Advances in Ma terials Physics and Che mist ry, 2012, 2, 253-255
doi:10.4236/ampc.2012.24B064 Published Online December 2012 (htt p://
Copyright © 2012 SciRes. AMPC
Obtai ning the thi n Semic onductive Covering Re-Se From
Sulphate Electrolyte
E. A. Salakhova, A. M. Aliyev
Institute of Chemical Problems of the ANAS 29, H. Javid ave., AZ1143, Baku, Azerbaijan
Received 2012
There have been investigated the kinetics and mechanism of the cathode electrodeposition of thin coverings Re-Se from the sulphate
electrol yte, cont aining NH4ReO4, Se O2 and H2SO4. On the base of X -ray phase analysis and by th e method of cyclic avometr y there
have been det ermined th e con ten t of ob tai ned co verin gs, el ectro sett led at th e vario u s concen tr ation s of co mpon ent s in elect ro lyte. the
co-deposition process was shown to be attended by depolarization, which is due to the energy release upon the formation of the alloy.
Keywords: Electrodeposition; Alloys; Rhenium; Selen; Semiconductive Cover
1. Introduction
Rhenium and its alloys have a unique physico-chemical prop-
erty, which provides their application in the most important
fields of modern technology [1,2]. The high temperature of
melting and stable mechanical properties at the high tempera-
tures provided its application in the heat-resistant alloys pro-
duction. The alloys of rhenium with selenium in the form of
thin photosensitive films are used in semi-conducting technol-
ogy. The semi-conducting films of alloys of rhenium with sele-
nium are usually obtained by the method of separate compo-
nents meeting together [3,4]. As the mentioned above method is
rather difficult, it demands complicated instruments and the
process is going at the high temperatures, we tried to apply
electroch emical method b ased on th e electro lysis of water s olu-
tions of selenium dioxide and ammonium perrenate in sulphuric
acid for obtaining the thin coverings of Re-Se alloys.
In order to obtain Re-Se alloy from the sulphate electrolyte
[5,6] we studied the joint electrodeposition of rhenium with
selenium and there was found the optimal regime for obtaining
a s emi-conducting alloy.
Analysis of results of indicated works showed that films de-
pend not only on the composition and nature of electrolyte, but
also o n t he material o f cathode.
The use of different according to the origin electrolytes in
order to obtain the thin coverings Re-Se, is certainl y conn ected
with the hardships which are usually met in every concrete
occasion and it’s directed to the search of the electrolyte com-
position, which gives the chance of obtaining the qualified ca-
thode films, suitable for use in different fields of modern tech-
The present work is a continuation of our investigations in
the field of electrochemical obtaining the semi-conducting al-
loys Re-Se and it’s devoted to the study of scientific basis of
the joint electrodeposition Re-Se alloy by the method of cycling
2. Methods of Experiment
For making the experiment there have been used the following
reactants : SeO2, H2SO4 (chemical p ure) and NH4ReO4 (pu re for
analysis). The experiments have been made in a glass cell pro-
vided with the water j acket .
The cycling avometer curves’ have been reading taken by
means of potentiostat P-5827M and 2D registering device
PDP4-002. As a workin g electrode t here have been u sed a pla-
tinum electrode with 0.15 square cm, and as comparative elec-
trode there have been used a chlorine-silver plate electrode, as
anode the platinum plate with 4 square sm. The acidity of
solution was determined by pH-meter 673M with the glass
electrode. The temperature of electrolyte was regulated by
means of thermostat UH. the content of Re-Se alloy compo-
nents has been analyzed as the following: 10 ml of concentrated
HNO3 were dissol ved whi le h eatin g and after rep eated evapo ra-
tion in the water boiler-both there was added 5 n of H3PO4 to
the solution. The obtained solution has been diluted in the
measured retort till 50 ml and then by extraction with isoamyl
spirit rhenium was separated from selenium. The rhenium has
been determined by photometry of rodanide complex at the
device FEK-56M [7], and selenium has been determined by
thiocarbomide complex [8].
X-ray graphical investigations of thin films Re-Se have been
carried out at difractometer URS-55 in CuKα-irradiation in
RKD camera 57,3.
3. The Results and Their D iscus sion
In order to study the mechanism of formation Re-Se allo y there
have been measured cycling avometer curves in different ac-
cording to composition electrolytes as well as there was held
the chemical and X-ray difractive analysis of cathode settle-
ments, obtain ed at the cert ain potentials.
For detailed investigation of the process of obtaining the thin
electrolytic coverings of Re-Se alloys you must have the infor-
mation about kinetics of deposition of separate components and
Copyright © 2012 SciRes. AMPC
alloys. With this aim there were indicated the polar curves of
Re-Se alloys extra ctions and of the sep arate metals at the pl ati-
num electrode.
As it is known the rhenium stays in sulphate electrolytes in
the form of ReO4 and i ts reduction co nsists of several separ ate
ReO4 + 8H+ + 7e Re + 4H2O
According to the work [9] the degree of ReO4 -ions goes
stage-by-stage and each stage of formation the intermediate
produ cts is charact erized b y a certain el ectrod e potential , which
becomes more negative in the process of rehabilitation, which
can also provide the approach of Re and Se potentials settle-
ReO4 + 2H+ + e ReO3 + H2O; E1 = +0,77V
ReO3 + 2H+ + 2e ReO2 + H2O; E2 = +0,4 V
ReO2 + 4H+ + 4e R e + 2H2O; E3 = +0 ,26V
Thus, the rhenium reduction in strong acid electrolytes goes
according to the stage, through the formation of intermediate
oxides film, about which tell us red and blue sediments in the
obtained film.
In order to have a whole information about the joint electro-
deposition o f Re with Se, there were measured the cycli ng polar
curves of rhenium in sulfate electrolyte at the different involu-
tions. There are two sharp waves on the curve of a cathode
halfcycle. One of them is at the potential 0,2 - 0,3 V, the ot he r
at(-0,3)-(0,4)V (s.c.e). Formation of these waves can be ex-
plained by the step mechanism of reduction the perrenate ions.
The character of anode halfcycle also proves this suggestion.
The anode wave forming at the potential 0,1-0,2V (s.c.e.) can
be explained by Re dissolving, and distinctly expressed peaks
to dissolving of ReO3 and ReO 2 correspondingly.
There have been studied the dependence of involution rate of
potential on the rise of limited current value. Dependence of
limited current from square root of potential involution rate has
a rectilinear character, which is observed in those cases, when
the deposition rate is controlled by ions diffusion to the surface
of cathode.
Then, in order to have additional information about the
processes taking place while Se deposition, there were meas-
ured cycling polar curves of Se in sulphate solutions at the dif-
ferent involution.
As it can be seen in the diagram on the cycling volt-ampere
curves of cathode deposition and anode oxidation of Se there
appears a wave, which refers correspondingly to rehabilitation
of SeO32 till Se and to oxidation of the obtained product till
SeO32. As well as it can b e seen from the d iagram th at with th e
rise of evolution rate the volt-ampere curves are shifted to the
positive side and at the involution of 80 mV/seс the wave dis-
appears and there is formed a maximum limited current.
Perhaps, while formation the wave of reduction the main role
plays the high resistance of cr eate d semi-cond u ctin g layer o f Se,
and therefore the process velocity decreases. With shifting the
pot ent ial to th e negative side a st ormy discharge of hydrogen on
the cathode takes p lace.
It’s been established, that electrochemical formation of thin
layer films goes through a number of complicated electro-
chemical reactions.
One of the factors influencing simultaneous deposition of
electrolyte components is the state of a platinum cathode. It’s
also well-known, that electrocatalytic activity of electrode sur-
face can change while depositing the other metals in a small
There were suggested several various mechanisms of elec-
trochemical rehabilitation of Se [10], in the field of positive
potentials (from +0.75 to +0.35 V s.c.e.).
As it follows from these works, deposition of H2SO3 is a
multistage process. At the first stage the adsorption of se acid
takes place, where on the surface of electrode the adsorbed
compounds of Se with intermediate degree of oxidation are
being formed.
There have been sh own the typical avogrammes of Se O2 so-
lution in sulphuric acid at the platinum electrode. According to
the results of investigations [5], the processes concerning peaks
C1 and C2 are connected with formation of adsorbed com-
pounds of Se with intermediate degrees of oxidation on the
electron surface:
1) deposition and reduction of Se compounds (IV) on the ac-
tive surfac e of plati num electrode
H2SeO3 + 2H+ + 2e H2SeO2 (Pt) + H2O; E = +0.70V
2) the current of reduction C2 is co nnect ed with th e pr ocess
an substrate surface, which reminds the deposition of amorph-
ous Se:
H2SeO2(Pt) + 2H + + 2e OSe (Pt) + 2H2O; E = +0.35V
Our results are coordinated with the literature information.
In order to investigate the joint electrodeposition and to study
kinetics and mechanism of the process of joint electrodeposi-
tion of Re with We from sulphate electrolyte there were taken
the cycling vo ltamper cu rves o f Se, Re and Re-S e alloy. The Re
deposition on platinum electrode takes place at the potential
about 0. 6 V (s.c . e), and Se at 0.5 V ( s .c.e.). th e curves of alloy
are quite different from the curves taken from solutions, having
separate components. The joint deposition of Re with We takes
place at the more positive potentials, than these metals extrac-
tion separately, i.e. both components in alloy are extracted by
depolarization. Such location of polar curves is observed in
those cases, when it’s possible to form a chemical compound
on the cat hode. The depol arization itself is a d irect evidence of
the fact that at the joint deposition there is a chemical interac-
tion between the components with formation of ReSe2 on the
catho de. Re + 2Se ReSe2
At the change of the direction of potential evolution on the
anode semi-cycles of voltampere curves, being obtained for
individual components, there is observed just one peak of anode
oxidation. For rhenium the pear of oxidation starts at the poten-
tial 0 .6 V (s.c.e.) and for S e about 0.95 V (s .c.e.).
However, there have been observed 3 peaks of anode oxida-
tion on the voltampere curve of the anode semi-cycle. The
peaks of oxidation, observed at 0.60 and 0.95 V (s.c.e.) no
doubt, are caused by Re and Se oxidation. The new peak of
oxidation, observed at the potential 0.80 V (s.c.e.) refers to the
oxidation of complex ReSe2, forming on the catho de according
to the reaction
ReSe2 = Re + 2Se + 2 e
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Hence, at the indicated potentials on the cathode the joint
deposition of Re with Se doesn’t take place and the only ca-
thodic product is Se.
The joint deposition of Re with Se starts at the potential
some about 0.20 V (s.c.e.) which is confirmed by the appear-
ance on the curve the anodic semi-cycle of the second wave
of anodic current at the potential 0.80 V (s.c.e.) connected with
ReSe2 oxidation.
The sedi ment v ery close to ReSe2 according to the composi-
tion is obtained in the interval of potentials 0.15 V (s.c.e.). By
shifting the potential to the negative side the content of Se in
cathodic sediments is rising. These sediments consist of
ReSe2+Se. according to X-ray phaseous analysis, the films,
having surplus quantity of Se and obtained at the potentials
more positive than 0.25 V, consist of two phases ReSe2 and Re.
The information taken from microanalyser showed that Re is
mostly in the lower layers of the films. And the films rich with
Se, obtained at the potential 0.10 V, consist of two phases
ReSe2 and Se. Here Se is located in the upper layers of the
The films, very close to ReSe2 according to their composition
are formed in the interval of potentials 0.25 V.
There were analyzed the content and morphology of thin
layers ReS e2, electrodep osited on the p latinum electrode. Fr om
the X-ray phaseous analysis it follows the film consist from
54% of Re and 46% of Se (according to the mass).
We have establi shed that the co mpound ReSe2 is cr ystallized
in triclinic syngony with the parameters of the lattice: a=6.7275
Å; b=6.6065 Å; c=6.7196 Å.
4. Conclusion
There have been in vesti gated th e kinetics an d mechani sm of the
cathode electrodeposition of thin coverings Re-Se from the
sulp hate electrolyte.
Was shown, that co-deposition of rhenium and selenium
occur with some depolarization, which is due to the energy
release upon the formation of the alloy.
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