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European Journal of Applied Sciences – Vol. 10, No. 1
Publication Date: February 25, 2022
DOI:10.14738/aivp.101.11575. Sani, O. M., Bougouma, M., Abdoulkadri, A. M., Ibrahim, N., & Legma, J. B. (2022). Study of the Anodic Dissolution Solutions of
Single Crystals of Molybdenum Diselenide (MoSe2) in KOH Media. European Journal of Applied Sciences, 10(1). 168-175.
Services for Science and Education – United Kingdom
Study of the Anodic Dissolution Solutions of Single Crystals of
Molybdenum Diselenide (MoSe2) in KOH Media
Ousmane Mahamane Sani
Faculty of Sciences and Technology
University of Agadez, Agdez, Niger
Faculty of Sciences and Technology
Norbert Zongo University, Koudougou, Burkina-Fasso
Moussa Bougouma
Faculty of Sciences and Technology
Norbert Zongo University, Koudougou, Burkina-Fasso
Ayouba Mahamane Abdoulkadri
Faculty of Sciences and Technology
Abdou Moumouni University, Niamey, Niger
Natatou Ibrahim
Faculty of Sciences and Technology
University of Agadez, Agdez, Niger
Faculty of Sciences and Technology
Abdou Moumouni University, Niamey, Niger
Jean Boukary Legma
Faculty of Sciences and Technology
Norbert Zongo University, Koudougou, Burkina-Fasso
ABSTRACT
This work is a contribution to the study of semiconductor materials that are used in
semiconductor electrolyte junctions for the conversion of light energy into
electrical energy. The study was carried out in KOH medium on single crystals of
molybdenum diselenide obtained by physical vapor transport and previously
characterized by different analysis techniques (SEM, XRD, etc.). A preliminary study
on standard molybdate ion solutions was first carried out in order to establish the
potential domain of molybdate ions. Cyclic anodic redissolution voltammetry was
used for the analysis of standard solutions and MoSe2 dissolving solutions obtained
by anodic attack at fixed potential. The results obtained show a reduction peak
towards -0.812V indicating the deposit during the pre-electrolysis. A first oxidation
peak at around -0.740V and a secondary peak at around -0.429V corresponding to
the oxidation of the deposit during redissolution. Analysis of the results shows that
MoSe2 is not stable in KOH media.
Keywords: Cyclic voltammetry; Molybdenum diselenide; anodic attack; kOH medium.
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Sani, O. M., Bougouma, M., Abdoulkadri, A. M., Ibrahim, N., & Legma, J. B. (2022). Study of the Anodic Dissolution Solutions of Single Crystals of
Molybdenum Diselenide (MoSe2) in KOH Media. European Journal of Applied Sciences, 10(1). 168-175.
URL: http://dx.doi.org/10.14738/aivp.101.11575
INTRODUCTION
The two-dimensional (2D) structural lamellar dichalcogenides of transition metals MX2 (M =
Mo, W... and X = S, Se, Te) are the subject of much research in the fields of photovoltaics,
photocatalysis, electronics. and thermoelectric, due to their many unprecedented chemical and
optoelectronic properties that are inaccessible in many materials [1-8]. They are generally
synthesized either by crystal growth by physical vapor transport [9-13] or by electrodeposition
in ionic media [14-19]. In the present work, the material studied is a single crystal of
molybdenum diselenide (MoSe2) obtained by chemical vapor transport with tellurium
tetrachloride (TeCl4) [9]. It has previously been characterized by different physical methods
(Scanning electron microscopy (SEM), X-ray diffraction (XRD), etc.) and these semiconductor
properties have been studied by measuring electrical conductivity and photo-current [9]. The
results obtained augur well for the use of the material as a working electrode in an
electrochemical photo cell for applied purposes. However, for a better use of the properties of
the semiconductor/electrolyte junction for use such as the conversion of solar energy into
electrical energy, the study of the semiconductor/electrolyte junction must put the emphasis
on the anodic dissolution of the material at fixed potential.
Indeed, the phenomenon of the dissolution of materials during electrolysis is a major problem
with all semiconductor electrodes and represents the main obstacle to their use in
electrochemical cells for applied purposes. It is therefore interesting to carry out any study of
the behavior of the material in various electrolytes under anodic polarization. The present work
is part of this dynamic. It consists in studying the behavior of MoSe2 in an electrolytic medium
by studying its dissolution by anodic attack at a fixed potential of 1.2 V for 24 hours in a basic
media. This will allow precise determination of the balance sheet of the charge transfer reaction
at the semiconductor/electrolyte interface in order to implement surface treatment means in
order to improve the performance of the MoSe2/junction. electrolyte.
MATERIAL AND METHODS
Equipment
The potentiostat used in this work is Radiometer analytical, voltalab PST050. It is directly
controlled by a computer equipped with a voltamaster 4 program. Its role is to ensure
automatic regulation of the potential difference imposed between the reference electrode and
the electrode under study. The measuring cell is associated with an MDE 150 type
polarographic stand which allows automatic control of the measurements. The cell is
essentially made up of three electrodes:
- a working electrode with a rotating disc with a glassy carbon tip, 3 mm in diameter;
- a reference electrode for silver chloride Ag/AgCl (3M KCl) type TR020 from Radiometer
analytical brand. Its potential is 208 mV relative to the normal hydrogen electrode
(ENH);
- an auxiliary electrode for platinum type TM020 from Radiometer analytical brand with
a large surface area through which passes the electric current necessary to produce the
desired potential difference;
- an arrival of argon for the solution bubbling.
Methods
The supporting electrolyte used is a solution of 0.1 M KCl dissolved in 0.02 M acetic acid-sodium
acetate buffer at pH 5. The analysis of the anodic dissolution solutions is preceded by that of
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European Journal of Applied Sciences (EJAS) Vol. 10, Issue 1, February-2022
Services for Science and Education – United Kingdom
the support electrolyte then preliminary experiments on standard solutions of sodium
molybdates (Na2MoO4,2H2O) dissolved in the support electrolyte in order to establish the
electroactivity range of molybdate ions. Before any measurement, the pH of the test sample is
adjusted to 5 in order to have in solution all the dissolved forms of molybdenum (VI) which are
reducible on glassy carbon. The oxygen dissolved in the solution is removed by bubbling away
with argon for 10 min. Solutions are prepared on the day of the experiment. For the quantitative
study of the solutions, cyclic voltammetry in anodic redissolution coupled with the metered
addition technique was used in this work.
Study of Standard Molybdate Ion Solutions
A stock solution of MoO42- (10-3 M) molybdate ions is prepared by dissolving the corresponding
amount of sodium molybdate (Na2MoO4.2H2O) in the supporting electrolyte. Solutions of lower
concentrations between 10-3 and 10-6 M are obtained by diluting the stock solution with the
electrolyte. A pre-electrolysis is carried out at a constant potential of 200 mV for 2 minutes.
Then a linear round trip potential scan is performed from 0 to -1000 mV/Ag.
Study of Anodic Dissolution Solutions
Dissolution of the MoSe2 material was carried out in a basic media (1 M KOH), the electrode
being subjected to a potential of 1.2 volts for 24 hours. The solution thus obtained is a solution
for dissolving the anodic material MoSe2 in the electrolytic media.
1 mL of this solution is taken, which is diluted 10 times with the supporting electrolyte (0.1 M
KCl + 0.02M acetic acid-sodium acetate buffer). The test portion is analyzed by cyclic
voltammetry using as the working electrode a rotating disk electrode with a glassy carbon tip
using the anodic redissolution technique. The method consists in carrying out, for 2 minutes, a
pre-electrolysis at constant potential of 2 mV and corresponding to the diffusion plateau so that
there is reduction of the molybdate ions.
Once the pre-electrolysis is complete, the metal deposited on the surface of the electrode is
redissolved by anodic oxidation by performing a linear return scan of potential from -1000 mV
to 0 mV (same conditions as the standard solutions).
RESULTS AND DISCUSSIONS
Study of Standard Molybdate Ion Solutions
Study of a Standard Solution of Molybdate Ions as a Function of the concentration
Figure 1 shows the voltammograms obtained by analysis of the support electrolyte and
standard solutions of molybdate ions of various concentrations. These solutions were obtained
by successive additions of 40 μL of the stock solution (10-3 M) to the support electrolyte. We
note the presence of a reduction peak towards -0.790 V, the height of which increases with the
addition.
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Sani, O. M., Bougouma, M., Abdoulkadri, A. M., Ibrahim, N., & Legma, J. B. (2022). Study of the Anodic Dissolution Solutions of Single Crystals of
Molybdenum Diselenide (MoSe2) in KOH Media. European Journal of Applied Sciences, 10(1). 168-175.
URL: http://dx.doi.org/10.14738/aivp.101.11575
Figure 1. Voltamograms of standard solutions of molybdate ions in KCl (0.1 M) + acetic acid- sodium acetate buffer; round trip scanning from 0 to -1000 mV at a speed of 50 mV/s : study as
a function of the concentration (C)
The reduction peak current values are determined by choosing a baseline against which to
measure the respective heights of each peak. The proportionality between the peak current and
the concentration of the standard solutions was verified by plotting the curve of the variation
of the current intensity of the reduction peaks as a function of the concentration of the standard
solutions (Figure 2). It can be seen that the curve obtained is linear with a correlation coefficient
equal to 0.993. This proves that the working electrode is well suited for this study.
Figure 2. Calibration curve i = f (C) of the working electrode
Study of a Standard Solution of Molybdate Ions as a Function of the Scanning Speed
Figure 3 shows the voltammograms obtained by analysis of a standard solution of molybdate
ions (6.54×10-5 M) as a function of the scanning speed. This solution was obtained by adding
y = 22.767x - 1.1658
R2 = 0.9939
0
10
20
30
40
50
0 0.5 1 1.5 2
i(μA/cm2)
C.10-5(mol/l)