1070-4272/03/7609-1438$25.00 2003 MAIK Nauka/Interperiodica Russian Journal of Applied Chemistry, Vol. 76, No. 9, 2003, pp. 1438 1443. Translated from Zhurnal Prikladnoi Khimii, Vol. 76, No. 9, 2003, pp. 1477 1482. Original Russian Text Copyright 2003 by Nagirnyi, Apostolova, Baskevich, Shembel’. APPLIED ELECTROCHEMISTRY AND CORROSION PROTECTION OF METALS Electrolytic Synthesis of Complex Oxide Systems by Cathodic Deposition of Molybdenum Oxide from Aqueous Solutions in the Presence of Nickel(II) and Thiosulfate Ions V. M. Nagirnyi, R. D. Apostolova, A. S. Baskevich, and E. M. Shembel’ Ukrainian State University of Chemical Engineering, Dnepropetrovsk, Ukraine Received February 27, 2002; in final form, June 2003 Abstract Cathodic processes occurring in electrolytic deposition of molybdenum oxide from aqueous solutions of sodium molybdate in the presence of nickel(II) and thiosulfate ions were studied. Conditions for formation of cathodic deposits in the form of complex oxide systems Mo Ni and Mo 4 O 11 MoS 2 were determined. The interest in electrolytic oxide materials is due to their enhanced electrochemical activity and the pos- sibility of creating thin-film ballast-free cathodes for lithium power cells by direct deposition of an oxide material in the form of a compact coating on a metal- lic support [1 3]. Previously, the possibility of elec- trolytic synthesis of molybdenum oxide with nonstoi- chiometric composition in high yield by cathodic deposition from ammonium molybdate solutions has been demonstrated [4]. With account of the modern tendency toward development of high-performance cathode materials for lithium batteries on the basis of complex multicomponent oxide systems, it seemed appropriate to study the possibility of obtaining these materials in quantitative yield by electrolytic deposition of molybdenum oxide in the presence of nickel(II) and thiosulfate ions. According to the results of preliminary experi- mental tests, cathodic deposits formed under certain electrolysis conditions from sodium molybdate solu- tions containing NiSO 4 are homogeneous mixtures of molybdenum oxide, nickel (NiO), and a single-phase compound of the type NiO Mo 4 O 11 , Ni x M 4 x O 11 + y . The presence of an electrolytic oxide system Mo Ni creates certain prerequisites for formation of a sulfide phase (NiS, MoS 2 , etc.) in joint deposition at the cathode of molybdenum and nickel oxides in the pres- ence of thiosulfate ions, which may be promoted by the catalytic activity of nickel compounds [5]. This is confirmed by X-ray diffraction patterns of deposits obtained by electrolysis from solutions containing mixtures of the compounds mentioned above. Of in- terest is a study of cathodic processes and of the prep- aration conditions and properties of cathodic deposits formed by electrolytic deposition of molybdenum oxide in the presence of nickel(II) and thiosulfate ions. As base for the study served Na 2 MoO 4 solution, which, in contrast to (NH 4 ) 2 MoO 4 , rules out forma- tion of complexes and molecular ammonia in the course of electrolysis. The solutions were prepared from chemicals of pure and analytically pure grades and distilled water. The electrolysis was performed in a temperature-controlled 0.2 dm 3 cell. As cathode samples served smooth 10 10 0.3-mm 12Cr18Ni9Ti steel plates with current lead in the form of a thin strip of the same steel. As anodes were used smooth plates of technical-grade VT-1 titanium with S c : S a = 1 : 5. The materials to be studied were obtained in the form of compact coatings on both sides of the cathode. The experiments were carried out in two-component solutions of Na 2 MoO 4 and NiSO 4 at their total con- centration of 0.12 0.14 M and concentration ratios of 7 : 1 to 1 : 12 (here and hereinafter, molar ratios). The first digits refer to the base component, and the sec- ond, to the doping component. To analyze the influence exerted by the total con- centration of the solutions on the nature of the proc- esses under study, experiments at higher concentra- tions (up to 0.17 0.19 M) were also carried out at a temperature of 85 3 C chosen on the basis of pre- liminary tests. The efficiency of the cathodic process was evaluated by the conventional current efficiency CE conv (wt %) on the assumption that the whole use- ful current is expended for formation of molybdenum oxide, whose formula is Mo 4 O 11 according to X-ray structural analysis. In this compound, molybdenum is