CN1960042A - Non noble metal catalyst for cathode of direct methanol fuel cell, and preparation method - Google Patents

Abstract

A direct methanol fuel cell cathode non-noble metal catalyst and a preparation method thereof belong to the field of fuel cell catalysts. Existing catalysts are generally noble metals, which are relatively expensive and easily poisoned. The active component of the catalyst is a transition metal nitride, and the carrier is Vulcan XC-72 activated carbon powder, wherein the mass percentage of the transition metal nitride in the active component is 1-6%. The method is to dissolve the transition metal macrocycle compound and Vulcan XC-72 activated carbon powder in an organic solvent, and ultrasonicate for 30-60 minutes; the mass ratio of the transition metal macrocycle compound to the Vulcan XC-72 activated carbon powder in the solvent is 1: 9-1:1; Stir and evaporate to dryness at room temperature, dry at 60-80°C to obtain powder, put it into a closed container, feed ammonia gas, the flow rate of ammonia gas is 0.5-3l/min, and the temperature of heat treatment is controlled at 600-1000 ℃, the heat treatment time is 0.5-10h, and the catalyst is obtained by naturally cooling down. The area specific activity of the carbon-supported platinum catalyst is 1.5 mA/cm ² ; the carbon-supported nitride catalyst of the present invention reaches 3.1 mA/cm ² , equivalent to twice the former. The process of the method is simple, and the process is easy to control.

Description

A kind of direct methanol fuel cell cathode non-noble metal catalyst and preparation method thereof

technical field

The invention belongs to the field of fuel cell catalysts.

Background technique

Direct methanol fuel cell is a kind of proton exchange membrane fuel cell, which uses solid polymer membrane as electrolyte and liquid or gaseous methanol as fuel. It is a kind of fuel cell and has many advantages of fuel cells: no pollution, quiet and efficient, and conducive to environmental protection. In addition, it does not require intermediate reforming or conversion devices, is light in weight and small in size, and simplifies battery design and operation. Due to the many advantages mentioned above, it is especially suitable for portable power sources for various purposes, such as mobile phones, notebook computers and electric vehicle power sources.

In direct methanol fuel cells, Pt/C catalysts are often used as cathode oxygen reduction electrocatalysts and are the most studied fuel cell catalysts. Since the noble metal Pt is relatively rare and expensive, which limits its practical application and complete commercialization, it is necessary to develop an oxygen reduction electrocatalyst containing little or no noble metal. Among them, carbon-supported metalloporphyrin compounds have made great progress in the application of heat treatment in this area. They have good catalytic activity and stability, and have methanol resistance properties. They are expected to become catalysts to replace noble metals. At present, there is a large gap between the performance of direct methanol fuel cells and commercial requirements. Another problem is that the methanol in the anode passes through the proton exchange membrane to reach the cathode, and will oxidize on the commonly used carbon-supported platinum cathode, poisoning the catalyst. This not only makes methanol not fully used, but also seriously affects the performance of the battery.

In the 1960s, it was discovered that transition metal macrocycles can be used as catalysts for oxygen reduction, but these transition metal chelates are unstable electrocatalysts when used directly. In response to this phenomenon, [Faubert G, Lalande G, Cote R, et al. Electrochimica Acta [J], 1996, 41 (10): 1689-1701.] and others adsorbed iron and cobalt tetraphenylporphyrin on On the carbon black, heat treatment is carried out under argon saturation, and the heat treatment temperature is 100-1000 ° C. The activity and stability of the catalyst can be improved by heat treatment. So far, most of the research has been carried out on heat treatment of fuel cell catalysts in an inert atmosphere. . Existing catalysts are generally noble metals, which are relatively expensive and easily poisoned.

Contents of the invention

The invention provides a direct methanol fuel cell cathode non-noble metal catalyst, characterized in that the active component is a transition metal nitride, and the carrier is Vulcan XC-72 activated carbon powder, wherein the mass percentage of the transition metal nitride in the active component The content is 1-6%.

Because nickel, iron, and manganese are all transition metal elements with very similar properties, and their porphyrins also have similar properties, so they also have similar oxygen reduction properties after heat treatment in ammonia gas.

The present invention also provides a method for preparing a direct methanol fuel cell cathode non-noble metal catalyst, which is characterized in that it comprises the following steps:

1) Dissolve the transition metal macrocycle compound and Vulcan XC-72 activated carbon powder in an organic solvent, and ultrasonicate for 30-60 minutes; wherein the transition metal macrocycle compound is molybdenum, cobalt, nickel, iron, manganese as the central metal ion One of mononuclear porphyrin and its derivatives; organic solvents are tetrahydrofuran, ethanol, acetone, isopropanol, N-N dimethylformamide, N-N dimethylacetamide, dimethyl sulfoxide, n-hexane, dichloromethane, One of chloroform, tetrachloromethane, pyridine or ether; the mass ratio of transition metal macrocyclic compound to Vulcan XC-72 activated carbon powder in the solvent is 1:9-1:1;

2) The above solution was stirred and evaporated to dryness at room temperature, and dried at 60-80°C to obtain powder;

3) Put the powder obtained in the above step 2) into an airtight container, feed ammonia gas, the flow rate of ammonia gas is 0.5-31/min, the temperature of heat treatment is controlled at 600-1000 °C, the heat treatment time is 0.5-10h, and the temperature is naturally lowered Get a catalyst.

The mononuclear porphyrin derivative is one of tetramethoxyporphyrin, tetrasulfonic porphyrin, tetraphenylporphyrin and octaethylporphyrin.

In step 1), the content of the active carbon in the organic solvent is 0.02-9g/L, and the content of the transition metal macrocyclic compound is 0.02-1g/L.

The process of the method is simple, and the process is easy to control. The X-ray diffraction analysis result of the direct methanol fuel cell catalyst prepared by the method shows that the active component of the obtained catalyst is nitride. The model of the transmission electron microscope is JEM-2010F, and the lens analysis results show that the obtained catalyst particles have a small particle size, basically 4-6nm, and are evenly dispersed. All raw materials used in the present invention are not precious metals, thereby realizing the non-noble metalization of the catalyst. The prepared carbon-supported nitride catalyst and the commonly used carbon-supported platinum catalyst were prepared into electrodes, and electrochemical tests were performed using a single-cell three-electrode system. The results of the cathodic polarization curve test showed that under the same test conditions, carbon-supported platinum The area specific activity of the catalyst is 1.5mA/cm ² ; the carbon-supported nitride catalyst of the present invention reaches 3.1mA/cm ² , which is twice as high as the former. In direct methanol fuel cell noble metal catalysts, cathode catalyst poisoning seriously affects the performance of the battery, and the results of cathode polarization curve tests show that the curves are basically unchanged before and after methanol, indicating that this catalyst has a good ability to resist methanol poisoning. The electrochemical test was also carried out under the single-cell three-electrode system, and the chronoamperometry curve showed that the oxidation current of the catalyst decayed slowly in acidic solution and had good stability.

The prepared catalyst was electrochemically tested using a single-cell three-electrode system. The counter electrode is a smooth platinum electrode, and the reference electrode is a mercurous sulfate electrode. The potentials described below are relative to this electrode. The electrolyte is 0.5mol/l H ₂ SO ₄ solution and 0.5mol/l H ₂ SO ₄ +0.5mol/l CH ₃ OH, N ₂ or O ₂ gas was passed for 30 minutes before the experiment, and the scan rate was 10mV/s. The electrochemical testing instrument is a Model 273A potentiostatic/current meter from EG&G Company of the United States.

Description of drawings:

Accompanying drawing 1 is the X-ray diffraction spectrum of the catalyst provided by the embodiment 4 of the present invention.

Accompanying drawing 2 is the cathodic polarization curve of the catalyst provided in Example 1 of the present invention in 0.5M H ₂ SO 4 solution.

Accompanying drawing 3 is the lens photo of the catalyst provided by Example 2 of the present invention.

Accompanying drawing 4 is the stability curve of the catalyst provided in Example 1 of the present invention.

Figure 5 is a linear sweep curve of the catalyst provided in Example 4 of the present invention in 0.5M H ₂ SO ₄ and 0.5M H ₂ SO ₄ +0.5 CH ₃ OH.

Detailed ways:

The present invention will be described in detail below through embodiments and in conjunction with the accompanying drawings.

Example 1

Molybdenum tetraphenylporphyrin and Vulcan XC-72 activated carbon powder were dissolved in tetrahydrofuran at a mass ratio of 1:9, and ultrasonicated for 60 minutes; the above solution was stirred at room temperature, evaporated to dryness, and dried at 80°C. The obtained powder was sealed in a quartz glass tube, and ammonia gas was introduced at a flow rate of 1 l/min. The heat treatment temperature was controlled at 700°C, and the reaction was carried out at this temperature for 3 hours. Then, the heating was stopped and cooled to room temperature to obtain a MoN/C catalyst. The lens photo shows that the particle size of MoN is 5-6nm. According to the attached diagram 2 of the cathodic polarization curve, the reduction onset potential of oxygen on the catalyst is -0.1V, the area specific activity is 3.1mA/cm ² , and the relative rotational speed and The area specific activity of the carbon-supported platinum catalyst is 1.5mA/cm ² under the same scanning rate, which is doubled, and the catalytic activity is better than that of the carbon-supported platinum catalyst. In the presence of methanol, the polarization curve of the catalyst does not change significantly, indicating that it has methanol-resistant properties. Accompanying drawing 4 is the chronocurrent curve of the catalyst, which shows that the oxidation current has basically no attenuation, and the stability of the catalyst is relatively good.

Example 2.

Molybdenum octaethylporphyrin and Vulcan XC-72 activated carbon powder were dissolved in acetone at a mass ratio of 1:1, and ultrasonicated for 50 minutes; the above solution was stirred at room temperature, evaporated to dryness, and dried at 60°C. The obtained powder was sealed in a quartz glass tube, and ammonia gas was introduced at a flow rate of 0.5 l/min. The heat treatment temperature was controlled at 700° C., and the reaction was carried out at this temperature for 4 hours. Then, the heating was stopped and cooled to room temperature to obtain a MoN catalyst. The lens photo of accompanying drawing 2 shows that the particle size of the catalyst is 5-6nm. The electrochemical cathodic polarization curve and the chronocurrent curve show that the performance of the catalyst is better than that of the carbon-supported platinum electrocatalyst.

Example 3

Molybdenum tetramethoxyporphyrin and Vulcan XC-72 activated carbon powder were dissolved in N-N dimethylacetamide at a mass ratio of 2:3, and ultrasonicated for 50 minutes; the above solution was stirred at room temperature, evaporated to dryness, and dried at 70°C. The obtained powder was sealed in a quartz glass tube, and ammonia gas was introduced at a flow rate of 2 l/min. The heat treatment temperature was controlled at 600° C., and the reaction was carried out at this temperature for 5 hours. Then, the heating was stopped and cooled to room temperature to obtain a MoN catalyst. The lens photos show that the particle size of the catalyst is 5-6nm. The electrochemical cathodic polarization curve and the chronocurrent curve show that the performance of the catalyst is better than that of the carbon-supported platinum electrocatalyst.

Example 4

Molybdenum tetrasulfonate porphyrin and Vulcan XC-72 activated carbon powder were dissolved in ethanol at a mass ratio of 2:3, ultrasonicated for 40 minutes; the above solution was stirred at room temperature, evaporated to dryness, and dried at 80°C. The obtained powder was sealed in a quartz glass tube, and ammonia gas was introduced at a flow rate of 3 l/min. The heat treatment temperature was controlled at 1000° C., and the reaction was carried out at this temperature for 4 hours. Then, the heating was stopped and cooled to room temperature to obtain a MoN catalyst. Accompanying drawing 1XRD pattern shows that the component of obtained catalyst is MoN, and the relatively good match of standard pattern. Lens photo shows that the particle size of catalyst is 5-6nm. Accompanying drawing 5 is this catalyst 0.5MH ₂ SO ₄ and 0.5MH ₂ SO ₄ The cathodic polarization curve of +0.5CH ₃ OH shows that there is no methanol oxidation peak on the catalyst in the presence of methanol, and the initial potential of the cathodic current for oxygen reduction in the two solutions is close, and there is no obvious negative shift phenomenon. The reduction current is only slightly reduced, which shows that the catalyst we prepared has good anti-methanol poisoning performance. The electrochemical cathodic polarization curve and chronoamperometric curve show that the catalytic performance of the catalyst has reached the catalytic performance of carbon-supported platinum electrocatalysts.

Example 5

Dissolve cobalt tetraphenylporphyrin and Vulcan XC-72 activated carbon powder in tetrachloromethane at a mass ratio of 1:9, and ultrasonicate for 30 minutes; the above solution is stirred at room temperature, evaporated to dryness, and dried at 80°C. The obtained powder was sealed in a quartz glass tube, and ammonia gas was introduced at a flow rate of 1 l/min. The heat treatment temperature was controlled at 900° C., and the reaction was carried out at this temperature for 3 hours. Then, the heating was stopped and cooled to room temperature to obtain a CoN catalyst. The lens photos show that the particle size of the catalyst is 5-6nm. The electrochemical cathodic polarization curve and the chronocurrent curve show that the performance of the catalyst is better than that of the carbon-supported platinum electrocatalyst.

Claims (4)

1. A direct methanol fuel cell cathode non-precious metal catalyst, characterized in that the active component is a transition metal nitride, and the carrier is Vulcan XC-72 activated carbon powder, wherein the mass percentage of the transition metal nitride in the active component 1-6%. 2. a preparation method of direct methanol fuel cell cathode non-noble metal catalyst, is characterized in that, comprises the following steps: 1) Dissolve the transition metal macrocycle compound and Vulcan XC-72 activated carbon powder in an organic solvent, and ultrasonicate for 30-60 minutes; wherein the transition metal macrocycle compound is molybdenum, cobalt, nickel, iron, manganese as the central metal ion One of mononuclear porphyrin and its derivatives; organic solvents are tetrahydrofuran, ethanol, acetone, isopropanol, N-N dimethylformamide, N-N dimethylacetamide, dimethyl sulfoxide, n-hexane, dichloromethane, One of chloroform, tetrachloromethane, pyridine or ether; the mass ratio of transition metal macrocyclic compound to Vulcan XC-72 activated carbon powder in the solvent is 1:9-1:1; 2) The above solution was stirred and evaporated to dryness at room temperature, and dried at 60-80°C to obtain powder; 3) Put the powder obtained in the above step 2) into a closed container, feed ammonia gas, the flow rate of ammonia gas is 0.5-3l/min, the temperature of heat treatment is controlled at 600-1000°C, the heat treatment time is 0.5-10h, and the temperature is naturally lowered Get a catalyst. 3. A method for preparing a direct methanol fuel cell cathode non-noble metal catalyst according to claim 2, characterized in that said mononuclear porphyrin derivatives are tetramethoxyporphyrin, tetrasulfonic porphyrin, Tetraphenylporphyrin, one of octaethylporphyrin. 4, a kind of direct methanol fuel cell cathode non-noble metal catalyst according to claim 2, it is characterized in that the content of active carbon in the organic solvent in step 1) is 0.02-9g/L, the content of transition metal macrocyclic compound is 0.02-1g/L.

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