Chemistry: electrical current producing apparatus – product – and – With pressure equalizing means for liquid immersion operation
Patent
1994-10-13
1997-07-08
Kalafut, Stephen
Chemistry: electrical current producing apparatus, product, and
With pressure equalizing means for liquid immersion operation
429 27, 429 41, 429 50, H01M 1208
Patent
active
056459521
DESCRIPTION:
BRIEF SUMMARY
The object of the invention is a method for storing and producing electrical energy in the type of electrochemical cell, where the cathode is a porous air electrode which takes oxygen from the ambient air, or to which oxygen is supplied by other means, and the anode is a hydrogen-containing metal hydride, and according to which method the hydrogen stored in the metal hydride anode and acting as fuel is oxidized through an electrolytic solution with oxygen supplied to the air electrode.
The prior art comprises fuel cells in which hydrogen gas is supplied to a negative electrode, that is, anode, and oxygen which is either pure or contained in air, is supplied to a positive electrode, that is, cathode. In the cell's overall reaction, the only reaction products formed in addition to electrical energy are water and some heat. The advantage of fuel cells is good efficiency and unpolluted reaction products. Their use is, however, limited for example in traffic applications, by the handling and storability of gaseous hydrogen.
The prior art also comprises so-called metal air cells, having a metal such as zinc, iron or aluminium as the anode, and an air electrode as the cathode. In these cells, the metal becomes oxidized and dissolves in the electrolyte. The advantage of the cells is a high energy density, and the disadvantages are e.g. self-discharging, that is, corrosion of the metal when at rest, and the gradual passivation of the surface of the metal. Prior art is represented by e.g. the following patents and patent applications: Sweden no. 358772 (H01M 4/86), WO 88/02931 (H01M 8/18), Norway no. 883432 (H01M 8/12), Norway no. 156469 (H01M 8/12) and European patent no. 0124275 (H01M 8/18).
The prior art is further represented by porous, gas-permeable air electrodes, or oxygen electrodes. The disadvantage of these solutions is, however, that the pressure of the electrolytic solution with respect to the ambient air cannot be significantly increased due to leaks. It is known to situate the catalyst layer on the surface against the electrolyte. The known materials used in air electrodes include highly electroconductive carbon, for example, so-called carbon black, Teflon as binder, and platinum, silver or different compounds such as cobolt tetraporphyrine as the catalyst. The prior art appears, for example, from the patents and patent applications DE-3332625 A1 (H01M 4/86), DE-3400022 A1 (H01M 4/86), DE-3632701 A1 (H01M 4/86), DE-3722019 A1 (H01M 4/86), DT-2547491 (H01M 4/86), DT-2556731 A1 (H01M 4/86), DE-3331699 A1 (H01M 4/86), U.S. Pat. No. 4,877,694 (H01M 4/86), Norway no. 802635 (H01M 4/86), U.S. Pat. No. 4,927,718 (H01M 4/86), and Sweden no. 324819 (H01M 4/86). These electrodes are sometimes called hybride electrodes --especially in connection with metal air cells--which is not the same as hydride electrodes, which are explained in greater detail below. The prior art of the air electrodes called hybride electrodes appears e.g. from the publications DE-2658520 A1 (H01M 4/86), DT-2611291 A1 (H01M 4/86), and DT-2455431 A1 (H01M 4/86).
It is also known to store hydrogen in different metals, metal alloys, and other compounds, which are collectively called hydrides. Hundreds of compounds which are able to absorb large amounts of hydrogen into themselves are known. With the different compounds, hydrogen absorption amounts of different magnitudes are achieved, and their equilibrium pressures --that is, the partial pressure of hydrogen in gas--depend on the composition of the hydride and on the temperature. Depending on the compound, the hydrogen absorption amounts of hydrides are typically of the order of 1-10% by weight, and the equilibrium pressures at room temperature are of the order of 0.1-10 bar. For example the LaNi.sub.5 H.sub.6 hydride and its different modifications such as LaNi.sub.2.5 Co.sub.2.4 Al.sub.0.1 and MmNi.sub.3.5 Co.sub.0.7 Al.sub.0.8 have been much studied. The capacity of the hydrides and the prior art appear, for example, from the patents and patent applications DT-2003749 (C01B 6/00), U.S. Pat
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Fomino Marina
Lamminen Jaakko
Lampinen Markku
Viitanen Minna
Kalafut Stephen
Lampinen Markku
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