CN101383416A - A method for improving the anti-CO performance of proton exchange membrane fuel cell - Google Patents

Abstract

The invention relates to a method for enhancing the resistance of a proton exchange membrane fuel cell to foreign gas, in particular to a method for enhancing the resistance of the fuel cell to CO. Catalyst which has catalytic action and oxidizing action to the CO gas is born in the anode diffuser layer of the proton exchange membrane fuel cell, under the condition of infusing a small amount of oxygen gas, the CO gas impurities which cause the performance of the proton exchange membrane fuel cell to be attenuated are catalyzed and oxidized when passing through the diffuser layer, and the CO gas impurities react to form CO2 which has small influence to the performance of the cell, therefore, the resistance of the proton exchange membrane fuel cell to the CO is enhanced, and the development and the application of the fuel cell are promoted.

Description

A method for improving the anti-CO performance of proton exchange membrane fuel cell

technical field

The invention relates to a method for improving the anti-CO performance of a proton exchange membrane fuel cell. Specifically, a catalyst Pt or Au that has a catalytic effect on CO gas is loaded in the anode diffusion layer of the proton exchange membrane fuel cell, and under the condition of injecting a small amount of oxygen, CO gas impurities are catalyzed to generate CO2 when passing through the diffusion layer, thereby improving the CO resistance performance of proton exchange membrane fuel cells, and promoting the development and application of fuel cells.

Background technique

At present, fuel cells are widely valued due to their high energy conversion efficiency and environmental friendliness, while proton exchange membrane fuel cells also have the characteristics of rapid start-up at room temperature, no electrolyte loss, and long life, and are considered to be the best choice for mobile power sources. Good candidate power supply. However, trace impurity gases in fuel (hydrogen or purified reformed gas) and oxidant (air or oxygen) may cause electrocatalyst poisoning and degrade battery performance, and these impurity gases are sometimes difficult to avoid. At present, in order to improve the life of PEMFC, that is, to improve the performance and durability of proton exchange membrane electrodes, many research institutions have done a lot of work on resisting the influence of impurity gases. Among them, carbon monoxide (CO) leads to electrode poisoning, which has been studied more. In document 1 US Patent 6,689,194, an impurity gas removal device is added between the hydrogen source and the anode of the fuel cell, and the device is filled with adsorption substances such as platinum, silver, tungsten, mica, and activated carbon. When the hydrogen flow containing impurity gas passes through the device, the adsorbent can remove carbon monoxide (CO), carbon dioxide (CO ₂ ) and other impurity gases through chemical adsorption. The advantage of this method is that it can be easily realized by replacing a new impurity gas removal device after the adsorption substance is saturated. The disadvantage is that an additional device needs to be added. In document 2 US Patent 4,910,099, it is proposed that 100-500 ppm of carbon monoxide (CO) can be oxidized to carbon dioxide ( CO ₂ ). This method has high efficiency and is easy to operate, but it will cause local overheating, damage the proton exchange membrane, shorten the life of the battery, and bring about safety issues for the battery system. In Document 3 US Patent 6,500,572, the above oxygen injection method is improved, instead of continuous oxygen injection, the amount of oxygen injected is controlled by a voltage signal from a carbon monoxide (CO) detector. Periodic or staged oxygen injection can also be used. This method can avoid the decrease of battery efficiency caused by local overheating and excess oxygen, but this method still cannot completely avoid the destruction of the catalyst and membrane due to the thermal effect caused by oxygen injection, and it is relatively complicated. In addition, in document 5 WO 00/36679, by loading Pt, Ru or PtRu catalyst on the flow field side of the anode diffusion layer, the CO resistance performance of the fuel cell was significantly enhanced under the condition of injecting a small amount of air.

Contents of the invention

The purpose of the present invention is to provide a method for improving the CO resistance performance of the proton exchange membrane fuel cell, which is simple and easy and does not require additional removal devices.

To achieve the above object, the technical solution adopted in the present invention is:

A method for improving the anti-CO performance of the fuel cell, in which a catalyst capable of catalytic oxidation of CO gas is carried in the anode diffusion layer of the proton exchange membrane fuel cell.

The catalyst is a Pt or Au catalyst; wherein the loading amount of the Pt or Au catalyst is 0.1-0.5 mg/cm ² , and the optimum range is 0.1-0.3 mg/cm ² ;

The specific operation process is: soak the carbon paper or carbon cloth used as the anode diffusion layer in the ethanol solution of 0.03-0.09mol/L chloroplatinic acid or chloroauric acid for 3-5min, dry at 60-100°C, and then The impregnated carbon paper is reduced at 400-800° C. for 2-8 hours in a hydrogen atmosphere, and the above-mentioned treated carbon paper can be used as an anode gas diffusion layer and prepared as an anode (hereinafter referred to as a modified anode).

Under the condition of injecting a small amount of oxygen, the CO gas impurity that will cause the performance degradation of the proton exchange membrane fuel cell will be catalyzed and oxidized when passing through the diffusion layer, and the reaction will generate CO ₂ that has little effect on the performance of the cell, thereby improving the performance of the proton exchange membrane fuel cell. The anti-CO performance has promoted the development and application of fuel cells.

The present invention has following advantage:

1. The method is simple and easy to implement. Since the catalyst for the impurity gas CO is carried in the gas diffusion layer, the CO gas impurity that will cause the performance degradation of the fuel cell through the catalytic reaction is oxidized when passing through the flow field, and produces CO ₂ that has very little influence on the performance of the fuel cell. Compared with literature 1 and literature 4, this method does not require additional impurity removal devices.

2. It can improve the performance and life of the fuel cell. Compared with Document 2, the oxidation of CO in the present invention should occur in the gas diffusion layer, avoiding local overheating caused by continuous oxygen injection at the anode inlet, and will not affect the electrocatalyst and The proton exchange membrane brings destruction.

3. Oxygen utilization rate is high. Since the Pt or Au catalyst in the diffusion layer has a good CO selective oxidation catalytic effect, the injected trace oxygen can effectively oxidize CO.

Description of drawings

Fig. 1 is a schematic diagram of the MEA structure in which a catalyst is loaded in the anode diffusion layer. When the fuel gas containing CO passes through the anode diffusion layer, under the action of the catalyst Pt or Au, the CO reacts with the injected trace oxygen to generate CO ₂ , thereby improving the CO resistance performance of the proton exchange membrane fuel cell.

Figure 2 is a comparison of the performance of the anti-CO MEA prepared using the modified anode and the conventional MEA in 100ppmCO/hydrogen, 0.1MPa, the anode room temperature humidification, the cathode saturation humidification, the battery temperature is 60 ° C, and the fuel gas flow rate: 50ml/min; The reduction temperatures of MEA1, MEA2 and MEA3 are 400, 600 and 800°C, respectively.

Figure 3 is a comparison of the performance of the anti-CO MEA prepared using the modified anode and the conventional MEA in 100ppmCO/hydrogen, 0.1MPa, the anode room temperature humidification, the cathode saturation humidification, the battery temperature is 60 ° C, the fuel gas flow rate: 50ml/min, The Pt catalyst loadings in the anode diffusion layers of MEA4, MEA5 and MEA2 are 0.1, 0.2 and 0.3 mg/cm ² respectively.

Figure 4 is a comparison of the performance of the anti-CO MEA prepared using the modified anode and the conventional MEA in 100ppmCO/hydrogen, 0.1MPa, the anode room temperature humidification, the cathode saturation humidification, the battery temperature is 60 ° C, the fuel gas flow rate: 50ml/min, The Au catalyst loadings in the anode diffusion layers of MEA6, MEA7 and MEA8 are 0.1, 0.2 and 0.3 mg/cm ² respectively.

Detailed ways

Example 1

Taking the preparation of MEA with 0.3mg/cm ² Pt catalyst on the anode diffusion layer as an example (MEA2 shown in Table 1), take a 77cm ² piece of Toray carbon paper and impregnate it in 0.084mol/L H ₂ PtCl ₆ ·6H ₂ O ethanol solution, take it out after 3 minutes, and dry it at 80°C. Subsequently, the carbon paper impregnated with chloroplatinic acid was placed in a quartz reaction tube, and the temperature of the quartz reaction tube was raised to 600 °C under the condition of passing hydrogen gas, and kept for 2 hours to ensure that the chloroplatinic acid in the carbon paper After complete reduction, carbon paper supporting 0.3 mg/cm ² Pt catalyst was obtained. In order to enhance the hydrophobicity of the diffusion layer, the treated carbon paper was used as the anode diffusion layer, which was soaked in PTFE emulsion and fired at 330°C for 40 minutes. The carbon paper loaded with the catalyst was subjected to hydrophobic treatment to prepare an electrocatalytic layer by spraying, and a modified anode with a diffusion layer loaded with 0.3 mg/cm ² Pt catalyst was obtained. The modified anode, Nafion 112 membrane, and cathode were hot-pressed at 140°C and 10MPa for 1 minute to obtain the MEA2 shown in Table 1.

The load of catalyst in the anode diffusion layer can be controlled by changing the concentration of chloroplatinic acid or chloroauric acid, and the size of catalyst particles in the anode diffusion layer can be controlled to a certain extent by changing the reduction temperature. The catalyst types, loads and reduction temperatures in the anode diffusion layer of the eight MEAs shown in Table 1 are different, and their preparation methods are the same as those mentioned above.

Table 1 Eight kinds of MEA prepared by changing the catalyst type, loading and reduction temperature in the anode diffusion layer

Using a single cell, the effective area of the cell is 5cm ² , the fuel gas (100ppmCO/H ₂ ) and air flow rates are 50ml/min and 600ml/min respectively, the operating pressure is 0.1MPa, the cell temperature is 60°C, and the anode and cathode are humidified The temperatures are: 25 and 60°C, respectively. After the battery was activated in pure hydrogen, 100ppm/H ₂ was introduced to investigate the CO resistance performance of the 8 MEAs in Table 1.

Figure 2 shows the battery polarization curves of anti-CO MEA and conventional MEA at 100ppmCO. From Figure 2, it can be seen that when hydrogen gas containing 100ppmCO is introduced, the battery performance is significantly attenuated, and the attenuation is particularly significant in the low current density range. Oxygen injection into the anode is a very effective method to improve the CO resistance performance of the battery. It can be seen from Figure 2 that even with conventional MEA, when 2% air is injected into the fuel gas, the performance of the battery is partially restored, but it is still not ideal. At 900mA/ ^cm2 , the voltage is only about 0.3V. By improving the electrode structure, that is, preparing some Pt particles in the diffusion layer, the performance of the battery can be effectively improved while the amount of oxygen injected is constant. For example, when MEA2 (reduction temperature: 600°C) is at 900mA/cm ² , the voltage can reach 0.566V (the corresponding value of reference MEA in pure hydrogen is 0.606V).

Figure 3 shows the effect of different Pt loadings in the diffusion layer against CO. The Pt loadings in the diffusion layer in MEA4, MEA5 and MEA2 are 0.1mg/cm ² , 0.2mg/cm ² and 0.3mg/cm ² respectively. It can be seen from Figure 3 that when the Pt loading in the diffusion layer is 0.2 and 0.3 mg/cm ² , the battery has good anti-CO performance, which is better than that of MEA4 with a Pt loading of 0.1 mg/cm ² .

Figure 4 shows the battery performance of the Au-loaded anti-CO MEA in the anode diffusion layer and the conventional MEA in 100ppm CO/H ₂ . It can be seen from the figure that, compared with the loading of Pt in the diffusion layer, the change of the Au loading in the diffusion layer has little effect on the anti-CO performance of the battery. MEA6 (Au: 0.1mg/cm ² ), MEA7 (Au :0.2mg/cm ² ) and MEA8 (Au:0.3mg/cm ² ) in 100ppm CO/H ₂ have similar battery performance, but the anti-CO performance is much stronger than conventional MEA.

Claims (4)

1, a kind of method that can improve fuel cell anti-CO performance, is characterized in that: in proton exchange membrane fuel cell anode diffusion layer, carry the catalyzer that CO gas has catalytic oxidation. ² , according to the method for improving the anti-CO performance of proton exchange membrane fuel cell according to claim 1, it is characterized in that: described catalyzer is Pt or Au catalyzer; Wherein the carrying amount of Pt or Au catalyzer is 0.1-0.5mg/cm . 3. The method for improving the CO resistance performance of a proton exchange membrane fuel cell according to claim 2, characterized in that: the loading amount of the Pt or Au catalyst is 0.1-0.3 mg/cm ² . 4, according to the method for improving the anti-CO performance of proton exchange membrane fuel cell according to claim 1, it is characterized in that: the specific operation process is, Immerse the carbon paper or carbon cloth used as the anode diffusion layer in the ethanol solution of 0.03-0.09mol/L chloroplatinic acid or chloroauric acid for 3-5min, dry at 60-100°C, and then put the impregnated carbon paper Reduction at 400-800° C. for 2-8 hours under a hydrogen atmosphere, and the above-mentioned treated carbon paper can be used as an anode gas diffusion layer.

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