G. Wójcik’s research while affiliated with University of Latvia and other places

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X-ray powder diffraction measurements of (Ti1−xZrx)4Ni2O0.3 (x=0, 0.25, 0.5, 0.75) alloys vacuum annealed at 1000°C exhibited the formation of the η-phase with filled the Ti2Ni-type structure in all samples. Hydrogen absorption studies revealed that Zr-containing alloys have higher hydrogen storage capacities (H/M∼1.25) compared to Ti4Ni2O0.3 (H/M=0.9). Desorption measurements have shown that the hydrogen was evacuated in vacuum mainly at 120–600°C and the stability of hydrides increased following the rise of the Zr-content. Electrochemical charge–discharge cycling of (Ti1−xZrx)4Ni2Ox revealed substantial dependence of capacity and cycle-life of these materials on the Ti/Zr ratio, oxygen content and electrode preparation.

The electrochemical behavior of the lead electrode has been studied by cyclic voltammetry (CV) in sulfuric acid solutions, with concentrations ranged from 0.05 to 5 M. Also, the effect of a sweep rate, the range of potential polarisation and temperature has been examined. Special attention has been paid to unusual anodic processes, i.e., “anodic excursion” peaks that accompany the main reduction peak. The presence of a small, and previously unrecognized cathodic peak, preceding “anodic excursion” peaks, has been documented. Since all these peaks appear on the CVs only when the electrode potential is cycled in a wide potential range, limited by hydrogen and oxygen evolution, it has been proposed that they are related to the reduction of the lead dioxide to the bare metal, occurring at high negative potentials. The presence of a small reduction peak preceding “anodic excursion” peaks, as well as the presence of the main reduction peak of the lead dioxide has also been related to the exposure of the bare metal. When the lead dioxide, formed at high positive potentials, is reduced (PbO2→PbSO4), a large increase of the molar volume is expected and, as a result, the surface cracks, exposing the bare metal. These parts of the surface are then oxidized in “anodic excursion” peaks. To repeat these redox processes, the electrode has to be reduced again at high negative potentials, i.e., at the conditions when reduction to the metal occurs. The CVs performed only in a positive potential range confirmed that the reduction of PbO2 to PbSO4, which follows the formation of PbO2, is not related to the “anodic excursion” peaks and it also means that no cracks of the surface occur, as long as the potential cycling of the electrode to high negative potentials, and the resulting reduction to the metal, are avoided. Therefore, when the lead electrode is used as a positive electrode in a battery, no corrosion due to the exposure of the bare metal is expected.

The hydrogen storage alloy electrodes of the type Ti4Ni2Oy (y=0, 0.3 and 0.6) and Ti3.5Zr0.5Ni2Oy (y=0.15 and 0.3) were investigated by impedance spectroscopy for potential application as negative electrode in alkaline secondary nickel-metal hydride (MH) batteries. The phase Ti4Ni2O0.30 was found to be electrochemically more stable during the cycling. The addition of copper or nickel powder as current collector improved the electrochemical behavior of the electrodes. It was possible in this way to decrease the charge transfer resistance. These additions have a negligible influence on the stability of electrode material during cycling.

The electrochemical performance of nickel deposited on reticulated vitreous carbon (RVC) has been investigated in solutions of KOH. For comparison, the study of sintered nickel and nickel deposited on gold wire behavior were also included. Our results indicate that the RVC covered with nickel is a good carrier for Ni(OH)2/NiOOH—an electrode material, used in rechargeable batteries. Ni/RVC saturated with Ni(OH)2 shows behavior similar or even better than that of sintered Ni saturated with Ni(OH)2.

At partially sustituted nonstechiometric AB 2 type alloys the influence of alloy addition such as Mn and Fe on electrochemical features of MH electrodes made of active alloy material have been studied on the ground of physicochemical and electrochemical investigations.

Multicomponent Zr-Ti-V-Ni-Cr-Fe and Zr-Ti-V-Ni-Cr alloy electrodes, with various Ti and Zr ratios, have been studied in alkaline solution by means of potentiodynamic current-overvoltage and galvanostatic overpotential-time responses during long-term continuous and intermittent charge-discharge cycles. The pressure-composition isotherms for absorption/desorption of hydrogen, evaluated from the equilibrium potential, have been compared with the gas phase isotherms. The kinetic data demonstrate the reversibility of hydrogen electrosorption in the investigated systems. An increased discharge efficiency has been established for electrodes with lower values of both the activation and diffusion resistance. The alloy with Fe and Ti:Zr at the atomic ratio 2:1 prepared by using vanadium-ferro-alloy is shown to meet the requirements for the negative electrode in secondary nickel-metal hydride batteries.

The effect of the composition of multicomponent Zr-Ti-V-Mn-Cr-Ni alloys on their hydrogen-storage capacity and on the rate of electrosorption /desorption of hydrogen was in vestigated under potentiodynamic as well as single-pulse and long-term galvanostatie conditions. The main characteristics of alloys and alloy electrodes were determined by their structural analysis by means of X-ray diffraction and scanning electron microscope, by specific surface area tests and by determination of the hydrogen absorption/desorption isotherms in the gas/solid phase system. It was found that only the alloys with a manganese content below a threshold could be used as electrode materials for Ni-MH batteries, whereas the modification of the electrode material by micro-encapsulation of alloy particles should limit the dissolution of manganese from the electrode material in a strong alkaline solution.

At partially substituted AB2 type alloys the influence of mutual relation Ti to Zr and of alloy addition such as Mn and Fe, on electrochemical features of MH electrodes made of active alloy material, have been studied. The active alloy material has been obtained by melting of integrant elements in an arc furnace. Preliminary characterization of the alloys contains determination of hydrogen absorption and desorption isotherm (PCT curves) as well as structural parameters tested by X-ray diffraction method (CuKa Ni filter). The hexagonal C14 crystallization system of the alloys and dependence of the unit cell volume and alloy capacity in relation to hydrogen, on Ti to Zr relation, have been determined. The electrochemical investigations include determination of the voltamperometric as well as pulse and prolonged galvanostatic curves. Investigated alloys have been determined as a good electrode material for rechargeable alkaline Ni-MH cells.

Alloys used to produce reversible, hydrogen storage electrodes in the form of metal hydride for nickel-metal hydride batteries are capable to cause a reversible electrochemical reaction in alkaline environment. Reactions occurred at the Ni-MH accumulators as well as the mechanism of the electrode reactions in this study, have been discussed. Selection criteria of hydrogen absorbing alloys, useful for electrode application and physical and chemical test methods enabling to make the selection, have been defined. In the final part of the paper the AB5, AB2, AB/A2B types of alloys and employed modification made by substitution another metals for the individual alloy components, thus enabling modification of the electrochemical features of electrode by quantitative and qualitative changes of the alloy, have been discussed. It was stated that the Ni-MH type accumulators indicate some very interesting features: absence of toxic components, high energy density, ability for high charge and discharge currents, good cycle life, capability to be completely recycled and that the application of the hydrogen absorbing alloys to Ni-MH type accumulators creates a chance to eliminate cadmium in alkaline Ni-Cd electrochemical system.