Chemistry: electrical current producing apparatus – product – and – With pressure equalizing means for liquid immersion operation
Patent
1997-08-27
2000-01-04
Nuzzolillo, Maria
Chemistry: electrical current producing apparatus, product, and
With pressure equalizing means for liquid immersion operation
429 41, 429 44, 429 33, H01M 822
Patent
active
060107987
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a fuel cell with a proton-conducting membrane, on which catalyst material and a collector are arranged on both sides.
Fuel cells are used for electrochemical conversion of chemical energy, in particular in the form of gaseous hydrogen and oxygen, into electrical energy. Of the large number of known types, so-called PEM fuel cells (PEM=polymer-electrolyte membrane) are preferred, for example for mobile use. The advantages of fuel cells of this type reside in a comparatively low operating temperature (up to about 100.degree. C.), in the absence of a corro-sive liquid electrolyte, in the stability with respect to carbon dioxide (CO.sub.2) and, finally, in a relatively simple mechanical structure. In addition to the cell housing, cooling units or separators, gas supply or distribution means and means for constructing fuel cell stacks from individual elements, PEM fuel cells actually consist essentially of two gas-permeable, porous, electrically conductive collectors on the anode and cathode sides, which are next to the solid-electrolyte membrane.
Between the collector and the membrane, there is in each case a catalyst in finely divided, catalytically active form, for example platinum or a platinum alloy. One side of the fuel cell is supplied with a combustible gas in particular hydrogen or a hydrogen-containing gas, and the other side is supplied with an oxidant, in particular oxygen or an oxygen-containing gas, such as air. Hydrogen is oxidized at the anode, protons being produced which diffuse through the membrane to the oxygen side; in this case, water is generally entrained with them (so-called drag effect). At the cathode, the protons recombine with reduced oxygen to form water, referred to as product water, which is removed in suitable fashion from the fuel cell.
Through the drag effect, water is drawn from the anode side of the membrane, so that this side dries out and therefore loses its function if not enough water is added. Further problems are the high costs for production of the membrane, and the lack of cost-efficient processes for producing membrane/electrode units with a low level of catalyst coating and high power density, in particular for operation with air at close to atmospheric pressure. Indeed, for relatively thick membranes, the ohmic losses have a power-reducing effect.
Technical solutions for fuel cells are already known (see, for example, DE-A 33 21 984 and EP-A 0 560 295). The gas-permeable, electron-conducting layers, that is to say collectors, used in this case are carbon paper (U.S. Pat. No. 4,215,183) and carbon fabric ("J. Appl. Electrochem.", Volume 22 (1992), pages 1 to 7); metal structures may also be considered (DE-A 42 06 490). The proton-conducting membranes used are perfluorinated sulfonated polymers such as nafion, raymion and permion ("Ber. Bunsenges. Phys. Chem.", Volume 94 (1990), pages 1008 to 1014). For the sake of convenience, the layer thickness of the membranes is between 50 and 200 .mu.m. Important properties of the membranes are heat-resistance (up to about 100.degree. C.), reduction and oxidation stability, resistance to acid and hydrolysis, sufficiently low electrical resistivity (<10 .OMEGA..multidot.cm) with ion conduction (H.sup.+) at the same time, low hydrogen or oxygen permeation and freedom from pin-holes. At the same time, the membranes should be as hydrophilic as possible in order, through the presence of water, both to ensure proton conduction and (by reversed diffusion of water to the anode) to prevent the membrane from drying out and therefore to prevent a reduction in the electrical conductivity. In general, properties of this type are achieved with materials which have no aliphatic hydrogen-carbon bonds, which, for example, is achieved by replacing hydrogen by fluorine or by the presence of aromatic structures; the proton conduction results from the incorporation of sulfonic acid groups (high acid strength).
The electrodes, that is to say the catalyst layers arranged between the collectors
REFERENCES:
patent: 4215183 (1980-07-01), MacLeod
patent: 4649091 (1987-03-01), McElroy
patent: 4678724 (1987-07-01), McElroy
patent: 5242764 (1993-09-01), Dhar
patent: 5399184 (1995-03-01), Harada
patent: 5672439 (1997-09-01), Wilkinson et al.
Wilson, M. et al., High Performance Catalyzed Membranes of Ultra-low Pt Loadings for Polymer Electrolyte Fuel Cells, Journal of the Electrochemical Society, vol. 139, No. 2 (1992), pp. L28-L30.
Lu Xianping, et al., "Thermal and electrical conductivity of monolithic carbon aerogels," Journal of Applied Physics, vol. 73 (1993), pp. 581-584.
Yasuda, K. et al., "Polymerization-Pressure Dependencies of Properties of Perfluorosulfonate Cation-Exchanger Thin Films by Plasma Polymerization," Ber. Bunsenges. Phys. Chem. 98 (1994), No. 4, pp. 631-635.
Uchimoto, Y. et al., "Thin Cation-Exchanger Films by Plasma Polymerization of 1,3-Butadiene and Methyl Benzenesulfonate," Journal of Electrochemical Society, vol. 138 (1991), pp. 3190-3193.
Scherer, G., "Polymer Membranes for Fuel Cells," Berichte der Bunsengesellschaft fur Physikalische Chemie, Bd. 94 (1990), pp. 1008-1014.
Wilson, M.. et al., "Thin-film catalyst layers for polymer electrolyte fuel cell electrodes," Journal of Applied Electrochemistry, vol. 22 (1992), pp. 1-7.
Extended Abstracts, vol. 93/1 (1993), p. 40, Abstract No. 31.
Chemical Abstracts, vol. 119, No. 6 (1993), Abstract No. 52795h.
Domke Wolf-Dieter
Hammerschmidt Albert
Nolscher Christoph
Suchy Peter
Nuzzolillo Maria
Siemens Aktiengesellschaft
Weiner Laura
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