541.135.5 We have studied the electrochemical properties of electrodes based on the intermetallic TiNi, obtained by powder metallurgy, with an austenite and martensite structure. The electrochemical and capacity characteristics of the electrodes were determined from the charging curve under nonequilibrium conditions, and also from the cyclic voltammetric curve in alkaline medium. We have studied the structural and phase changes during absorption − desorption of hydrogen and the effect of the structure on activation and the hydrogen sorption capacity. We have shown that electrodes made from titanium nickelide with a two-phase structure (austenite, martensite) are easily activated and have a higher hydrogen capacity than electrodes with a single-phase austenite structure.Titanium nickelide TiNi was one of the first compounds used as electrode material for reversible cathode storage of hydrogen in an alkaline electrolyte [1]. More recent work has been connected with study of the electrochemical characteristics [2, 3] and their dependence on polarization conditions [4], structure [5], and the technology used to make the electrodes [2, 5, 6]. The greatest number of publications are devoted to the study of the possibility of improving the energy and operating life characteristics of titanium nickelide by creating multicomponent derivatives of TiNi [6-9], modification of the surface by coatings [7,10], and activation of the surface [5, 6, 10].Deformation stresses arising in phase transformations of the material absorbing hydrogen are one of the major reasons for degradation of the material and consequently the decrease in its discharge capacity when cycled. Study of the deformation of porous specimens of intermetallics based on LaNi 5 , Laves phases based on TiCr 2 and TiNi in reversible hydrogenation in the gas phase showed that only the titanium nickelide specimens reversibly absorbed hydrogen without fracture, despite the substantial change in dimensions [11]. In the work under consideration, the ability of TiNi to deform without fracture is connected with martensitic transformations occurring in the material. We know [12] that TiNi, within the homogeneity limits of the chemical composition, can exist as two phases: hightemperature cubic B2 (austenite) and rhombohedral B19′ (martensite), and the phase transformation B2 → B19′ is reversible. The austenitic-martensitic transition was observed in electrolytic hydrogenation of deformable electrodes made from compact TiNi alloys in a sulfuric acid electrolyte [13,14]. In this case, the phase transformations are due to deformation stresses created by the absorbed hydrogen in the crystal lattice of the B2 phase, but no hydride phases are observed. In [15], when TiNi powder with a B2 type structure was saturated with gaseous hydrogen, formation of a stoichiometric hydride TiNiH was established; and [16] gives TiNiH 1.4 as the end product of hydrogenation of TiNi (the phase composition was not indicated).Thus analysis of the literature showed that there have been no targe...
