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AssigneeSgl Carbon SE
InventorsPeter Wilde, Michael Maendle, Heiko Leinfelder, Josef Steinhart
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This invention relates to electrode substrates for electrochemical cells, particularly low-temperature fuel cells, and processes for their production. Low-cost carbon fiber paper structures are used as precursor for preparation of an all-carbon product that has a high electric conductivity and porosity and can be processed in a continuous reel-to-reel mode. These paper materials are further impregnated and processed to adjust the final product properties. This all-carbon electrode substrate is not brittle thereby avoiding the main disadvantage of the prior art.
A carbon fiber electrode substrate comprising a paper made from carbon fibers, wherein the carbon fibers employed have a diameter of from about 6 to about 10 μm, and a mean length of from about 3 to about 20 mm, wherein at least a part of the voids between the fibers constituting the paper are filled with carbonaceous particles, which carbonaceous particles comprise particles of graphite and of other forms of elemental carbon, wherein the thickness of the paper is from 0.05 to 0.4 mm, and wherein the bending radius to which the paper can be subjected without breaking is 250 mm or more.
A process for the production of carbon fiber electrode substrates, comprising the steps of
A process for the production of carbon fiber electrode substrates, comprising the steps of
Dependencies are inferred from the claim text.
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Inert electrodes with catalytic activity, e.g. for fuel cells: porous electrodes
Treating the starting powders individually or as mixtures: curing of mixtures
Obtained by reactions only involving carbon-to-carbon unsaturated bonds: halogen-containing polymers, e.g. PVC
Burning or sintering processes: reaction sintering of free metal- or free silicon-containing compositions
Term end not estimated
The invention relates to electrode substrates for electrochemical cells, particularly Polymer Electrolyte Membrane Fuel Cells (PEMFC) and Phosphoric Acid Fuel Cells (PAFC), and processes for their production.
A fuel cell converts a fuel such as hydrogen, and an oxidant, typically oxygen or air, via electrochemical reactions into electricity, reaction products and excess heat. As shown in FIG. 1, a single fuel cell 1 is typically constituted of an electrolyte layer e.g. a proton-conducting polymer membrane 2, sandwiched between two typically flat porous electrodes 3 and 4, individually referred to as the anode and the cathode. The electrodes 3 and 4 are comprised of reactant-permeable electron-conducting substrates 3′ and 4′ with the surfaces adjacent to the electrolyte covered with thin porous active layers 3″ and 4″ containing the electrocatalysts typically comprising metals from the platinum group.
Oxidation of hydrogen at the anode catalyst layer 3″ generates protons and electrons. The protons are transferred across the electrolyte to the cathode. The electrons travel via an external circuit to the cathode. At the cathode catalyst layer 4″, oxygen is reduced by consumption of two electrons per atom to form oxide anions which react with the protons that have crossed the electrolyte layer to form water.
FIG. 1 is an exploded side view of a single cell showing the structure of a phosphoric acid, or a membrane, fuel cell, viz., a flat plate electrode fuel cell where the electrode substrate of the present invention can be applied.
FIG. 2 is a side view (cross-section) of an ES with a pore size gradient according to this invention.
FIG. 3 is a side view (cross-section) of an ES with a property gradient perpendicular to the planar direction according to this invention.
For the sake of clarity only a few of the carbon fibers constituting the paper have been shown in FIGS. 2 and 3.
It is preferred that the carbon fiber electrode substrate has a mass fraction of carbon in the form of carbon fibers and carbonaceous particles is at least about 94%.
It is further preferred that the carbon fiber electrode substrate has a porosity, stated as the ratio of the open volume to the sum of the open volume, the volume occupied by the carbon fibers, and the volume occupied by all solid materials comprising fillers, of at least 80%.