Evolution Electrodeposition of Functional Ni-Re Alloys

Electrodeposition of Functional Ni-Re Alloys for Hydrogen Evolution Piotr Zabinski, Agnieszka Franczak and Remigiusz Kowalik ECS Trans. 2012, Volume 41, Issue 33, Pages 39-48. doi: 10.1149/1.3702411 Email alerting service

Receive free email alerts when new articles cite this article - sign up in the box at the top right corner of the article or click here

To subscribe to ECS Transactions go to: http://ecst.ecsdl.org/subscriptions

© 2012 ECS - The Electrochemical Society

Downloaded on 2012-07-27 to IP 193.50.213.32 address. Redistribution subject to ECS license or copyright; see www.esltbd.org

ECS Transactions, 41 (33) 39-48 (2012) 10.1149/1.3702411 © The Electrochemical Society

Electrodeposition of Functional Ni-Re Alloys for Hydrogen Evolution P. R. Zabinski a, A. Franczak a, b and R. Kowalik a a

Laboratory of Physical Chemistry and Electrochemistry, Faculty of Non-Ferrous Metals, AGH University of Science and Technology, Krakow, Poland b current address: DTI URCA, BP 1039, 51687 Reims Cedex2, France The aim of this work was to obtain Ni – Re binary alloy by a simple method of electrodeposition. Nickel – rhenium alloys have been deposited from nickel sulfamate and ammonium perrhenate electrolyte with citrate-anion additives. The effects of bath temperature, current density, bath composition and influence of magnetic field were studied. The impacts of these parameters on hydrogen evolution process for obtained Ni – Re alloys were examined. The deposited layers were determined by optical and scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray fluorescence (XRF).

Introduction Until recently, chromium coatings were considered as irreplaceable coverage for elements of metals surfaces working in different, usually difficult, conditions. Unfortunately, manufacture and application of conventional chromium coatings are a serious threat to the environment because of toxic and carcinogenic character of chromates compounds used to produce the layers. Hence, it is necessary to replace the production methods of chromium coatings by technologies which are more friendly to the environment and offer more possibilities for developing and incorporating processes of alternative techniques [1-4]. This problem can be solved by using coatings from alloys such as Ni-W, Ni-Re, Co-W and ternary alloys with addition of other elements. Ni – Re alloys seem to be very promising due to their high hardness, low grindability, satisfactory anticorrosive properties and also high bath stabilization for electrochemical deposition [510, 15-17]. Coatings based on nickel and cobalt with addition of rhenium as well as nickel and cobalt modified by rhenium powder are more and more frequently used as cathode materials characterized by lower overpotential for hydrogen evaluation in electrocatalytic processes [18]. Materials presenting high electrocatalytic properties are usually expensive and often demonstrate low mechanical strength. Therefore, electrodeposited Ni-Re alloys can be used as active electrodes obtained by applying the active coating on a surface that is available, durable and easy to machining. The cathode materials characterized by low hydrogen evolution overpotential and high catalytic activity include electrodes made from precious metals, mainly platinum or nickel and cobalt-based coatings produced by electrochemical methods [11-14]. It seems that it is advisable to obtain Ni – Re alloys by electrolytic deposition from aqueous solutions. These coatings are characterized by a high electrocatalytic activity,


39

ECS Transactions, 41 (33) 39-48 (2012)

low overpotential for hydrogen evolution, large extension of the surface and good corrosion resistance. Thus, obtained alloys can be used, inter alias, in solar-powered water electrolysis systems and the hydrogen obtained though decomposition of water could be used for the production of methane by hydrogenation of carbon dioxide.

Experimental Procedure Ni-Re alloys were deposited from aqueous solution containing 0.1-0.001 M NH4ReO4, 93 mM Ni(NH2SO3)2.4H2O and 34 mM C6H8O7 as a complexion agent and the pH value was 5. The investigations were divided into five stages. Each measurement consisted of three series and was related to the impact of different parameters such as: bath temperature, current density and time of electrodeposition. All of the experiments were carried out in a 150 ml cell. The cathode was a copper disc of an area of 3.14 cm2 and a platinum grid was used as a counter electrode. The cells used for electrodeposition were 40 mm wide, 100 mm long and 45 mm high. Platinum metal anodes were placed vertically at both ends of the cell, facing each other at a distance of 90 mm. A copper metal cathode was placed vertically in the centre of the cell. Before the deposition, the substrates were chemically etched in a 1:1 mixture of concentrated H2SO4 and HNO3 for 30 s. According to preliminary experiments, agitation of the electrolyte did not affect significantly the composition and hydrogen evolution performance of the deposits because of violent hydrogen evolution during electrodeposition, and for this reason the electrodeposition was carried out in a stagnant condition. The composition of metallic elements in the electrodes prepared in this way was analyzed with the use of XRF Philips MiniPal. The current efficiency for electrodeposition was estimated based on the mass and composition of the deposit. The structure of the electrodes was identified by X-ray diffraction using Cu Kα radiation. The grain size of the deposits was estimated from the full width at half maximum of the most intense diffraction line by Scherrer's equation. The hydrogen evolution activity of the electrodes was examined in 8 M NaOH solution at 90oC by galvanostatic polarization. A cell of acrylic resin with the specimen electrode, a platinum counter electrode and an external saturated calomel reference electrode of a reversible potential of 0.810V for the hydrogen reaction were applied. The ohmic drop was corrected using the current interruption method.

Results and Discussion The Effect of Temperature The electrodeposition process was carried out in different bath temperatures, from 20oC to 70oC. The obtained Ni-Re coatings, depending on the bath temperature, contained 78-81 % at. of Ni and 18-27 at. of Re (Figure 1a). Rising the temperature to 40oC caused an increase of Ni content in the alloy. In higher temperatures, up to 70oC, a decrease of Ni content was observed. With a high amount of Ni in the coating, a stable process efficiency (PE) equal to 52% (Figure 1b) was observed. When the bath temperature was increasing and the content of Ni was decreasing, lower values of PE


40


100

100

80

80

60

60 PE, [%]

Metal content, [% at.]

were observed. The changes of PE are related to violent hydrogen evolution during alloy electrodeposition. When the content of nickel in alloy is low, the lower current is lost for hydrogen evolution.

Ni Re

40

40

20

20

0

0 0

20

40

60

0

80

20

40

0

60

80

0

T, [ C]

T, [ C]

a.

b.

Figure 1. Impact of the bath temperature on the composition (a) and the process efficiency (b) of Ni-Re coatings. With an increase of the bath temperature, there also occurred changes in morphology of the obtained alloys. Coatings deposited from a bath at low temperatures were characterized by coarse-grains and roughness. When the temperature grew up, the obtained coatings were more fine-grained and homogeneous (Figure 2).

a)

b)

c)

d)


41


e)

f)

Figure 2. SEM microphotography of the Ni-Re alloys obtained from different bath temperature: a) 200C, b) 300C, c) 400C, d) 500C, e) 600C, f) 700C. X-ray diffraction analysis allowed to determine changes in the structure of the obtained alloys depending on the bath temperature from which they were deposited – Figure 3. For lower bath temperatures (up to 500C) the deposit consists of a mixture of hcp rhenium and fcc nickel. The peaks are broad which suggests the presence of very small grains of the deposit. There are no reflections from copper – the substrate. It means that the deposit was thick. Increasing the temperature over 60 0C leads to deposition of thinner layer of alloy. The presence of reflection from copper substrate is noticed. The peaks coming from fcc Ni disappear due to lowering nickel content in the deposited layer and only reflections from hcp Re deposit are present. Diffractions patterns corresponding to higher bath temperatures 50-700C (with more diffused peaks) indicate changes in the alloy structure towards being more amorphous. It is consistent with SEM observations when alloys deposited at high temperature are fine-grained. 3 (220)

Intensity / a.u.

1 hcp Re 2 fcc Ni 3 fcc Cu

2.9 nm

1 (100)

0

70 C Ni-27.4Re

1 (002) 1 (101)

0

60 C Ni-20.9Re

3.6 nm

2 (111)

0

50 C Ni-20.6Re

4.7 nm

2 (220)

0

5.8 nm

40 C Ni-18.4Re

7.6 nm

2 (200) 300C Ni-19.8Re 0

20 C Ni-24.8Re

9.5 nm

30

1 (110)

40

50

60

70

80

2θ / degrees (Cu K ) α

Figure 3. XRD pattern of Ni-Re layers obtained from a different bath temperatures. The Effect of the Current Density The electrodeposition process was carried out at different current densities: 25, 50, 75 and 100 mA/cm2. The obtained Ni-Re coatings contained 45-84 % at. of Ni and 15-54 % at. of Re (Figure 4a). The process performed at the lowest current density – 25 mA/cm2,


42


resulted in a similar content of both metals in the layer. An increase of current density caused an increase of nickel content and a decrease of rhenium content at the same time. An increase of current density increased polarization of the electrodes and was needed to use higher voltage of electrolysis. It had an influence on excessive consumption of electricity. The increase of current density affected positively the process efficiency but only in case of deposition of nickel coatings with high gloss. In the deposition of anticorrosion coatings, like Ni-Re coating, increasing current density was accompanied by the process efficiency decrease – Figure 4b. 80

90 80

60

60 PE, [%]


70

Ni Re

50

40

40 20

30 20

0

10 25 25

42

50

59

75 76

93

20

100

2

40

60

80

100

2

Current density, [mA/cm ]

Current density, [mA/cm ]

a.

b.

Figure 4. Impact of the current density on the composition (a) and the process efficiency (b) of Ni-Re coatings. The process in which alloy deposition was carried out at low current densities such as 25 and 50 mA/cm2, created a layer with the highest contents of Re and similar morphology – Figure 5. A decay of boundaries between flat grains took place. It improved homogeneity of the alloy. By increasing the current density, a decrease of Re content in the coating was observed. It promoted growth of thick grains of the cathode deposit and corrupted the quality of the layers. The distribution of grains is characteristic for high content of nickel atoms. In fact, the obtained coatings were rough, dull, tiny and usually not covered uniformly on the whole surface.

a)

b)


43


c)

d)

Figure 5. SEM microphotography of the Ni-Re alloys obtained from different current densities: a) 25 mA/cm2, b) 50 mA/cm2, c) 75 mA/cm2, d) 100 mA/cm2. 1 hcp Re 2 fcc Ni 3 fcc Cu

Intensity / a.u.

2

100 mA/cm Ni-15Re

2 (200)

25 nm

1 (110) 2 (220)

2 1 (002) 75 mA/cm Ni-19.3Re 1 (100) 1 (101) 15.2 nm

3 (220)

2

50 mA/cm Ni-27.4Re 2.9 nm 2

25 mA/cm Ni-54.9Re

5.8 nm

30

40

50

60

70

80


Figure 6. XRD pattern of Ni-Re layers obtained from a different current density. As a result, amorphous alloys were obtained and it was confirmed by broad and flat reflections on the diffraction patterns (Figure 6). The increase of current density is connected with a decrease of process efficiency and the change of alloys composition. An appearance of sharp reflections indicating changes in the structure from amorphous to the crystalline can be observed on the diffraction patterns. The presence of crystalline hcp rhenium in fcc crystalline nickel matrix was observed. Raising the current density resulted in obtaining very thick layers and non-uniform covering of the surface, which was confirmed by the presence of sharp peak on diffraction patterns for current density such as: 50, 75 and 100 mA/cm2 corresponding to the presence of fcc copper. Changes in the alloy structure also caused changes in the sizes of the grains which grew with an increase of the current density. The Effect of the Concentration of NH4ReO4 In order to check the effect of rhenium salt concentration in electrolyte, three different NH4ReO4 concentrations were used: 0.1, 0.001 and 0.0001 M. Ni-Re alloys indicated the following content of elements: 45-79 % at. of Ni and 20-54 % at. of Re – Figure 7a. The increase of the NH4ReO4 concentration from 0.001 M to 0.1 M caused an increase of the content of rhenium in the alloy. It meant a decrease of nickel content from 80 % at. to 42 % at.


44


100

60 Ni Re

50

40 60

PE, [%]


80

40

30

20 20

10 0 0.001

0.01

0

0.1

0.001

3

Concentration of NH ReO , [mol/dm ] 4

0.1

0.01 3

Concentration of NH ReO , [mol/dm ]

4

4

a.

4

b.

Figure 7. Impact of the NH4ReO4 concentration on the composition (a) and the process efficiency (b) of Ni-Re coatings. The increase of the NH4ReO4 concentration also increased the process efficiency – Figure 7b. At the lowest concentration the process efficiency amounted at only about 10 %. When the concentration was raising, an increase in the process efficiency was observed up to 57 % at the highest NH4ReO4 concentration. It can be explained by hydrogen evolution accompanying the deposition of Ni. A higher content of Ni in alloys leads to lower current efficiency.

b)

a)

c) Figure 8. SEM microphotography of the Ni-Re alloys obtained from the bath of different NH4ReO4 concentration: a) 0.001M, b) 0.01 M, c) 0.1 M.


45


Electrodeposition of Ni-Re alloys from the baths of lowest concentration contributed to decreasing rhenium content in the alloys and had a significant impact on the morphology and quality of the cathode deposit (Figure 8). The obtained coatings were non-uniform, rough and formations of holes could be observed. Those holes are coming from stationary hydrogen bubbles present on the surface during electrodeposition. When the concentration was higher, rhenium content grew and the grains transformed into the flat dendrites-like grains. The increase of the NH4ReO4 concentration caused changes in the structure of the alloy from crystalline to the amorphous one – Figure 9. 1 hcp Re 2 fcc Ni 3 fcc Cu

3 (220)

0.001 M NH ReO Ni-20.3Re 4

4

Intensity / a.u.

3 (111) 3 (200) 7.6 nm

2 (111) 1 (002) 0.01 M NH ReO Ni-23.5Re 4

15.2 nm

1 (110) 2 (220)

0.1 M NH ReO Ni-54.9Re

5.8 nm

30

4

2 (200)

1 (100)

4

40

50

4

60

70

80


Figure 9. XRD pattern of Ni-Re layers obtained from the bath of different NH4ReO4 concentration. When the concentration was very low, sharp reflections could be observed which corresponded to the presence of crystalline fcc nickel and fcc copper. The layer of deposit was very thin, due to very low current efficiency. Increasing the concentration of the NH4ReO4 caused an increase of the process efficiency and rhenium content in the alloy. Sharp peaks corresponding to the presence of fcc nickel and fcc copper and also to weak peaks from hcp rhenium can be observed on the diffraction patterns. The obtained cathode deposit was crystalline. At the highest value of the Re salt concentration in electrolyte, rhenium content was increasing and the deposit changed its structure from crystalline to the amorphous one. Electrocatalytic Properties of Ni-Re Alloys Electrocatalytical properties of alloys or metals are related to morphology of alloys and/or intrinsic activity of alloys components. By changing the deposition conditions we could tune up the electrocatalytic activity of the deposit due to different morphology or composition. The electrocatalytic properties were found in alloys with the highest rate of rhenium content. The best activity for hydrogen evolution was demonstrated by alloys deposited at 20 and 700C (Figure 10a). The Tafel slope of these two cases was 120 and 140 mV/dec, respectively. In other cases, worsening of catalytic properties was observed due to lower rhenium content in the alloy and the range of the Tafel slope was from 210 to 240 mV/dec. The differences between the properties of the alloys could have occurred not only because of rhenium content but also due to different morphology of the alloys. In case of temperature influence, the catalytical activity seemed to be related to the rhenium content. Alloys deposited at 20 and 700C had different morphology (coarse at 200C and smooth at 700C) and high rhenium content, above 24 % at.


46


10

4

4

10 0 20 C Ni-24.8Re

2

25 mA/cm Ni-54.9Re

0

70 C Ni-27.4Re

10

3

10

2

2

3

50 mA/cm Ni-27.4Re

2

Current density [A/m ]

2

Current density, [A/m ]

10

0 30 C Ni-19.8Re

0

50 C Ni-20.6Re

10

2

10

2

75 mA/cm Ni-19.3Re

0

60 C Ni-20.9Re

1

1

10

0 40 C Ni-18.4Re

10

2

100 mA/cm Ni-15.Re 0

0

10 0

-0.2

-0.4

-0.6

-0.8

0

-1

-0.2

-0.4

-0.6

-0.8

-1

η, [V]

η, [V]

Figure 10. Galvanostatic polarization curves for Ni-Re alloys electrodeposited from baths with different temperatures (a) and at different current densities. For the alloys obtained by electrodeposition at different current densities, the best catalytic properties were also found in alloys with the highest rhenium content. The Tafel slope was 100 mV/dec for 25 mA/cm2 and 200 mV/dec for 50 mA/cm2. When the current density was increased over 50 mA/cm2, rhenium content in the alloy decreased and catalytic properties were worsened (Figure 10b). The next parameter influencing the content of metals in the alloys is electrolyte composition. For the alloys deposited from electrolyte of different concentration of NH4ReO4, the best catalytic properties were observed in alloys with high rhenium content. The high activity for hydrogen evolution was noticed in alloys with Re content of 23 % at. or more. The Re content was crucial for catalytical activity, whereas the morphology or structure had no impact. Those alloys were deposited from the electrolyte of 0.01 M or more of NH4ReO4 (Figure 11). 10

4

0.01 M NH ReO Ni-23.5Re

2

Current density, [A/m ]

4

10

3

10

2

10

1

10

0

4

0.1 M NH ReO Ni-54.9Re 4

4

0.001 M NH ReO Ni-20.3Re 4

0

-0.2

-0.4

-0.6

4

-0.8

-1

η, [V]

Figure 11. Galvanostatic polarization curves for Ni-Re alloys electrodeposited from electrolyte with different NH4ReO4 concentration.


47


Conclusions The studies carried out over the electrolytic deposition of Ni-Re alloys resulted in the following conclusions. The best conditions for electrodeposition of Ni-Re alloys with the highest rhenium content, and process efficiency are: the concentration and composition of the bath 0.1 M NH4ReO4, 93 mM Ni(NH2SO3)2 4H2O and 34 mM C6H8O7; bath temperature – 700C; current density – 25 mA/cm2; time of the deposition – 120 minutes. Alloys obtained in high process efficiency conditions were characterized by a compact microstructure. An increase of the rhenium content in the alloy to 23 % at. or more improved the catalytic properties of Ni-Re alloys.

Acknowledgments The financial support from Polish Ministry of Education and Science under contract No. DPN/N27/GDRE-GAMAS/2009 and 694/N-POLONIUM/2010/0 is gratefully acknowledged. The research was carried out in the frames of GAMAS European Research Network.

References 1. 2. 3. 4.

P. I. Kirichenko and V. E. Mikryukov, High Temp. Sci., 2, 176 (1964). L. Wang, Y. Gao, Q. Xue, et al., Surf. Coat. Technol., 200, 3719 (2006). G. Nawrat, M. Gonet, K. Gatnar, Przemysł Chemiczny, 85/8-9, 854 (2006). Ł. M. Jakimienko, Elektrodnyje materialy w prikladnoj elektrochimii, Izd. Chimija, Moskwa (1977). 5. D. Kopyto, W. Gnot, G. Nawrat, Chemik, 7, 175 (2001). 6. J. Socha., J. Weber., Podstawy elektrolitycznego osadzania stopów metali, INP, Warszawa (2001). 7. N. D. Nikolic, H. Wang, H. Cheng, et al, J. Magnetism Magnetic Mater., 272, 2436 (2004). 8. T. Fahidy, Prog. Surf. Sci, 68, 155 (2001). 9. A. Krause, Elektrokrystallization von kobalt und kupfer unter Einwirkung Homogener Magnetfelder, Ph.D. Thesis, Dresden Technische Universitat, Dresden (2006). 10. W. Gumowska, E. Rudnik, I. Harańczyk, Korozja i ochrona metali przed korozją: ćwiczenia laboratoryjne, Wyd. AGH, Kraków (1997). 11. E. M. Savitaskii, M. A. Tylkina, K. B. Povarova, Rhenium alloys with nickel, Nauka, Moscow (1965). 12. W. Rutkowski., St Stolarz., M Raźniewska., et al, Nowe Metale Techniczne, WNT, Warszawa (1962). 13. W. Shirong, The electrodeposition and property study of Nickel-Rhenium Alloy, M. S. Harbin Institute of Technology, P. R. China (1995). 14. Corrosion of Nickel-Base Alloys, Key to Metals, http://keytometals.com. 15. O. N. Vingradov-Zhabrov, L. M. Minchenko, N. O. Esina, et al, J. Mining Metal, 39 (1-2) B, 149 (2003). 16. E. O. Ezugwu, Z. M. Wang, A. R. Machado, J. Mater. Proc. Tech, 86, 1 (1999). 17. A. Naor, N. Eliaz, and E. Gileadi, Electrochimica Acta, 54, 6028 (2009). 18. C. R. K. Rao and D. C. Trivedi, Coordination Chemistry Reviews, 249, 613 (2005).


48