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ISSN 2522-1841 (Online) ISSN 0005-2531 (Print)
UDC 54.544.6
ELECTROCHEMICAL BEHAVIOR OF BISMUTH IONS IN CITRATE SOLUTIONS
S.P.Javadova1, V.A.Majidzade1, S.F.Jafarova1, T.A.Aliyev2, A.Sh.Aliyev\ D.B.Tagiyev1
M.Nagiyev Institute of Catalysis and Inorganic Chemistry, Ministry of Science and Education
of the Republic of Azerbaijan
Institute of Natural Resources
Received 12.01.2023 Accepted 24.02.2023
The scientific paper is devoted to the electrochemical reduction of bismuth ions from citrate electrolytes. The kinetics and mechanism of the process and the influence of various factors on the electroreduction process of bismuth ions were studied by recording cyclic and linear polarization curves on Pt, Ni and Ni/Bi electrodes. The effective activation energy and diffusion coefficient were calculated according to the obtained data. The results of the calculation show that the electroreduction process of the bismuth ions from citrate solutions is accompanied by diffusion polarization.
Keywords: bismuth ions, electroreduction, polarization, citrate electrolyte, Randles-Sevcik equation.
doi.org/10.32737/0005-2531-2023-4-5-12
Introduction
The microelectronics, photoelectroche-mistry and radio engineering developments require the use of special coatings to improve the functionality of materials [1-3]. Bismuth and its alloys are also encountered among such materials. Due to their unique physical and chemical properties, they have become the object of numerous electrochemical studies attracting the attention of both chemists and physicists.
Bismuth and its alloys exhibit good thermoelectric properties. Therefore, the possibility of obtaining coatings with valuable physical and chemical properties attracts attention [4-11].
Bismuth is the most diamagnetic of all metals. It is possessed of low thermal conductivity and high electrical resistance, and is the most low-melting and least toxic among heavy metals. The presence of bismuth, even in small quantities, significantly affects the quality and properties of electroplated coatings.
As is known, identified solutions for the deposition of bismuth are strongly acidic and aggressive due to their tendency to hydrolysis. Therefore, the development of stable electrolytes for the electrochemical deposition of bismuth and its alloys is important from a practical standpoint.
There are a number of works in the litera-5ture concerning the electrochemical deposi-
tion of bismuth and its alloys from various electrolytes.
The electroreduction of Bi(III) ions on a bismuth electrode from solutions containing nitric, sulfuric or perchloric acids was studied by the method of cyclic voltammetry [12]. When studying solutions containing only nitric acid, as well as sulfuric or perchloric acids together with Bi(III) ions, it was concluded that the cathode wave proceeds from the reduction of nitrate ions catalyzed by electrodeposited bismuth.
During the electrodeposition of bismuth [13] onto some metallic substrates obtained from nitrate solutions, the deposits begin to nucleate instantly over the entire surface of the substrate and the grains measure from 1 to 5 p,m size. Measurements on Cu and Au electrodes were studied in detail depending on the deposition potential. It was found that at a higher negative potential, that is, at a higher current density, there is a strong tendency for the growth of A (012), in particular, on (111) - on structured Au substrate. In addition, nucleation on Au is instantaneous.
Also in [14], the electrodeposition of bismuth from nitrate solutions was studied by cyclic voltammetry and chronoamperometry. The author's results show that chronoampero-metry is an important method for the electro-
deposition of bismuth on glass-carbon electrodes. Experimental transient processes of the current are analyzed according to the Sharifker-Hills and Hermann-Tarallo models. It was found that the nucleation and growth of grains has a 3D mechanism for 1 and 5 mM Bi3+ regardless of deposition potentials.
Bi was deposited by the galvanostatic way from a solution of concentrated hydrochloric acid [15]. Morphology resembling a stack of flakes appeared at lower current densities. At higher current densities, Bi was electrodeposited as dendrites. The current efficiency decreased significantly during deposition above -0.2 V compared to Ag/AgCl. The magnetic field application increased the current density, but slightly decreased the current efficiency. The surface morphology at the macroscopic scale improved significantly at higher current densities, while preferential growth of lamellar deposits appeared at lower current densities.
The authors of [16] obtained metallic bismuth of various morphologies with particle sizes within nanometer and micrometer on Pt, Au, Al and ITO electrodes at room temperature by elec-trodeposition. It was determined that the size and morphology of the films strongly depend on the deposition conditions - deposition potential, current density, electrode and electrolyte. The results of scanning and transmission electron microscopy showed that the deposited bismuth particles exhibit a variety of shapes - T-shaped rod, bundle, frame and strip-like shapes. A significant positive effect of magnetoresistance is observed even at room temperature [16].
Thin films of bismuth [17] were obtained by electrochemical method on n-GaAs s110d. Bismuth films up to several hundred nanometers have a strong s018d texture, whereas thicker films are polycrystalline. The barrier height of n-GaAs/Bi contacts is 0.62 eV, about 0.2 eV lower than for electrodeposited bismuth films on GaAs s100d.
In [18], bismuth is electrochemically deposited from trilonate solutions. Study of the kinetics of the process shows that electrode-position is a catalytic electrode process followed by a first-order chemical reaction. It was
found that the properties of coatings depend on the structure of deposits. As the grain size decreases, an increase in microhardness and corrosion rate of coatings is observed.
The work [19] also studied the electro-deposition of bismuth at 600C from ionic liquids containing a mixture of choline chloride and oxalic acid. The bismuth concentration in the solution is 10 mM. The processes were studied on Pt and Cu substrates by cyclic voltammetry and electrochemical impedance spectroscopy. The process time of electrolysis carried out at 600C in the potential range -0.22 - (-0.37) V is 30-120 minutes. The results show that the ionic liquid of choline chloride can be considered as a promising replacement for aqueous baths for the electrochemical deposition of Bi and its alloys.
The kinetics, mechanism and influence of various factors on the electroreduction of bismuth ions from tartrate electrolytes was studied on Pt electrodes by recording cyclic and linear polarization curves on Pt electrodes. The results show that the electroreduction process of bismuth ions from tartrate solutions at a potential
range of 0.5 - (-0.35) V occurs in multiple
1/2
stage. The dependence between ip and v indicates that the electroreduction process is accompanied by diffusion polarization [20, 21].
As is seen from the analysis of the literature, the study of the electroreduction of bismuth ions or the electrodeposition of bismuth was carried out from different electrolytes, and there are no specific patterns for this process.
The purpose of the work is to study the electrochemical reduction of bismuth ions from more environmentally friendly - citrate electrolytes for further co-electrodeposition of Bi2Se3 thin films.
Experimental part
The electrolyte for bismuth deposition was prepared by dissolving citric acid at the rate of 1 g per 100 ml of water, Bi(NO3)3 • 5H2O ("reagent grade" JSC "Vekton", Russia) was dissolved in 2 ml of HCl, then both solutions were mixed. The electrolyte had the following composition: 0.01 mol/l Bi(NO3)3-5H2O+2-10-3 HCl + 5-10-2 mol/l C6H8O7.
This composition of the electrolyte is due to the fact that complete dissolution of the bismuth salt does not occur when the amount of acid is less than 2-10- mol/l, and an increase in the amount of acid leads to hydrolysis of the solution.
Polarization curves were recorded in an
IVIUMSTAT Electrochemical Interface poten-
tiostat. An electrochemical three-electrode cell
with a capacity of 100 ml was used to this end.
Pt, Ni and Ni/Bi electrodes with an area of 0.6 2 2 2 cm , 2 cm , and 2 cm , respectively, served as a
working electrode. The reference electrode was a silver chloride electrode, and the auxiliary electrode was a platinum plate with an area of 4 cm2. Universal ultra-thermostat UTU-4 was utilized to regulate the temperature in the electrolyzer.
Since platinum electrodes require periodic cleaning they were cleaned in concentrated nitric acid and then washed with double-distilled water before experiments. After each experiment, the platinum electrode should be kept in boiling nitric acid containing a small amount of FeCl3 for 30 minutes. After this, they should be thoroughly washed with distilled water and finally rinsed with alcohol or acetone [22].
The surface of the Ni electrodes is mechanically ground off, treated with diluted HNO3 acid for 30 seconds before experiments to remove oxide layers, immersed in alcohol or acetone, and finally washed with bidistilled
water. Electrochemical polishing of Ni electrodes was carried out in a solution consisting of 55 ml of H2SO4, 55 ml of H3PO4, 50 ml of H2O (T = 293 - 303K, i = 50 A/dm2, t = 180 sec.), and then washed with bidistilled water [22].
Results and discussion
Experimental study of the kinetics and mechanism of cathodic deposition of metals is a complex task, which is associated with some specific features of this process. The cathode surface is not constant, continuously changes based on the deposition of metal during electrolysis.
The electrochemical reduction of bismuth ions from citrate solutions was carried out by the potentiodynamic polarization method. The process was studied on Pt, Ni and Ni/Bi electrodes to illuminate the kinetics and mechanism.
As is seen from Figure 1, the electrochemical reduction of these ions on the Pt electrode occurs in stages in the potential range of 0.6 - (-0.2) V.
According to the authors, this is due to the fact that bismuth compounds of different compositions are formed in the electrolyte: Bi-OCl, HBiCl4, etc.
The polarization curves recorded by the potentiodynamic method show that the double electrical layer is formed and the resulting compounds decompose in the potential range 0.60.3 V in the initial stage (Figure 1 b).
Fig.1. Cyclic polarization curve of the electroreduction of bismuth ions from citrate electrolyte on the Pt electrode. Electrolyte (mol/l): 0.01 Bi(NO3)3-5H2O+2-10-3 HCl+5-10-2 QftA, T=298K, EV=0.02 V/sec. a - total process; b - initial stage.
Then, the following process occurs in the potential range 0.3-0.07 V [23]:
BiCl4- + 3e = Bi + 4Cl-
BiOCl + 2H+ + 3e = Bi + H2O + Cl- (1)
• 3+
Bi3+ is reduced to Bi after 0.07 V potential by the following reaction [23]:
Bi3+ + 3e = Bi (2)
The consecutive process obtained from the polarization curves (Fig. 1a, b) shows that the first bismuth nuclei appear on the Pt substrates and then after -0.05 V potential, the deposition of Bi accelerates and the electrode surface is completely covered with a black film of bismuth during all these stages. An increase in the current value from 7.2 10-5 A to 1.6-10-3 A also proves this.
For comparison, the kinetics and mecha-
nism of electrochemical reduction of bismuth ions were also studied on Ni (Figure 2) and Ni/Bi (Figure 3) substrates. The reason for studying the process on Pt and Ni substrates up to -0.4 V, and on Ni/Bi substrates up to -0.8 V, is that hydrogen evolution is observed after these potentials. Hydrogen evolution interferes with the electrochemical reduction of bismuth ions in the course of the study and therefore the study was carried out up to the hydrogen evolution potential. Comparison of Figures 1, 2 and 3 shows that the electrochemical reduction of bismuth ions on all 3 electrodes begins at a potential of -0.05 V. Anodic dissolution of the process under study on Pt, Ni and Ni/Bi substrates begins with a potential of -0.12 V, - 0.85 and -0.83 V, respectively.
Fig. 2. Cyclic polarization curve of electroreduction of the bismuth ions from citrate electrolyte on the Ni electrode. Electrolyte (mol/l): 0,01 Bi(NO3)3 -5H2O +
T = 298K, EV = 0.02 V/sec.
2-10-3 HCl+5-10-2 C6H8O
Fig. 3. Cyclic polarization curve of electroreduction of the bismuth ions from citrate electrolyte on the Ni/Bi electrode. Electrolyte (mol/l): 0,01 Bi(NO3)3 • 5H2O +
T = 298K, EV = 0.02 V/sec.
2-10-3 HCl + 5-10-2 C6H8O
Fig. 4. The temperature dependence of the electroreduction process of the bismuth ions in citrate electrolyte on the Pt substrate. Electrolyte (mol/l): 0.01 mol/l Bi(NO3)3 • 5H2O + 2-10-3 HCl + 5-10-2 C6H8O7, EV = 0.02 V/sec., T, K: ▲ - 298; - 308; - 318; - 328; - 338; - 348.
Next, Gorbachev's method was used [24] to determine the kinetics of the electroreduction process of the bismuth ions. First of all, the effect of the temperature on the electroreduction process of bismuth ions was studied. The effect of temperature was studied by the potentio-dynamic method in the ranges of 298-348K (Figure 4).
It is clear from the recorded polarization curves that the electrochemical reduction of bismuth ions will change in a more positive direction depending on the influence of the temperature. Since, the electrochemical reduction of bismuth ions at 298 K and 348 K occurs at -0.045 V and -0.015 V, respectively. The de-
pendence was plotted between lgik and 1/T to study the kinetics of the electrochemical reduction process in the potential range -0.08-(-0.23) V using these polarization curves (Figure 5) tga is calculated from the obtained lines.
Next, the value of the effective activation energy is calculated according to the equation Aef. = 2.3Rtana. The obtained result shows that the electrochemical reduction of bismuth ions from citrate electrolytes is accompanied by diffusion polarization (Figure 6).
The effect of the concentration of bismuth ions on the process was also studied to improve the quality of the deposited films and find the optimal electrolysis mode.
Fig. 5. The dependence between lgik and 1/T.
Fig. 6. The potential dependence of the activation energy.
The effect of concentration on the process was studied in the range of 0.0005 - 0.06 mol/l. Figure 7 shows linear polarization curves of the effect of bismuth ion concentration on the electroreduction process. The polarization curves show that the influence of concentration on the process occurs in different ways. Starting from 0.0005 mol/L to 0.01 mol/L, the electrochemical reduction shifts to more positive direction with increasing concentration of bismuth ions in the electrolyte. After 0.01 mol/l, the effect of concentration on the electroreduc-tion process is opposite. That is, the reduction
potential shifts to more negative direction with increasing concentration. In our opinion, after 0.01 mol/l, stabler bismuth complexes are formed with increasing Bi ions concentration in the electrolyte. Therefore, the decomposition of these complexes gets harder and the electrore-duction of bismuth ions occurs at more negative potentials.
The electroreduction of bismuth ions has been studied in the 0.005 - 0.1 V/sec. range of scanrate. Linear polarization curves of the process are shown in Figure 8.
Fig. 7. The effect of the concentration of the bismuth ions on the electroreduction process on the Pt substrate. Electrolyte (mol/l): Bi(NO3)3-5H2O +2-10-3 HCl+5-10-2 mol/l C6H8O7, EV = 0.02 V/sec, T=298K. Concentration (mol/L): ▲ - 0.0005; - 0.005; • 0.01; - 0.03; - 0.06.
Fig. 8. Electroreduction of bismuth ions on Pt substrates at different scanrate. Electrolyte (mol/l): 0.01 Bi(NO3)3 • 5H2O + 2-10"3 HCl + 5-10"2 C6H8O7. T=298K, Scanrate (V/sec.): ▲ - 0.005; - 0.02; - 0.04; - 0.06; - 0.08; - 0.1.
Fig. 9. ip -E dependence of the electroreduction process of the bismuth ions from the citrate electrolyte on the Pt electrode. Scanrate (V/sec.): 1 - 0.005; 2 - 0.02; 3 - 0.04; 4 - 0.06; 5 - 0.08; 6 - 0.1.
As is seen from the figure, the current expended on the electroreduction process increases with an increase in the scanrate value. Since, currents at 0.005 V/sec. and at 0.1 V/sec. are 1.923-10-3 A and 1.07-10-2 A, respectively. In addition, a shift to more positive direction in the reduction potential is also observed. This is approximately -0.02 V.
1/2
Relationship between ip and v was also plotted (Figure 9) to clarify the kinetics and mechanism of the electroreduction process of bismuth ions. As is seen from the figure, there is a straight-line correlation between them. ip linearly increases with an increase in the scanrate value.
In addition, the diffusion coefficient of bismuth ions for the electroreduction process was calculated using the Randles-Sevcik equation:
3 11
ip = 2,686 • 10sn2ACD2V2
where ip is the peak value of the current density in the cyclic polarization curves, n is the number of electrons included in the half-reaction for re-
9
dox pairs, A is the electrode area (cm2), C is the
concentration of bismuth ions in the electrolyte
(molcm-3), D is the coefficient diffusion 2 1 1 (cm sec.- ), V - scanrate (mV sec.- ). From here
i U
D2 =-
3 1 2,686-10s-n2^CV2
The diffusion coefficient for the electro-reduction process of bismuth ions calculated
3
according to this formula is equal to 1.03*10" cm2- sec -1.
This also proves that the electroreduction process is accompanied by diffusion kinetics.
Conclusion
The electrochemical reduction of bismuth ions from citrate electrolytes was studied on Pt, Ni, Ni/Bi electrodes using the voltammetric method. When studying the kinetics and mechanism of the process according to the cyclic and linear polarization curves, it was found out that the nature of polarization in this case is accompanied by a diffusion nature.
The results of all experiments show that the concentration of bismuth ions and temperature affect the electroreduction process of bismuth ions from citrate electrolytes. The optimal electrolysis mode and electrolyte composition for the electroreduction process of bismuth ions were selected according to these studies.
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SiTRAT MOHLULLARINDA BiSMUT iONLARININ ELEKTROKiMYOVi DAVRANI§I
S.P.Cavadova, V.A.Macidzada, S.F.Cafarova, T.A.Oliyev, A.§.Oliyev, D.B.Tagiyev
Maqala sitrat elektrolitindan bismut ionlannin elektrokimyavi reduksiyasina hasr edilmiçdir. Pt, Ni va Ni/Bi elektrodlannda tsiklik va xatti polarizasiya ayrilarinin çakmasila bismut ionlannin elektroreduksiya prosesinin kinetikasi, mexanizmi va prosesa müxtalif amillarin tasiri ôyranilmiçdir. Alinmiç naticalar asasinda effektiv aktivlaçdirma enerjisi va diffuziya amsali hesablanmiçdir. Hesablamalarin naticalari göstarir ki, sitrat mahlullarindan bismut ionlarinin elektroreduksiya prosesi diffuzion polyarizasiyasi ila mûçayiat olunur.
Açar sözlzr: bismut ionlari, elektroreduksiya, polyarizasiya, sitrat elektroliti, Randles-Çevçik t3nliyi.
