Wyniki 1-2 spośród 2 dla zapytania: authorDesc:"Agnieszka Giemza"

High rate dischargeability of hydride electrode modified with magnetron sputtered MCrFeCoNi (M = V or Mn) coatings DOI:10.15199/40.2018.8.3

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1. Introduction Nickel - metal hydride (Ni/MH type) rechargeable batteries have attracted a wide range of research interest because of good cyclic stability, easy activation ability and environmental friendliness [10,13,20,25,26,29,30]. As hydrogen storage material the alloys based on LaNi5 compound are most often applied for battery negative electrodes. However, discharge capacity decreases for these electrodes with cycling due to the alloy pulverization and oxidation of its constituents in strongly alkaline environment [11,15]. Surface modification of hydrogen storage compounds is an effective way to improve such electrochemical properties of hydride electrodes as hydrogen capacity, exchange current density of H2O/H2 system and their cycle life [3,7,12,18]. Among modification methods of surface layers manufacturing on powder particles the magnetron sputtering technology seems to be particularly promising. It allows to produce thin (up to 1μm thick) multimetallic, catalytic layers on active material substrates. High entropy alloys (HEAs) can be effectively used as targets in magnetron sputtering process. Constituents of HEAs can consist of metals improving anticorrosion-, catalytic,- mechanical- and exploitation properties of hydrogen storage particles. The HEAs contain at least five main components in an atomic ratio of 5 to 35%. They have higher entropy of mixing compared to traditional alloys. These alloys possess a number of attractive properties useful for surface modification such as: good thermal stability [16], high hardness and strength [4,5] as well as resistance to oxidation and corrosion [9,14,21,22]. The high rate discharge ability (HRD) is regarded as one of the most important indicators to characterize a hydride electrode exploitation properties. HRD of the electrode alloys are closely related to the electrode material charge-transfer ability and the atomic hydrogen diffusivity [24]. For unmodified LaNi4.5C[...]

Effect of cycling on hydrogen diffusivity in LaNi4.5Co0.5 composite electrode using constant potential discharge techniques DOI:10.15199/40.2018.11.2

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1. Introduction For studies under modification of hydride alloy composition, its crystal lattice structure, encapsulation of its particles with different metallic coatings, long lasting corrosion degradation as a result of cycling etc., the great interest is to know the role of above mentioned interactions on resulting atomic hydrogen diffusivity through the electrode material [20,21,23,24]. Hydrogen storage materials, e.g. of AB5 stoichiometry (A = rare earth metal, usually lanthanum, sometimes partially substituted with other active elements including magnesium, B = transition group element, usually nickel, often partially substituted with other transitionor main group metals), apart from large capacity, cycling stability, ability to fast activation or resistance to corrosion should exhibit satisfactory diffusivity of atomic hydrogen. In practice, there appears many different limitations and coincidences which influence resulting hydrogen transport across the electrode material. Therefore, authors dealing with atomic hydrogen diffusivity of powder hydride materials use so called apparent diffusion coefficients which can differ from the real, lattice diffusion coefficients (DH). Among physicochemical methods applied for evaluation of hydrogen diffusion coefficients in metal hydride alloys one should mention nuclear magnetic resonance [5,11] quasi-elastic neutron scattering [18], EIS-spectroscopy [7] and various electrochemical techniques, like cyclic voltammetry or chronoamperometric constant potential discharge methods [13,15,16,25]. The diffusion coefficients of atomic hydrogen in common metal hydride materials, depending on applied method, can vary by up to five orders of magnitude (for room temperatures and for AB5 type alloys the values of apparent diffusion coefficients have been found between 10-12 and 10-7 cm2s-1) [8,12,13]. From practical point of view, it is not necessary for hydride materials to determine a “ge[...]

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