JP4512946B2 - Coolant composition for fuel cell - Google Patents

Description

  The present invention relates to a coolant composition used for cooling a fuel cell, particularly an automobile fuel cell, and more particularly to a coolant composition for a fuel cell that has low conductivity and excellent thermal characteristics.

The fuel cell receives the supply of a fuel gas containing hydrogen on the anode side and the supply of an oxidizing gas containing oxygen on the cathode side, thereby causing an electrochemical reaction (H ₂ + (1/2) O ₂ → H ₂ O) is an apparatus that obtains an electromotive force.

  As described above, the fuel cell directly converts chemical energy of the fuel supplied to the fuel cell into electric energy, and is known as a device having very high energy efficiency.

  However, since the electrochemical reaction is an exothermic reaction, heat is generated and released to the outside when the fuel cell is operated. For this reason, the fuel cell is required to have a configuration for removing heat generated during operation of the fuel cell and maintaining the operating temperature of the fuel cell within a predetermined temperature range.

  A fuel cell is generally configured as a multi-layer stack structure in which single cells and separators, which are power generation units, are alternately stacked. A flow path of a predetermined shape is formed in the stack structure, and cooling is performed in the flow path. By circulating the water, heat generated with the progress of the electrochemical reaction was removed by the cooling water, and the operating temperature of the fuel cell was kept within a predetermined range.

  Conventionally, as a fuel cell having such a structure, cooling water is circulated through a flow path formed in the stack structure of the fuel cell to cool the stack, and the cooling water heated by cooling the stack is used as a radiator, etc. It is known that the cooling water is cooled in the heat exchange section and the cooled cooling water is supplied again to the flow path in the fuel cell (see, for example, JP-A-6-188013).

  However, the temperature of the cooling water discharged from the stack of the fuel cell is as low as about 60 to 90 ° C., whereas the external environment temperature around the heat exchange section such as a radiator is about 20 to 40 ° C. Since the temperature difference from the temperature of the water is small, the heat dissipation efficiency of the heat exchanging part such as a radiator is poor, and the heat exchanging area of the heat exchanging part has to be widened in order to sufficiently exhaust heat. For this reason, there has been a problem that a large heat exchange section must be installed in the fuel cell system.

  On the other hand, since the coolant of the fuel cell flows directly through the flow path of the stack that is generating power and directly cools the stack, if the electrical conductivity of the coolant is high, the electricity generated in the stack is This causes a problem that the electricity flows to the side and loses electricity to reduce the power generation in the fuel cell.

  For this reason, pure water having low conductivity, in other words, high electrical insulation, was used as the conventional fuel cell coolant to prevent leakage to the outside of the stack.

  However, in the case of an intermittent operation type fuel cell such as a fuel cell for an automobile, for example, the coolant is lowered to the ambient temperature when it is not operated. In particular, when there is a possibility of use below freezing point, there is a possibility that the battery performance of the fuel cell is impaired, such as freezing in pure water and damage to the cooling plate due to volume expansion of the coolant.

  Under such circumstances, it is conceivable to use glycols, alcohols, glycol ethers or the like as a base for the coolant of a fuel cell, particularly an automobile fuel cell, for the purpose of antifreezing.

  However, glycols, alcohols, glycol ethers, and the like have inferior thermal properties compared to water, and in particular have a property of low thermal conductivity.

  For this reason, when the coolant based on these is used, it is difficult for the coolant to take away the heat generated from the inside of the stack. Since efficiency also worsens, there existed a problem that the heat exchange part with a large thermal radiation area had to be installed.

  On the other hand, in order to increase the thermal conductivity of a heat medium or the like, a method for improving the heat transfer performance of the heat medium itself by adding fine particles of metal or metal oxide having high heat conductivity to the heat medium is known. (See, for example, Transaction of the ASME, Journal of Heat Transfer 121, p280, 1999, US Patent No. 6,221,275B1, or WO01 / 98431A1).

However, these technologies do not consider low conductivity, which is important as a coolant for fuel cells. Therefore, when the technology is applied as it is to a coolant composition for fuel cells, it becomes conductive by long-term use. Could cause increased sex.
In light of the above technical problem, the present inventors have conducted extensive research on a fuel cell coolant composition that has low electrical conductivity and excellent thermal characteristics, and as a result, has completed the present invention.

  That is, an object of the present invention is to provide a fuel cell coolant composition having low electrical conductivity and excellent thermal characteristics.

  Hereinafter, the fuel cell coolant composition of the present invention (hereinafter simply referred to as the composition) will be described in more detail. The composition of the present invention relates to a coolant composition used for cooling a fuel cell, in particular, a fuel cell for an automobile, and any one of copper oxide, aluminum oxide, titanium oxide in the base, or these It contains metal oxide fine particles made of a mixture.

  As the base, one kind selected from glycols, alcohols and glycol ethers having low electrical conductivity (preferably 50 μS / cm or less) and non-freezing (performance not to freeze even at 0 ° C. or less) or A base comprising two or more bases or one or two or more bases selected from glycols, alcohols and glycol ethers and water can be mentioned.

  Examples of glycols include one selected from ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,3-propanediol, 1,3-butanediol, 1,5-pentanediol, and hexylene glycol, or The thing which consists of 2 or more types can be mentioned.

  Examples of alcohols include one or more selected from methanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol, and octanol.

  Examples of glycol ethers include ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, triethylene glycol monomethyl ether, tetraethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monoethyl ether, triethylene glycol monoethyl ether, tetraethylene glycol monomethyl ether. Examples thereof include one or more selected from ethyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, and tetraethylene glycol monobutyl ether.

  As the water, ion-exchanged water or distilled water having low conductivity is used.

  As the metal oxide fine particles, copper oxide, aluminum oxide, titanium oxide, or a mixture thereof can be used. By containing the fine particles of these metal oxides, the composition of the present invention absorbs heat generated with the progress of the electrochemical reaction in the stack structure due to the high thermal conductivity of the fine particles, and highly efficient exhaustion. Heat will be made.

As the metal oxide fine particles , those having an average particle diameter of 0.001 to 0.1 μm are used . If the average particle size is less than 0.001 μm, sufficient thermal properties, particularly thermal conductivity, cannot be provided to the composition, and if the average particle size is greater than 0.1 μm, This will cause adverse effects such as poor dispersibility.

Metal oxide fine particles are contained in a proportion of 0.1 to 15% by weight. When the content of the metal oxide fine particles is less than 0.1% by weight, sufficient thermal characteristics, in particular, thermal conductivity cannot be provided to the composition, and the content of the metal oxide fine particles is 15% by weight. If it exceeds 50%, the effect of the increase in the content cannot be expected, which is uneconomical.

  Further, since the metal oxide fine particles have a small average particle size of 0.001 to 0.1 μm, they are relatively stably dispersed. However, in order to further stabilize, the low conductivity of the composition is not increased. In addition, a fine particle dispersant can be contained within a range where it can be maintained at a low conductivity, preferably 50 μS / cm or less. Examples of the fine particle dispersant include an anionic surfactant, a cationic surfactant, and a nonionic surfactant.

  Examples of the anionic surfactant include carboxylate, sulfonate, sulfate ester salt, phosphate ester salt, etc. In addition, low molecular weight compounds and polymer type compounds are also used as the anionic surfactant. be able to. Examples of nonionic surfactants include polyoxyethylene alkylphenol ether, polyoxyethylene alkyl ether, and polyoxyethylene fatty acid ester.

  In addition to the above surfactants, polymer dispersants such as tripolyphosphate, fine particle dispersants such as cellulose ethers such as methylcellulose and carboxymethylcellulose, and water-soluble polymers such as polyvinyl alcohol are also included in the composition. The low conductivity can be contained in a range that can be maintained at a low conductivity, preferably 50 μS / cm or less without increasing the low conductivity.

  The composition of the present invention may further contain a rust preventive additive. The anticorrosive additive is not particularly limited, and a conventionally known anticorrosive additive can be used. When added to the base, the conductivity of the composition is low, preferably 50 μS. It is more desirable to maintain the fluctuation of conductivity within the range of 0 to 10 μS / cm even when used for a long period of time.

  As such a rust preventive additive, a substance that suppresses the oxidation of the base and prevents an increase in the conductivity of the coolant composition, or blocks ions that elute in the coolant system, and the coolant composition Mention may be made of substances that prevent an increase in the electrical conductivity of the object.

  Examples of substances that suppress the oxidation of the base and prevent an increase in conductivity include phenolsulfonic acid, chlorophenol, nitrophenol, bromophenol, aminophenol, dihydroxybenzene, oxine, hydroxyacetophenone, methoxyphenol, 2, 6-di-tert-butyl-p-cresol, tert-butyl-4-methoxyphenol, 2,6-di-tert-butyl-4-ethylphenol, 4,4-butylidenebis- (3-methyl-6-tert -Butylphenol), 2,2-methylenebis- (4-methyl-6-tert-butylphenol), phenol compounds composed of one or more selected from 2,2-bis (p-hydroxyphenyl) propane be able to.

  Examples of the substance that blocks ions and prevents the increase in conductivity include hydrocarbon carbonyl compounds, amide compounds, imide compounds, and diazole compounds.

  Examples of the hydrocarbon carbonyl compound include 2,4-pentanedione, 3-methyl-2,4-pentanedione, 3-ethyl-2,4-pentanedione, 3-propyl-2,4-pentanedione, 3- n-butyl-2,4-pentanedione, 2,3-heptanedione, 2,5-hexanedione, phthalaldehyde, benzaldehyde, dihydroxybenzaldehyde, pentanone, 2-acetylcyclopentanone, cyclohexanone, cyclohexanedione, 2,2 , 6,6-tetramethyl-3,5-heptanedione, or one or more selected from the group consisting of 2,6-heptanedione.

  Examples of the amide compound include one or more selected from benzamide, methylbenzamide, nicotinic acid amide, picolinic acid amide, anthranilamide, succinic acid amide, oxalic acid diamide, acetamide, 2-pyrrolidone, and caprolactam. Things can be mentioned.

  Examples of the imide compound include those composed of one or more selected from succinimide, phthalic imide, maleic imide, glutaric imide, 1,8-naphthalimide, alloxan, and purpuric acid. Can do.

  Examples of the diazole compound include imidazoline, 1,3-diazole, mercaptoimidazoline, mercaptoimidazole, benzimidazole, mercaptobenzimidazole, methylimidazole, dimethylimidazole, imidazole-4,5-dicarboxylic acid, 1,2-diazole, methylpyrazole. The thing which consists of 1 type, or 2 or more types chosen from among these can be mentioned.

  As content of a rust preventive additive, it is desirable to set it as the range of 0.001-10.0 weight% with respect to a base. When the content of the rust preventive additive is less than the above range, sufficient rust preventive power cannot be obtained, and when the content of the rust preventive additive is larger than the above range, only the increased amount is obtained. The effect of is not obtained, it becomes uneconomic.

  Hereinafter, the composition of the present invention will be described in more detail with reference to Examples. As shown in Table 1 below, as a preferred example of the composition of the present invention, a composition based on ethylene glycol and ion-exchanged water with 5% aluminum oxide having an average particle size of 30 nm added is used for oxidation. The thing which does not add aluminum was used as a comparative example.

  For each of the compositions of Examples and Comparative Examples shown in Table 1, the initial conductivity (μS / cm), the conductivity after the durability test (μS / cm), and the thermal conductivity (W / mK) were measured. The results are shown in Table 2. Regarding the measurement of the conductivity after the durability test, the temperature of the coolant for cooling the fuel cell is usually about 80 ° C., but the durability test was conducted at 120 ° C. for the purpose of acceleration, and the conductivity after 168 hours was measured. The rate was measured.

  From Table 2, the compositions of the examples not only have low initial conductivity, but also the conductivity after the endurance test is small compared to the comparative example and excellent in low conductivity. Was confirmed. Further, when the thermal conductivities were compared, an increase in thermal conductivity of about 10% was confirmed by the addition of aluminum oxide fine powder. From the above, it was confirmed that the compositions according to the examples of the present invention have low electrical conductivity and excellent thermal characteristics.

  The present invention includes, for example, an antifoaming agent, a colorant and the like within a range that can be maintained at a low conductivity, preferably 50 μS / cm or less without increasing the low conductivity of the composition. Can be freely implemented within the range described in the above.

Claims (2)

A low-conductivity coolant composition for cooling a fuel cell,
A base composed of one or more selected from glycols, alcohols and glycol ethers, or one or more selected from glycols, alcohols and glycol ethers and water. A ratio of 0.1 to 15% by weight of fine particles having an average particle diameter of 0.001 to 0.1 μm of a base containing and a metal oxide made of any of copper oxide, aluminum oxide, and titanium oxide, or a mixture thereof A coolant composition for a fuel cell, comprising: The coolant composition for fuel cells according to claim 1, further comprising a rust preventive additive.