Fuel cell and fuel cell coolant compositions

Abstract

This invention is directed to coolant compositions, particularly coolant compositions useful n fuel cells, and to fuel cells containing such coolant compositions. The coolant compositions or heat transfer fluids of this invention have and retain low electrical conductivity through extended periods of use. These coolant or heat transfer fluids are composed of a base composition and an additive package which imparts the property of retaining low electrical conductivity for extended periods of time. The base composition can be de-ionized water (DI water) alone or a mixture of DI water and a freezing point depressant of the types well-known in the art (e.g., propylene glycol). The additive package contains an organic corrosion inhibitor and a polymeric ion suppressant. The use of both components of the additive package is important.

Description

CROSS-REFERENCE TO RELATED APPLICATION [0001] This application is a divisional of co-pending U.S. patent application Ser. No. 10 / 282,351 filed Oct. 30, 2002.FIELD OF THE INVENTION [0002] The invention relates to the field of heat transfer processes. Specifically, the invention concerns heat transfer fluids or coolants for use in the cooling of a fuel cell stack. More specifically, the invention relates to heat transfer fluid compositions comprising blends containing (1) de-ionized water, (2) a freezing point depressant, (3) an organic corrosion inhibitor, and (4) a polymeric ion suppressant specifically selected to react with both positive (cations) and negative ions (anions). BACKGROUND OF THE INVENTION [0003] A fuel cell generates electrical power by converting the chemical energy of a fuel continuously into electrical energy by way of an electrochemical reaction, silently, without combustion. Fuel cells typically utilize hydrogen as the fuel and oxygen (usually from air) as the o...

AI Technical Summary

Benefits of technology

[0020] Generally, the corrosion inhibitors previously suggested for use in coolants are ionic in nature. The corrosion inhibitor of this invention, however, is organic in nature (and generally non-ionic). Illustrative of such organic materials are azoles, aromatic hydroxy compounds, and amines. Examples of suitable azoles include benzotriazole, tolyriazole, methyl benzotriazoles (e.g., 5-methyl-1H-benzotriazole), mercaptobenzoimidazole (e.g., 2-mercaptobenzoimidazole), and mercaptobenzothiazole. Similarly, suitable aromatic hydroxy compounds include salicylaldoxime, salicyl alcohol, methyl gallate, propyl gallate, octyl gallate, and dodecyl gallate. Further, suitable amines preferably include alcohol amines, for example, monoethanol amine, diethanol amine, triethanol amine, and morpholine. These organic corrosion inhibitors can be used alone or in combination with each other. It is believed that these are well known corrosion inhibitors function by providing a surface film to prevent exposure of the materials of the cell and cell stack to the coolant composition.

Problems solved by technology

However, resistivity decreases with time because DI water easily picks up ions from metals and other sources.

In addition, water freezes at 0° C. thus making DI water alone unsuitable for use in colder places.

Unfortunately, the typical ethylene glycol and propylene glycol based automotive antifreezes are very conductive to electricity due to the presence of salt based corrosion inhibitors normally employed in such products.

Furthermore, glycols tend to form glycolic acid causing corrosion of metal components which ultimately increases the electrical conductivity of the coolant.

Hydrocarbon and silicone based fluids while having some of the desirable characteristics of a fuel cell coolant are flammable and not compatible with commonly used gaskets and hose materials such as silicone and ethylene propylenediene monomer (EPDM).

Typically employed fluorocarbons, such as hydrofluoro ethers (HFEs) and perfluorinated fluoroethers have many good properties for a fuel cell coolant, but the cost of fluorinated compounds is very high and generally makes their use in fuel cell applications (particularly civilian applications) prohibitively expensive.

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