Membrane electrode unit for electrochemical equipment

Abstract

The invention concerns a membrane electrode unit (MEU) for electrochemical equipment, especially for membrane fuel cells. The membrane electrode unit has a “semi-coextensive” design and contains an ionically conductive membrane, two catalyst layers, and gas distributor substrates of different sizes on the front and back sides. The first gas distributor substrate has smaller surface dimensions than the ionically conductive membrane, while the second gas distributor substrate has the same area as the ionically conductive membrane. The membrane electrode unit has, because of its special design, a stable structure that can be handled well, and which exhibits advantages for sealing the reactive gases off from each other and in its electrical properties. In particular, the hydrogen penetration current is distinctly reduced. The membrane electrode unit is used in PEM fuel cells, direct methanol fuel cells, electrolyzers, and other electrochemical equipment.

Description

BACKGROUND OF THE INVENTION [0001] The invention concerns the technological field of electrochemistry and describes a membrane electrode unit (“MEU”) for electrochemical equipment such as fuel cells (membrane fuel cells, PEMFC [polymer electrolyte membrane fuel cells], DMFC; etc.), electrolyzers, or electrochemical sensors. A process for producing the membrane electrode unit, and its use, are also described. [0002] Fuel cells convert a fuel and an oxidizing agent, located apart from each other at two electrodes, into electrical current, heat and water. The fuel can be hydrogen or a hydrogen-rich gas. The oxidizing agent can be oxygen or air. The process of energy conversion in the fuel cell is distinguished by a particularly high efficiency. Because of that, fuel cells combined with electrical motors are gaining importance as alternatives for the usual combustion engines. [0003] The polymer electrolyte fuel cell (PEM fuel cell) is particularly suitable for use in electric automobile...

AI Technical Summary

Benefits of technology

[0018] Therefore, it was the objective of the present invention to provide a membrane electrode unit, which overcomes the disadvantages of the state of the art and, in particular, proves to be a better design concept.

Problems solved by technology

Membrane electrode units (MEUs) with projecting membrane edges are, however, susceptible to mechanical damage in production and assembly.

Such damages easily result in failure of the cell because the membrane must separate the gas spaces for the reactive gases, hydrogen and oxygen, from each other.

Membrane damage occurs particularly easily if very thin membranes (i.e., to 25 μm thickness) are used.

That causes problems in MEU production, especially for continuous processes.

Enclosing the MEU and subsequent compression can result in failure of the cell in case of damage or perforation of the membrane.

On cutting or separating the MEUs and in other subsequent process steps, there is a danger of the electrodes being short-circuited (by fibers from the gas distributor substrate, for instance).

This means that short circuits and failures can often occur in production of MEUs by the coextensive design.

The gas-tight seal between the reactive oxygen (or air) and hydrogen is another problem in the coextensive design.

That is scarcely possible because of the fine pores in the gas distributor substrates and catalyst layers.

That results in lowering of the open cell voltage (OCV) and, because of that, in a lower electrical capacity of the MEU.

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