Solid State Hydrogen Pumping and Storage Material

This invention relates to hydrogen storage systems and more particulary to a solid-state hydrogen storage system.

Hydrogen gas is attractive as a fuel for use in transportation systems because it has the highest density of energy per unit weight of any fuel and is non-polluting. Present methods of storing hydrogen are suitable for industrial uses but are inappropriate for use in transportation systems. Accordingly, systems for storing and pumping hydrogen are an important subject of research and development.

Hydrogen storage in solid materials, referred to as solid state storage hereinafter, is being developed as an alternative to more standard methods of storage such as storage in compression tanks. A great advantage of solid-state storage is the achievement of storage densities several times that of liquid hydrogen. Additionally, hydrogen stored in a solid is relatively safe to handle without the normal problems of fire and explosion.

Heretofore, most of the solid materials utilized for hydrogen storage have been crystalline solids. A major problem with those materials has been the high pressure required to overcome the surface energy barrier of the material in order to force hydrogen into the bulk thereof. Additional problems with crystalline materials include the requirement of high temperatures for discharging stored hydrogen from the solid materials and surface poisoning in the presence of atmospheric gases that reduces absorption and discharge rates.

Accordingly, an object of the present invention is to provide a solid-state hydrogen storage material that does not require high pressure for efficient absorbtion or high temperature for efficient discharge.

A further object of the present invention is to provide a solid-state hydrogen material that is not impaired by atmospheric exposure and that does not discharge hydrogen at room temperature.

The above and other objects are achieved in the present invention which comprises a layer of an amorphous binary alloy of a lanthanide and iron, nickel or cobalt disposed on a suitable substrate and overcoated with a palladium metal layer. The present invention absorbs hydrogen at low pressures, resists surface poisoning, stores hydrogen at room temperature, and discharges hydrogen by heating the storage material to a relatively moderate temperature.

FIG. 1 is a cross-sectional view of a solid-state hydrogen storage material.

FIG. 2 is a schematic diagram of a hydrogen pumping system.

Referring to the Figure, the solid-state hydrogen storage material of the present invention is depicted. A storage layer of an amorphous binary metal alloy 10 is deposited on a substrate 12. The amorphous alloy is overcoated with a layer of palladium metal (Pd) 14.

Briefly, the hydrogen is absorbed through the palladium overcoat 14 and stored in the storage layer 10. The palladium overcoat 14 increases the absorption rate dramatically while inhibiting surface poisoning.

Suitable substrates for the storage layer include glass and plastic. The nature of the substrate is not critical to the invention because the amorphous alloy adheres to most surfaces. One particulary promising substrate is a thin plastic sheet, such as Mylar, that provides a very large surface area that can be enclosed in a small volume by folding the plastic sheet.

The amorphous binary metal alloy is composed of a lanthanide and either iron, nickel, or cobalt. The layer 10 of amorphous alloy may be deposited on the substrate by electron beam co-deposition at room temperature and with vacuum pressure in the 10.sup.-6 to 10.sup.-7 Torr range. However, any method of simultaneous, in vacuum deposition of the iron, nickel, or cobalt and lanthanide components of the amorphous alloy onto the substrate can be utilized. The overcoating of palladium may be similarly applied.

Actual tests were conducted employing a storage layer of an amorphous gadolinium-iron alloy (a-GdFe). The storage material was exposed to various gases including air. It was discovered that after such exposure a-GdFe without a palladium overcoat did not absorb hydrogen for pressures up to several thousand microns. However, a-GdFe overcoated with only 30 Angstroms of palladium absorbed hydrogen at a rapid rate, even after exposure to air. This high absorption rate was demonstrated at room temperature. Palladium overcoats of only 10 Angstroms were found to be effective.

The palladium overcoated a-Gd Fe storage layer demonstrated resistance to surface layer poisoning by atmospheric gases and the ability to absorb hydrogen at pressures below 100 microns.

Although absorption takes place at room temperature subsequent heating to 80.degree. C. is sufficient to discharge most of the hydrogen from the alloy. Complete discharge of hydrogen is achieved at 180.degree. C. The hydrogen absorption and discharge rates were verified by resistivity, magnetization, x-ray and ferromagnetic resonance measurements.

The thickness of the a-Gd Fe layer was varied from 1,000 Angstroms up to 35,000 Angstroms. It was found that for thicknesses above 35,000 Angstroms the storage layer would separate from the substrate due to expansion caused by hydrogen absorption.

The ratio of gadolinium to iron in the amorphous alloy is variable. Effective operation of Pd overcoated a-Gd Fe was obtained for gadolinium to iron ratios ranging from 2 to 1 (30% Fe) to 1 to 9 (90% Fe).

As stated above, the solid-state storage material absorbs hydrogen gas, at room temperature and at pressures below 100 microns. Thus, the storage material is ideally suited for use in high-vacuum hydrogen pumping systems. A hydrogen pumping system utilizing the present invention is depicted in FIG. 2.

Turning now to FIG. 2, a vacuum chamber 20 is connected by a flange 22 to a pumping chamber 24 with multi-turn sheets of the storage material siutated therein. If the temperature of the storage material 26 is below 80.degree. C. rapid absorption of hydrogen by the storage material will pump the hydrogen gas from the vacuum chamber 20.

The pumping capability of the storage material will decrease as it becomes saturated with hydrogen. However, the storage material may be reactivated by heating the storage material above 80 C. and flushing the pumping system with nitrogen or some other gas.

The above-described properties of a GdFe have also been observed for storage layers fabricated of either amorphous terbium-iron or dysprosium-iron alloys.

It is predicted that the properties described above for an embodiment of the invention with a storage layer of amorphous gadolinium iron alloy will also be present when any lanthanide is substituted for gadolinium. Basis for this prediction is the known hydrogen absorption properties of crystalline lanthanide-iron alloys and the observed increase in hydrogen absorbtion rates and resistance to surface poisoning of palladium overcoated alloys. Several tests have been performed that support the validity of the predicted utility of amorphous lanthanide iron alloys. As stated above, tests were conducted utilizing storage layers fabricated of amorphous terbium-iron and dysprosium-iron alloys. The deposition techniques, storage layer and palladium overcoat thicknesses, and lanthanide to iron ratios were the same as described above for an a-GdFe storage layer. The high absorption rate and storage capability at room temperature observed for a-GdFe was also observed for amorphous terbium-iron and dysprosium-iron alloys.

It is also predicted that cobalt and nickel may be substituted for iron. Basis for the prediction is the known hydrogen absorbtion properties of crystalline lanthanide-cobalt and lanthanide-nickel alloys.

The constituents of the amorphous binary alloy selected for a particular application will be determined by practical factors such as cost and availability.

Obviously, numerous (additional) modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.