TW201419645A - Proton exchange membrane and its membrane electrode assembly for high temperature fuel cells - Google Patents

Abstract

Provided is a proton exchange membrane adapted for used in a high temperature proton exchange membrane fuel cell operated at 150 DEG C to 250 DEG C. The proton exchange membrane contains phosphoric acid doped polybenzimidazole (PBI) and metal phosphates. The metal phosphates are selected from the group consisting of titanium phosphates, antimony phosphates, and a combination of the two.

Description

Proton exchange membrane and membrane electrode set for high temperature fuel cells

The present invention relates to a proton exchange membrane, and in particular to a proton exchange membrane having phosphorylated polybenzimidazole (PBI) and a metal phosphate, and a membrane electrode assembly having such a proton exchange membrane.

A fuel cell (FC) is a power generation device that converts chemical energy into electrical energy. Fuel cells have the advantages of low pollution, low noise, high energy density and high energy conversion efficiency. They are highly developed clean energy conversion equipment. Various types of fuel cells have different application markets depending on their operating principles and operating environment. Proton exchange membrane fuel cells and direct methanol fuel cells are two important types of fuel cells, both of which are based on the use of proton exchange membranes for electrochemical reactions. A device that obtains electrical energy.

In the conventional fuel cell technology, a fuel cell using a Nafion membrane as an electrolyte is considered to be the most suitable as a mobile power source, and a Nafion-based electrolyte is a tetrafluoroethylene-based copolymer polymer compound which is below 80 ° C. In the working environment, it has excellent proton conductivity, and its conductivity is similar to that of dilute hydrochloric acid. However, a proton exchange membrane using a Nafion-based electrolyte needs to be used in a high-humidity environment to achieve such a high proton conductivity. If the humidity is insufficient, the membrane dehydrates and the proton conductivity rapidly decreases, and the membrane is increased. The impedance of the electrode group, together with the battery power Decreased, energy conversion efficiency is reduced, and even partial membrane damage. Therefore, in order to match such electrolytes, a humidifier is often required in a fuel cell system, and a humidifier generally accounts for a relatively large proportion of the equipment cost of the battery.

In addition, carbon poisoning is also a common problem in fuel cells. Taking a hydrogen proton exchange membrane fuel cell as an example, the anode reaction is usually based on Pt as a catalyst to catalyze the decomposition of hydrogen into protons, and the cathode reaction is the reduction of oxygen into water. Due to the high price of high-purity hydrogen fuel and low storage density, in order to reduce fuel costs and increase the energy density of storage, it is generally desirable to use a lower purity hydrogen fuel, even a liquid methanol or ethanol fuel, but whether it is liquid hydrocarbon The compound, or the recombined syngas fuel, has the problem of poisoning carbon monoxide, that is, the presence of carbon monoxide impurities in the hydrogen fuel occupies the activation site on the catalytic catalyst Pt and reduces the ability of the Pt to catalyze the reaction.

Based on the aforementioned problems, the current development of fuel cell technology has a tendency to increase the operating temperature. The reason is that in a high temperature environment (for example, 150 ° C to 250 ° C), evaporation of moisture is rapid, and it is difficult and impractical to control the environment to high humidity, so that the setting of the humidifier becomes unnecessary. However, we still need to find a membrane material that can quickly conduct protons at high temperatures as an electrolyte. Higher operating temperatures also allow carbon monoxide to be more readily desorbed from Pt to allow the fuel to contain higher carbon impurities, thereby increasing the flexibility of the fuel that can be used. Furthermore, since the reaction rate is high at high temperatures, it is even possible to use a cheaper catalyst in addition to Pt. In view of this, the development of proton exchange membranes for high temperature environments has become the current fuel. One of the important ways to improve battery technology.

The invention provides a proton exchange membrane which can maintain good proton conduction ability under high temperature environment (150 ° C ~ 250 ° C).

The present invention provides a membrane electrode assembly suitable for fabricating a fuel cell that can operate in a high temperature environment.

The present invention provides a proton exchange membrane for use in a fuel cell, the proton exchange membrane comprising phosphorylated polybenzimidazole and a metal phosphate. The metal phosphate is selected from the group consisting of titanium phosphates, phosphonium phosphates, and combinations thereof.

In one embodiment of the invention, the metal phosphate is present in an amount of from 5 wt% to 50 wt%, based on the total weight of the proton exchange membrane.

In an embodiment of the invention, the metal phosphate may contain a dopant species, and the dopant species is selected from the group consisting of ruthenium, osmium, iron, osmium, iridium, and magnesium.

The present invention provides a membrane electrode assembly for a fuel cell, the membrane electrode assembly comprising a proton exchange membrane, an anode catalyst layer and a cathode catalyst layer as described above. The proton exchange membrane has a first surface and a second surface opposite to each other. The anode catalyst layer is disposed on the first surface. The cathode catalyst layer is disposed on the second surface.

In an embodiment of the invention, the anode catalyst layer comprises a proton conductive material and a catalytic material.

In an embodiment of the invention, based on the total weight of the anode catalyst layer, The content of the proton conductive material is 2 wt% to 15 wt%.

In an embodiment of the invention, the cathode catalyst layer comprises a proton conducting material and a catalytic material.

In one embodiment of the invention, the proton conductive material is present in an amount of from 2 wt% to 15 wt%, based on the total weight of the cathode catalyst layer.

In one embodiment of the invention, the proton conducting material comprises a metal phosphate, a phosphorylated polybenzimidazole or a combination thereof, the metal phosphate being selected from the group consisting of titanium phosphates, phosphonium phosphates, and combinations thereof.

In an embodiment of the invention, the proton conductive material comprises a combination of a metal phosphate and a phosphorylated polybenzimidazole, and the metal phosphate content is 5 based on the total weight of the metal phosphate and the phosphorylated polybenzimidazole. Wt%~50 wt%.

Based on the above, the proton exchange membrane of the present invention incorporates a metal phosphate in a phosphorylated polybenzimidazole, and the proton exchange membrane of the present invention is bonded by a ionic bond between a metal ion and a phosphate ion in the metal phosphate. It can effectively prevent the detachment of phosphoric acid from the proton exchange membrane, so that the fuel cell can maintain excellent performance under high temperature environment.

The above described features and advantages of the present invention will be more apparent from the following description.

A first embodiment of the present invention provides a proton exchange membrane suitable for conducting protons but not conducting electrons. Therefore, in a particular embodiment, the proton exchange membrane can be disposed at the cathode and anode of the fuel cell. between, To conduct protons from the anode to the cathode.

In the first embodiment, the proton exchange membrane contains phosphorylated polybenzimidazole and a metal phosphate.

Polybenzimidazole is a polymer material commonly used to prepare proton exchange membranes, which has the advantages of good thermal stability, acid and alkali resistance, low gas permeability and low methanol permeability. In the present specification, "phosphorylated polybenzimidazole" means that a polybenzimidazole basic amine group in a structure is bonded to phosphoric acid by hydrogen bonding. The phosphorylated polybenzimidazole system has the ability to conduct protons. In the first embodiment, a film made of polybenzimidazole may be immersed in a phosphoric acid solution to carry out a phosphorylation treatment. Of course, the manner of phosphorylation is not limited thereto, and any means for allowing hydrogen phosphate or polybenzimidazole to generate hydrogen bonds or other substantial bonds is encompassed within the scope of the present invention.

In the first embodiment, the metal phosphate is selected from the group consisting of titanium phosphate, strontium phosphate, and the like. Since metal phosphate is rich in phosphate, it has excellent proton conductivity. Furthermore, in the metal phosphate, the phosphate and the metal ion are bonded by an ionic bond, and the ionic bond is a strong bond compared to the hydrogen bond, and is not easily broken due to an increase in temperature, so Even in high temperature environments (150 ° C ~ 250 ° C), the phosphate is still fixed to the metal ions and is not easily lost, thereby maintaining the proton exchange capacity of the proton exchange membrane in a high temperature environment.

In the first embodiment, the metal phosphate may further contain a dopant substance, and the dopant substance is selected from the group consisting of ruthenium, osmium, iron, osmium, iridium, and magnesium.

The present invention is not particularly limited as long as it can form a film having sufficient mechanical strength. The content of metal phosphate in the proton exchange membrane. However, in the first embodiment, the content of the metal phosphate is about 5 wt% to 50 wt% based on the total weight of the proton exchange membrane, and the membrane is easily broken when the content of the metal phosphate is too high, and the heat resistance is too low when the content is too high. Sexual and ionic conductivity effects are too small.

1 is a schematic view of a membrane electrode assembly according to a second embodiment of the present invention.

Referring to FIG. 1, a second embodiment provides a membrane electrode assembly that can be used in a fuel cell. According to the second embodiment, the membrane electrode assembly 100 includes a proton exchange membrane 102, an anode catalyst layer 104, and a cathode catalyst layer 106, which may be the proton exchange membrane described in the first embodiment.

In the second embodiment, the proton exchange membrane 102 is disposed between an anode (not shown) of a fuel cell and a cathode (not shown). The proton exchange membrane has a first surface 102a and a second surface 102b that are opposite each other with the first surface 102a facing the anode and the second surface 102b facing the cathode.

The anode catalyst layer 104 is disposed on the first surface 102a (ie, between the anode and the proton exchange membrane 102), and the material thereof may include a proton conductive material and a catalytic material. The catalyst material can be, for example, a high area carbon material carrying a platinum catalyst (Pt/C) mixture. For example, a platinum catalyst can catalyze the oxidation reaction of hydrogen molecules (H ₂ ). When the hydrogen molecules are adsorbed onto the platinum catalyst, the hydrogen molecules are dissociated into protons by the catalytic action of the platinum catalyst. The high-area carbon material acts as a carrier for the platinum catalyst to prevent aggregation of the platinum catalyst particles and increase their surface area, thereby promoting catalysis. In addition, high-area carbon materials also have the function of conducting electrons.

The proton conductive material may include a metal phosphate, a phosphorylated polybenzamide An azole or a combination thereof, wherein the metal phosphate is the same as described in the first embodiment. That is, the proton conductive material of the anode catalyst layer 104 may contain only metal phosphate or phosphorylated polybenzimidazole, or may contain both metal phosphate or phosphorylated polybenzimidazole.

In embodiments where the proton conducting material comprises a combination of a metal phosphate and a phosphorylated polybenzimidazole, the metal phosphate may be present in an amount of, for example, 5 wt%, based on the total weight of the metal phosphate and the phosphorylated polybenzimidazole. ~50 wt%.

In addition to the proton conducting material and the catalytic material, the anode catalyst layer 104 may also include a binder (eg, polyvinylidene fluoride (PVDF)) and a trace amount of solvent (eg, N-methyl-pyrrolidone). The proton conductive material may be present in an amount of from 2 wt% to 15 wt%, based on the total weight of the anode catalyst layer 104.

In the second embodiment, the cathode catalyst layer 106 is disposed on the second surface 102b of the proton exchange membrane 102 (ie, between the cathode and the proton exchange membrane 102), and the material thereof may also include a proton conductive material. With catalytic materials. The catalytic material in the cathode catalyst layer 106 may be an n-doped carbon supported pyrites ruthenium RuSe ₂ . The selection of the proton conductive material in the cathode catalyst layer 106 may be the same as described above for the anode catalyst layer 104, wherein the content range of each component (metal phosphate, phosphorylated polybenzimidazole or a combination thereof) may also be used. The same as previously described for the anode catalyst layer 104.

<Experimental example>

Hereinafter, the proton exchange membrane of the present invention and the membrane electrode assembly produced using the same proton exchange membrane will be further described by way of experimental examples. However, the present invention is not limited to the specific experimental examples described below.

Experimental example one

(A) Synthetic PBI

4.508 g of 3,3'-diamino-benzidine and 3.492 g of isophthalic acid and 200 g of phosphoric acid or polyphosphoric acid ( Polyphosphoric acid) is mixed to obtain a reaction mixture. The synthesis was carried out at 200 ° C under a nitrogen atmosphere, and the reaction was continued for three days to obtain a synthesized product. Thereafter, about 1000 ml of a 5 wt% caustic soda solution was added to the synthesis product to neutralize the phosphoric acid. About 4 liters of deionized water was added to the synthesis product, which was boiled at 100 ° C and dried. The dried product was pulverized to give a tan powder.

(B) synthetic metal phosphate

22.44 g of cerium chloride (SbCl ₅ ) was dissolved in hydrochloric acid to prepare a 0.75 M hydrazine solution, and then mixed with 85% phosphoric acid (0.225 mol (22.05 g)), and reacted at 80 ° C at 120 ° C. Drying is carried out, followed by calcination at 300 ° C to 500 ° C to obtain a cerium phosphate powder.

In a similar manner, titanium chloride can be used to synthesize titanium phosphate. The composition of the metal phosphate is approximately pyrophosphate, but is rich in phosphorus.

(C) Preparation of proton exchange membrane

4.0 g of PBI powder, 4.0 g of lithium chloride (LiCl ₂ ), and 92.0 g of N,N-dimethylacetamide (DMAC) were reflux-mixed under a nitrogen atmosphere at 150 ° C. The PBI was dissolved to give a yellow-brown solution. After filtering the solution, the solution was concentrated under vacuum to change the solution concentration to 4 wt% PBI/DMAC. This solution was mixed with cerium phosphate powder (weight ratio of cerium phosphate powder to PBI of about 1:2). After mixing, it was ground in a ball mill manner to obtain a uniformly dispersed colloid. Then, part of the DMAC solvent was removed under vacuum, and then a large-area coating was performed. Thereafter, heating is carried out between 120 ° C and 100 ° C to remove the remaining DMAC solvent. The membrane was immersed in a large amount of deionized water to leach lithium chloride, and then the membrane was immersed in 85% phosphoric acid at 80 ° C for phosphorylation, which was immersed for three days. Thereby, a phosphorylated PBI and a ruthenium phosphate composite film can be obtained.

(D) Preparation of an electrode catalyst layer

0.35 g of catalyst material (JM HiSPEC3000 Pt/C 20 wt%), 0.039 g of binder (PVDF), and 12.0 g of solvent (NMP) were mixed, and the ultrasonic wave was evenly oscillated, and then 0.094 g of yttrium phosphate was added. Salt powder. Thereafter, a dispersing aid is added, and then ultrasonic shock is used to synthesize the anode catalyst ink.

The cathode catalyst ink is prepared similarly to the anode catalyst ink except that the catalyst material is replaced by JM HiSPEC3000 Pt/C 20wt%, which is 0.42 grams of pyrite-based RuSe ₂ (40 wt% RuSe) supported on nitrogen-doped carbon. ₂ / C).

The anode catalyst ink and the cathode catalyst ink are separately coated on both sides of the composite film prepared in the step (C), and dried to complete the preparation of the membrane electrode assembly.

Figure 2 shows the power performance of a membrane electrode set at 100-180 °C using hydrogen fuel and air oxidant. The electrolyte of the membrane electrode assembly comprises 85 wt% phosphorylated PBI and 15 wt% strontium phosphate, and the cathode and anode are electrodes containing platinum catalyst. When operated at 180 ° C, the power system exceeds 300 mW cm ^{-2 .} It represents a more prominent function of the novel composition of this membrane electrode assembly. If the bismuth phosphate is replaced by titanium phosphate, the power will be reduced, but there is still a performance of 250 mW cm ^-2 or more in power.

The dispersibility of the catalyst material in the catalyst ink has a great influence on the performance of the fuel cell. Mixing the metal phosphate into the catalyst ink can make the dispersibility of the catalyst material better, and thereby improve the fuel cell. Performance.

Experimental example 2

(A) Synthesis of PBI/SbCl ₅ composite powder

The step (A) of Experimental Example 2 is similar to the step (A) of Experimental Example 1, and the difference is that in the synthesis of PBI, in addition to the components described in Experimental Example 1, 1.0 g of SbCl ₅ was mixed to prepare PBI/. SbCl ₅ composite powder.

(B) Preparation of proton exchange membrane

5.0 g of PBI/SbCl ₅ composite powder, 5.0 g of lithium chloride (LiCl ₂ ), and 115 g of N,N-dimethylacetamide (DMAC) at 150 ° C in nitrogen The PBI/SbCl ₅ composite powder was dissolved under reflux in an atmosphere to obtain a yellow-brown solution. After filtering the solution, the solution was concentrated under vacuum to change the solution concentration to 4 wt% PBI/DMAC. Grinding by ball milling gives a uniformly dispersed colloid. Then, part of the DMAC solvent was removed under vacuum, and then a large-area coating was performed. Thereafter, heating is carried out between 120 ° C and 100 ° C to remove the remaining DMAC solvent. The membrane was immersed in a large amount of deionized water to leach lithium chloride, and then the membrane was immersed in 85% phosphoric acid at 80 ° C, phosphorylated, and immersed for three days. Thereby, a phosphorylated PBI and a ruthenium phosphate composite film can be obtained.

(C) preparing an electrode catalyst layer

The step (C) of Experimental Example 2 is similar to the step (D) of Experimental Example 1, and the difference is that it is replaced by a powder made of a composite film of phosphorylated PBI and strontium phosphate. Bismuth phosphate powder.

Comparing the ionic conductivity of phosphorylated PBI and bismuth phosphate composite membrane and phosphorylated PBI membrane, as shown in Fig. 3, the ionic conductivity of the membrane without cerium phosphate was the highest at 160 °C, about 0.01- 0.02 S cm ^-1 , while the ionic conductivity of the bismuth phosphate-added film increases to 0.05-0.06 S cm ^-1 , and its temperature range is relatively high, reaching 250-260 ° C.

In summary, the present invention proposes a proton exchange membrane and a fuel cell to which the proton exchange membrane is applied. Since it is made of a PBI substrate that can withstand high temperatures, the fuel cell can be used in a high temperature environment (for example, 150 ° C ~ 250 ° C). The use of a phosphoric acid-rich metal phosphate is thereby utilized to eliminate the setting of the humidifier in the fuel cell system. Further, the use of the fuel cell having the proton exchange membrane of the present invention in a high temperature environment can improve the problem of poisoning of carbon monoxide. That is, the carbon monoxide impurity present in the hydrogen fuel promotes its desorption from the platinum metal surface at a higher ambient temperature when adsorbed to the platinum catalyst in the electrode catalyst. Furthermore, when a fuel cell using PBI as a proton exchange membrane substrate is used in a high temperature environment, phosphoric acid bonded to PBI by hydrogen bonding may be affected by high temperature and cannot be fixed to PBI, thereby reducing protons of the proton exchange membrane. Conductivity; however, the proton exchange membrane of the present invention is in PBI The metal phosphate is mixed in, which can effectively fix the phosphate, so that the fuel cell can maintain excellent performance under high temperature environment.

Although the present invention has been disclosed in the above embodiments, it is not intended to limit the invention, and any one of ordinary skill in the art can make some modifications and refinements without departing from the spirit and scope of the invention. The scope of the invention is defined by the scope of the appended claims.

100‧‧‧ membrane electrode group

102‧‧‧Proton exchange membrane

102a‧‧‧ first surface

102b‧‧‧second surface

104‧‧‧Anode catalyst layer

106‧‧‧ Cathode catalyst layer

1 is a schematic view of a membrane electrode assembly according to a second embodiment of the present invention.

Figure 2 shows the power performance of a 100 ° C ~ 180 ° C membrane electrode set.

Figure 3 is a graph comparing the ionic conductivity of a phosphorylated PBI with a ruthenium phosphate composite membrane and a phosphorylated PBI membrane.

100‧‧‧ membrane electrode group

102‧‧‧Proton exchange membrane

102a‧‧‧ first surface

102b‧‧‧second surface

104‧‧‧Anode catalyst layer

106‧‧‧ Cathode catalyst layer

Claims (12)

A proton exchange membrane comprising: phosphorylated polybenzimidazole; and a metal phosphate selected from the group consisting of titanium phosphate, phosphonium phosphate, and the like. The proton exchange membrane according to claim 1, wherein the content of the metal phosphate is 5 wt% to 50 wt% based on the total weight of the proton exchange membrane. The proton exchange membrane according to claim 1, wherein the metal phosphate comprises a dopant selected from the group consisting of ruthenium, osmium, iron, osmium, iridium and magnesium. A membrane electrode assembly comprising: the proton exchange membrane according to any one of claims 1 to 3, which has a first surface and a second surface opposite to each other; an anode catalyst layer, the system configuration And on the first surface; and a cathode catalyst layer disposed on the second surface. The membrane electrode assembly of claim 4, wherein the anode catalyst layer comprises a proton conductive material and a catalytic material. The membrane electrode assembly of claim 5, wherein the proton conductive material is present in an amount of from 2 wt% to 15 wt%, based on the total weight of the anode catalyst layer. The membrane electrode assembly of claim 5, wherein the proton conductive material comprises a metal phosphate, a phosphorylated polybenzimidazole or a combination thereof, the metal phosphate being selected from the group consisting of titanium phosphate Bismuth phosphate A group of combinations of them and the like. The membrane electrode assembly of claim 7, wherein the proton conductive material comprises a combination of the metal phosphate and the phosphorylated polybenzimidazole, and the metal phosphate is present in the metal phosphate The total weight of the phosphorylated polybenzimidazole is 5 wt% to 50 wt%. The membrane electrode assembly of claim 4, wherein the cathode catalyst layer comprises a proton conductive material and a catalytic material. The membrane electrode assembly of claim 9, wherein the proton conductive material is present in an amount of from 2 wt% to 15 wt% based on the total weight of the cathode catalyst layer. The membrane electrode assembly of claim 9, wherein the proton conductive material comprises a metal phosphate, a phosphorylated polybenzimidazole or a combination thereof, the metal phosphate being selected from the group consisting of titanium phosphate a group consisting of strontium phosphate and combinations thereof. The membrane electrode assembly of claim 11, wherein the proton conductive material comprises a combination of the metal phosphate and the phosphorylated polybenzimidazole, and the metal phosphate is contained in the metal phosphate The total weight of the phosphorylated polybenzimidazole is 5 wt% to 50 wt%.