New Mathematical Formulation for the Deposition Potential and

Article Cite This: J. Phys. Chem. C XXXX, XXX, XXX−XXX

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New Mathematical Formulation for the Deposition Potential and Atomic Radius: Theoretical Background and Applications to Sn−Ln Intermetallic Compounds Hengbin Xu,† Milin Zhang,*,†,‡ Yongde Yan,† Debin Ji,*,† Pu Wang,† Min Qiu,‡ and Li Liu‡ †

Key Laboratory of Superlight Materials and Surface Technology, Ministry of Education, College of Materials Science and Chemical Engineering, Harbin Engineering University, Harbin 150001, China ‡ College of Science, Heihe University, Heihe 164300, China S Supporting Information *

ABSTRACT: Purification of rare earth elements is challenging due to their chemical similarities. The interaction and behavior of alloys involving stannous chloride (SnCl2) and lanthanide metals are discussed in the present paper. We investigate the quantitative relationship between the deposition potential of lanthanides with SnCl2 and atomic radius by employing electrochemical techniques, involving cyclic voltammetry (CV), square wave voltammetry (SWV) and open-circuit chronopotentiometry (OCP). Our electrochemical study on the formation intermetallic compounds is based on Sn in LiCl−KCl melts on molybdenum electrodes at 873 K. With the same experimental conditions, different deposits (e.g., Sn−La, Sn−Pr, Sn− Gd, Sn−Dy and Sn−Er) were obtained by using identical substrates. We establish the relationship between the deposition potential and the atomic radii of lanthanides by deriving a mathematical equation from the sorting out and summarizing of the data. The predictions for the existence and the deposition potentials of unknown intermediate phases (e.g., Sn−Ce, Sn−Nd, Sn−Yb and Sn−Lu) were made. From our results, open-circuit chronopotentiometry is potentially a valuable methodology to formally verify the correctness of the forecast. X-ray diffraction pattern (XRD), scanning electron micrograph (SEM) and energy-dispersive spectrometry (EDS) data further verify the reliability of the linear equation.

1. INTRODUCTION Two particular groups of chemical elements in the periodic table share a certain similarity in their unique properties;1 these are the so-called “‘lanthanides”’ and “‘actinides’”, which have 4fand 5f-unfilled electron shells, respectively. These names are derived from the first elements of the two groups: lanthanum (Z = 57) and actinium (Z = 89). The rare-earth elements consist of 17 elements, that is 15 lanthanides, from lanthanum (Z = 57) to lutetium (Z = 71), and the third main-group elements, scandium (Z = 21) and yttrium (Z = 39).2−4 Although research studies have put forward many empirical and theoretical formulas in regard to the performance of the homologues, a quantitative law that can be easily and widely applied in various structures and physical and chemical properties has yet to be formulated Rare earth elements (REEs) (which are also known as the lanthanide series in the periodic table of elements) are widely distributed geographically; they are chiefly mined, concentrated, and separated in China.5−7 In recent years, rare earth metals of high purity, and alloys based on a rare earth and a light or transition metal, are of practical interest for their functional properties, i.e., their excellent magnetic properties, hydrogen absorbing or permeable properties, and catalytic properties.8−10 © XXXX American Chemical Society

Because of their unique properties, they are widely used nowadays in different fields, such as high-performance magnets, fluorescent materials, chemical sensors, and high-temperature superconductors. Owing to these attractive prospects, the demand for rare earth metals and alloys is expected to increase in the future.11−13 Because of the growing global rare earth demand, which is projected at an annual growth rate of 5% through to 2020,14 and their indispensable roles in diverse applications, rare earth metals are categorized as critical raw materials by the U.S. Department of Energy and the European Commission.15 Conventional processing techniques used to produce intermetallic compounds are generally through a combination of melting, casting, powder grinding, and consolidation by hot pressing.16 Research on simpler and more environment-friendly RE processing techniques with higher single-step efficiencies has attracted attention in recent years. The use of molten salts, and particularly molten chlorides, are well-known as good reaction media for performing selective solubilization or Received: November 30, 2017 Revised: January 20, 2018 Published: January 30, 2018 A

DOI: 10.1021/acs.jpcc.7b11782 J. Phys. Chem. C XXXX, XXX, XXX−XXX

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The Journal of Physical Chemistry C

Figure 1. Cyclic voltammograms obtained on a Mo electrode (a) in LiCl−KCl melt before (red line) and after (black line) the addition of SnCl2 (2.0 wt %); (b) in LiCl−KCl melt before (red line) and after (black line) addition of PrCl3 (2.0 wt %); (c) in LiCl−KCl−SnCl2 melt before (red line) and after (black line) addition of PrCl3 (2.0 wt %). Temperature: 873 K. Scan rate: 0.1 V/s.

these intermetallic compounds. Then the derivation of a mathematical equation enabled us to speculate on the deposition potential of intermetallic compounds of Sn with other elements, and to compare the difference of experimental data (by measurement using open-circuit chronopotentiometry) and predictive value (by the obtained mathematical equation). Finally, electrolysis was carried out on a Mo electrode to validate the feasibility of using the mathematical equation.

precipitation in chemical reactions, providing a unique opportunity for electrowinning and electrorefining of highpurity rare earth metals, as well as for electrochemical synthesis of their alloys.17−19 Recently, the preparation of alloy compounds was studied by electrochemical codeposition and reduction on reactive electrodes in molten salts. As a new method of forming these alloy films, a molten salt electrochemical process, which utilizes the cathodic reduction of rare earth (La, Pr, Gd, Dy and Er) ions on metal substrates (Sn), has been studied in the authors’ laboratory. Another important issue concerning rare earths and molten salts is the pyrochemical reprocessing of nuclear fuel, which is considered a promising option for advanced fuel cycles.20−24 For achieving nuclear fuel closed circulation and sustainable development, efficient pyroprocessing of spent fuel becomes the core concern.25 In addition, molten salt electrolysis is the key step in pyroprocessing technology; therefore, it is necessary to investigate the electrochemical properties of lanthanides and actinides. Because of the close similarity of chemical properties, actinide elements can be simulated and predicted through the research findings of lanthanide elements.26−29 The purpose of the present work is to derive a mathematical equation which defines the linear relationship of deposition potentials and atomic radii of lanthanides. Our research forms part of a program to examine the Ln series in chloride melts. First, we carried out a study of the electrochemical behavior of LiCl−KCl−SnCl2 system with different REEs on inert electrodes at 873 K to determine the deposition potentials of

2. EXPERIMENTAL SECTION 2.1. Preparation and Purification of the Melt. A mixture of LiCl−KCl (45:45 wt %, analytical grade. Sinopharm Chemical Reagent Co., Ltd.) was first dried under vacuum for more than 72 h at 473 K to remove excess water, and then melted in an alumina crucible placed in a quartz cell in an electric furnace. The temperature of the melts was measured with a nickel chromium/nickel−aluminum thermocouple sheathed with an alumina tube. Prior to electrolysis, metal ion impurities in the melts were removed by pre-electrolysis at −2.00 V (vs Ag/AgCl) for 4 h. Sn(II), La(III), Pr(III), Gd(III), Dy(III) and Er(III) ions were introduced into the LiCl−KCl melts in the form of dehydrated SnCl2, LaCl3, PrCl3, GdCl3, DyCl3 and LaCl3 powders (analytical grade) following preelectrolysis. Before each experiment, HCl was bubbled into the melt to remove oxide ions. Then Ar gas was bubbled into the melt to remove remanent HCl, oxygen and water, to maintain the oxygen content and moisture levels below 1 ppm. All B


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of Pr metal. Only one pair of redox peaks observed implies that the reduction of praseodymium is a one-step reaction. Figure 1c illustrates the comparison of the cyclic voltammograms obtained on the surface of a Mo electrode (S = 0.322 cm2) in LiCl−KCl eutectic melts at 873 K containing: (i) Sn(II) and (ii) a mixture of Sn(II) and Pr(III) ions. Cyclic voltammograms were obtained in LiCl−KCl−SnCl2 melt before (red line) and after (black line) addition of PrCl3 (2.0 wt %) on Mo (S = 0.322 cm2) electrode at 873 K. A new group of signals (I/I′) was detected after the addition of PrCl3 in LiCl−KCl−SnCl2 eutectic melts. The cathodic peak I (which corresponds to the deposition of Sn−Pr intermetallic compound) is observed from −1.65 V (vs Ag/Ag+). Signal I′, corresponding to the dissolution of a Sn−Pr intermetallic compound, is observed at about −1.18 V. It is noteworthy that with the addition of PrCl3 into LiCl−KCl−SnCl2, the intensity of peak D increases while the peak E decreases. It was attributed to two aspects. On one hand, the reduction peak D and redox peaks of metal Pr (Figure 1b) are very close and overlapped with each other, resulting in the increasing electrochemical signal of peak D. On the other hand, the change of peak intensity should be determined by the concentration of SnCl2. The Sn−Pr intermetallic compounds will be more easily formed than the Sn−Li intermetallic compounds. Thus, the concentration of Sn(II) in the formation of Sn−Li intermetallic compound is decreased, resulting in the decreased in the strength of electrochemical signal (peak E). 3.2. Square-Wave Voltammetry. Square-wave voltammetry is considered as ‘‘electrochemical spectroscopy’’ due to its ability to provide a closer insight into various redox mechanisms; in the family of pulse voltammetric techniques,31,32 it is popular, more exploited and sensitive than cyclic voltammetry. In our further investigation of the electrochemical behavior in LiCl−KCl−SnCl2 (2.0 wt %)−PrCl3 (2.0 wt %) melts, Figure 2 shows the square wave voltammograms obtained in the LiCl−KCl−SnCl2 melts after the addition of PrCl3 at a step potential of 1 mV and frequency of 20 Hz, plotted from −2.5 to 0.6 V on Mo electrodes (S = 0.322 cm2) at 873 K. Eight obvious peaks are observed. According to the reduction potentials of Pr and Li on Mo electrode in Figure 1,

electrochemical experiments were carried out in a purified eutectic mixture under an inert argon atmosphere; the working temperature, 873 K, was controlled with a nickel−chromium thermocouple and kept to ±2 K. 2.2. Electrochemical Apparatus and Electrodes. Cyclic voltammetry (CV), square wave voltammetry (SWV) and open circuit chronopotentiometry (OCP) were employed using an Autolab PGSTAT 302N (Metrohm, Ltd.) with Nova 1.8 software package. A silver wire (d = 1 mm, 99.99% purity) dipped into a solution of AgCl (1.0 wt %) in LiCl−KCl (63.8:36.2 mol %) eutectic melts contained in 3 mm diameter quartz tube was used as the reference electrode. All potentials were referred to this Ag+/Ag couple. The bottom of the alundum tube is polished to be very thin, which is used as a diaphragm. A spectral pure graphite rod (d = 6 mm) served as the counter electrode. The working electrodes were molybdenum wires (d = 1 mm, 99.99% purity); the lower end of the molybdenum wires were polished thoroughly using SiC paper, then cleaned ultrasonically with dilute hydrochloric acid and ethanol prior to use. Between each measurement working electrodes were cleaned by applying an anodic polarization. The active electrode surface area was determined after each experiment by measuring the immersion depth of the electrode in the molten salts.

3. RESULTS AND DISCUSSION 3.1. Cyclic Voltammetry. The electrochemical behaviors of Sn(II) and Pr(III) on a molybdenum electrode (S = 0.322 cm2) in LiCl−KCl melts at 873 K were studied, respectively. A typical cyclic voltammogram of LiCl−KCl−SnCl2 (2.0 wt %) melts at 873 K on a molybdenum electrode is shown in Figure 1a. Compensation of the solution resistance (R = 0.25 Ω) was applied, as determined by a positive feedback technique. The black curve represents the voltammogram before the addition of SnCl2. Only one pair of cathodic/anodic (A/A′) signals is observed which corresponds to the deposition and dissolution of liquid Li, and the oxidation of chloride ions (Cl2 evolution). However, when SnCl2 was added into the blank LiCl−KCl melts, as shown in the red curve, the CV displays six new redox pairs. The positive part of the potential window exhibits the presence of two reversible waves; the cathodic peak F observed at around −0.32 V (vs Ag/Ag+) is related to the reduction of Sn2+ species to metallic Sn. During the reverse scan, the peak F′ observed at around −0.16 V (vs Ag/Ag+) corresponds to the oxidation of Sn formed during the reduction step. We observe also a second wave with two well-defined peaks G/G′ at −0.16 and +0.06 V (vs Ag/Ag+). The former corresponds to the reduction of Sn(IV) ions to Sn(II).30 Apart from the F/F′ G/ G′ system, the signals B, C, D and E are attributed to the formation of four Sn−Li intermetallic compounds at −2.33, −2.20, −2.11 and −2.04 V (vs Ag/Ag+). In the anodic direction, the corresponding anodic current peaks B′, C′, D′ and E′ are associated with the dissolution of Sn−Li alloys at −2.21, −2.10, −2.02 and −1.93 V (vs Ag/Ag+), respectively. Figure 1b shows typical cyclic voltammetry (CV) curves in the LiCl−KCl melts before and after the addition of 2.0 wt % praseodymium(III) chloride (PrCl3) on Mo electrodes (S = 0.322 cm2) at 873 K. The black curve of LiCl−KCl melts has no additional reaction signal within the examined electrochemical window except the peaks, A/A′, corresponding to the reduction/oxidation of Li. The red curve clearly shows a new pair of peaks, Ia/Ia′, at around −1.99 V/−1.87 V (vs Ag/Ag+), which are ascribed to the formation and subsequent reoxidation

Figure 2. Square wave voltammograms of the LiCl−KCl melts after the addition of SnCl2 (2.0 wt %) and PrCl3 (2.0 wt %) on Mo electrode at 873 K. Pulse height: 25 mV. Potential step: 1 mV. Frequency: 20 Hz. C


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electrode, showing seven potential plateaus 1, 2, 3, 4, 5, 7 and 8 at about −2.37, −2.23, −2.13, −2.04, −1.99, −0.39 and −0.28 V(vs Ag/Ag+), respectively. Of these, the potential plateaus 2, 3, 4 and 5 are interpreted as the four intermetallic compounds of Sn and Li. The more positive plateau (plateau 7) at about −0.39 V (vs Ag/Ag+) observed in curves c and d relates to Sn(II)/Sn redox couple. Curve d demonstrates an example of the open circuit chronopotentiogram transient curves obtained in LiCl−KCl−SnCl2 (2.0 wt %)−PrCl3 (2.0 wt %) melt. Within this process, we observe a new potential plateau 6 at about −1.21 V (vs Ag/Ag+) when the composition of the electrode is within a range of a two-phase (Sn and Pr) coexisting state; plateau 6 is attributed to the formation Sn−Pr intermetallic compounds. Apart from plateau 6, no other plateaus are observed between plateaus 5 and 7, indicating that no other Sn−Pr intermetallic compounds form in this system. However, the step-time phase of each plateau is distinct from each other in length, which is considered to be affiliated with the formation rate of each intermetallic compound. A similar phenomenon can be observed in other molten salt systems.41−46 To demonstrate the reproducibility of the experiment, we repeated the measurements several times, and assessed the degree of variation by calculating the standard deviation. For assigning the attribution of the redox peaks and identify the real reaction, the CV, SWV and OCP were registered at different reversion potentials, respectively. The values of reduction/oxidation peak potentials are presented in Table S1. 3.4. Relationship between Deposition Potentials and Atomic Radius. To study the deposition potential of Sn−Pr alloy compounds and other intermetallic compounds (Sn−La, Sn−Pr, Sn−Er, Sn−Gd and Sn−Dy), we carried out cyclic voltammetry, square-wave voltammetry and open-circuit chronopotentiometry (details shown in Figure S1−S4).The deposition potentials of lanthanides with SnCl2 in LiCl−KCl melt and the atomic radius of lanthanides are presented in Table 1.

the attribution of the eight peaks is confirmed. In addition to peaks A, F, H and I corresponding to the reactions of Li(I)/Li, Pr(III)/Pr, Sn(II)/Sn and Sn(IV)/ Sn(II), respectively, the cathodic signal G, at about −1.61 V (vs Ag/Ag+), is ascribed to the formation of Sn−Pr alloy compound. The peaks B, C, D and E, identified at −2.29, −2.16, −2.08 and −2.04 V (vs Ag/ Ag+), correspond to the formation of three different Sn−Li intermetallic compounds, respectively. 3.3. Open-Circuit Chronopotentiometry. Open-circuit chronopotentiometry is a convenient and proven technique for the study of potential alloy formation in both qualitative and quantitative modes;29,33−39 it is suitable for the study of potential alloy formation and dissolution.34,40 By this means, samples of thin layers of Sn−Pr intermetallic compounds were prepared by potentiostatic electrolysis at the Mo electrodes for short periods of 10 s at a potential of −2.5 V, to ensure the formation of the greatest number of intermetallic compounds. After that, during a phase without current, where only intermetallic diffusion occurs, the open-circuit potential was recorded vs time. When deposited Li metal reacts with Sn and diffuses into the bulk of the Mo electrode, the electrode potential shifts toward more positive values following successive plateaus. As shown in open circuit chronopotentiometry curves (Figure 3), we clearly see some plateaus, from which nine

Table 1. Atomic Radius and the Deposition Potentials of Lanthanides with Sn

Figure 3. Open circuit chronopotentiometry curves obtained on a Mo electrode at 873 K after potentiostatic electrolysis at −2.5 V (vs Ag/ Ag+) for 10 s in LiCl−KCl melt (curve a), LiCl−KCl−PrCl3 (2.0 wt %) melt (curve b), LiCl−KCl−SnCl2 (2.0 wt %) (curve c), LiCl− KCl−SnCl2 (2.0 wt %)−PrCl3 (2.0 wt %) melt (curve d).

potential plateaux are labeled. Curve a exhibits an example of the open circuit potential transient curves on a Mo electrode (S = 0.322 cm2) in LiCl−KCl melt after potentiostatic electrolysis at −2.5 V (vs Ag/Ag+) for 10 s at 873 K. Curves b, c and d correspond to the open circuit chronopotentiogram transient curves obtained in LiCl−KCl−PrCl3 (2.0 wt %) melt, in LiCl− KCl−SnCl2 (2.0 wt %) melt and in LiCl−KCl−SnCl2 (2.0 wt %)−PrCl3 (2.0 wt %) melt after potentiostatic electrolysis at −2.5 V (vs Ag/Ag+) for 10 s at 873 K, respectively. From curve a, we observe a large and stable plateau (plateau 1) at about −2.37 V, relating to the reduction of Li(I) on a Mo electrode in the melt. From curve b, plateau 9 is ascribed to Pr(III)/Pr(0), curve c corresponds to the open circuit chronopotentiogram obtained in LiCl−KCl−SnCl2 (2.0 wt %) melt at the Mo

element

atomic radius (Å)

deposition potential of lanthanides with SnCl2 (V vs Ag+/Ag)

La Pr Er Gd Dy

1.877 1.828 1.757 1.802 1.773

−1.203 −1.216 −1.257 −1.224 −1.249

The change in deposition potential follows a similar trend to the change in atomic radius, indicating a close relationship between the atomic radii and the deposition potentials of lanthanides with Sn. After an extensive experiment, we establish the relationship between the deposition potential and the atomic radii of lanthanides by deriving a mathematical equation from the sorting out and summarizing of the data, as the following: 1/(E*r 3) = a(x1 ln x1 + x 2 ln x 2) + b r1/(r1 + r2) = x1 , r2/(r1 + r2) = x 2

r = (r2/r1)3 D


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The Journal of Physical Chemistry C Here E is the deposition potential of lanthanides with Sn, r2 and r1 are the atomic radii of lanthanide elements and Sn, respectively. Figure 4 shows the relationship of 1/(E*r3) and

so that the corresponding linear equations will probably not be consistent. The linear equation measurements allow us to speculate on the deposition potential of Sn alloys with Ce, Nd, Lu and Yb, as mentioned above. From the phase diagram of SnREEs binary system, we found that Sn−Pm, Sn−Ho, Sn−Eu, and Sn−Tm intermetallic compounds cannot be formed. The predicted deposition potential of Sn−Ce, Sn−Nd, Sn−Yb and Sn−Lu intermetallic compounds are as follows: −1.212, −1.214, −1.204 and −1.274 V (vs Ag/Ag+), respectively. Open-circuit chronopotentiometry is potentially a valuable method of verification to formally prove correctness of the forecast. Thereby, Figure 5 allows the evaluation of the successive deposition potentials of formation of each compound of Sn−Ce, Sn−Nd, Sn−Yb and Sn−Lu. The deposition potentials measured by open-circuit chronopotentiometry are −1.212, −1.215, −1.208 and −1.272 V. Table 2 compares the differences in predictive and experimental values. The calculated deviations are less than Table 2. Comparison of Predictive and Experimental Values for the Deposition Potentials of Lanthanides with Sn

3

Figure 4. Fitted curve of 1/(E*r ) and (x1 ln x1 + x1 ln x1).

(x1 ln x1 + x2 ln x2). The slope of the fitted curve in Figure 4 was used to calculate the deposition potential of lanthanides with Sn data of intermetallic compounds. As seen in Figure 4, the linear equation is Y = 9.11 + 13.85X, R2 = 0.998. Each equation will be subject to experimental error,

element

predictive value (V vs Ag+/Ag)

experimental value (V vs Ag+/Ag)

deviation (%)

Ce Nd Yb Lu

−1.212 −1.214 −1.204 −1.274

−1.212 −1.215 −1.208 −1.272

0.00 0.08 0.33 0.16

Figure 5. Open circuit chronopotentiometry curves obtained on a Mo electrode at 873 K after potentiostatic electrolysis at −2.5 V (vs Ag/Ag+) for 10 s in LiCl−KCl−SnCl2 (2.0 wt %)−CeCl3 (2.0 wt %) melt (a), LiCl−KCl−SnCl2 (2.0 wt %)−NdCl3 (2.0 wt %) melt (b), in LiCl−KCl−SnCl2 (2.0 wt %)−YbCl3 (2.0 wt %) melt (c), and in LiCl−KCl−SnCl2 (2.0 wt %)−LuCl3 (2.0 wt %) melt (d). E


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Figure 6. (a) XRD pattern of deposit obtained by potentiostatic electrolysis at −1.30 V on molybdenum electrodes in LiCl−KCl−SnCl2 (2.0 wt %)−CeCl3 (2.0 wt %) molten salts for 2 h at 873 K. (b) SEM, (c) EDS analysis and (d, e) mapping analysis of the Sn−Ce alloys.

distributions of Sn and Ce elements in the alloy, SEM with EDS analysis and mapping analysis of the alloy sample were obtained by potentiostatic electrolysis at −1.30 V on molybdenum electrodes in LiCl−KCl−SnCl2 (2.0 wt %)− CeCl3 (2.0 wt %) molten salts for 2 h at 873 K (shown in Figure 6b−e). EDS quantitative analysis (Figure 6c) shows that the deposits are composed of Sn, Ce, Cl and O; the Cl and O are thought to have been mixed when the samples were prepared. The cerium and tin are distributed homogeneously (Figure 6d,e). The SEM micrographs of the cross section after electrode surface potentiostatic electrolysis at −1.212 V for 2 h are shown Figure S5.

0.33%, which suggest that the linear equation possesses good applicability. As noted above, to further verify that the equation can be extrapolated to the other lanthanides, for example Ce, we used potentiostatic electrolysis as a suitable technique to investigate the formation of Sn−Ce intermetallic compounds. 3.5. Potentiostatic Electrolysis and Characterization of the Sn−Ce alloys. To characterize the Sn−Ce intermetallic compounds and to associate the predictive deposition potential with the composition of the deposit, we carried out potentiostatic electrolysis with a solution of SnCl2 and CeCl3 in the eutectic LiCl−KCl mixture on a Mo electrode, for periods ranging from 120 to 180 min, at −1.212 V of predictive value. Following the deposition, the deposits were washed by ethylene glycol (99.8%) and stored inside a glovebox until their analysis. The surface of the samples were analyzed by XRD and EDS, and the surface morphology of the deposits was observed by scanning electron microscopy (SEM). Figure 6 shows the X-ray diffraction pattern of the alloy sample obtained by potentiostatic electrolysis from the LiCl− KCl−SnCl2 (2.0 wt %)−CeCl3 (2.0 wt %) melts. The XRD pattern of the sample shows that CeSn3 phases form; only one identified CeSn3 alloy (No. 65-0659) indicates that the plateaus correspond to the formation of CeSn3 in the open-circuit potential transient curve of Figure 5a. To examine the

4. CONCLUSIONS The electrochemical behavior of tin was studied in a eutectic LiCl−KCl mixture using different substrates, with Mo as an inert working electrode. This study clearly shows that molten salt electrodeposition is a powerful technique for investigating the deposition potential of lanthanides with Sn. Cyclic voltammetry, square-wave voltammetry, and open circuit chronopotentiometry techniques reveal the formation of SnRE intermetallic compounds. From our results we conclude that Sn−Ce alloys are easily obtained using a Mo electrode and constant potential deposition. F


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A linear equation relating deposition potential with the atomic radius was obtained; it can be extended to actinides for predicting the deposition potential according to the atomic radius. Currently, the intermetallic compounds deposition potentials of other transition metals with lanthanides are now under study, as well as testing and verifying the correctness and universal applicability of the equation presented in this paper. The significance of this equation provides the scientific community with a more reliable theoretical basis at an early stage of separation.

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ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jpcc.7b11782. Different reversion potentials of the CV, SWV, and OCP, respectively; electrochemical behavior of other intermetallic compounds (Sn−La, Sn−Er, Sn−Gd, Sn−Dy); and SEM micrographs of the cross section (PDF)

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AUTHOR INFORMATION

Corresponding Authors

*(M.Z.) Telephone: +86-451-82569890. E-mail: zhangmilin@ hrbeu.edu.cn. *(D.J.) E-mail: [email protected]. ORCID

Hengbin Xu: 0000-0001-6161-8267 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The work was financially supported by the China Scholarship Council, the National Natural Science Foundation of China (51574097, 51774104, 21790373, and 11675044), the Science Foundation of Heilongjiang Province (LC2016018), the Fundamental Research Funds for the Central Universities (HEUCF171005), the Foundation for University Key Teacher of Heilongjiang Province of China and Harbin Engineering University (1253G016 and HEUCFQ1415), the Scientific Research and Special Foundation Heilongjiang Postdoctoral Science Foundation (LBH-Q15019, LBH-Q15020 and LBHTZ0411), and a project funded by the China Postdoctoral Science Foundation (2017M621244).

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REFERENCES

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