The changes in surface structure of polyfaceted single crystal platinum spheres subjected to repetitive square-wave potential treatments in acid solution have been studied. The dependence of the prevailing type of change on symmetry, potential limits and frequency of the periodic potential has been determined. Results are discussed on the basis of different reactions occurring within definite potential windows and distinct rate controlling processes depending on the operating conditions. Accordingly, the surface restructuring involves a predominant change in either the real surface area, the cr :stallographic orientation or the entire surface morphology .

Since 1990, there has been an ongoing collaboration among the authors in the three laboratories to (1) prepare alloys of the AB 5 and AB 2 types, using arc-melting/annealing and mechanical alloying/annealing techniques;(2) examine their physico-chemical characteristics (morphology, composition); (3) determine the hydrogen absorption/resorption behavior @ressure-composition isotherms as a function of temperature); and (4) evaluate their performance characteristics as hydride electrodes (charge/discharge, capacity retention, cycle life, high rate capability). This review article presents the work carried out on representative AB5 and AB2 type modified alloys (by partial substitution or with small additives of other elements).The purpose of the modification was to optimize the thermodynamics and kinetics of the hydriding/dehydriding reactions and enhance the stabilities of the alloys for the desired battery applicationslThe results of our collaboration, to date, demonstrate that (1) alloys prepared by arcmelting/annealing and mechanical alloying/annealing techniques exhibit similar morphology, composition and hydriding/dehydriding characteristics; (2) alloys with the appropriate small amounts of substituent or additive elements:(i) retain the single phase structure, (iN improve the hydriding/dehydriding reactions for the battery applications, and (iii) enhance the stability in the battery environment; and (3) the AB2 type alloys exhibit higher energy densities than the AB5 type alloys but the state-of-the-art, commercialized batteries are predominantly manufactured using AB 5 type alloys. RATIONALE FOR INVESTIGATIONS AND CRITERIA FOR ALLOY SELECTIONThe interest in alloys for hydrogen storage in nickel/hydrogen and, particularly, in nickel/metal hydride batteries is gaining momentum because of the high performance characteristics of these batteries, in respect to energy efficiency, energy density, high rate charge/discharge capability and cycle life. Previous studies at CESHR, TEES-TAMUS have shown that the high rate of self-discharge in nickel/hydrogen batteries is due to the direct reduction of the nickel oxyhydroxide to nickel oxide (1-4). In these batteries, hydrogen is stored as a compressed gas and because of the high pressure of hydrogen the rate of transport to the nickel oxide electrode is quite rapid. In order to elucidate the mechanism of the self-discharge reaction and find methods for its inhibition, microcalorimetric and electrochemical techniques were used. These studies showed that the rate of self-discharge is proportional to the hydrogen pressure in the battery and the activity of nickel oxyhydroxide.Several types of potential inhibitors were incorporated in the nickel oxide electrode, during its fabrication or added to the electrolyte, to elucidate their effects on the rate of self-discharge.Though some additives such as lead, cobalt, and cadmium were found to have some effect, the rate of self-discharge could not be reduced significantly. Thus, this work showed that the only way in which ...

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