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Journal of Alloys and Compounds 432 (2007) 323–332

Cu–Ni materials prepared by mechanical milling: Their properties andelectrocatalytic activity towards nitrate reduction in alkaline medium

Laurence Durivault a,b, Oleg Brylev a,b, David Reyter a,b, Mathieu Sarrazin a,b,Daniel Bélanger a,∗, Lionel Roué b

a Département de Chimie, Université du Québec à Montréal, C.P. 8888, Succursale Centre-Ville, Montréal, Québec, Canada H3C 3P8b INRS-Energie, Matériaux et Télécommunications, 1650 blvd. Lionel Boulet, C.P. 1020, Varennes, Québec, Canada J3X 1S2

Received 24 March 2006; received in revised form 30 May 2006; accepted 6 June 2006Available online 18 July 2006

bstract

CuxNi1−x materials (0 ≤ x ≤ 100) were elaborated by high-energy ball milling. The milling conditions were optimized using the compositioni80Cu20. Utilizing a ball-to-powder mass ratio of 2 and a milling time of 6 h, one can obtain nanocrystalline Ni80Cu20 alloys (crystallite size50 nm) with a good milling yield (>95%) and with a very low Fe contamination (

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24 L. Durivault et al. / Journal of Allo

2NO2− + 4H2O + 6e− → N2(g) + 8OH−,

U0 (V) versus SHE = 0.41 (3)

2NO2− + 3H2O + 4e− → N2O(g) + 6OH−,

U0 (V) versus SHE = 0.15 (4)

2H2O + 2e− → H2(g) + 2OH−,U0 (V) versus SHE = −0.83 (5)he desired cathodic process is the reduction of nitrate to nitro-en corresponding to Eqs. (1) and (3), and the hydrogen evo-ution represents the main parasitic cathodic reaction (Eq. (5)).

ith decreasing potential (e.g. more negative potentials), theuppression of NO3− reduction could be explained by the pre-ominant H adsorption [8], thus one can be expected that theeduction of NO3− could be more efficient on the electrodesith poor H adsorption.The electrochemical reduction of NO3− and NO2− has been

tudied on various metals, metallic oxides and other electrodes9–15]. Transition metals demonstrated interesting electrocat-lytic properties for the reduction of nitrate and nitrite butmmonia formation seems to be predominant [10,11,15–27].he highest catalytic activity was found for Cu, Rh and Ptlectrodes. Pure Ni electrode shows a lower catalytic activ-ty than Cu and Pt, despite a similar mechanism of nitrateeduction to ammonia, via nitrite as intermediate product, wasroposed for the case of alkaline solutions (NaHCO3 + NaNO3r NaOH + NaNO3) [8,28]. This mechanism involves at leastwo stages occurring at different potentials. On a copper cath-de, NO3− can be reduced to NO2− at −1.1 V versus saturatedalomel electrode (SCE) and to NH3 with a high yield at −1.4 Versus SCE [29]. On the other hand, the electrolysis of NO3−n the presence of NaOH and Na2CO3 on a Ni electrode pro-uces N2 at a low current density and mainly NH3 at a higherurrent density [15]. In addition, it was found that the use ofimetallic electrodes allows the reduction selectivity to be con-rolled. The best example was given by de Vooys et al. for Pd–Culectrodes when a selectivity 60% can be achieved for nitrogenormation [30]. These results were explained by the bi-functionalharacter of the catalyst, whereby NO3− ions are reduced toO2− (and/or NO) on Cu sites and the subsequent reduction to2 occurs on Pd sites. In our investigation, bimetallic Cu–Niaterials were studied. They are acceptable for drinking water

reatment and not so expensive for the use in an industrial scale.oreover, since Cu presents a high electrochemical activity

or nitrate reduction, one can expect that copper would readilyransform NO3− into NO2− and then Ni (like Pd) may reduceO2− to N2.Several methods were proposed for the preparation of

imetallic and alloyed Cu–Ni particles, for example, the reduc-ion of a mixture of nickel and copper compounds under hydro-

en [31–33], and the evaporation of a Cu–Ni alloy and co-ondensation with organic solvents [34]. The synthesis of Cu–Niimetallic powders using carbonates and nitrates of Ni and Cu,nd ethylene glycol serving as solvent and reducing agent was

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Compounds 432 (2007) 323–332

eported [35]. High-energy milling (or mechanosynthesis) islso a powerful method to elaborate catalysts with advancedroperties. This is essentially related to their nanostructuredharacter and to the presence of numerous structural defects.owever, this technique was only little used for the preparationf Cu–Ni materials (Cu20Ni80 [36] and Cu87Ni13 [37]) and it isf a significant interest to investigate the effect of some experi-ental parameters of mechanical milling on the elaboration of

uch Cu–Ni materials.In this study, Cu–Ni materials with different composition

ere elaborated by mechanical milling and then tested for thelectrochemical reduction of NO3− in alkaline medium for therst time, to the best of our knowledge. Optimal milling con-itions (i.e. milling time and ball-to-powder mass ratio) wereetermined for the composition Ni80Cu20. Then a series ofi100−xCux materials (0 ≤ x ≤ 100) was prepared under theseptimized conditions and characterized by scanning electronicroscopy (SEM) and X-ray diffraction (XRD). Electrochem-

cal experiments (cycling voltammetry (CV) and electrolyses inO3−-containing medium) were performed on pelletized elec-

rodes to evaluate the catalytic activity and selectivity of theall-milled Cu–Ni materials for the nitrate reduction in alkalineedium.

. Experimental

.1. Materials preparation

Ni100−xCux materials (with x varying from 0 to 100) were prepared byigh-energy ball milling from elemental Ni (99.5% purity, −325 mesh) andu powders (99.9% purity, −325 mesh) using a Spex 8000 laboratory mill. Theowder mixture was introduced into a hardened steel vial (capacity of 55 mL)ith three hardened steel balls (two of diameter 14 mm and one of 11 mm, totalass of 22.7 g). The vial was loaded and sealed under argon atmosphere in a

love box. The variation of the powder load from 2.27 to 11.35 g allows differentall-to-powder mass ratios (BPR) to be obtained (10:1, 5:1 and 2:1). The millinguration was varied from 30 min to 40 h.

.2. Materials characterization

The morphology of the powders was examined by a JEOL JSM 6300F scan-ing electron microscope equipped with energy dispersive spectroscopy (EDS)or composition analysis.

XRD data were collected from 35◦ to 105◦ (2θ) with a step of 0.02◦ (acquisi-ion time of 2 s) on a Bruker D8 diffratometer (Cu K� radiation). The diffractionrofiles were analyzed by Rietveld refinement with Fullprof program [38] usinghe model developed by Stephens [39]. A LaB6 standard sample was used toetermine the instrumental broadening which was considered in the Rietveldnalysis.

A three-electrode cell was used for the CV measurements. The workinglectrode was made by cold pressing 1 g of as-milled powder onto 0.2 g of Cuowder into a stainless steel dye of 1 cm diameter with a load of 12 tonnes cm−2or 10 min. The resulting pellet was glued to a glass tube with silveraint.

The reference electrode was an Hg/HgO (1 M NaOH) electrode and theounter electrode was a Pt mesh. The electrolyte was either 1 M NaOH orM NaOH + 1 M NaNO3 aqueous solution. The geometrical surface area of

he working electrode exposed to the electrolyte was 1 cm2, and the values of

urrent density below in the text were calculated with respect to this area. Beforeach experiment, the solutions were purged with argon during 15 min. CV mea-urements were carried out between −0.6 and −1.6 V versus Hg/HgO at a scanate of 20 mV s−1. Five cycles were sufficient for every Cu–Ni electrode to reachstationary state.

L. Durivault et al. / Journal of Alloys and Compounds 432 (2007) 323–332 325

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.3. Chemical analysis of nitrate reduction products

In order to establish and to quantify the products of nitrate reductionn Cu–Ni pellets, the electrolysis was performed either in potentiostatic oralvanostatic mode in a two-compartment cell designed in our laboratoryFig. 1). The compartments of the cell were separated by a Nafion® 117embrane, Hg/HgO electrode mounted in a Luggin capillary and Pt gridere used as a reference and counter electrode, respectively. Preliminarilyegassed 1 M NaOH + 1 M NaNO3 and 1 M NaOH aqueous solutions weretilized in the cathodic and anodic compartment, respectively. All the aque-us solutions were prepared with ultrapure water (18 M�, obtained from aybron/Barnstead Nanopure II system) and purged with argon for 30 min. Aolartron 1470 potentiostat/galvanostat was employed for the electrochemicalxperiments.

Solution samples were regularly taken for the quantitative determinationf NO3−, NO2−, NH2OH and NH4+/NH3(aq). The NO3− concentration wasvaluated by UV–vis spectroscopy (Hewlett Packard 8452A) according tohe absorbance peak at 220 nm [40], while NH2OH was quantified by thebsorbance at 710 nm [41]. The content of nitrite anions was assessed accord-ng to the absorbance maximum at 544 nm belonging to the diazonium complexormed by reaction involving NO2−, sulfanilamide (Aldrich) and N-(1-naphtyl)-thylenediamine dihydrochloride (98%, Aldrich) [40]. Ammonia concentrationn solution was evaluated by Nessler’s classic method described elsewhere [40].as samples were regularly taken during the electrolysis and injected into aas chromatograph (Varian 3000, molecular sieve 5A and 200 cm × 0.3 cm).alibrating curves were recorded with gas mixtures with known composition

Praxair) to quantify the formation of H2, N2 and N2O [42]. For each compo-ition, three electrolyses were performed in galvanostatic mode with a currentensity of 0.15 A cm−2 and one electrolysis was done in potentiostatic mode atpotential of −1.3 V versus Hg/HgO. All the potentials below in the text wille referred to the Hg/HgO electrode.

. Results and discussion

.1. Synthesis and characterization of Cu–Ni materials

In course of ball milling, powder particles are subjected toigh-energy collisions which cause the cold welding and frac-ure of powder particles. The essential condition for a successful

echanical alloying is to reach an optimal balance between coldelding and fracturing [43]. In our case due to the high ductil-

ty of Cu powder, this balance is difficult to achieve and thus,

xcessive cold welding between powder particles was observeds well as the one between powder particles and milling tools.herefore, the milling yield (defined as the ratio of the pow-er masses after and before milling) is substantially decreased.

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sed for the electrolysis of NO3−-containing solutions.

or example, after 40 h of milling with a BPR of 10:1, only0 wt.% of Ni80Cu20 powder can be recovered, the rest beingompletely adhered to the milling tools. Previous authors havebserved the dominant particle coalescence in Cu and Cu–Niystems, leading to a complete adherence of the powder onto theilling media in the extreme case [36,44]. Moreover, it is well

nown that face-centered-cubic (fcc) metals (e.g. Ni, Cu, Al)ave a stronger tendency to form agglomerates during millinghan other metals (like Mg) with a hexagonal close-packed struc-ure, which are more brittle [43]. A common approach to reducexcessive cold welding and to promote fracturing is the addi-ion of organic compounds (typically, 1–3 wt.% of stearic acid,eptane, methanol) to the starting powder mixture. This processontrol agent (PCA) is adsorbed at the surface of milled particlesnd thus, impedes the direct metal-to-metal contact required forold welding. However, the PCA could be a source of pollutionecause its decomposition during the milling process may causearbon, oxygen and hydrogen contamination of final materials43], which may alter its ulterior electrochemical properties. Inddition, the erosion of vial and balls may occur during milling,eading to the transfer of Fe (and to a less extent, Cr and Ni)rom the milling tools to the powder particles. In our case, after0 h of milling with a BPR of 10:1, Ni80Cu20 powder contains0 at.% of Fe (and 3 at.% of Cr). This level of contaminations very high and unacceptable. Thus, in order to decrease theowder contamination and to prevent excessive cold welding,he optimization of milling conditions has been performed bytudying the influence of the milling duration and the BPR onhe final product characteristics. This optimization procedureas been focused on the materials with a Ni80Cu20 compositionsee below).

SEM micrographs of the starting Cu and Ni powders as wells Ni80Cu20 powder milled for different durations (BPR = 10:1)re represented in Fig. 2. These pictures clearly demonstratehe evolution of powder morphology with increasing millingime. The starting Cu and Ni powders consist of more or lesspherical particles with a diameter around 10 �m (Fig. 2a and b,

espectively). After 30 min of milling, thin irregular flakes withsize of 0.5–1.5 mm and a thickness lower than 100 �m are

roduced (Fig. 2c), indicating that micro-forging and cold weld-ng processes are very significant at the early stage of milling.

326 L. Durivault et al. / Journal of Alloys and Compounds 432 (2007) 323–332

Fig. 2. SEM micrographs of the starting Cu and Ni powders compared with the Ni80Cu20 powder obtained at different milling times (BPR = 10:1).


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uring further milling (1–3 h), powder fracturing becomes pre-ominant and the platelets are broken into smaller irregulararticles (Fig. 2d and e). However, the balance between weld-ng and fracturing has not been reached at this stage of millinget. Indeed, extensive particle coalescence occurs again duringurther milling leading to the formation of very large plateletsf ∼1–3 mm with a thickness larger than 100 �m after 6 h ofilling (Fig. 2f). Upon further milling, the particle size decreases

gain (Fig. 2g, 10 h of milling) reaching a nearly homogeneousarticle size distribution. After 20 h of milling, the formationf dense and more or less equiaxed particles with a diameter200–400 �m is observed (Fig. 2h). The powder morphol-

gy does not change significantly for a longer milling durationFig. 2i, 40 h of milling), showing the equilibrium between coldelding and fracturing. The fact that these two processes prevail

uccessively in the milling cycle, i.e. cold welding (0–30 min),racturing (30 min–1 h), cold welding (1–6 h) and again frac-uring (6–20 h) before reaching an equilibrium (≥20 h), mayeflect a significant modification of the mechanical properties of

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he milled powder related to: (i) the formation of Cu–Ni alloy,ii) the evolution of its composition due to the Fe contaminationy milling tools erosion and/or (iii) the grain size reduction andccumulation of microstrains into the materials.

Fig. 3 represents the evolution of iron contamination fori80Cu20 powder with an increasing milling duration at dif-

erent BPR (10:1, 5:1 and 2:1). The Fe contamination of milledowders increases with growing milling time and substantiallyepends on the BPR. For example after 20 h of milling, the Feontent attains 23 at.% for a BPR of 10:1 compared to 12 andat.% for BPR = 5:1 and 2:1, respectively. Only the powdersilled at BPR = 2:1 possess an acceptable level of iron con-

amination (i.e.


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ig. 3. Variation of the iron content in the Ni80Cu20 powder with increasingilling duration for different BPR (10:1, 5:1 and 2:1).

omplete vial coating with the powder mixture, which couldimit its erosion during the milling process.

XRD patterns of Ni80Cu20 powder (BPR = 2:1) as a functionf milling duration are shown in Fig. 4. The diffraction pat-ern of the sample milled for 1 h is indexed with two phases:cc Cu and fcc Ni. After 6 h of milling, the Cu peaks disap-ear and the diffraction patterns can be indexed with a singlecc phase which suggests the formation of a Cu–Ni solid solu-ion. For comparison, Cu peaks are no longer detectable afterh of milling with a BPR of 5:1 and 1 h for BPR = 10:1 (XRDatterns not shown), confirming that the higher the BPR is, theigher the ball-to-powder collision probability is and therefore,he faster the mechanical alloying occurs. These XRD resultseveal the straightforward formation of Ni80Cu20 alloy through-ut the milling process, in agreement with the complete solid

olubility at room temperature for the Cu–Ni system, accordingo the phase diagram [45]. In addition, the Bragg peaks broaden-ng (related to the grain size reduction and microstrain increase)s observed with increasing milling time. A progressive shift of

ig. 4. XRD patterns of Ni80Cu20 samples (BPR = 2:1) for different millingurations.

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ig. 5. Lattice parameter of Ni–Cu solid solution as a function of milling timeor Ni80Cu20 materials with BPR = 2:1, 5:1 and 10:1.

u–Ni phase peaks to lower diffraction angles is also detecteds the milling time increases, pointing out the increase in Cu–Nihase lattice parameter. Rietveld refinement of the XRD patternsas performed in order to determine the variation of the latticearameter, crystallite size and strain of Ni80Cu20 materials as aunction of the milling time and BPR value.

The evolution of the lattice parameter of Cu–Ni solid solutions a function of the milling duration for different BPR is pre-ented in Fig. 5. Using Vegard’s law [46], the lattice parameterf Ni80Cu20 alloy can be estimated as 3.54 Å taking account ofhe lattice parameters of unmilled Cu and Ni (3.61 and 3.52 Å,espectively). This value is attained after 2 h of milling forPR = 10:1 and 5:1 compared to 6 h for BPR = 2:1 (Fig. 5), con-rming that the alloying process occurs at the early stages ofilling and is accelerated by the increase in the BPR value. Fur-

her milling induces an increase in the lattice parameter, which isccentuated with increasing BPR. This raise in the lattice param-ter is attributed to the incorporation of Fe into Cu–Ni alloy, inccordance with Fe content measurements (Fig. 3).

Fig. 6 shows the crystallite size variation of as-milledi80Cu20 powders with increasing milling duration at differ-

nt BPR values. The exact determination of the crystallite sizef the starting Ni and Cu coarse-grain powders was not possi-le due to instrumental broadening limitations and thus, theirrystallite size is considered as >100 nm. At the early stages ofilling, the Cu–Ni crystallite size decreases very rapidly reach-

ng a nearly constant value after 20 h of milling, suggesting thathe equilibrium in the milling process is reached within thiseriod of milling. The final crystallite size after 40 h of millings 22, 16 and 9 nm for BPR = 2:1, 5:1 and 10:1, respectively. Itas suggested that the ultimate grain size achievable by milling

s determined by the competition between the heavy mechanicaleformation introduced into particles and the rate of recovery

uring milling [47]. The plastic deformation and the recoveryehavior of the milled materials depend strongly on its phys-cal properties. The general trend of a decreasing grain sizeith increasing bulk modulus and melting temperature of milled


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cc metals has been clearly demonstrated. In the present case,e contamination, dependent on BPR, may influence the finalrystallite size by modifying the deformation and recovery pro-esses during milling because the introduction of Fe (and to aess extent, Cr) into Cu–Ni solid solution is expected to increasets bulk modulus and melting point, taking into considerationhe physical properties of the contaminants. In addition, the facthat the final crystallite size is lower at higher BPR may be alsoelated to the limitation of the recovery process because, whenPR value increases, the ball-to-powder collision probability

ncreases and thus, the recovery period between two deforma-ion (collision) events in single particle is assumed to be shorter.

The dependence of the microstrain in Ni80Cu20 materialsith milling time for different BPR is shown in Fig. 7. ForPR = 10:1 and 5:1, the strain increases with growing milling

ime to attain a maximum after 20 h of milling and then decreasesown to about 0.3% after 40 h of milling proving that the micros-rain recovery occurs. It can be noted that the maximum strain

evel corresponds to the milling time at which the constant grainize is achieved (Fig. 6). For BPR = 2:1, the strain variation withilling time is less noticeable with a slight increase during the

ig. 7. Strain evolution with milling time for Ni80Cu20 sample with BPR = 2:1,:1 and 10:1.

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ig. 8. XRD patterns of Cu–Ni materials milled for 6 h (BPR = 2:1) for differentompositions.

arly stage, reaching 0.3% after 10 h of milling indicating thatlastic deformation and recovery processes are in equilibrium.

Afterwards, Ni100−xCux alloys (with x varying from 0 to 100)ave been synthesized using the optimized milling parametersi.e. BPR = 2:1, milling time of 6 h) which leads to an effectiveechanical alloying without excessive Fe contamination and

old welding, as shown previously for Ni80Cu20 system. SEMicrographs (not shown) indicate almost similar powder mor-

hology for all the compositions (i.e. thick and regular pellets of1–3 mm, as shown previously in Fig. 2f). The milling yield is

lose to 100% (i.e. there is no strong adherence of the powderso the milling tools) and the level of iron contamination for the

illed powders is very low (


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ig. 10. Variation of the crystallite size and the lattice strains of Cu–Ni materialsilled for 6 h (BPR = 2:1) for different compositions.

o 3.61 and 3.52 Å for starting Cu and Ni powders, respectively).his indicates the absence of major defects and vacancies in theilled materials and may reflect their strong ability to recov-

ry. As shown in Fig. 10, the limited strain is around 0.3% inhe milled materials, which points to the fact that the recoveryccurs during the milling. The crystallite size of Ni100−xCuxlloys varies with their compositions and reaches a minimumalue of about 24 nm for Ni40Cu60. This curve shows a morefficient crystalline refinement of the alloys compared to purei and Cu metals.

.2. Electrochemical investigation of Cu–Ni materials

The results presented above clearly show that milling influ-nced the structure and morphology of Cu–Ni materials. How-ver, the iron contamination can significantly alter their proper-ies. Thus, only the materials with low Fe content (i.e. obtained atPR = 2:1, milling time of 6 h) were used for the electrochem-

cal studies. They were characterized by cycling voltammetrynd electrolyses in nitrate-containing solutions.

CV curves for NixCu100−x electrodes (0 < x < 100) in 1 MaOH were recorded and compared to those of Cu and Niowders ground under the same conditions (Fig. 11a). In thenvestigated potential range, no peak related to the formation oreduction of oxidized metallic species is observed. The increasen the current at negative potentials is related to H2 evolution.he increase in Ni content causes an earlier onset of H2 evolu-

ion which is consistent with a higher activity of Ni for hydrogeneduction. Indeed, the exchange current densities of Cu and Nin NaOH solution are 1 × 10−7 and 7.9 × 10−7 A cm−2, respec-ively [48]. Higher current for Ni80Cu20 materials compared toure Ni might be explained by the variation of electrochemicallyctive surface area which is difficult to estimate.

CV curves obtained in 1 M NaOH + 1 M NaNO3 solution

nder the same experimental conditions are shown in Fig. 11b.he onset of the cathodic current occurs at more positive poten-

ials, and in the region of H2 formation its values are aboutwo times higher than in the absence of NO3−, confirming the

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ig. 11. CV curves (fifth cycle) in (a) 1 M NaOH and (b) 1 M NaOH + 1 MaNO3 of NixCu100−x electrodes (0 < x < 100, obtained at BPR = 2:1, milling

ime 6 h). Scan rate 20 mV s−1.

oexistence of hydrogen evolution and nitrate reduction. Theoltammograms can be divided into three groups according tohe intensity of the reduction current: (i) Ni60Cu40, Ni80Cu20 andi (high reduction current), (ii) Ni20Cu80 and Ni40Cu60 (aver-

ge reduction current) and (iii) Cu (low reduction current). Inhe case of Ni-enriched materials, a higher current for potentialsore negative than −0.9 V can be explained by the increase in

he faradaic yield of NH3 formation, since the reduction of NO3−o NH3 needs eight electrons, whereas the nitrate transformationo nitrite consumes only two electrons.

In order to confirm this hypothesis, the quantification of prod-cts formed in course of the electrolyses (in galvanostatic andotentiostatic modes) of nitrate solutions on Cu–Ni electrodesas performed. For the whole series of NixCu100−x materials,

he analyses of reaction products revealed the formation of onlyitrite ions and ammonia. For milled Cu, N2O was detected buthe current efficiency for its formation did not exceed 0.3%. Forll the products of nitrate reduction the current efficiency (CE)alues were calculated by dividing the charge consumed for theormation of a given product by the total charge passed dur-ng the electrolyses. For the calculation of the selectivity (S) forO2− and NH3 formation, only the charge consumed for NO3−

eduction was taken into account. Its value was obtained by the

ubtraction of the charge consumed for H2 formation from theotal one.

Table 1 shows the CE values obtained at Cu–Ni electrodes inourse of potentiostatic electrolysis (at −1.3 V for 24 h) of 1 M


Table 1Current efficiencies (CE) of the NO3− reduction products for different Cu–Nimaterials

CE (%) Electrode material

Ni Ni80Cu20 Ni60Cu40 Ni40Cu60 Ni20Cu80 Cu

CE(H2) 6.2 6.1 3.1 7.7 4.2 6.1CE(NH3) 92.9 91.4 94.1 72.2 73.8 50.3CE(NO −) 0.9 2.5 2.8 20.1 22.0 43.6

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As it can be seen in Table 2, the calculated values ofNO3− destruction rate vary from 6.4 × 10−4 mol cm−2 h−1 (Ni)to 9.8 × 10−4 mol cm−2 h−1 (Cu). This confirms the previous

2

lectrolysis at −1.3 V vs. Hg/HgO in 1 M NaOH + 1 M NaNO3 solution, elec-rolysis time 24 h.

aNO3 + 1 M NaOH. The addition of 20 at.% of Ni to Cu drasti-ally changes the selectivity for ammonia formation, contrary tohe addition of 20 at.% of Cu to Ni. Nickel and Ni-enriched alloysre very selective for the NH3 formation and even 40 at.% of Cuannot reverse the situation. Copper and Cu-enriched alloys areess selective for NH3, but reduces well NO3− to NO2−. Theurrent efficiency of H2 formation was low (

332 L. Durivault et al. / Journal of Alloys and

Table 2k1 values (s−1) and nitrate destruction rates (mol cm−2 h−1) for different Cu–Nimaterials

Electrode material k1 (×10−6 s−1) NO3− destruction rate(×10−4 mol cm−2 h−1)

Ni 5.7 6.4Ni80Cu20 5.5 6.3Ni60Cu40 5.9 6.7Ni40Cu60 6.5 7.3Ni20Cu80 6.8 7.6C

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lectrolysis at 0.15 A cm−2 in 1 M NaOH + 1 M NaNO3 solution, electrolysisime 9 h.

eports of a lower catalytic activity of Ni with respect to Cu inlkaline solutions [8,28].

. Conclusions

A series of NixCu100−x materials (0 ≤ x ≤ 100) were elab-rated by high-energy ball milling and characterized by XRDnd SEM. The milling conditions were optimized using the com-osition Ni80Cu20. Utilizing a ball-to-powder mass ratio of 2,ne can obtain nanocrystalline Ni80Cu20 alloy (crystallite size50 nm) with a good milling yield (>95%) and with a very lowe contamination (

Documents

Cu–Ni materials prepared by mechanical milling: Their ...€¦ · 20 alloys (crystallite size 95%) and with a very low Fe contamination