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Electrocrystallization of lead dioxide: Influence of early stages of nucleation on phase composition
Accepted Manuscript Electrocrystallization of lead dioxide: influence of early stages of nucleation on phase composition O. Shmychkova, T. Luk’yanenko, A. Piletska, A. Velichenko, R. Gladyshevskii, P. Demchenko, R. Amadelli PII: DOI: Reference:
S1572-6657(15)00154-X http://dx.doi.org/10.1016/j.jelechem.2015.03.031 JEAC 2060
To appear in:
Journal of Electroanalytical Chemistry
Received Date: Revised Date: Accepted Date:
16 January 2015 21 March 2015 27 March 2015
Please cite this article as: O. Shmychkova, T. Luk’yanenko, A. Piletska, A. Velichenko, R. Gladyshevskii, P. Demchenko, R. Amadelli, Electrocrystallization of lead dioxide: influence of early stages of nucleation on phase composition, Journal of Electroanalytical Chemistry (2015), doi: http://dx.doi.org/10.1016/j.jelechem.2015.03.031
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Electrocrystallization of lead dioxide: influence of early stages of nucleation on phase composition O. Shmychkovaa, T. Luk'yanenko a, A. Piletskaa, A. Velichenkoa,*, R. Gladyshevskiib, P. Demchenkob, R. Amadellic
a
Ukrainian State University of Chemical Technology, 8, Gagarin Ave., 49005 Dniepropetrovsk, Ukraine
b c
Lviv National Ivan Franko University, 6, Kirila i Mephodiya Str., 79005 Lviv, Ukraine
Istituto per la Sintesi Organica e la Fotoreattivita – Consiglio Nazionale delle Recerche (ISOFCNR), Dipartimento di Chimica, Universita di Ferrara, via L. Borsari, 46–44121 Ferrara, Italy
Abstract. It has been revealed that coatings obtained from methanesulfonate bath at investigated conditions (10 mA⋅cm-2; pH=1.0) are almost entirely composed of α-phase. It was found that the gradual transition from α- to β-phase in the coating occurs in the presence of additives in deposition electrolytes. It was proposed to use charge coming on the formation of nuclei as the correlation parameter to predict the phase composition of obtained lead dioxide deposits. Electrocrystallization of PbO2 begins with the formation of a monolayer on the electrode surface, then the formation and growth of three-dimensional nuclei takes place. The simultaneous formation of α and β phases results in the presence of two linear areas on the plot of (j-j1)1/3 vs. time for the progressive growth of crystals. The formation of one phase is noticeably lagged behind the other. At layer-by-layer crystallization and significant lagging of one of phases may occur ingesting of growing centres of one phase by another.The type of lagging phase depends on the nature of electrolyte: for nitrate bath it is β, for methanesulfonate – α.
Keywords: Lead dioxide, Methanesulfonate electrolyte, Nucleation and growth, Phase composition.
1. Introduction Electrodes based on lead dioxide doped by ionic additives are known to be of great interest for investigation owing to tailoring solid state properties as well as electrocatalytic activity of PbO2 [1−7]. Particular attention should be paid to ionic additives in high oxidation states +3, and +4 *
Corresponding author. Tel: +380563772974. E-mail address: [email protected] (A. Velichenko)
(compared to places of cation vacancies of lead dioxide, in which Pb2+-ions are known to be localized). It is recognized [8-11], that there are two zones on the lead dioxide surface: crystal (PbO2) and hydrated [PbO(OH)2], that are in equilibrium and are capable to exchange cations and anions with the ions present in the bulk. Lead ions replacement both in hydrated and crystal zone would cause not only the change of amount of oxygen-containing particles in each zone, but their binding energies, that in turn will change the electrocatalytic activity of materials. The radii of the ions [12] in the oxidation state + 2, + 3 (Bi3+ − 1.03;Ce3+ − 1.02; Sn2+ − 1.18 Å) are close to ionic radius of Pb2+ (1.19 Å), ions in a higher oxidation state + 4 and + 5 (Bi5+ − 0.76;Ce4+ − 0.87; Sn4+ − 0.69 Å) are close to the ionic radius of Pb 4+ (0.78 Å). The ionic radius of F- (1.33 Å) is close to radii of OH- (1.37 Å) or O2- (1.40 Å). Hence, lead ion substitution on them is possible in both zones. This was the criterion for choosing of dopants. In the present work we examine early stages of electrocrystallization of PbO2 from methanesulfonate electrolytes that contain various ionic additives (Bi3+, Ce3+, Sn4+, [NiF6]2-, [SnF6]2-) and identify correlations between the deposition conditions and phase composition of coatings. It should be pointed out that such data is currently absent in the literature.
2. Experimental All chemicals were reagent grade. Electrodeposition regularities of doped lead dioxide were studied on a Pt disk electrode (Pt-DE, 0.19 cm2) by steady-state voltammetry, chronoamperometry. The Pt-DE surface was treated, before use, by the procedure described in [13]. Such preliminary treatment permits to achieve a reproducible surface. Voltammetry measurements were carried out in a standard temperature-controlled three-electrode cell. All potentials were recorded and reported vs. Ag / AgCl / KCl (sat.). The inversion voltamperometry was used for estimation of the deposition regularities of lead dioxide both in nitrate and methanesulfonate electrolytes. The method consisted in the accumulation
of pre-analyzed oxide on the working electrode by the electrolysis at a controlled potential and its subsequent electrochemical dissolving under the linearly changing potential. Electrodeposition of lead dioxide was studied in the methanesulfonate / nitrate electrolytes that contained 1 M CH3SO3H / HNO3, 0.01 M Pb(CH3SO3)2 / Pb(NO3)2 and 0.01 M additive (Bi(NO3)3, Ce(NO3)3, (CH3COO)4Sn, K2[NiF6], K2[SnF6]) depending on purposes of the experiments. In other section of experiments platinized titanium was used as substrate. Titanium sheet was treated as described in [13] before platinum layer depositing. Lead dioxide coatings were electrodeposited at anodic current density 10 mА сm-2 and temperature (282±2) К or (298±2) K. The coating thickness was ~ 50 µm. X-ray powder diffraction data were collected on a STOE STADI P automatic diffractometer [14] equipped with linear PSD detector (transmission mode, 2 θ/ω-scan; Cu Kα1 radiation, curved germanium (1 1 1) monochromator; 2θ-range 6.000≤2θ≤102.945 °2θ with step 0.015 °2θ; PSD step 0.480 °2θ, scan time 50 s/step). Qualitative and quantitative phase analysis was performed using the PowderCell program [15]. For selected samples with relatively high degree of crystallinity the Rietveld refinement was carried out using FullProf.2k (version 5.40) program [16, 17].
3. Results and Discussions 3.1. Early stages of nucleation and growth of lead dioxide Current transients for PbO2 deposition on Pt disk electrode were obtained for investigation of initial stages lead dioxide electrodeposition from methanesulfonate electrolytes. A typical j-t curve of PbO2 deposition is shown on Fig. 1. Observed transient can be divided on several characteristic regions [18]: the current density step in the initial period of electrode polarization corresponding to charging of the double electrical layer; induction period corresponding to the time required for beginning of the phase formation; maximum current density due to a decrease in the concentration
of electroactive species in the near electrode space and the achievement of a quasi-stationary current density. The type of transient is determined by the electrode potential. At low polarizations (E=1.55 V) the biggest induction period with a further stretched maximum of current is observed. Increasing of an anodic polarization leads to a substantial decreasing of the induction period and to increasing of current maximum. A linear relationship between the natural logarithm of the induction time of crystallization and the applied potential with negative slope is observed both for nitrate and methanesulfonate electrolytes (Fig. 2). Such dependence shows that the electrocrystallization of PbO2 begins with the formation of a monolayer on the entire surface of the electrode, and then the formation and growth of nuclei occurs. Growth of lead dioxide occurs through layer-by-layer crystallization, so each following layer is formed on the renewed surface. According to transients obtained from nitrate and methanesulfonate electrolytes (Fig. 3), one can conclude that despite the same concentration of lead ions in solution, there are significant differences in currents of the deposition that is an unusual effect caused, probably, by adsorption of negatively charged lead methanesulfonate complexes on positively charged electrode [19]. Lead dioxide formation takes place at constantly renewed surface. Particles like Pb(CH3SO3)2, Pb(CH3SO3)+ or Pb(CH3SO3)3– can be adsorbed on the growing oxide surface from the bulk. According to [19] data, three lead(II)-methanesulfonate complexes are characterized as being the predominant species, thus particles like Pb(CH3SO3)2 and Pb(CH3SO3)3– can be in the surface layer. With the potential growth the electrode surface will become redundant positively charged, that would promote the binding of particles with the opposite sign on the surface. Complex compounds with a neutral or negative charge, adsorbed on the surface, would facilitate the lead dioxide crystallization on a positively charged electrode surface. Similar phenomena for the processes occurring in the limiting current region have been described in [20]. It is clear from transients (Fig. 4) that an increase of a current delay corresponding to the induction time can be observed if ionic dopants are present in the deposition bath. This indicates
difficulties in the initial stages of the phase formation of lead dioxide. For the analysis of obtained transients we used the model, described in [18], and calculated current densities for instantaneous and progressive nucleation. Fig. 5 represents the plots of (j-j1)1/3 and (j-j1)1/2 vs. time for a transient obtained at 1620 mV. At this potential difference between instantaneous and progressive nucleation is not apparent. Plot of (j-j1)1/2 vs. t deviates from linearity and curve downwards indicating that (j-j1) is proportional to t to the powers smaller than 2, and the plot of (j-j1)1/3 vs. t has a slight tendency to curve downwards indicating that (j-j1) is proportional to t to the powers slightly less than 3. But, in accordance with results, obtained for nitrate bath in [18], it may be assumed that our experimental data also follows more closely the plot of (j-j1)1/3 vs. t. The existence of two linear parts in the plot of (j-j1)1/3 vs. t (Fig. 6) indicates the simultaneous deposition of two phases of PbO2, and the formation of one phase is noticeably lagged behind the other. The type of lagging phase depends on the nature of electrolyte: for nitrate bath it is β, for methanesulfonate – α. Moreover, as has been shown by investigations using inversion voltamperometry, the reduction of deposits obtained from the methanesulfonate bath (α-phase) occurs at a lower potential than such for coatings deposited from nitrate bath (β-phase, Fig. 7) 3.2. Texture and phase composition Data about morphology of deposits are described in detail in our previous publications [4−6]. Let’s focus on the phase composition of investigated deposits. As has been determined by X-ray powder diffraction all of our investigated samples contain two phases: α-PbO2 (structure type Fe2N0.94, space group Pbcn) and β-PbO2 (structure type TiO2 rutile, space group P42/mnm). The difference was observed only in the ratio of these two phases and also in the degree of crystallinity (Table 1). No significant differences in the unit cell dimensions were found between the two electrolytes (Table 2). The peak intensities are rather low. This confirms probably the decreasing of the size of
crystals of lead dioxide formed at higher current densities. However, it should be noted that such an effect is possible when water entrapment by porous structure of lead dioxide takes place, as shown in [21]. The temperature of deposition also provides a significant influence on the phase composition. It is shown [1], that with the temperature growth the content of β-phase in lead dioxide deposit increases. We observed a similar effect when the temperature rises from 298 to 313 K. Individual phases consist of compounds formed by dopants have not been detected in none of investigated samples. Taking into account their low content in the deposit, even in the case of formation of such phases, their amount would be clearly insufficient to detect by X-ray diffraction. However, a whole number of indirect data, in particular differences in the phase composition and the crystallographic orientation of the individual faces indicate the possibility of incorporating of ionic additives into crystal lattice instead of Pb(IV). According to obtained data one can conclude that the nature of depositing electrolyte considerably influences on the phase composition of lead dioxide coatings and on crystallographic orientations of individual faces. Thus, lead dioxide deposited from nitrate bath mainly composed of β-phase [1, 2], whereas coatings obtained from methanesulfonate bath are almost entirely composed of α-phase. The temperature of deposition influences on the phase composition of PbO2-coatings. Thus, an increase of temperature leads to the growth of β-phase in the coating. At the same time, the rising of temperature also increases the peaks intensity on the diffractogramm. The latter, probably, indicates an increase in crystal size. Differences in the phase composition of obtained materials have been also detected as changing pH of the solution. Thus, the growth of pH from 1.0 to 5.0 leads to an increase of β-phase content in the coating. A similar effect makes the addition of dopants in deposition electrolytes. It has been found that the content of β-phase of PbO2 increases in the next line of additives: Сe3+
As shown by the results of studies a number of crystals with orthorhombic lattice is proportional to the charge (integrated peak area) coming on formation of two-dimensional nuclei (Fig. 8). Thus, these results indicate that such phenomenon can be used as the correlation parameter to predict the phase composition of materials involved. Moreover, according to the reference data [22] (Table 3), the thermodynamic potential of the formation of α-phase PbO2 is lower than of the β-phase PbO2, hence at a fixed deposition potential the formation of two-dimensional cluster with orthorhombic lattice is more favorable thermodynamically. This in turn suggests that the phase composition is largely influenced not by the nature of the substrate but by kinetic difficulties in initial stages of crystallization depending on the composition of the deposition electrolyte.
4. Conclusions According to obtained data one can conclude that the nature of depositing electrolyte considerably influences on the phase composition of lead dioxide coatings and on crystallographic orientations of individual faces. Coatings obtained from methanesulfonate bath are almost entirely composed of α-phase. It was found for the first time that addition of dopants in deposition electrolytes leads to growth of β-phase content in deposits. Charge coming on the formation of two dimensional nuclei can be used as the correlation parameter to predict the phase composition of obtained lead dioxide deposits.
References [1] X. Li, D. Pletcher, F. C. Walsh, Electrodeposited lead dioxide coatings, Chem. Soc. Rev. 40 (2011) 3879. [2] C. T. J. Low, D. Pletcher, F. C. Walsh, The electrodeposition of highly reflective lead dioxide coatings, Electrochem. Commun. 11 (2009) 1301.
[3] Y. Liu, H. Liu, Comparative studies on the electrocatalytic properties of modified PbO2 anodes, Electrochim. Acta 53 (2008) 5077. [4] O. Shmychkova, T. Luk'yanenko, A. Velichenko, L. Meda, R. Amadelli, Bi-doped PbO2 anodes: electrodeposition and physico-chemical properties, Electrochim. Acta 111 (2013) 332. [5] O. Shmychkova, T. Luk'yanenko, A. Velichenko, R. Amadelli, Electrodeposition of Ce-doped PbO2, J. Electroanal. Chem 706 (2013) 86. [6] O. Shmychkova, T. Luk'yanenko, R. Amadelli, A. Velichenko, Physico-chemical properties of PbO2-anodes doped with Sn4+and complex ions, J. Electroanal. Chem. 717−718 (2014) 196. [7] A. B. Velichenko, R. Amadelli, E. V. Gruzdeva, T. V. Luk’yanenko, F. I. Danilov, Electrodeposition of lead dioxide from methansulfonate solutions, J. Power Sources 191 (2009) 103. [9] P. Ruetschi, R. Giovanoli, On the presence of OH- ions, Pb2+ ions and cation vacancies in PbO2, Power Sources 13 (1991) 81. [10] D. Pavlov, I. Balkanov, T. Halachev, P. Rachev, Hydration and amorphization of active mass PbO2 particles and their influence on the electrical properties of the lead-acid battery positive plate, J. Electrochem. Soc., 136:11 (1989) 3189. [11] D. Pavlov, I. Balkanov, The PbO2 Particle: exchange reactions between ions of the electrolyte and the PbO2 particles of the lead-acid battery positive active mass, J. Electrochem. Soc., 139 (1992) 1830. [12] D. Pavlov, The lead-acid battery lead dioxide active mass − a gel-crystal system with proton and electron conductivity, J. Electrochem. Soc., 139 (1992) 3075. [13] N. N. Greenwood, A. Earnshaw, Chemistry of elements, Oxford, New York, Toronto, Sydney, Paris, Frankfurt: Pergamon press Ltd., 1985, 1542 p. [14] A. B. Velichenko, D. V. Girenko, S. V. Kovalyov, A. N. Gnatenko, R. Amadelli, F. I. Danilov, Lead dioxide electrodeposition and its application: influence of fluoride and iron ions, J. Electroanal. Chem. 454 (1998) 203.
[15] STOE WinXPOW, version 3.03. Darmstadt: Stoe & Cie GmbH, 2010. [16] W. Kraus, G. Nolze, PowderCell for Windows (version 2.4). – Berlin: Federal Institute for Materials Research and Testing, 2000. [17] J. Rodriguez-Carvajal, Recent developments of the program FULLPROF, Commission on Powder Diffraction (IUCr), Newsletter 26 (2001) 12. [18] T. Roisnel, J. Rodriguez-Carvajal, WinPLOTR: a Windows tool for powder diffraction patterns analysis, Mater. Sci. Forum 378–381 (2001) 118. [19] M. Y. Abyaneh, V. Saez, J. Gonzalez-Garcia, T. J. Mason, Electrocrystallization of lead dioxide: Analysis of the early stages of nucleation and growth, Electrochim. Acta 55 (2010) 3572. [20] M. D. Capelato, J. A. Nobrega, E. F. A. Neves, Complexing power of alkanesulfonate ions: the lead-methanesulfonate system, J. Apl. Electrochem. 25 (1995) 408. [21] A. B. Velichenko, T. V. Luk’yanenko, N. V. Nikolenko, R. Amadelli, F. I. Danilov, Nafion effect on the lead dioxide electrodeposition kitetics, Russ. J. Electrochem. 43 (2007) 118. [22] D. J. Payne, R. G. Egdell, D. S. L. Law, Experimental and theoretical study of the electronic structures of α-PbO2 and β-PbO2, J. Mater. Chem. 17 (2007) 267. [23] C. Daniel, J. O. Besenhard, Handbook of battery materials, 2nd ed., Wiley-VCH, 2011, 1023 p.
FIGURE CAPTIONS Fig. 1. Current transients for PbO2 deposition on Pt disk electrode from 0.01 M Pb(CH3SO3)2+1 M CH3SO3H at different deposition potentials Fig. 2. Plot of the natural logarithm of the induction period of crystallization vs. potential for methanesulfonate (1) and nitrate (2) electrolytes Fig. 3. Current transients for PbO2 deposition at 1.55 V on Pt disk electrode from different electrolytes: 1 – 0.01 M Pb(NO3)2+1 M HNO3; 2 – 0.01 M Pb(CH3SO3)2+1 M CH3SO3H Fig. 4. Current transients for PbO2 deposition on Pt disk electrode at 1620 mV from electrolytes: 1 – 0.01 M Pb(CH3SO3)2+1 M CH3SO3H (1)+0.01 M Bi3+; 2 – (1)+0.001 M Ce3+; 3 – (1)+0.01 M Sn4+ Fig. 5. Plots of (j-j1)1/3 and (j-j1)1/2 vs. time for a transient recorded during the electrocrystallization of PbO2 from a solution of 0.01M Pb(CH3SO3)2 +1M CH3SO3H at an applied potential of 1.62 V Fig. 6. Analysis of plot of (j-j1)1/3 vs. time for a transient recorded during the electrocrystallization of PbO2 from a solution of 0.01M Pb(CH3SO3)2 +1M CH3SO3H at an applied potential of 1.62 V Fig.7. Inversion voltammograms cathodic branches (scan range 1.4 to 0.6 V) in 1M HClO4 Lead dioxide previously deposited on Pt electrode from solutions containing 0.1 М Pb(CH3SO3)2+1 M CH3SO3H (), 0.1 М Pb(NO3)2+1 M HNO3 (- -). v=50 mV/s. Fig. 8. α-Phase PbO2 content versus electricity, that is coming on the formation of two dimensional nuclei at early stages of nucleation and growth of oxide
Fig. 1
Fig. 2
Fig. 3
Fig. 4
Fig. 5
Fig. 6
Fig. 7
Fig. 8
Table 1. The phase composition of lead dioxide coatings depending on deposition conditions* Solution 0.1 M Pb(NO3)2+1 M HNO3 (N) N N N 0.1 M Pb(NO3)2+0.11 M HNO3 0.1 M Pb(CH3SO3)2+0.11 M CH3SO3H 0.1 M Pb(CH3SO3)2+1 M CH3SO3H (M) M M M M+0.001 M Bi3+ M+0.01 M Bi3+ M+0.001 M Ce3+ M+0.003 M Ce3+ M+0.01 M Sn4+ M+0.01 M [SnF6]2– M+0.01 M [NiF6]2–
* Samples are deposited at j=10 mA/cm2.
T/K 282 298 313 333 298 298 282 298 313 333 282 282 298 298 298 298 298
Content /w.%/ α-PbO2/β-PbO2 36/64 25/75 17/83 15/85 14/86 17/83 59/41 90/10 83/17 33/67 65/35 5/95 83/17 19/81 44/56 0/100 38/62
Table 2. Lattice parameters of lead dioxide coatings depending on nature of electrolyte Sample description 0.1M Pb(CH3SO3)2+ 1M CH3SO3H 0.1M Pb(NO3)2+ 1M HNO3
Lattice parameters, Å (α/β) Reliability factors a b c RI / RP, RWP, REXP 4.9888(3) / 5.9415(4) 5.4529(3) / 0.0510 4.95222(8) – 3.38184(10) 0.0488 / 0.0800, 0.105, 0.0716 4.9854(6) / 5.9429(7) 5.4544(5) / 0.0503 4.94871(5) – 3.37931(6) 0.0339 / 0.0703, 0.0954, 0.0597
Table 3. Standard thermodynamic values for Pb(IV) oxides Value
α-PbO2
β-PbO2
0 ∆H 298 , kJ/mol
–265.8
–276.6
0 ∆S 298 , J/mol⋅K
92.5
76.4
0 ∆G 298 , kJ/mol
–299.5
–219.3
Research Highlights • Modified PbO2 electrodeposited from methanesulfonate electrolytes was investigated • Dopants influences on texture and phase of electrodeposited PbO2 were studied • The gradual transition from α- to β-phase in the coating occurs in the presence of additives was observed • Charge of the nuclei formation as the correlation parameter to predict the phase composition was proposed
S1572-6657(15)00154-X http://dx.doi.org/10.1016/j.jelechem.2015.03.031 JEAC 2060
To appear in:
Journal of Electroanalytical Chemistry
Received Date: Revised Date: Accepted Date:
16 January 2015 21 March 2015 27 March 2015
Please cite this article as: O. Shmychkova, T. Luk’yanenko, A. Piletska, A. Velichenko, R. Gladyshevskii, P. Demchenko, R. Amadelli, Electrocrystallization of lead dioxide: influence of early stages of nucleation on phase composition, Journal of Electroanalytical Chemistry (2015), doi: http://dx.doi.org/10.1016/j.jelechem.2015.03.031
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Electrocrystallization of lead dioxide: influence of early stages of nucleation on phase composition O. Shmychkovaa, T. Luk'yanenko a, A. Piletskaa, A. Velichenkoa,*, R. Gladyshevskiib, P. Demchenkob, R. Amadellic
a
Ukrainian State University of Chemical Technology, 8, Gagarin Ave., 49005 Dniepropetrovsk, Ukraine
b c
Lviv National Ivan Franko University, 6, Kirila i Mephodiya Str., 79005 Lviv, Ukraine
Istituto per la Sintesi Organica e la Fotoreattivita – Consiglio Nazionale delle Recerche (ISOFCNR), Dipartimento di Chimica, Universita di Ferrara, via L. Borsari, 46–44121 Ferrara, Italy
Abstract. It has been revealed that coatings obtained from methanesulfonate bath at investigated conditions (10 mA⋅cm-2; pH=1.0) are almost entirely composed of α-phase. It was found that the gradual transition from α- to β-phase in the coating occurs in the presence of additives in deposition electrolytes. It was proposed to use charge coming on the formation of nuclei as the correlation parameter to predict the phase composition of obtained lead dioxide deposits. Electrocrystallization of PbO2 begins with the formation of a monolayer on the electrode surface, then the formation and growth of three-dimensional nuclei takes place. The simultaneous formation of α and β phases results in the presence of two linear areas on the plot of (j-j1)1/3 vs. time for the progressive growth of crystals. The formation of one phase is noticeably lagged behind the other. At layer-by-layer crystallization and significant lagging of one of phases may occur ingesting of growing centres of one phase by another.The type of lagging phase depends on the nature of electrolyte: for nitrate bath it is β, for methanesulfonate – α.
Keywords: Lead dioxide, Methanesulfonate electrolyte, Nucleation and growth, Phase composition.
1. Introduction Electrodes based on lead dioxide doped by ionic additives are known to be of great interest for investigation owing to tailoring solid state properties as well as electrocatalytic activity of PbO2 [1−7]. Particular attention should be paid to ionic additives in high oxidation states +3, and +4 *
Corresponding author. Tel: +380563772974. E-mail address: [email protected] (A. Velichenko)
(compared to places of cation vacancies of lead dioxide, in which Pb2+-ions are known to be localized). It is recognized [8-11], that there are two zones on the lead dioxide surface: crystal (PbO2) and hydrated [PbO(OH)2], that are in equilibrium and are capable to exchange cations and anions with the ions present in the bulk. Lead ions replacement both in hydrated and crystal zone would cause not only the change of amount of oxygen-containing particles in each zone, but their binding energies, that in turn will change the electrocatalytic activity of materials. The radii of the ions [12] in the oxidation state + 2, + 3 (Bi3+ − 1.03;Ce3+ − 1.02; Sn2+ − 1.18 Å) are close to ionic radius of Pb2+ (1.19 Å), ions in a higher oxidation state + 4 and + 5 (Bi5+ − 0.76;Ce4+ − 0.87; Sn4+ − 0.69 Å) are close to the ionic radius of Pb 4+ (0.78 Å). The ionic radius of F- (1.33 Å) is close to radii of OH- (1.37 Å) or O2- (1.40 Å). Hence, lead ion substitution on them is possible in both zones. This was the criterion for choosing of dopants. In the present work we examine early stages of electrocrystallization of PbO2 from methanesulfonate electrolytes that contain various ionic additives (Bi3+, Ce3+, Sn4+, [NiF6]2-, [SnF6]2-) and identify correlations between the deposition conditions and phase composition of coatings. It should be pointed out that such data is currently absent in the literature.
2. Experimental All chemicals were reagent grade. Electrodeposition regularities of doped lead dioxide were studied on a Pt disk electrode (Pt-DE, 0.19 cm2) by steady-state voltammetry, chronoamperometry. The Pt-DE surface was treated, before use, by the procedure described in [13]. Such preliminary treatment permits to achieve a reproducible surface. Voltammetry measurements were carried out in a standard temperature-controlled three-electrode cell. All potentials were recorded and reported vs. Ag / AgCl / KCl (sat.). The inversion voltamperometry was used for estimation of the deposition regularities of lead dioxide both in nitrate and methanesulfonate electrolytes. The method consisted in the accumulation
of pre-analyzed oxide on the working electrode by the electrolysis at a controlled potential and its subsequent electrochemical dissolving under the linearly changing potential. Electrodeposition of lead dioxide was studied in the methanesulfonate / nitrate electrolytes that contained 1 M CH3SO3H / HNO3, 0.01 M Pb(CH3SO3)2 / Pb(NO3)2 and 0.01 M additive (Bi(NO3)3, Ce(NO3)3, (CH3COO)4Sn, K2[NiF6], K2[SnF6]) depending on purposes of the experiments. In other section of experiments platinized titanium was used as substrate. Titanium sheet was treated as described in [13] before platinum layer depositing. Lead dioxide coatings were electrodeposited at anodic current density 10 mА сm-2 and temperature (282±2) К or (298±2) K. The coating thickness was ~ 50 µm. X-ray powder diffraction data were collected on a STOE STADI P automatic diffractometer [14] equipped with linear PSD detector (transmission mode, 2 θ/ω-scan; Cu Kα1 radiation, curved germanium (1 1 1) monochromator; 2θ-range 6.000≤2θ≤102.945 °2θ with step 0.015 °2θ; PSD step 0.480 °2θ, scan time 50 s/step). Qualitative and quantitative phase analysis was performed using the PowderCell program [15]. For selected samples with relatively high degree of crystallinity the Rietveld refinement was carried out using FullProf.2k (version 5.40) program [16, 17].
3. Results and Discussions 3.1. Early stages of nucleation and growth of lead dioxide Current transients for PbO2 deposition on Pt disk electrode were obtained for investigation of initial stages lead dioxide electrodeposition from methanesulfonate electrolytes. A typical j-t curve of PbO2 deposition is shown on Fig. 1. Observed transient can be divided on several characteristic regions [18]: the current density step in the initial period of electrode polarization corresponding to charging of the double electrical layer; induction period corresponding to the time required for beginning of the phase formation; maximum current density due to a decrease in the concentration
of electroactive species in the near electrode space and the achievement of a quasi-stationary current density. The type of transient is determined by the electrode potential. At low polarizations (E=1.55 V) the biggest induction period with a further stretched maximum of current is observed. Increasing of an anodic polarization leads to a substantial decreasing of the induction period and to increasing of current maximum. A linear relationship between the natural logarithm of the induction time of crystallization and the applied potential with negative slope is observed both for nitrate and methanesulfonate electrolytes (Fig. 2). Such dependence shows that the electrocrystallization of PbO2 begins with the formation of a monolayer on the entire surface of the electrode, and then the formation and growth of nuclei occurs. Growth of lead dioxide occurs through layer-by-layer crystallization, so each following layer is formed on the renewed surface. According to transients obtained from nitrate and methanesulfonate electrolytes (Fig. 3), one can conclude that despite the same concentration of lead ions in solution, there are significant differences in currents of the deposition that is an unusual effect caused, probably, by adsorption of negatively charged lead methanesulfonate complexes on positively charged electrode [19]. Lead dioxide formation takes place at constantly renewed surface. Particles like Pb(CH3SO3)2, Pb(CH3SO3)+ or Pb(CH3SO3)3– can be adsorbed on the growing oxide surface from the bulk. According to [19] data, three lead(II)-methanesulfonate complexes are characterized as being the predominant species, thus particles like Pb(CH3SO3)2 and Pb(CH3SO3)3– can be in the surface layer. With the potential growth the electrode surface will become redundant positively charged, that would promote the binding of particles with the opposite sign on the surface. Complex compounds with a neutral or negative charge, adsorbed on the surface, would facilitate the lead dioxide crystallization on a positively charged electrode surface. Similar phenomena for the processes occurring in the limiting current region have been described in [20]. It is clear from transients (Fig. 4) that an increase of a current delay corresponding to the induction time can be observed if ionic dopants are present in the deposition bath. This indicates
difficulties in the initial stages of the phase formation of lead dioxide. For the analysis of obtained transients we used the model, described in [18], and calculated current densities for instantaneous and progressive nucleation. Fig. 5 represents the plots of (j-j1)1/3 and (j-j1)1/2 vs. time for a transient obtained at 1620 mV. At this potential difference between instantaneous and progressive nucleation is not apparent. Plot of (j-j1)1/2 vs. t deviates from linearity and curve downwards indicating that (j-j1) is proportional to t to the powers smaller than 2, and the plot of (j-j1)1/3 vs. t has a slight tendency to curve downwards indicating that (j-j1) is proportional to t to the powers slightly less than 3. But, in accordance with results, obtained for nitrate bath in [18], it may be assumed that our experimental data also follows more closely the plot of (j-j1)1/3 vs. t. The existence of two linear parts in the plot of (j-j1)1/3 vs. t (Fig. 6) indicates the simultaneous deposition of two phases of PbO2, and the formation of one phase is noticeably lagged behind the other. The type of lagging phase depends on the nature of electrolyte: for nitrate bath it is β, for methanesulfonate – α. Moreover, as has been shown by investigations using inversion voltamperometry, the reduction of deposits obtained from the methanesulfonate bath (α-phase) occurs at a lower potential than such for coatings deposited from nitrate bath (β-phase, Fig. 7) 3.2. Texture and phase composition Data about morphology of deposits are described in detail in our previous publications [4−6]. Let’s focus on the phase composition of investigated deposits. As has been determined by X-ray powder diffraction all of our investigated samples contain two phases: α-PbO2 (structure type Fe2N0.94, space group Pbcn) and β-PbO2 (structure type TiO2 rutile, space group P42/mnm). The difference was observed only in the ratio of these two phases and also in the degree of crystallinity (Table 1). No significant differences in the unit cell dimensions were found between the two electrolytes (Table 2). The peak intensities are rather low. This confirms probably the decreasing of the size of
crystals of lead dioxide formed at higher current densities. However, it should be noted that such an effect is possible when water entrapment by porous structure of lead dioxide takes place, as shown in [21]. The temperature of deposition also provides a significant influence on the phase composition. It is shown [1], that with the temperature growth the content of β-phase in lead dioxide deposit increases. We observed a similar effect when the temperature rises from 298 to 313 K. Individual phases consist of compounds formed by dopants have not been detected in none of investigated samples. Taking into account their low content in the deposit, even in the case of formation of such phases, their amount would be clearly insufficient to detect by X-ray diffraction. However, a whole number of indirect data, in particular differences in the phase composition and the crystallographic orientation of the individual faces indicate the possibility of incorporating of ionic additives into crystal lattice instead of Pb(IV). According to obtained data one can conclude that the nature of depositing electrolyte considerably influences on the phase composition of lead dioxide coatings and on crystallographic orientations of individual faces. Thus, lead dioxide deposited from nitrate bath mainly composed of β-phase [1, 2], whereas coatings obtained from methanesulfonate bath are almost entirely composed of α-phase. The temperature of deposition influences on the phase composition of PbO2-coatings. Thus, an increase of temperature leads to the growth of β-phase in the coating. At the same time, the rising of temperature also increases the peaks intensity on the diffractogramm. The latter, probably, indicates an increase in crystal size. Differences in the phase composition of obtained materials have been also detected as changing pH of the solution. Thus, the growth of pH from 1.0 to 5.0 leads to an increase of β-phase content in the coating. A similar effect makes the addition of dopants in deposition electrolytes. It has been found that the content of β-phase of PbO2 increases in the next line of additives: Сe3+
As shown by the results of studies a number of crystals with orthorhombic lattice is proportional to the charge (integrated peak area) coming on formation of two-dimensional nuclei (Fig. 8). Thus, these results indicate that such phenomenon can be used as the correlation parameter to predict the phase composition of materials involved. Moreover, according to the reference data [22] (Table 3), the thermodynamic potential of the formation of α-phase PbO2 is lower than of the β-phase PbO2, hence at a fixed deposition potential the formation of two-dimensional cluster with orthorhombic lattice is more favorable thermodynamically. This in turn suggests that the phase composition is largely influenced not by the nature of the substrate but by kinetic difficulties in initial stages of crystallization depending on the composition of the deposition electrolyte.
4. Conclusions According to obtained data one can conclude that the nature of depositing electrolyte considerably influences on the phase composition of lead dioxide coatings and on crystallographic orientations of individual faces. Coatings obtained from methanesulfonate bath are almost entirely composed of α-phase. It was found for the first time that addition of dopants in deposition electrolytes leads to growth of β-phase content in deposits. Charge coming on the formation of two dimensional nuclei can be used as the correlation parameter to predict the phase composition of obtained lead dioxide deposits.
References [1] X. Li, D. Pletcher, F. C. Walsh, Electrodeposited lead dioxide coatings, Chem. Soc. Rev. 40 (2011) 3879. [2] C. T. J. Low, D. Pletcher, F. C. Walsh, The electrodeposition of highly reflective lead dioxide coatings, Electrochem. Commun. 11 (2009) 1301.
[3] Y. Liu, H. Liu, Comparative studies on the electrocatalytic properties of modified PbO2 anodes, Electrochim. Acta 53 (2008) 5077. [4] O. Shmychkova, T. Luk'yanenko, A. Velichenko, L. Meda, R. Amadelli, Bi-doped PbO2 anodes: electrodeposition and physico-chemical properties, Electrochim. Acta 111 (2013) 332. [5] O. Shmychkova, T. Luk'yanenko, A. Velichenko, R. Amadelli, Electrodeposition of Ce-doped PbO2, J. Electroanal. Chem 706 (2013) 86. [6] O. Shmychkova, T. Luk'yanenko, R. Amadelli, A. Velichenko, Physico-chemical properties of PbO2-anodes doped with Sn4+and complex ions, J. Electroanal. Chem. 717−718 (2014) 196. [7] A. B. Velichenko, R. Amadelli, E. V. Gruzdeva, T. V. Luk’yanenko, F. I. Danilov, Electrodeposition of lead dioxide from methansulfonate solutions, J. Power Sources 191 (2009) 103. [9] P. Ruetschi, R. Giovanoli, On the presence of OH- ions, Pb2+ ions and cation vacancies in PbO2, Power Sources 13 (1991) 81. [10] D. Pavlov, I. Balkanov, T. Halachev, P. Rachev, Hydration and amorphization of active mass PbO2 particles and their influence on the electrical properties of the lead-acid battery positive plate, J. Electrochem. Soc., 136:11 (1989) 3189. [11] D. Pavlov, I. Balkanov, The PbO2 Particle: exchange reactions between ions of the electrolyte and the PbO2 particles of the lead-acid battery positive active mass, J. Electrochem. Soc., 139 (1992) 1830. [12] D. Pavlov, The lead-acid battery lead dioxide active mass − a gel-crystal system with proton and electron conductivity, J. Electrochem. Soc., 139 (1992) 3075. [13] N. N. Greenwood, A. Earnshaw, Chemistry of elements, Oxford, New York, Toronto, Sydney, Paris, Frankfurt: Pergamon press Ltd., 1985, 1542 p. [14] A. B. Velichenko, D. V. Girenko, S. V. Kovalyov, A. N. Gnatenko, R. Amadelli, F. I. Danilov, Lead dioxide electrodeposition and its application: influence of fluoride and iron ions, J. Electroanal. Chem. 454 (1998) 203.
[15] STOE WinXPOW, version 3.03. Darmstadt: Stoe & Cie GmbH, 2010. [16] W. Kraus, G. Nolze, PowderCell for Windows (version 2.4). – Berlin: Federal Institute for Materials Research and Testing, 2000. [17] J. Rodriguez-Carvajal, Recent developments of the program FULLPROF, Commission on Powder Diffraction (IUCr), Newsletter 26 (2001) 12. [18] T. Roisnel, J. Rodriguez-Carvajal, WinPLOTR: a Windows tool for powder diffraction patterns analysis, Mater. Sci. Forum 378–381 (2001) 118. [19] M. Y. Abyaneh, V. Saez, J. Gonzalez-Garcia, T. J. Mason, Electrocrystallization of lead dioxide: Analysis of the early stages of nucleation and growth, Electrochim. Acta 55 (2010) 3572. [20] M. D. Capelato, J. A. Nobrega, E. F. A. Neves, Complexing power of alkanesulfonate ions: the lead-methanesulfonate system, J. Apl. Electrochem. 25 (1995) 408. [21] A. B. Velichenko, T. V. Luk’yanenko, N. V. Nikolenko, R. Amadelli, F. I. Danilov, Nafion effect on the lead dioxide electrodeposition kitetics, Russ. J. Electrochem. 43 (2007) 118. [22] D. J. Payne, R. G. Egdell, D. S. L. Law, Experimental and theoretical study of the electronic structures of α-PbO2 and β-PbO2, J. Mater. Chem. 17 (2007) 267. [23] C. Daniel, J. O. Besenhard, Handbook of battery materials, 2nd ed., Wiley-VCH, 2011, 1023 p.
FIGURE CAPTIONS Fig. 1. Current transients for PbO2 deposition on Pt disk electrode from 0.01 M Pb(CH3SO3)2+1 M CH3SO3H at different deposition potentials Fig. 2. Plot of the natural logarithm of the induction period of crystallization vs. potential for methanesulfonate (1) and nitrate (2) electrolytes Fig. 3. Current transients for PbO2 deposition at 1.55 V on Pt disk electrode from different electrolytes: 1 – 0.01 M Pb(NO3)2+1 M HNO3; 2 – 0.01 M Pb(CH3SO3)2+1 M CH3SO3H Fig. 4. Current transients for PbO2 deposition on Pt disk electrode at 1620 mV from electrolytes: 1 – 0.01 M Pb(CH3SO3)2+1 M CH3SO3H (1)+0.01 M Bi3+; 2 – (1)+0.001 M Ce3+; 3 – (1)+0.01 M Sn4+ Fig. 5. Plots of (j-j1)1/3 and (j-j1)1/2 vs. time for a transient recorded during the electrocrystallization of PbO2 from a solution of 0.01M Pb(CH3SO3)2 +1M CH3SO3H at an applied potential of 1.62 V Fig. 6. Analysis of plot of (j-j1)1/3 vs. time for a transient recorded during the electrocrystallization of PbO2 from a solution of 0.01M Pb(CH3SO3)2 +1M CH3SO3H at an applied potential of 1.62 V Fig.7. Inversion voltammograms cathodic branches (scan range 1.4 to 0.6 V) in 1M HClO4 Lead dioxide previously deposited on Pt electrode from solutions containing 0.1 М Pb(CH3SO3)2+1 M CH3SO3H (), 0.1 М Pb(NO3)2+1 M HNO3 (- -). v=50 mV/s. Fig. 8. α-Phase PbO2 content versus electricity, that is coming on the formation of two dimensional nuclei at early stages of nucleation and growth of oxide
Fig. 1
Fig. 2
Fig. 3
Fig. 4
Fig. 5
Fig. 6
Fig. 7
Fig. 8
Table 1. The phase composition of lead dioxide coatings depending on deposition conditions* Solution 0.1 M Pb(NO3)2+1 M HNO3 (N) N N N 0.1 M Pb(NO3)2+0.11 M HNO3 0.1 M Pb(CH3SO3)2+0.11 M CH3SO3H 0.1 M Pb(CH3SO3)2+1 M CH3SO3H (M) M M M M+0.001 M Bi3+ M+0.01 M Bi3+ M+0.001 M Ce3+ M+0.003 M Ce3+ M+0.01 M Sn4+ M+0.01 M [SnF6]2– M+0.01 M [NiF6]2–
* Samples are deposited at j=10 mA/cm2.
T/K 282 298 313 333 298 298 282 298 313 333 282 282 298 298 298 298 298
Content /w.%/ α-PbO2/β-PbO2 36/64 25/75 17/83 15/85 14/86 17/83 59/41 90/10 83/17 33/67 65/35 5/95 83/17 19/81 44/56 0/100 38/62
Table 2. Lattice parameters of lead dioxide coatings depending on nature of electrolyte Sample description 0.1M Pb(CH3SO3)2+ 1M CH3SO3H 0.1M Pb(NO3)2+ 1M HNO3
Lattice parameters, Å (α/β) Reliability factors a b c RI / RP, RWP, REXP 4.9888(3) / 5.9415(4) 5.4529(3) / 0.0510 4.95222(8) – 3.38184(10) 0.0488 / 0.0800, 0.105, 0.0716 4.9854(6) / 5.9429(7) 5.4544(5) / 0.0503 4.94871(5) – 3.37931(6) 0.0339 / 0.0703, 0.0954, 0.0597
Table 3. Standard thermodynamic values for Pb(IV) oxides Value
α-PbO2
β-PbO2
0 ∆H 298 , kJ/mol
–265.8
–276.6
0 ∆S 298 , J/mol⋅K
92.5
76.4
0 ∆G 298 , kJ/mol
–299.5
–219.3
Research Highlights • Modified PbO2 electrodeposited from methanesulfonate electrolytes was investigated • Dopants influences on texture and phase of electrodeposited PbO2 were studied • The gradual transition from α- to β-phase in the coating occurs in the presence of additives was observed • Charge of the nuclei formation as the correlation parameter to predict the phase composition was proposed