CN1840582A - Electrolyte for fuel cell, membrane electrode assembly, and method for producing electrolyte for fuel cell - Google Patents

Abstract

The invention provides an electrolyte for a fuel cell, which is characterized in that the electrolyte for a fuel cell contains a basic polymer and an organic phosphonic acid represented by general formula (1), and the electrolyte for a fuel cell containing a basic polymer can suppress acid Dimensional changes before and after addition reduce the occurrence of wrinkles, etc. In the formula, R represents an alkyl group, an aryl group, an acyl group, an amino group, a phosphono group or a derivative of these functional groups, and n is 1 or 2.

Description

Electrolyte for fuel cell, membrane electrode assembly, and method for producing electrolyte for fuel cell

technical field

The present invention relates to a fuel cell, and in particular, to an electrolyte membrane for a fuel cell and a membrane-electrode assembly that can be used in a fuel cell that can operate in a non-humidified state.

Background technique

A solid polymer fuel cell using a solid polymer membrane as an electrolyte is known. A solid polymer fuel cell uses a proton-conducting polymer electrolyte membrane as an electrolyte, and generally includes an anode (fuel electrode), a cathode (oxidant electrode), and a polymer electrolyte membrane disposed between the anode and the cathode. A catalyst layer for promoting oxidation of fuel is provided on the anode of the solid polymer fuel cell, and a catalyst layer for promoting reduction of an oxidizing agent is provided at the cathode of the solid polymer fuel cell.

As the fuel supplied to the anode of the solid polymer fuel cell, hydrogen, hydrogen-containing gas, mixed vapor of methanol and water, methanol aqueous solution, and the like are generally used. As the oxidizing agent supplied to the cathode of the solid polymer fuel cell, oxygen, oxygen-containing gas, or air can generally be used.

As a material for the polymer electrolyte membrane, a sulfonate perfluorinated polymer having a main chain composed of a fluorinated olefin and a fluorinated fluorinated polymer containing a sulfonic acid group at the end can generally be used. Side chains made of vinyl ethers. Such a polymer electrolyte membrane exhibits sufficient ion conductivity when generating electricity by impregnating an appropriate amount of water.

Therefore, in the conventional polymer electrolyte fuel cell, it is necessary to manage the water content of the polymer electrolyte membrane, leading to the complexity and size of the fuel cell system.

In order to avoid the problem of moisture management caused by the polymer electrolyte membrane, as a method to replace the conventional polymer electrolyte membrane, a non-humidification electrolyte membrane that can conduct protons in a non-humidification state has been developed.

For example, Patent Document 1 discloses materials such as polybenzimidazole doped with phosphoric acid as a non-humidifying polymer electrolyte membrane.

[Patent Document 1] JP-A-11-503262

Contents of the invention

The problem to be solved by the invention

When phosphoric acid is incorporated into a basic polymer film such as polybenzimidazole, the basic polymer film causes dimensional changes due to the hygroscopicity of phosphoric acid. In addition, phosphoric acid is emitted from the basic polymer film due to its hygroscopicity. As a result, the shrinkage of the basic polymer film and the wrinkling of the basic polymer film are caused. Therefore, special environmental equipment such as a drying room is required for storage of the produced basic polymer membrane, membrane-electrode assembly, or stack assembly, resulting in problems such as difficulty in production and increase in production cost.

Summary of the invention

The present invention has been made in view of such problems, and an object of the present invention is to provide an electrolyte for fuel cells containing an alkaline polymer that can suppress dimensional changes before and after addition of acid, and can cause less wrinkles. Another object of the present invention is to provide a membrane electrode assembly having improved gas diffusibility, the membrane electrode assembly using a fuel cell electrolyte containing a basic polymer.

means of solving problems

One aspect of the present invention is an electrolyte for a fuel cell. The fuel cell electrolyte is characterized by containing a basic polymer and an organic phosphonic acid represented by the following general formula (1).

[chemical formula 1]

In the formula, R represents an alkyl group, an aryl group, an acyl group, an amino group, a phosphono group or a derivative of these functional groups, and n is 1 or 2.

Accordingly, it is possible to obtain a fuel cell electrolyte having a proton conductivity equivalent to that of conventional fuel cell electrolytes and suppressing dimensional changes and wrinkles.

In the fuel cell electrolyte of the above scheme, the basic polymer is preferably selected from polybenzimidazoles, poly(pyridines), poly(pyrimidines), polyimidazoles, polybenzothiazoles, polybenzoxazoles , polyoxadiazoles, polyquinolines, polyquinoxalines, polythiadiazoles, poly(tetrazopyrenes), polyoxazoles, polythiazoles, polyvinylpyridines and polyvinyl Choose from imidazoles. In addition, in the fuel cell electrolyte of the above aspect, the basic polymer may further contain poly-2,5-benzimidazole.

In the fuel cell electrolyte of the above aspect, the basic polymer may also be cross-linked. Thereby, the strength of the basic polymer increases, and the fuel cell electrolyte is less likely to shrink.

In the fuel cell electrolyte of the above aspect, the organic phosphonic acid is preferably selected from ethyl phosphonate, methyl phosphonate, and octyl phosphonate. In addition, the organic phosphonic acid may be an organic phosphonic acid represented by the following general formula (2).

[chemical formula 2]

In the formula, R' represents an alkyl group, an aryl group, an acyl group, an amino group, a phosphono group or a derivative of these functional groups, and m is 1 or 2.

In the fuel cell electrolyte of the above aspect, phosphoric acid may be added in an amount of 800 mol% or less, preferably 200 mol% or less, based on the above-mentioned basic polymer. Thereby, moisture absorption by phosphoric acid can be suppressed, and the rate of rise of the unit cell voltage can be increased.

The water content of the fuel cell electrolyte of the above aspect may be 20% or less. In addition, the definition of moisture content will be described later. In addition, the expansion and contraction ratio of the electrolyte for the above-mentioned fuel cell may be 20% or less. In addition, the definition of the scaling ratio will be explained later.

Another aspect of the present invention is a membrane electrode assembly. This membrane electrode assembly is characterized in that it has any one of the above fuel cell electrolytes, an anode bonded to one surface of the fuel cell electrolyte, and a cathode bonded to the other surface of the fuel cell electrolyte, In addition, at least one of the anode and the cathode contains the organic phosphonic acid represented by the above general formula (1).

Therefore, by using an electrolyte for a fuel cell whose proton conductivity is at the same level as that of a conventional fuel cell electrolyte and which can suppress dimensional changes or wrinkles, special facilities such as a drying room are not required for manufacturing a membrane-electrode assembly. , so the manufacturing cost can be reduced. In addition, by adding an organic phosphonic acid to at least one of the anode and the cathode, the interface resistance between the electrode (anode and/or cathode) and the fuel cell electrolyte can be reduced, and gas diffusivity can be improved.

In this membrane electrode assembly, at least one of the anode and the cathode may contain an organic phosphonic acid selected from ethyl phosphonate, methyl phosphonate, and octyl phosphonate.

In this membrane electrode assembly, the total amount of the organic phosphonic acid contained in the fuel cell electrolyte, the organic phosphonic acid contained in the anode, and the organic phosphonic acid contained in the cathode may be based on the basic polymer 100 to 800 mol% of the standard.

Another aspect of the present invention is a membrane electrode assembly. The membrane electrode assembly is characterized by comprising any one of the fuel cell electrolytes described above, an anode bonded to one face of the fuel cell electrolyte, and a cathode bonded to the other face of the fuel cell electrolyte, and, At least one of the anode and the cathode contains a hydrolyzable phosphoric acid compound represented by the following general formula (3).

[chemical formula 3]

In the formula, R represents an alkyl or alkoxyalkyl group, and n is 1 or 2.

Therefore, by using an electrolyte for a fuel cell whose proton conductivity is at the same level as that of a conventional fuel cell electrolyte and which can suppress dimensional changes or wrinkles, special facilities such as a drying room are not required for manufacturing a membrane-electrode assembly. , so the manufacturing cost can be reduced. In addition, by adding a phosphoric acid compound to at least one of the anode and the cathode, the interface resistance between the electrode (anode and/or cathode) and the fuel cell electrolyte can be reduced, and gas diffusivity can be improved.

In this membrane electrode assembly, at least one of the anode and the cathode may contain a phosphoric acid compound selected from ethyl phosphate, methyl phosphate, butyl phosphate, oleyl phosphate, and dibutyl phosphate.

In addition, in the membrane electrode assembly, at least one of the anode and the cathode may contain a phosphoric acid compound selected from monoethyl phosphate, monomethyl phosphate, mono-n-butyl phosphate, and mono-n-octyl phosphate.

In addition, in this membrane electrode assembly, the total amount of the organic phosphonic acid contained in the fuel cell electrolyte, the phosphoric acid compound contained in the anode, and the phosphoric acid compound contained in the cathode may be based on the basic polymer 5 to 800 mol% of the standard.

Still another aspect of the present invention is a method for producing an electrolyte for a fuel cell. The method for producing an electrolyte for a fuel cell is characterized by comprising a step of forming a film of a basic polymer and a step of impregnating the basic polymer in an aqueous solution in which an organic phosphonic acid represented by the general formula (3) is dissolved.

In the method for producing an electrolyte for a fuel cell, the organic phosphonic acid can be selected from ethyl phosphonate, methyl phosphonate, and octyl phosphonate.

Description of drawings

FIG. 1 is a diagram schematically showing a TG graph used for calculating a water content.

Fig. 2 is a graph showing time changes in water content measured in Example 1 and Comparative Example 1 stored at 22° C. and 62% RH after adding an acid by the above water content evaluation method.

FIG. 3 is a graph showing the results of measuring the open-loop voltage and the change in unit cell resistance with time for the fuel cell electrolyte of Example 2 at 150° C. under non-humidified conditions.

FIG. 4 is a graph showing current-voltage characteristics of Example 2 and Comparative Example 2. FIG.

FIG. 5 is a graph showing current-voltage characteristics of Example 3 and Comparative Example 2. FIG.

6 is a graph showing shrinkage characteristics obtained by TMA measurement of the fuel cell electrolytes of Example 1 and Example 4. FIG.

7 is a graph showing measurement results of cell voltage rise characteristics of fuel cells using the fuel cell electrolytes of Examples 1 and 5. FIG.

Detailed ways

(implementation 1)

The fuel cell electrolyte according to this embodiment contains a basic polymer and an organic phosphonic acid represented by the following general formula (4).

[chemical formula 4]

In the formula, R represents an alkyl group, an aryl group, an acyl group, an amino group, a phosphono group or a derivative of these functional groups, and n is 1 or 2.

(basic polymer)

The basic polymer is preferably selected from polybenzimidazoles, poly(pyridines), poly(pyrimidines), polyimidazoles, polybenzothiazoles, polybenzoxazoles, polyoxadiazoles, polyquinolines Classes, polyquinoxalines, polythiadiazoles, poly(tetrazopyrenes), polyoxazoles, polythiazoles, polyvinylpyridines and polyvinylimidazoles. As the polybenzimidazoles, for example, poly-2,5-benzimidazole can be used.

The basic polymer is preferably crosslinked by a crosslinking agent. Basic polymers can be cross-linked to increase the strength of electrolytes for fuel cells and suppress shrinkage. The crosslinking agent is not particularly limited as long as it is suitable for the above-mentioned crosslinking reaction of the basic polymer. As an example of a crosslinking agent, a urethane crosslinking agent is mentioned.

(organic phosphonic acid)

The organic phosphonic acid is preferably selected from ethyl phosphonate, methyl phosphonate, octyl phosphonate. The organic phosphonic acid impregnated in the fuel cell electrolyte is preferably 100 mol % or more based on the basic polymer. When the added amount of the organic phosphonic acid is less than 100 mol % based on the basic polymer, functions such as proton conductivity in the electrolyte for a fuel cell will decrease.

In addition, as the organic phosphonic acid, an organic phosphonic acid represented by the following general formula (5) can be used.

[chemical formula 5]

In the formula, R' represents an alkyl group, an aryl group, an acyl group, an amino group, a phosphono group or a derivative of these functional groups, and m is 1 or 2.

For example, the following compound (6) represents HEDP (hydroxyethane diphosphonic acid) when m=1 and R′=CH ₃ in the above general formula (5). HEDP is available from Nippon Chemical Industry Co., Ltd. under the trade name Defrock EH06 (60% aqueous solution of HEDP).

[chemical formula 6]

In addition, the fuel cell electrolyte according to the present embodiment has a stretch rate determined by a stretch rate evaluation method described later to be 20% or less, preferably 10% or less.

The electrolyte for a fuel cell according to this embodiment uses an organic phosphonic acid that lacks water absorption as the acid added to the basic polymer, so it has the characteristics of little dimensional change before and after the addition of the organic phosphonic acid, and is less prone to wrinkling.

In addition, the fuel cell electrolyte according to the present embodiment is obtained by impregnating a basic polymer in an aqueous organic phosphonic acid solution. Therefore, the moisture content of the organic phosphonic acid gradually decreases over time after impregnation, in the drying process, in the process of assembling it into a fuel cell, and in the process of using it as a product. After being assembled in a fuel cell as a product, the water content of the electrolyte for fuel cells is almost zero in the end when it is operated under normal conditions such as 150°C and non-humidification.

(Moisture content evaluation method)

The water content of the fuel cell electrolyte is explained below.

First, thermogravimetry (TG) is performed on the organic phosphonic acid itself added to the basic polymer, and the temperature T1 at which the mass of the organic phosphonic acid rapidly decreases due to decomposition or dehydration is grasped. If the temperature T1 is about 150°C or higher, it can be confirmed that the mass loss up to around 100°C is not related to the organic phosphonic acid, but is caused by the evaporation of water contained in the sample for the sample whose water content is to be measured. In addition, it was confirmed that the mass of each of the above-mentioned organic phosphonic acids does not decrease sharply up to 160°C.

Next, the TG measurement is performed on the sample to be measured for the moisture content. Fig. 1 schematically shows a TG diagram for calculating the water cut. In FIG. 1 , the mass change at a temperature of about 100° C. is not related to organic phosphonic acid, but is caused by evaporation of water contained in the sample. The mass change around temperature T1 is caused by decomposition or dehydration of organic phosphonic acid. The masses W1, W2 at the inflection points S1, S2 corresponding to the mass change around the temperature T1 are measured, respectively. The moisture content is calculated|required by the calculation formula of moisture content=(W1-W2)/W1*100.

In addition, the temperatures corresponding to the inflection points S1 and S2 are preferably determined by differential thermogravimetry (DTG). In DTG, since the positions of the inflection points S1, S2 appear as peaks, the mass at the inflection points S1, S2 can be determined from the peak positions of the DTG.

(Evaluation method of stretch rate)

The calculation method of the stretching ratio S of the fuel cell electrolyte is explained below. The stretch rate S can be obtained by the formula of S=(Y-X)/X*100(%). Here, X represents the length of a predetermined side of the fuel cell electrolyte before the organic phosphonic acid is added to the basic polymer, and Y represents the fuel cell electrolyte at any time after the organic phosphonic acid is added to the basic polymer. The specified side length of the electrolyte.

In addition, various additives may be added to the fuel cell electrolyte of Embodiment 1. For example, in the fuel cell electrolyte of Embodiment 1, phosphoric acid may be added in an amount of 800 mol% or less, more preferably 200 mol% or less, based on the basic polymer. By setting the amount of phosphoric acid added to 800 mol% or less based on the basic polymer, moisture absorption due to phosphoric acid can be suppressed, and the rate of increase in cell voltage can be increased. Furthermore, by setting the amount of phosphoric acid added to 200 mol% or less based on the basic polymer, moisture absorption due to phosphoric acid can be further suppressed, and the increase rate of cell voltage can be increased. On the contrary, when the amount of phosphoric acid added exceeds 800 mol % based on the basic polymer, the moisture absorption suppression effect due to the addition of organic phosphonic acid decreases, and the dimensional change of the fuel cell electrolyte becomes significant.

(implementation 2)

The membrane electrode assembly of the present embodiment is obtained by bonding an anode to one surface of the fuel cell electrolyte and bonding a cathode to the other surface of the fuel cell electrolyte.

The membrane-electrode assembly of this embodiment is characterized in that at least one of the anode and the cathode contains the organic phosphonic acid represented by the above general formula (4). In the membrane electrode assembly of the present embodiment, since the proton conductivity is at the same level as that of conventional fuel cell electrolytes, and the fuel cell electrolyte that can suppress dimensional changes and wrinkles, etc. is used, it is not necessary to manufacture the membrane electrode assembly. On the other hand, special equipment such as a drying room is required, so that the manufacturing cost can be reduced. By adding an organic phosphonic acid to at least one of the anode and the cathode, the interface resistance between the electrode and the fuel cell electrolyte can be reduced and the gas diffusivity can be improved.

The anode or cathode to which the organic phosphonic acid is added can be obtained by drying at 80° C. for 120 minutes after coating the organic phosphonic acid on the anode or cathode. In addition, the drying temperature and drying time can be appropriately changed.

The organic phosphonic acid contained in at least one of the anode and the cathode is preferably selected from ethyl phosphonate, methyl phosphonate, and octyl phosphonate.

In the membrane electrode assembly of the present embodiment, the total amount of the organic phosphonic acid contained in the fuel cell electrolyte, the organic phosphonic acid contained in the anode, and the organic phosphonic acid contained in the cathode is preferably the above-mentioned 100-800 mol% of the basic polymer.

When the total amount of organic phosphonic acid is in the range of 100 to 800 mol% of the basic polymer, sufficient proton conductivity can be obtained under power generation conditions, so the necessary amount of organic phosphonic acid may be small. Therefore, the manufacturing cost of the membrane electrode assembly can be reduced.

When organic phosphonic acid is added to both the anode and the cathode, it is preferable that the amount of organic phosphonic acid added to the anode is larger than the amount of organic phosphonic acid added to the cathode.

Thereby, the interface resistance between the electrode and the fuel cell electrolyte can be further reduced, and the gas diffusivity can be further improved.

(Embodiment 3)

The membrane electrode assembly of the present embodiment is obtained by bonding an anode to one surface of the fuel cell electrolyte and bonding a cathode to the other surface of the fuel cell electrolyte.

The membrane electrode assembly of this embodiment is characterized in that at least one of the anode and the cathode contains a phosphoric acid compound represented by the following general formula (7). In the membrane electrode assembly of the present embodiment, since the proton conductivity is at the same level as that of conventional fuel cell electrolytes, and the fuel cell electrolyte that can suppress dimensional changes and wrinkles, etc. is used, it is not necessary to manufacture the membrane electrode assembly. On the other hand, special equipment such as a drying room is required, so that the manufacturing cost can be reduced. By adding a phosphoric acid compound to at least one of the anode and the cathode, the interface resistance between the electrode and the fuel cell electrolyte can be reduced and gas diffusivity can be improved.

[chemical formula 7]

In the formula, R represents an alkyl or alkoxyalkyl group, and n is 1 or 2.

The anode or cathode to which the phosphoric acid compound is added can be obtained by drying at 80° C. for 120 minutes after coating the phosphoric acid compound on the anode or cathode. In addition, the drying temperature and drying time can be appropriately changed.

The phosphoric acid compound contained in at least one of the anode and the cathode is preferably selected from ethyl phosphate, methyl phosphate, butyl phosphate, oleyl phosphate, and dibutyl phosphate.

In addition, the phosphoric acid compound contained in at least one of the anode and the cathode is preferably selected from monoethyl phosphate, monomethyl phosphate, mono-n-butyl phosphate, and mono-n-octyl phosphate.

In addition, the phosphoric acid compound contained in at least one of the anode and the cathode is preferably butoxyethyl phosphate.

In the membrane electrode assembly according to the present embodiment, the total amount of the organic phosphonic acid contained in the fuel cell electrolyte, the organic phosphonic acid contained in the anode, and the organic phosphonic acid contained in the cathode 5 to 800 mol% of the basic polymer is preferable.

Example

(Example 1)

Next, a production method in the case of using polybenzimidazole (PBI) as the basic polymer and monoethyl phosphate as the organic phosphonic acid as a typical fuel cell electrolyte of the present invention will be described.

First, PBI (20%) was dissolved in dimethylacetamide containing LiCl (2%). The PBI solution was poured on a glass plate to make a PBI film.

Next, in a beaker, 0.13 g (0.00042 mol) of the PBI film was immersed in a 40% ethyl phosphonate solution (solvent: water) at room temperature for 2 hours. The ethyl phosphonate solution was maintained at 60°C with a hot water bath. Then, the PBI film was taken out, and the remaining solvent adhering was removed by wiping with a cloth to prepare an electrolyte for a fuel cell. The mass after dipping was 0.22 g. As will be described later, since the water content of the fuel cell electrolyte of this example is almost 0, the mass of ethyl phosphonate added is approximately 0.09 g (0.00081 mol). From this result, it was found that the doping rate (dup rate) of ethyl phosphonate was 192 mol% based on PBI.

(comparative example 1)

For comparison with Example 1, an electrolyte for a fuel cell obtained by adding phosphoric acid to PBI was prepared.

After producing a PBI film in the same manner as in Example 1, 0.15 g (0.00049 mol) of the PBI film was immersed in an 85% phosphoric acid solution in a beaker at room temperature for 24 hours. Then, the PBI film was taken out, and the remaining solvent adhering was removed by wiping with a cloth to prepare an electrolyte for a fuel cell. The mass after dipping was 0.58 g. From this result, it can be seen that the doping rate of phosphoric acid is 900 mol% based on PBI.

(Evaluation result of moisture content)

Fig. 2 is a graph showing time changes in water content measured in Example 1 and Comparative Example 1 stored at 22° C. and 62% RH after adding an acid by the above water content evaluation method.

It can be seen that the fuel cell electrolyte of Comparative Example 1 has an increase in water content over time due to the hygroscopicity of phosphoric acid. In Comparative Example 1, the water content reached 25% after adding phosphoric acid for 9 hours. In addition, in Comparative Example 1, moisture in the air was absorbed by the fuel cell electrolyte, resulting in volume expansion of the fuel cell electrolyte, and a phenomenon in which phosphoric acid overflowed out of the fuel cell electrolyte was confirmed. From this, it can be inferred that the total mass of phosphoric acid and PBI decreased with the passage of time in the fuel cell electrolyte of Comparative Example 1.

On the other hand, in Example 1, there was almost no change in weight even if left in the atmosphere, so it was confirmed that the above-mentioned problems were solved.

(Evaluation result of expansion ratio)

Table 1 shows the expansion and contraction ratios before and after adding monoethyl phosphate and phosphoric acid to the fuel cell electrolytes of Example 1 and Comparative Example 1, respectively. The conditions after adding the acid were to stand at 22° C. and 62% RH for 9 hours. It can be seen that in the case of Comparative Example 1, the expansion and contraction rate was as high as 25%, and wrinkles were likely to occur. In order to assemble the membrane electrode assembly or stack, special measures such as the use of a drying room were required. On the other hand, in Example 1, the expansion and contraction rate was suppressed to 6%, and no dimensional change or occurrence of wrinkles was found.

Table 1 Scalability (%) Example 1 6 Comparative example 2 25

(Example 2)

A membrane electrode assembly was produced by bonding an anode to one surface of the fuel cell electrolyte obtained in Example 1, and bonding a cathode to the other surface. HT140E-W manufactured by E-TEK Co., Ltd. was used for the anode and the cathode. In order to reduce the interfacial resistance between the electrolyte membrane and the electrodes, ethyl phosphonate was added on the surface of the anode and cathode. The amount of ethyl phosphonate added to the anode and cathode was 200 mol % based on PBI.

(comparative example 2)

A membrane electrode assembly was produced by bonding an anode to one surface of the fuel cell electrolyte obtained in Example 1, and bonding a cathode to the other surface. HT140E-W manufactured by E-TEK Co., Ltd. was used for the anode and the cathode. In order to reduce the interfacial resistance between the electrolyte membrane and the electrodes, 105% by weight phosphoric acid was added to the surface of the anode and cathode. The amount of phosphoric acid added to the anode and cathode was 800 mol% based on PBI.

(Measurement result of proton conductivity)

The electrolytes for fuel cells obtained in Example 2 and Comparative Example 2 were respectively assembled in fuel cell cells, and the proton conductivity was measured. The temperature of the fuel cell during proton conductivity measurement was 150° C., and the flow rates of hydrogen and air were 100 (NCCM) and 200 (NCCM), respectively. In addition, the area of the electrode for the fuel cell was 7.8 cm ² .

As a result, the proton conductivity of Comparative Example 2 was 7×10 ^-2 S/cm, whereas the proton conductivity of Example 2 was 6×10 ^-2 S/cm, and the proton conductivity of Example 2 was confirmed. On the same level as Comparative Example 2.

(open-loop voltage, cell resistance versus time)

Fig. 3 is a graph showing the results of measuring the open-loop voltage and cell resistance over time for the membrane electrode assembly of Example 2 at 150°C under non-humidified conditions. In the fuel cell electrolyte of Example 2, good results were confirmed, such as no decrease in open-loop voltage or increase in cell resistance, when 2000 hours or more passed.

(Measurement results of current-voltage characteristics)

The membrane electrode assemblies obtained in Example 2 and Comparative Example 2 were respectively assembled in fuel cells, and the current-voltage characteristics were measured under non-humidified conditions. The temperature of the fuel cell during the measurement of the current-voltage characteristics was 150° C., and the flow rates of hydrogen and air were 100 (NCCM) and 200 (NCCM), respectively. In addition, the area of the electrode for the fuel cell was 7.8 cm ² .

FIG. 4 is a graph showing current-voltage characteristics of Example 2 and Comparative Example 2. FIG. The load capable of generating a cell voltage of 0.3 (V) or more was 0.8 A/cm ² in Comparative Example 2, whereas it was increased to 1.0 A/cm ² in Example 2. It can be seen that In Example 2, gas diffusivity was improved.

It is presumed that the reason is that phosphoric acid is a complete liquid, so it has high mobility, and it is difficult to maintain the three-phase interface formed by the catalyst, reaction gas, and electrolyte due to the progress of wetting. On the contrary, ethyl phosphonate has low mobility, The three-phase interface is easily maintained.

(Example 3)

The membrane electrode assembly of Example 3 can be produced by using HEDP instead of ethyl phosphonate in the same procedure as in Example 1. The fuel cell electrolyte junction can be produced in the same procedure as in Example 1 by using HEDP instead of ethyl phosphonate. obtained between the anode and cathode. Among them, the doping rate of HEDP in the fuel cell electrolyte was 240 mol % based on the PBI position. In addition, the doping ratios of HEDP in the anode and the cathode were 150 mol % and 90 mol %, respectively.

The current-voltage characteristics of the membrane electrode assembly of Example 3 were measured under the same measurement conditions as those of the membrane electrode assembly of Example 2. FIG. 5 is a graph showing current-voltage characteristics of Example 3 and Comparative Example 2. FIG. In the membrane electrode assembly of Example 3, similarly to Example 2, the load capable of generating a predetermined cell voltage was greater than that of Comparative Example 2. That is, the membrane electrode assembly of Example 3 exhibited better gas diffusibility than that of Comparative Example 2.

(Shrinkage test results of electrolytes for fuel cells)

The shrinkage characteristics of fuel cell electrolytes caused by the presence or absence of crosslinking of basic polymers were tested using a thermomechanical analysis apparatus (TMA). Specifically, after the sample was heated to 150°C, a compressive load was applied to the sample at a rate of 18kgfcm ^-2 /hr, and the compressive load was controlled to be constant after the compressive load reached 18kgfcm ^-2 . After the load is applied, the shrinkage characteristics of the sample are obtained by measuring the position change of the probe. As samples, the fuel cell electrolytes of Example 1 described above and Example 4 described later were used.

(Example 4)

The fuel cell electrolyte of Example 4 has ethyl phosphonate added to cross-linked PBI.

The fuel cell electrolyte of Example 4 was prepared in the same manner as in Example 1 except that PBI crosslinked with a crosslinking agent was used.

6 is a graph showing shrinkage characteristics obtained by TMA measurement of the fuel cell electrolytes of Example 1 and Example 4. FIG. It can be seen that when the PBI is an uncrosslinked fuel cell electrolyte (Example 1), as the compression load increases, the shrinkage proceeds rapidly, and after the compression load reaches a certain value, it still shrinks slowly. On the contrary, when the PBI is a cross-linked fuel cell electrolyte (Example 4), it can be seen that as the compression load increases, the shrinkage proceeds more slowly than in Example 1, but when the compression load reaches a certain value, the shrinkage progresses almost stop. That is, by crosslinking PBI, the shrinkage of the fuel cell electrolyte is reduced.

(Measurement results of the rise characteristics of the cell voltage)

The fuel cell electrolytes of Example 1 and Example 5 described later were respectively assembled into fuel cell units, and under non-humidification conditions, the output voltage was measured with the current density kept constant (0.3A/cm ² ). time changes. The temperature of the fuel cell when the output voltage was measured was 150° C., and the flow rates of hydrogen and air were 100 (NCCM) and 200 (NCCM), respectively. In addition, the area of the electrode for the fuel cell was 7.8 cm ² .

In addition, HT140E-W manufactured by E-TEK Co., Ltd. was used as the anode and cathode bonded to the fuel cell electrolyte membranes of Examples 1 and 5.

(Example 5)

The fuel cell electrolyte of Example 5 differs from Example 1 in that phosphoric acid is added to the fuel cell electrolyte containing PBI and ethyl phosphonate. The doping ratios of ethyl phosphonate and phosphoric acid in the fuel cell electrolyte of Example 5 are based on PBI, and both are 100 mol%. In the fuel cell electrolyte of Example 5, after the addition sequence of ethyl phosphonate in the preparation sequence of the fuel cell electrolyte shown in Example 1, 85% phosphoric acid solution was dispersed, and after doping with 100 mol% phosphoric acid, it was heated at 120° C. obtained by drying for 2 hours.

7 is a graph showing measurement results of cell voltage rise characteristics of fuel cells using the fuel cell electrolytes of Examples 1 and 5. FIG. It can be seen that the fuel cell using the fuel cell electrolyte of Example 5 not only increases the unit cell voltage at the same time as compared with Example 1, but also shortens the rise time when the unit cell voltage reaches a certain value. As a result, the fuel cell can be shipped earlier, and the time required to manufacture the fuel cell can be shortened, thereby reducing the manufacturing cost.

Claims (18)

1. An electrolyte for a fuel cell, characterized in that it contains an alkaline polymer and an organic phosphonic acid represented by the following general formula (1), [chemical 1] In the formula, R represents an alkyl group, an aryl group, an acyl group, an amino group, a phosphono group or a derivative of these functional groups, and n is 1 or 2. 2. The fuel cell electrolyte according to claim 1, wherein the above-mentioned basic polymer is selected from the group consisting of polybenzimidazoles, poly(pyridines), poly(pyrimidines), polyimidazoles, polybenzothiazoles Classes, polybenzoxazoles, polyoxadiazoles, polyquinolines, polyquinoxalines, polythiadiazoles, poly(tetrazopyrenes), polyoxazoles, polythiazoles, poly Vinylpyridines and polyvinylimidazoles. 3. The fuel cell electrolyte according to claim 1, wherein the basic polymer contains poly-2,5-benzimidazole. 4. The fuel cell electrolyte according to claim 1, wherein the basic polymer is cross-linked. 5. The fuel cell electrolyte according to claim 1, wherein said organic phosphonic acid is selected from ethyl phosphonate, methyl phosphonate and octyl phosphonate. 6. according to the fuel cell electrolyte of claim 1 record, it is characterized in that, above-mentioned organic phosphonic acid represents with following general formula (2): In the formula, R' represents an alkyl group, an aryl group, an acyl group, an amino group, a phosphono group or a derivative of these functional groups, and m is 1 or 2. 7. The fuel cell electrolyte according to claim 1, wherein phosphoric acid is added in an amount of 800 mol% or less based on the basic polymer. 8. The fuel cell electrolyte according to claim 1, wherein the water content is 20% or less. 9. The fuel cell electrolyte according to claim 1, wherein the expansion and contraction ratio is 20% or less. 10. A membrane electrode assembly comprising the fuel cell electrolyte according to claim 1, an anode bonded to one face of the fuel cell electrolyte, and an anode bonded to the other face of the fuel cell electrolyte. on the cathode, characterized in that, At least one of the anode and the cathode contains an organic phosphonic acid represented by the general formula (1). 11. The membrane electrode assembly according to claim 10, wherein at least one of the anode and the cathode contains an organic phosphonic acid selected from ethyl phosphonate, methyl phosphonate, and octyl phosphonate. 12. The membrane electrode assembly according to claim 10, wherein the amount of the organic phosphonic acid contained in the fuel cell electrolyte, the amount of the organic phosphonic acid contained in the anode, and the organic phosphonic acid contained in the cathode The total amount of the amount is 100 to 800 mol% based on the above-mentioned basic polymer. 13. A membrane electrode assembly comprising the fuel cell electrolyte according to claim 1, an anode bonded to one face of the fuel cell electrolyte, and an anode bonded to the other face of the fuel cell electrolyte. The cathode on above is characterized in that at least one of the above-mentioned anode and the above-mentioned cathode contains a hydrolyzable phosphoric acid compound represented by the following general formula (3), In the formula, R represents an alkyl or alkoxyalkyl group, and n represents 1 or 2. 14. The membrane-electrode assembly according to claim 13, wherein at least one of the anode and the cathode contains a compound selected from ethyl phosphate, methyl phosphate, butyl phosphate, oleyl phosphate, and dibutyl phosphate. of phosphoric acid compounds. 15. The membrane-electrode assembly according to claim 13, wherein at least one of said anode and said cathode contains a compound selected from monoethyl phosphate, monomethyl phosphate, mono-n-butyl phosphate, and mono-n-octyl phosphate. of phosphoric acid compounds. 16. The membrane electrode assembly according to claim 13, wherein the amount of the organic phosphonic acid contained in the fuel cell electrolyte, the amount of the phosphoric acid compound contained in the anode, and the amount of the phosphoric acid compound contained in the cathode are The total amount of the amount is 5 to 800 mol% based on the above-mentioned basic polymer. 17. A method for manufacturing an electrolyte for a fuel cell, characterized in that it has: a step of forming a basic polymer into a film, and A step of impregnating the above-mentioned basic polymer in an aqueous solution in which the organic phosphonic acid represented by the above-mentioned general formula (1) is dissolved. 18. The method for producing an electrolyte for a fuel cell according to claim 17, wherein the organic phosphonic acid is selected from ethyl phosphonate, methyl phosphonate, and octyl phosphonate.

Images