. Journal of Electroanalytical Chemistry 1998; 454(1):115 
 e21. 
 i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 3 6 ( 2 0 1 1 ) 1 2 1 1 2 
 e1 2 1 2 0 
 12119

pageNum = 9

[25] Los P, Rami A, Lasia A. Hydrogen evolution reaction on Ni 
 eAl 
 electrodes. Journal of Applied Electrochemistry 1993;23(2): 135 
 e40. 
 [26] Hitz C, Lasia A. Experimental study and modeling of 
 impedance of the her on porous Ni electrodes. Journal of Electroanalytical Chemistry 2001;500(1 
 e2):213e22. 
 [27] Joe¨l F, Danielle M, Legoux JG. Wire-arc sprayed nickel based 
 coating for hydrogen evolution reaction in alkaline solutions. International Journal of Hydrogen Energy 1999;24(6):519 
 e28. 
 [28] Solmaz R, Do¨ner A, S‚ahin _I, Yuce AO, Kardas G, Yazici B, et al. 
 The stability of NiCoZn electrocatalyst for hydrogen evolution activity in alkaline solution during long-term electrolysis. International Journal of Hydrogen Energy 2009; 34(19):7910 
 e8. 
 [29] Jafarian M, Azizi O, Gobal F, Mahjani MG. Kinetics and 
 electrocatalytic behavior of nanocrystalline CoNiFe alloy in 
 hydrogen evolution reaction. International Journal of Hydrogen Energy 2007;32(12):1686 
 e93. 
 [30] Zha QX. Introduction to electrode kinetics. Beijing: Science 
 Press; 2002. p. 237. 
 [31] Carvalho JD, Tremiliosi-Filho GAL, Srinivasan AI, Wanger S, 
 Wroblowa H. Electrode materials and processes for energy conversion and storage. Pennington: The Electrochemical Society; 1987. p. 356. 
 [32] Zheng HJ, Huang JG, Wang W, Ma CN. Preparation of nano- 
 crystalline tungsten carbide thin film electrode and its electrocatalytic activity for hydrogen evolution. Electrochemistry Communications 2005;7(10):1045 
 e9. 
 [33] Wang LP, Zhang JY, Gao Y, Xue QJ, Hua LT, Xu T. Grain size 
 effect in corrosion behavior of electrodeposited nanocrystalline Ni coatings in alkaline solutions. Scripta Materialia 2006;55(7):657 
 e60. 
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 12120

pageNum = 10

pageNum = 11

pageNum = 12

capacity of the porous Ni3Al and the typical CV recorded at different sweep rates is displayed in Fig. 4(a) . Stationary double layer currents are seen between the potential ranging from 
 0.28 to 0.18 V vs Hg/HgO. In this region, the average of 
 capacitive current is proportional to the double layer capaci- tance, and the variation of the average of double layer current 
 densities jdl,ave 
 ¼ (jjcj þ jjaj)/2 as a function of potential sweep 
 rate is described as following [21] : 
 jdl;ave ¼ 
 
 jc 
 j þ jja 
 
 2 
 ¼ Cd1 
 
 dE=dt 
 
 (1) 
 where Cd1 is the double layer capacitance of electrode, and jc and ja are cathodic and anodic current density, respectively. Plots of current density against sweep rate for all the three studied electrodes exhibit good linear relationship, as pre- sented in Fig. 4(b) . Therefore, the capacitances of three elec- trodes can be estimated from the slopes. The relative magnitude of the respective roughness factor, Rf, is calculated by assuming the value of 20 
 mF cm2 for the capacitance of 
 smooth mercury electrode, and the results are summarized in Table 1 . The results indicate that both the capacitance order and roughness factor order are: porous Ni3Al 
 > foam Ni > bulk 
 Ni, indicating that porous Ni3Al has the largest active surface area. 
 The linear sweep cathodic polarization for HER in 6 M KOH 
 is illustrated in Fig. 4(c). It shows that the cathodic current densities of the three electrodes increase as the overpotential increases. Moreover, the onset potential of porous Ni3Al for 
 Fig. 1 
 e SEM morphology of porous NieAl: (a) green 
 compacts; (b) sintered porous Ni 
 eAl; (c) cross-section 
 morphology, and the inset is a magnification of (c). 
 Fig. 2 
 e Pore distribution of porous Ni3Al. 
 Fig. 3 
 e Phase transformation of porous NieAl during the 
 sintering procedure. 
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transfer resistance (Rct) as well as highest value of the esti- mated exchange current density ( j0) confirms that the porous Ni3Al electrode exhibits higher electrocatalytic activity toward hydrogen evolution than those foam Ni and pure compact Ni electrodes. 
 3.4. 
 Effect of parameters on the electrocatalytic 
 properties 
 3.4.1. 
 Effect of electrolyte concentration 
 The effect of electrolyte concentration on HER is investigated and the results are illustrated in Fig. 6 . Fig. 6(a) is the LSV curve recorded in KOH solution with concentrations ranging from 0.1 M to 8 M at a scan rate of 10 mV s 
 1. Fig. 6(b) shows the 
 variation of current density for HER as a function of KOH concentration ( j 
 eC ) on porous Ni3Al electrode at the potential 
 of 
 1.3 V. The current densities increase with the increase of 
 KOH concentration up to 6 M, and decrease thereafter. Apparently, porous Ni3Al electrode exhibits the best electro- catalytic activity for HER in 6 M KOH solution. 
 It is generally accepted that the HER mechanism in alkaline 
 solution is a combination of reaction steps involving the formation of adsorbed hydrogen [22,23]: 
 M 
 þ H2O þ e.K1 
 EK 
 1 
 MHads 
 þ OH ðVolmerÞ 
 (2) 
 MHads 
 þ H2O þ e.K2 
 EK 
 2 
 H2 
 þ M þ OH ðHeyrovskyÞ 
 (3) 
 where the subscript ads represents the adsorbed status, ki and ki (i ¼ 1, 2) are the rate constants of the forward and backward 
 reactions, which are influenced by the concentration of OH and H2O. It is well known that an appropriate increase of the electrolyte concentration will increase solution conductivity and ion activity, which are advantageous to ionic transfer in the solution. During the HER process, H2O and OH are competitively adsorbed on the electrode surface. When the electrolyte concentration is higher than 6 M, the increase of the concentration of electrolyte may result in an increase in the viscosity and a decrease in the ion activity, which in turn influences the departure of the bubbles and electron transfer. 
 Table 1 
 e Electrochemical properties of porous Ni3Al electrode observed at potentials close to the limits of the studied 
 domain. 
 Electrocatalysts 
 Tafel slope 
 (mV/dec) 
 i0 (mA/cm 
 2) 
 Cd ( 
 mF/cm2) 
 Rf 
 i0/Srealf 
 a (mA/cm2) 
 Onset potential 
 (V vs Hg/HgO) 
 I1.35V (mA/cm 
 2) 
 Pure flake Ni 
 107 
 0.007 
 234 
 11.7 
 5.9 
 104 
 1.25 
 10.1 
 Foam Ni 
 130 
 0.03 
 1007 
 50.4 
 6.15 
 104 
 1.15 
 26.9 
 Porous Ni3Al 
 219 
 1.9 
 10,930 
 546.5 
 3.4 
 103 
 0.95 
 90.1 
 a Note: the exchange current of real surface area. 
 Fig. 5 
 e Nyquist plots for porous Ni3Al electrode at different 
 overpotentials. 
 Fig. 6 
 e Influence of KOH concentration on the catalytic 
 activity of porous Ni3Al electrode for hydrogen evolution: 1: 0.1 mol LL 
 1; 2: 0.5 mol LL1; 3: 2 mol LL1; 4: 4 mol LL1; 5: 
 6 mol LL 
 1; 6: 8 mol LL1. 
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Fig. 10. No significant changes are observed on the surface morphology of porous Ni3Al after immersion in 6 M KOH solution in comparison with that of as-prepared porous Ni3Al specimen shown in Fig. 1(b). Moreover, the ion concentration of Al and Ni in the alkaline solution after soaking for 124 h is about 4.32 
 106 g mL1 and 1 108 g mL1, respectively, suggest- 
 ing that the dissolution of Al and Ni is neglectable. Accordingly, the passive film may function as a barrier to improve the corrosion resistance of porous Ni3Al in alkaline solution. 
 4. 
 Conclusions 
 Ni3Al intermetallic compound with porous structure was prepared through elemental powders reaction synthesis. The fabricated porous Ni3Al had a narrow pore size distribution with a mean pore diameter of around 1 
 mm. The onset 
 potential of hydrogen evolution on porous Ni3Al is higher than that of foam Ni and dense Ni materials. The best catalytic performance was found for HER in 6 M alkaline solution. The apparent activation energy of porous Ni3Al was 30.1 kJ mol 
 1. 
 Polarization measurements suggested that the formation of a passive film on porous Ni3Al surface increased its corrosion resistance, but had little influence on its catalytic activity for the HER in alkaline medium. The excellent performance of hydrogen evolution of porous Ni3Al may be ascribed to its specific characteristic and porous structure. Porous Ni3Al exhibits better electrocatalytic activity toward hydrogen evolution reaction and electrochemical stability in alkaline solution, which is of important for practical application in water electrolysis for hydrogen generation. 
 Acknowledgments 
 This research was financially supported by the National Natural Science Foundation of China (No. 20476106, No. 50721003 and No. 20636020) and by the National Natural Science 
 Funds 
 for 
 Distinguished 
 Young 
 Scholar 
 (No. 
 50825102), “973” program (No. 2009B623400), “863” program (2006AA03Z511). 
 r e f e r e n c e s 
 [1] Ramachandran R, Raghu KM. An overview of industrial uses 
 of hydrogen. International Journal of Hydrogen Energy 1998; 23(7):593 
 e8. 
 [2] Armor JN. Catalysis and the hydrogen economy. Catalysis 
 Letters 2005;101(3 
 e4):131e5. 
 [3] Holladay JD, Hu J, King DL, Wang Y. Review: an overview of 
 hydrogen production technologies. Catalysis Today 2009; 139(4):244 
 e60. 
 [4] Marozzi CA, Chialvo AC. Development of electrode 
 morphologies of interest in electrocatalysis: part 2: hydrogen evolution reaction on macroporous nickel electrodes. Electrochimica Acta 2001;46(6):861 
 e6. 
 [5] Losiewicza B, Budnioka A, Ro´wi 
 nskia E, Giewkaa E, Lasia A. 
 The structure, morphology and electrochemical impedance study of the hydrogen evolution reaction on the modified 
 nickel electrodes. International Journal of Hydrogen Energy 2004;29(2):145 
 e57. 
 [6] Kibria MF, Mridha MS, Khan AH. Electrochemical studies of 
 a nickel electrode for the hydrogen evolution reaction. International Journal of Hydrogen Energy 1995;20(6):435 
 e40. 
 [7] Zheng Haitao, Mathe Mkhulu. Hydrogen evolution reaction 
 on single crystal WO3/C nanoparticles supported on carbon in acid and alkaline solution. International Journal of Hydrogen Energy 2011;36(3):1960 
 e4. 
 [8] Rosalbino F, Maccio` D, Saccone A, Angelini E, Delfino S. 
 Fe 
 eMoeR (R ¼ rare earth metal) crystalline alloys as 
 a cathode material for hydrogen evolution reaction in alkaline solution. International Journal of Hydrogen Energy 2011;36(3):1965 
 e73. 
 [9] Adriana NC, Sergio ASM, Luis AA. Studies of the hydrogen 
 evolution reaction on smooth Co and electrodeposited Ni 
 eCo 
 ultramicroelectrode. Electrochemistry Communications 1999;1(12):600 
 e4. 
 [10] Tanaka S, Hirose N, Tanaki T. Evaluation of Raney-nickel 
 cathodes prepared with aluminum powder and tin powder. International Journal of Hydrogen Energy 2000;25(5):481 
 e5. 
 [11] Ramazan S, G 
 }ufe´za K. Hydrogen evolution and corrosion 
 performance of NiZn coatings. Energy Conversion and Management 2007;48(2):583 
 e91. 
 [12] Chen LL, Andrzei L. Ni 
 eAl Powder electrocatalyst for 
 hydrogen evolution: effect of Heat-treatment on morphology, composition, and kinetics. Journal of the Electrochemical Society 1993;140(9):2464 
 e72. 
 [13] Miao HJ, Piron DL. Composite-coating electrodes for hydrogen 
 evolution reaction. Electrochimica Acta 1993;38(8):1079 
 e85. 
 [14] Endoh E, Otouma H, Morimoto T. Advanced low hydrogen 
 overvoltage cathode for chlor-alkali electrolysis cells. International Journal of Hydrogen Energy 1988;13(4):207 
 e13. 
 [15] Xu CX, Wang LQ, Wang RY, Wang K, Zhang Y, Tian F, et al. 
 Nanotubular mesoporous bimetallic nanostructures with enchanced electrocatalytic performance. Advanced Materials 2009;21(21):2165 
 e9. 
 [16] Tanaka Sh, Hirose N, Tanaki T, Ogata YH. Effect of Ni 
 eAl 
 precursor alloy on the catalytic activity for a Raney-Ni cathode. Journal of the Electrochemical Society 2000;147(6): 2242 
 e5. 
 [17] Wu L, Dong HX, He YH. Preparation and corrosion resistance 
 in KOH solution of porous Ni3Al. Chinese Journal of Materials Research 2011;25(2):118 
 e23. 
 [18] Dong HX, He YH, Jiang Y, Wu L, Zou J, Xu NP, et al. Effect of Al 
 content on porous Ni 
 eAl alloys. Materials Science and 
 Engineering A 2011;528(13 
 e14):4849e55. 
 [19] He YH, Jiang Y, Xu NP, Zou J, Huang BY, Liu CT, et al. 
 Fabrication of Ti 
 eAl micro/nanometer-sized porous alloys 
 through Kirkendall effect. Advanced Materials 2007;19(16): 2102 
 e6. 
 [20] Crabb EM, Ravikumar MK. Synthesis and characterisation of 
 carbonsupported PtGe electrocatalysts for CO oxidation. Electrochimica Acta 2001;46(7):1033 
 e41. 
 [21] Bai C, Hong L, Li JB, Li X, Yang J, Tao J. Core-ring structured 
 NiCo2O4 nanoplatelets: synthesis, characterization, and electrocatalytic applications. Advanced Functional Materials 2008;18(9):1440 
 e7. 
 [22] Andrea K, Nicolae V, Waltraut B, Narcis D. Kinetics of 
 hydrogen evolution reaction on skeleton nickel and nickel 
 etitanium electrodes obtained by thermal arc spraying 
 technique. International Journal of Hydrogen Energy 2007; 32(15):3258 
 e65. 
 [23] Rami A, Lasia A. Kinetics of hydrogen evolution on Ni 
 eAl 
 alloy electrodes. Journal of Applied Electrochemistry 1992; 22(4):376 
 e82. 
 [24] Lasia A. Hydrogen evolution/oxidation reactions on porous 
 electrodes. Journal of Electroanalytical Chemistry 1998; 454(1):115 
 e21. 
 i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 3 6 ( 2 0 1 1 ) 1 2 1 1 2 
 e1 2 1 2 0 
 12119

pageNum = 18

[25] Los P, Rami A, Lasia A. Hydrogen evolution reaction on Ni 
 eAl 
 electrodes. Journal of Applied Electrochemistry 1993;23(2): 135 
 e40. 
 [26] Hitz C, Lasia A. Experimental study and modeling of 
 impedance of the her on porous Ni electrodes. Journal of Electroanalytical Chemistry 2001;500(1 
 e2):213e22. 
 [27] Joe¨l F, Danielle M, Legoux JG. Wire-arc sprayed nickel based 
 coating for hydrogen evolution reaction in alkaline solutions. International Journal of Hydrogen Energy 1999;24(6):519 
 e28. 
 [28] Solmaz R, Do¨ner A, S‚ahin _I, Yuce AO, Kardas G, Yazici B, et al. 
 The stability of NiCoZn electrocatalyst for hydrogen evolution activity in alkaline solution during long-term electrolysis. International Journal of Hydrogen Energy 2009; 34(19):7910 
 e8. 
 [29] Jafarian M, Azizi O, Gobal F, Mahjani MG. Kinetics and 
 electrocatalytic behavior of nanocrystalline CoNiFe alloy in 
 hydrogen evolution reaction. International Journal of Hydrogen Energy 2007;32(12):1686 
 e93. 
 [30] Zha QX. Introduction to electrode kinetics. Beijing: Science 
 Press; 2002. p. 237. 
 [31] Carvalho JD, Tremiliosi-Filho GAL, Srinivasan AI, Wanger S, 
 Wroblowa H. Electrode materials and processes for energy conversion and storage. Pennington: The Electrochemical Society; 1987. p. 356. 
 [32] Zheng HJ, Huang JG, Wang W, Ma CN. Preparation of nano- 
 crystalline tungsten carbide thin film electrode and its electrocatalytic activity for hydrogen evolution. Electrochemistry Communications 2005;7(10):1045 
 e9. 
 [33] Wang LP, Zhang JY, Gao Y, Xue QJ, Hua LT, Xu T. Grain size 
 effect in corrosion behavior of electrodeposited nanocrystalline Ni coatings in alkaline solutions. Scripta Materialia 2006;55(7):657 
 e60. 
 i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 3 6 ( 2 0 1 1 ) 1 2 1 1 2 
 e1 2 1 2 0 
 12120

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