Synthesis, crystal structure, and electrochemical hydrogenation of the La2Mg17-xMx (M = Ni, Sn, Sb) solid solutions European Journal of Chemistry 12 (2) (2021) 197-203 European Journal of Chemistry ISSN 2153-2249 (Print) / ISSN 2153-2257 (Online) – Copyright © 2021 The Authors – Atlanta Publishing House LLC – Printed in the USA. This work is published and licensed by Atlanta Publishing House LLC – CC BY NC – Some Rights Reserved. https://dx.doi.org/10.5155/eurjchem.12.2.197-203.2092 European Journal of Chemistry View Journal Online View Article Online Synthesis, crystal structure, and electrochemical hydrogenation of the La2Mg17-xMx (M = Ni, Sn, Sb) solid solutions Vasyl Kordan 1,*, Vitalii Nytka 1, Ivan Tarasiuk 1, Oksana Zelinska 1 and Volodymyr Pavlyuk 1,2 1 Department of Inorganic Chemistry, Faculty of Chemistry, Ivan Franko National University of Lviv, Kyryla i Mefodiya St., 6, 79005 Lviv, Ukraine kordan50@gmail.com (V.K.), vetalnitka@gmail.com (V.N.), tarasiuk.i@gmail.com (I.T.), oksana.zelinska@gmail.com (O.Z.), vpavlyuk2002@yahoo.com (V.P.) 2 Institute of Chemistry, Jan Długosz University of Częstochowa, Armii Krajowej Ave, 13/15, 42200, Częstochowa, Poland * Corresponding author at: Department of Inorganic Chemistry, Faculty of Chemistry, Ivan Franko National University of Lviv, Kyryla i Mefodiya St., 6, 79005 Lviv, Ukraine. e-mail: vasyl.kordan@lnu.edu.ua (V. Kordan). 10.5155/eurjchem.12.2.197-203.2092 Received: 30 January 2021 Received in revised form: 24 March 2021 Accepted: 31 March 2021 Published online: 30 June 2021 Printed: 30 June 2021 The crystal structure of La2Mg17-xSnx solid solution was determined by single crystal X-ray diffraction for the first time. This phase crystallizes in hexagonal symmetry with space group P63/mmc (a = 10.3911(3), c = 10.2702(3) Å, V = 960.36(6) Å3, R1 = 0.0180, wR2 = 0.0443 for the composition La3.65Mg30Sn1.10) and is related to the structure of CeMg10.3 and Th2Ni17-types which are derivative from the CaCu5-type. A series of isotypical solid solutions La2Mg17-xMx (M = Ni, Sn, Sb, x ~0.8) was synthesized and studied by X-ray powder diffraction, energy dispersive X-ray spectroscopy and fluorescent X-ray spectroscopy. All solid solutions crystallize with the structure related to the Th2Ni17-type. The electrochemical hydrogenation confirmed the similar electrochemical behavior of all studied alloys. The amount of deintercalated hydrogen depends on the physical and chemical characteristics of doping elements and increases in the sequence Sn < Mg < Sb < Ni. The most geometrically advantageous sites are octahedral voids 6h of the initial structure, thus a coordination polyhedron for H-atom is an octahedron [HLa2(Mg,M)4]. Hydrides Hydrogenation Electrochemistry Intermetallic phases Electron microscopy Single crystal structure Cite this: Eur. J. Chem. 2021, 12(2), 197-203 Journal website: www.eurjchem.com 1. Introduction Nowadays, materials related to the production, storage and conversion of energy are in great demand in different fields of technology and industry. The most profitable energy storage is possible during the accumulation of charge in various batteries or storage stations. Most of the batteries use intermetallic phases or composites with metallic matrix as electrodes [1]. Phases with large voids, such as R5M3 (Mn5Si3-type structure), are suitable for Li or Mg intercalation and can be promising electrode materials for corresponding Li-ion and Mg-ion batteries [2-5]. In the era of the development of alternative energy sources, the modern research works are associated with the study of the hydrogenation of alloys, which can be used for hydrogen storage purposes and as electrode materials for nickel metal hydride batteries. Materials with the best hydrogen absorption properties were developed on the basis of the structure types CaCu5, MgCu2, MgZn2, MgNi2, CeNi3, Gd2Co7, ZrNiAl, Mo2FeB2, Th2Zn17, Th2Ni17 and their derivatives. Doping of metals and alloys by s- or p-elements positively influence on the electrochemical and sorption properties of the samples of electrodes. For instance, doping of magnesium by Li and Al improves its hydrogen sorption and corrosion resistance [6,7], doping of Tb2Ni17 by Li, Mg, Al, Ge, Sn, Sb and Bi also enhances its corrosion resistance and discharge time of the battery [8]. The alloys containing Mg became popular for the development of light and safe for the environment materials. As a basis are the phases that crystallize in the structure type CaCu5 or its derivatives [9-15]. Gas hydrogenation and optimization of the synthesis procedure of the composite based on the mixture of La2Mg17 and LaNi5 is presented in Ref. [16]. In this case, LaNi5 accelerates the hydrogen sorption and desorption processes. The solubility of Sn in the La2Mg17 phase does not exceed 2 at. % at 500 °C according to Ref. [17], while in our research the solubility reaches 4 at. % at 400 °C that is confirmed by X-ray powder diffraction (XRD) and energy dispersive X-ray spectroscopy (EDX). The purpose of this research is to study the crystal structure of La2Mg17-xMx solid solutions and find the correlation between composition of the electrodes and their electrochemical characterization during hydrogenation/ dehydrogenation processes. ABSTRACT RESEARCH ARTICLE KEYWORDS https://dx.doi.org/10.5155/eurjchem.12.2.197-203.2092 https://www.eurjchem.com/ https://dx.doi.org/10.5155/eurjchem.12.2.197-203.2092 mailto:kordan50@gmail.com mailto:vetalnitka@gmail.com mailto:tarasiuk.i@gmail.com mailto:oksana.zelinska@gmail.com mailto:vpavlyuk2002@yahoo.com mailto:vasyl.kordan@lnu.edu.ua http://www.eurjchem.com/ https://crossmark.crossref.org/dialog/?doi=10.5155/eurjchem.12.2.197-203.2092&domain=pdf&date_stamp=2021-06-30 198 Kordan et al. / European Journal of Chemistry 12 (2) (2021) 197-203 2021 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.12.2.197-203.2092 Scheme 1 2. Experimental 2.1. Synthesis of samples Lanthanum, tin, antimony, nickel (commercial, small pieces), and magnesium (commercial powder) with nominal purity > 99.9 wt. % were used as starting materials. Similar method of synthesis is described in [5]. Alloys with the composition La10.5Mg85.5M4, (M = Ni, Sn, Sb) were prepared by induction melting (re-melted two times) of pressed pellets of pure components (excess of Mg was 5 wt. % and Sb was 2 wt. %) under the purified argon atmosphere. To reach homogeneity the samples were sealed in evacuated silica tubes, annealed at 400 °C for 2 months and finally quenched in cold water. During the synthesis, the lost of weight did not exceed 2 wt. %. Higher annealing temperature, for example 600 °C causes the interaction of magnesium with surface of silica tube and further component loss. 2.2. Phase analysis The phase analysis of the alloys before electrochemical processes was mainly carried out by powder X-ray diffraction using a diffractometer DRON-2.0M (FeKα-radiation, λ = 1.93608 Å, 20° ≤ 2θ ≤ 100°). The refinement of lattice para- meters (least squares refinement method) was performed using LATCON [18] and PowderCell [19] programs. Qualitative and quantitative composition of the observed phases was studied using scanning electron microscope TESCAN Vega3 LMU (Oxford Instruments energy dispersive X- ray analyzer, Aztec ONE system) and REMMA-102-02. X-ray fluorescent spectroscopy (spectrometer ElvaX Pro) was used for investigation of the integral composition of electrodes before and after hydrogenation. 2.3. Electrochemical measurements Electrochemical hydrogenation of a binary La2Mg17 and three ternaries (doped by 4 at. % of Ni, Sn, and Sb) alloys was carried out in 2-electrode Swagelok-type cells. The battery prototype consisted of a negative electrode containing 0.3 g of the studied alloy and a positive electrode containing a mixture of dried Ni(OH)2 (mixture of α- and β-modifications) with 10 wt. % of graphite. A separator soaked in 6M KOH electrolyte (prepared from KOH with 99 wt. % purity, commercial) was placed between the electrodes to avoid contact. Chrono- potentiograms of the Ni-MH battery prototypes were obtained in galvanostatic regime over 50 cycles using galvanostat MTech G410-2 [20]. The amount of deintercalated H-atoms per formula unit (H/f.u.) was determined for studied electrodes using Faraday’s formula, where H-content is directly propor- tional to the discharge time and inversely proportional to the amount of electrode material. The electrochemical reactions that occur on the electrodes can be presented by Scheme 1. 2.4. Single crystal determination The crystal structure of the La2Mg17-xSnx solid solution was studied by single crystal X-ray diffraction (diffractometer Xcalibur Oxford Diffraction, ССD-detector, Мо Kα1-radiation, ω- scan mode). A single crystal for investigation was selected from the alloy with the composition La10.5Mg85.5Sn4. Absorption correction was performed by an empirical method using SADABS [21]. The analysis of the crystal structure was carried out by direct method using SHELXS [22] and full matrix least squares refinement on F2 was performed using SHELXL [23]. 3. Results and discussion 3.1. Crystal structure of the La3.65Mg30Sn1.10 During the systematic investigation of the interaction between metallic components in the systems La–Mg–{Sn, Sb}, we observed the formation of the solid solutions of substitution on the basis of the binary phase La2Mg17 (ordered model with structure type Th2Ni17, space group P63/mmc, Pearson’s code hP38, Z = 2) with the homogeneity range up to 4 at.% of Sn or Sb. This structure is suitable for hydrogen storage and the phases with the same or relative crystal structure can serve as a negative electrode material in Ni-MH batteries. Detailed study of the crystal structure of this solid solution was carried out by single crystal X-ray powder diffraction on the sample La10.5Mg85.5Sn4, from which an irregularly shaped single crystal was selected. Solution the structure by direct methods indicated a significant disorder of the structure and the presence of split positions for La2Sn2 and Sn1Sn3. The refined composition from X-ray data is La3.65Mg30Sn1.10. The crystal data and details of the structure refinement for La3.65Mg30Sn1.10 are given in Table 1. The standardized atomic positions and thermal displacement parameters are given in Table 2. The results of structural refinement show that the formation of a La2Mg17-xSnx solid solution takes place by a complex mechanism. If the binary phase La2Mg17 dissolves tin, the Mg-atoms are replaced by Sn-atoms in a site 4f and additional Sn-atoms are inserted in the positions 4e and 2d, which are empty in the initial binary structure. The insertion of Sn atoms in the site 2b causes the subtraction of La atoms from 2b site because La2Sn2 are in the split position. It proves that La3.65Mg30Sn1.10 is more closely related to CeMg10.3-type (disordered model) [24], however, it also differs from it due to the redistribution of atoms at some sites. (Table 3). The La3.65Mg30Sn1.10 structure is strongly disordered, as evidenced by the presence of adjacent atomic sites, which can not be occupied simultaneously, and by the existence of split positions. Therefore, in the average structure, two subcells (A and B) can be selected, with the fraction ratio of subcell A to subcell B as 4:1 (Figure 1). The A subcell has a composition La4Mg30Sn0.86 and B subcell has a composition La2Mg30Sn0.24. Detailed crystal chemical analysis shows that La1 and La2 atoms are enclosed in a pseudo-Frank-Kasper polyhedra [La1Mg18Sn20] and [La2Mg18] respectively. For all Mg and Sn3 atoms typical is icosahedral coordination. The Sn1 and Sn2 atoms are enclosed in 14-vertex polyhedra [Sn1Mg12SnLa] and [Sn2Mg12Sn2] that can be treated as bicapped hexagonal antiprisms. The unit cell and coordination polyhedra of atoms are shown in Figure 2. Kordan et al. / European Journal of Chemistry 12 (2) (2021) 197-203 199 2021 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.12.2.197-203.2092 Table 1. Crystal data and details of the structure refinement for La3.65Mg30Sn1.10. Parameters Compound Empirical formula La3.65Mg30Sn1.10 Formula weight (g/mol) 1366.7 Temperature (K) 298 Crystal system Hexagonal Space group P63/mmc a, (Å) 10.3911(3) b, (Å) 10.3911(3) c, (Å) 10.2702(3) Volume (Å3) 960.36(6) Z 1 ρcalc (g/cm3) 2.363 μ (mm1) 5.17 F(000) 623 Crystal size (mm3) 0.06 × 0.06 × 0.02 Radiation MoKα (λ = 0.71073) 2Θ range for data collection (°) 2.3 to 26.3 Index ranges -12 ≤ h ≤ 12, -12 ≤ k ≤ 12, -12 ≤ l ≤ 12 Reflections collected 8711 Independent reflections 408 [Rint = 0.0261] No. of reflections with I > 2σ(I) 339 Data/parameters 408/28 Goodness-of-fit on F2 1.27 Final R indexes [I≥2σ(I)] R1 = 0.0180 wR2 = 0.0443 Final R indexes [all data] R1 = 0.0241, wR2 = 0.0498 Largest diff. peak/hole (e Å-3) 0.34/-0.86 Table 2. Fractional atomic coordinates and thermal displacement parameters (Å2) for for La3.65Mg30Sn1.10. Atoms Wyckoff sites x y z Uiso/Ueq Occ. (<1) La1 2c 1/3 2/3 1/4 0.01499(18) La2 2b 0 0 1/4 0.0183(2) 0.827(3) Mg1 12k 0.36045(16) 0.03294(16) 1/4 0.0246(3) Mg2 12j 0.16402(7) 0.32803(14) 0.02035(13) 0.0221(3) Mg3 6g 1/2 0 0 0.0195(4) Sn1 4f 1/3 2/3 0.6018(2) 0.025 0.2174(15) Sn2 4e 0 0 0.1015(12) 0.027 0.0404(12) Sn3 2d 1/3 2/3 3/4 0.027 0.032(2) Atoms U11 U22 U33 U12 U13 U23 La1 0.0151(2) 0.0151(2) 0.0147(3) 0.00757(11) 0.000 0.000 La2 0.0165(2) 0.0165(2) 0.0220(4) 0.00824(12) 0.000 0.000 Mg1 0.0395(8) 0.0261(7) 0.0159(6) 0.0222(6) 0.000 0.000 Mg2 0.0164(5) 0.0253(7) 0.0277(6) 0.0126(3) 0.0012(3) 0.0024(6) Mg3 0.0156(6) 0.0236(9) 0.0220(8) 0.0118(4) -0.0005(4) -0.0010(8) Figure 1. La3.65Mg30Sn1.10 as a composite structure of A and B subcells. The La3.65Mg30Sn1.10 (own type), La2Mg17 (Th2Ni17-type), and CeMg10.3 (own type) structures are related to the parental CaCu5-type structure (space group P6/mmm). As a result of tripling of the unit cell (1:5 stoichiometry) and replacing of a large atom (rare-earth element) with a pair of smaller atoms (transition element or other), we turn to the stoichiometry 2:17. By similar replacing, we can obtain other stoichiometry such as 2:7, 5:19, 3:22, 3:29, etc. Insertion of additional atoms causes the formation of CeMg10.3 and La3.65Mg30Sn1.10 structures. The differences between these types of structures can be observed during the analysis of atomic networks that form magnesium atoms (Figure 3). 200 Kordan et al. / European Journal of Chemistry 12 (2) (2021) 197-203 2021 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.12.2.197-203.2092 Table 3. Distribution of atoms in the Wyckoff sites for the La2Mg17, La3.65Mg30Sn1.10, and Ce1.71Mg17.58 structures. Wyckoff sites La2Mg17 La3.65Mg30Sn1.10 Ce1.71Mg17.58 Atoms SOF Atoms SOF Atoms SOF 12 Mg 1.000 Mg 1.000 Mg 1.000 12j Mg 1.000 Mg 1.000 Mg 1.000 6g Mg 1.000 Mg 1.000 Mg 1.000 4f Mg 1.000 Sn 0.217 Mg 0.985 4e - - Sn 0.040 Mg 0.305 2d - - Sn 0.032 Ce 0.015 2c La 1.000 La 1.000 Ce 1.000 2b La 1.000 La 0.826 Ce 0.695 Figure 2. Unit cell and coordination polyhedra of atoms for La3.65Mg30Sn1.10. Figure 3. Magnesium atomic nets in the La3.65Mg30Sn1.10, La2Mg17, and CeMg10.3 related structures. 3.2. Powder XRD and EDX studies of La2Mg17-xMx alloy The synthesized samples with the compositions La10.5Mg89.5, La10.5Mg85.5Sn4, La10.5Mg85.5Sb4 and La10.5Mg85.5Ni4 were ingots of silver color and metallic luster and stable in air at room temperature. X-ray analysis showed the formation 2:17-phase (binary or ternary phases, ordered model) and small amounts of the other phases. The composition of this phase from EDX-analysis is La11.2(5)Mg88.8(9) (Figure 4a). In binary alloy, the trace amount of LaMg3 (structure type BiF3, space group Fm-3m, a = 7.4807(5) Å, V = 418.63(8) Å3) was observed. The cubic phase (LaMg3) did not show the corrosion stability in the electrolyte and after hydrogenation we observed traces of La2O3. Ni-contained alloys (from EDX-analysis La10.3(4)Mg85.3(7) Ni4.4(7)) besides the main solid solution phase with nominal composition La2Mg16.2Ni0.8 (Figure 4b) contained also the phase with high content of Mg (LaMg~12, composition from EDX- analysis is La8.2(7)Mg90.6(9)Ni1.2(9)). Kordan et al. / European Journal of Chemistry 12 (2) (2021) 197-203 201 2021 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.12.2.197-203.2092 (a) (b) (c) (d) Figure 4. SEM-images (BSE-mode) of La10.5Mg89.5 (a), La10.5Mg85.5Ni4 (b), La10.5Mg85.5Sn4 (c) and La10.5Mg85.5Sb4 (d). Authors [25] also confirmed that the solubility of Ni in the 2:17-phase does not exceed 4-5 at. %. Authors [26] also were interested in electrochemical hydrogenation alloys of La-Mg-Ni system. Tin-contained alloy contained the main phase La2Mg16.2Sn0.8 (main phase, from EDX-analysis La10.6(5)Mg85.7(8)Sn3.7(9)) and trace amount of ~Mg (dark phase, see Figure 4c, La1.8(7)Mg98.0(6) Sn0.2(6)) and cubic LaMg3-xSnx (light points, La24.3(5)Mg73.4(6) Sn2.3(7)). Similar content of phases is presented for Sb-contained alloy. Predicted solid solution La2Mg16.2Sb0.8 (main phase, see Figure 4d) was with the composition La11.1(5)Mg84.2(8)Sb4.7(6). Trace amounts of Mg (La2.2(6)Mg95.9(8)Sb1.9(8)) and cubic LaMg3- xSbx (La24.8(5)Mg72.2(7)Sb3.0(7), а = 7.4639(8) Å, V = 415.8(1) Å3) phase were observed. 3.3. Electrochemical hydrogenation of La2Mg17-xMx All samples before and after electrochemical processes were examined by X-ray powder diffraction (diffractometer DRON-2.0M, Fe Kα-radiation), X-ray fluorescent spectroscopy and EDX-analysis. Spectral analysis (Figure 5) confirmed the changes in electrode composition occurred as a result of hydrogenation. The main reason for it was the etching of surface and the forming of oxides of La and Sn on the surface that is associated with interaction of the electrode surface with an electrolyte, and this reaction affects the discharge capacity. The grain size decreased by hydrogenation, the surface of electrode grains became more porous and the morphology of the grain surface was changed. Also, the composition of the grains was shifted in the direction of reducing the lanthanum content. Electrochemical hydrogenation was carried out in two- electrode Swagelok-type cells at galvanostatic mode (2 mA/cm2) to 3 H/f.u. For the binary and Sn-containing electrodes, we observed the formation and evolution of molecular hydrogen that correlates well with the discharge curves. In our opinion by gas hydrogenation we can obtain the hydrides with high H-content because high temperature and high pressure activates more grains. At the beginning of hydrogenation H-atoms occupy the octahedral voids with the position 6h forming the coordination polyhedra from two large and four small atoms (La2Mg4). Similar octahedral coordination of hydrogen atoms can be observed in the CaCu5-type structure. When the H-content is larger than 3 H/f.u., the tetrahedral composition 12i are occupied by hydrogen [27]. We think that H-atoms can occupy the tetrahedral positions of La2Mg17-xMx only by at high pressure or other extreme conditions. At experimental conditions we did not observe any evidences of structure decomposition after dehydrogenation. Smaller amount of hydrogen (rectilinearly depends on the discharge time) was observed during dehydrogenation for La2Mg17 (1.36 H/f.u.) and La2Mg16.2Sn0.8 (1.01 H/f.u.); in this case gas evolution took place as a side effect. Reversible content of hydrogen for the electrode on the basis of La2Mg16.2Sb0.8 is 1.70 H/f.u. and for La2Mg16.2Ni0.8 is 1.73 H/f.u. (Figure 6). After 50 cycles of electrochemical hydrogenation/dehydrogenation, the capacity of the battery prototype somewhat declined. It depends on the partial amorphization of the material and etching of the surface. While the electrochemical properties of the electrode materials depend on the corrosion stability of the alloys in the electrolyte solution (6 M KOH). In our previous works [5-7], doping Tb2Ni17-based electrodes by s-elements (Li, Mg) and Sb led to the increasing of the corrosion stability and hydrogen sorption ability. Nominal discharge voltage for the batteries with La2Mg17- xMx electrodes is bigger than in commercial batteries with AB5 or AB2 electrodes and is ~1.25-1.30 V. For example, the batteries based on AB5- and A2B17-electrodes with high Ni- content demonstrated the nominal discharge voltage in the range of 1.10-1.20 V. 202 Kordan et al. / European Journal of Chemistry 12 (2) (2021) 197-203 2021 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.12.2.197-203.2092 Table 4. Unit cell parameters for 2:17 phases before hydrogenation (initial) and after hydrogenation (hydride of inclusion). Phase / hydride a, Å c, Å V, Å3 ΔV/V, % La2Mg17 10.339(1) 10.259(1) 949.7(2) 0.96 La2Mg17Hx 10.365(1) 10.303(2) 958.8(2) La2Mg16.2Sn0.8 10.3478(6) 10.2728(7) 952.6(1) 0.45 La2Mg16.2Sn0.8Нx 10.3629(8) 10.2888(9) 956.9(1) La2Mg16.2Sb0.8 10.343(1) 10.222(1) 947.0(2) 1.18 La2Mg16.2Sb0.8Hx 10.392(4) 10.245(4) 958.2(6) La2Mg16.2Ni0.8 10.329(2) 10.236(2) 945.8(3) 1.43 La2Mg16.2Ni0.8Hx 10.381(3) 10.279(4) 959.3(6) (a) Integral composition – La10.3Mg89.7 (b) Light phase – La9.9Mg90.1; dark phase – ~La26.9Mg33.2O39 (oxides) (c) Integral composition – La9.6Mg86.6Sn3.8 (d) Light phase – La9.2Mg88.5Sn2.3; dark phase – oxides based on La, Sn Figure 5. SEM-images of electrodes on the basis of La10.5Mg89.5 and La10.5Mg85.5Sn4 before (a), (c), and after (b), (d) 50 cycles of electrochemical hydrogenation. Figure 6. Selected discharge curves (30-th cycle) for the Ni-MH prototype batteries with La2Mg17-xMx (M = Sn, Sb, Ni) as negative electrodes. Changes in unit cell parameters of the solid solutions after electrochemical hydrogenation are presented in Table 4. For all samples after hydrogenation, we observed the increasing of the unit cell volume. As one can see, the unit cell parameters of the studied phases correlate well with the atomic radius of the alloying components (rMg = 1.60 Å, rNi = 1.24 Å, rSn = 1.62 Å, rSb = 1.59 Å). 4. Conclusion Crystal structure of the solid solution La2Mg17-xSnx was determined by single crystal X-ray diffraction on the sample with the stoichiometry La3.65Mg30Sn1.10. The phase crystallizes in the hexagonal symmetry with the space group P63/mmc and is related to the structure of Th2Ni17 (ordered) and CeMg10.3 (disordered). The structure of La3.65Mg30Sn1.10 is strongly disordered and characterized by the split of some positions. Therefore, in the average structure, two subcells (A and B) can be selected, with the fraction ratio of subcell A to subcell B as 4:1. The A subcell has a composition La4Mg30Sn0.86 and B subcell has a composition La2Mg30Sn0.24. The solubility of tin in the binary La2Mg17 intermetallic compound, studied by powder XRD and EDX-analysis, reaches 4 at. %. Solubility of Ni and Sb in the La2Mg17 compound is similar. The unit cell parameters of the solid solution La2Mg17-xMx (M = Ni, Sn, Sb) correlate well with the atomic radii of doping components. As the electrode Kordan et al. / European Journal of Chemistry 12 (2) (2021) 197-203 203 2021 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.12.2.197-203.2092 materials studied, the alloys demonstrate the increasing of capacity in the line La2Mg16.2Sn0.8 (1.01 H/f.u.) < La2Mg17 (1.36 H/f.u.) < La2Mg16.2Sb0.8 (1.70 H/f.u.) < La2Mg16.2Ni0.8 (1.73 H/f.u.) at 30-th cycle of charge/discharge. After 50 cycles of electrochemical measurements, the small shifting of electrode composition, changing of the morphology and grain size were observed. Supporting information CCDC-2059085 contains the supplementary crystallo- graphic data for this paper. These data can be obtained free of charge via https://www.ccdc.cam.ac.uk/structures/, or by e- mailing data_request@ccdc.cam.ac.uk, or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44(0)1223-336033 and may be obtained from FIZ Karlsruhe, 76344 Eggenstein-Leopoldshafen, Germany (fax: (+49)7247-808-666; e-mail: crysdata@fiz- karlsruhe.de). Disclosure statement Conflict of interests: The authors declare that they have no conflict of interest. Author contributions: All authors contributed equally to this work. Ethical approval: All ethical guidelines have been adhered. Sample availability: Samples of the compounds are available from the author. ORCID Vasyl Kordan https://orcid.org/0000-0001-8319-5816 Vitalii Nytka https://orcid.org/0000-0002-6090-9473 Ivan Tarasiuk https://orcid.org/0000-0002-6590-5527 Oksana Zelinska https://orcid.org/0000-0002-2931-9870 Volodymyr Pavlyuk https://orcid.org/0000-0003-1893-2706 References [1]. Besenhard, J. O. Handbook of Battery Materials; Besenhard, J. O., Ed.; Wiley-Vch, 1999. [2]. Balińska, A.; Kordan, V.; Misztal, R.; Pavlyuk, V. J. Solid State Electrochem. 2015, 19 (8), 2481–2490. [3]. Kowalczyk, G.; Kordan, V.; Stetskiv, A.; Pavlyuk, V. Intermetallics (Barking) 2016, 70, 53–60. [4]. Stetskiv, A.; Kordan, V.; Tarasiuk, I.; Zelinska, O.; Pavlyuk, V. Chem. Met. Alloys 2014, 7(1/2), 106-111. http://www.chemetal-journal.org/ ejournal14/CMA0282.pdf (accessed Apr 6, 2021). [5]. Kordan, V.; Zelinska, O.; Pavlyuk, V.; Oshchapovsky, I.; Serkiz, R. Chem. Met. Alloys 2016, 9(1/2), 84-91. https://chemetal-journal.org/ ejournal18/CMA0327.pdf (accessed Apr 6, 2021). [6]. 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Introduction 2. Experimental 2.1. Synthesis of samples 2.2. Phase analysis 2.3. Electrochemical measurements 2.4. Single crystal determination 3. Results and discussion 3.1. Crystal structure of the La3.65Mg30Sn1.10 3.2. Powder XRD and EDX studies of La2Mg17-xMx alloy 3.3. Electrochemical hydrogenation of La2Mg17-xMx 4. Conclusion Supporting information Disclosure statement ORCID References PrintField10: PrintField11: PrintField12: PrintField13: PrintField14: PrintField15: PrintField16: PrintField20: PrintField21: PrintField22: PrintField23: PrintField24: PrintField25: PrintField26: