Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Reexamination Certificate
2002-10-10
2004-05-18
Weiner, Laura (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
C420S583000, C420S584100, C420S588000, C420S900000, C148S442000
Reexamination Certificate
active
06737194
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to alloys in which hydrogen may be stored, more particularly to such alloys or materials which are non-pyrophoric on exposure to ambient atmosphere, and most particularly to such non-pyrophoric alloys which may have a heterogeneous spectrum of hydrogen bonding energies.
BACKGROUND OF THE INVENTION
Hydrogen, generally considered to be the ultimate fuel, presents numerous potential benefits to be realized as well as numerous difficulties to be overcome. With capacity to serve as a fuel for combustion engines, other processes in which heat energy is derived from combustion and used; as well as a direct source of electrochemical energy in direct conversion processes such as, for example, those used in electrochemical fuel cells, hydrogen presents opportunities for production of energy without the creation of waste products bearing disposal difficulties.
The products of hydrogen combustion, whether thermal or electrochemical, are energy and water. Neither of these is toxic, neither presents difficulties of disposal of greenhouse gases, soot, or radioactive waste. From the standpoint of being a useful, high-energy content fuel, hydrogen is an excellent candidate for most of the uses in which fossil fuels are currently used. When used for direct conversion to electrical energy in a fuel cell, hydrogen does not yield oxides of carbon which often poison catalytic material used in such electrochemical cells, nor is radioactive waste generated as is the case with electricity-supplying nuclear-powered generators.
With these tremendous benefits accruing to its use as a fuel, some burdens in the use of hydrogen as a fuel may be expected. They are present and provide challenge to overcome. The greatest difficulties with hydrogen as a fuel lie in its containment and transportation. Hydrogen may be liquefied but there is tremendous cost involved in cooling and compressing; additionally the containment vessel cannot be completely sealed; tremendous losses are incurred through evaporation. Compression of the gas itself is costly, although not nearly so much as liquefication, and requires stout, durable, and heavy containers. Both are inefficient forms of storage in terms of energy storage per unit volume. Other storage means are would be useful.
Storage of hydrogen as a solid is appealing as enhanced volumetric efficiency is available. Various metals and metal alloy compositions are available for storage of hydrogen within the metallic crystal lattice; generally as a hydride. Such materials will generally release heat upon charging, take-up of hydrogen, absorption of hydrogen, or hydriding. Conversely, heat is necessary to release stored hydrogen from the metallic structure. The important reversible reaction to keep in mind is:
M+H⇄MH+heat
in which M is a metal or metal composition in which hydrogen may be stored. And H is atomic hydrogen. Generally something serving to catalyze the breakup of hydrogen molecules into hydrogen atoms will be helpful prior to this reaction.
There are two general types of hydrogen-storage alloys available. These are the so-called “high-temperature alloys” and the “low-temperature alloys”. The heat of reaction for the reversible transition provided above is the basis for the differentiation and the basis of the invention described here. As a general matter, magnesium-based hydrogen storage alloys are high-temperature alloys as they generate a great deal of heat during hydriding and require a similar amount of heat to reverse the reaction and release hydrogen; their storage capacities are generally beyond about 5% by weight.
Low temperature alloys, generally transition-metal based and often of the AB
2
structure, generate less heat during charging or hydriding, require less heat to release hydrogen, and have storage capacities generally around or below about 2% hydrogen by weight. Such alloys will normally release hydrogen at ambient temperatures simply by opening a valve and on whatever container is used for containment of the storage material, thereby reducing the hydrogen pressure around the storage material or alloy which in turn drives the previous reaction forward.
Either of the two broad categories of hydrogen storage alloys will generally have enhanced hydrogen take-up or absorption with greater effective surface area or smaller particle size. Another possible reaction exists with these alloys, particularly the low-temperature alloys:
M+0⇄MO+heat
Again, for this reaction to proceed forward, something will normally catalyze the dissociation of molecular oxygen to atomic oxygen. This can be and generally is a competing reaction with the hydriding/dehydriding reactions. Normally, the oxygen absorption by the alloy will occur preferentially when available, since the oxides of the storage metals provide a lower energy ground state than do the hydrides. Attainment of a lower energy ground state involves evolution of greater heat than a higher energy ground state, the forward reaction above generates tremendous heat. Such heat generation is the basis of the need for the current invention.
The low temperature alloys, particularly in light of their easy acceptance of oxygen and rapid formation of oxides, likely will release tremendous amounts of heat upon exposure to ambient atmosphere. Such rapid release of heat yields a material which can easily heat to glowing red almost instantaneously and burst into flames and/or ignite other material nearby whose ignition temperature is at or below the temperature of the glowing metal. These alloys or hydrogen storage materials because of their affinity for oxygen are normally simply pyrophoric. Such pyrophoricity means that the materials must be treated with respect and handled with care under non-reactive atmosphere. Even more important, from the standpoint of distribution and enhancement of hydrogen storage capacity, the pyrophoric nature of these materials require special handling (read: more costly) in transportation. The means by which they may be shipped is also severely circumscribed; generally, for example, such materials normally may not be shipped by air in light of their pyrophoric nature. Thus, the pyrophoric nature of some hydrogen storage alloys is one of the main safety issues concerning the commercial use of hydrogen storage in hydride alloy form.
Here we specifically describe the basic means in which multi-elemental hydrogen storage materials are atomically engineered and designed into non-pyrophoric hydrogen storage alloys by considering them as a system. These multi-elemental alloys can also be made in a non-equilibrium manner so that not only compositional disorder is produced, but also the desired local chemical order is formed. This revolutionary breakthrough has been made possible by considering the materials as a system and thereby utilizing chemical modifiers and the principles of disorder and local order, pioneered by Stanford R. Ovshinsky (one of the instant inventors), in such a way as to provide the necessary catalytic local order environments, such as surfaces and at the same time designing bulk characteristics for storage and high rate charge/discharge cycling. In other words, these principles allow for tailoring of the material by controlling the particle and grain size, topology, surface states, catalytic activity, microstructure, and total interactive environments for storage capacity.
The earliest work at atomic engineering of hydrogen storage materials is disclosed by Stanford R. Ovshinsky (one of the present inventors) in U.S. Pat. No. 4,623,597 (“the '597 patent”), the contents of which are incorporated by reference. Ovshinsky, described disordered multicomponent hydrogen storage materials for use as negative electrodes in electrochemical cells for the first time. In this patent, Ovshinsky describes how disordered materials can be tailor made to greatly increase hydrogen storage and reversibility characteristics. Such disordered materials are formed of one or more of amorphous, microcrystalline, intermedia
Huang Baoquan
Ovshinsky Stanford R.
Young Rosa T.
Energy Conversion Devices Inc.
Mau II Frederick W.
Schumaker David W.
Siskind Marvin S.
Weiner Laura
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