CN1225807C - Direct methanol fuel cell anode catalyst and method for preparing the same - Google Patents

Abstract

The present invention relates to an anode catalyst Pt-W-Sn/C for direct methanol fuel batteries A method for preparing the anode catalyst comprises: black carbon is dispersed in distilled water, H2PtCl6, tungstate and tin salt are added, and then, the solution is stirred to make metal salt and H2PtCl6 thoroughly adsorbed; a reducing agent is added drip by drip for reduction and precipitation, and after complete reaction, precipitates are washed by distilled water, filtered and dried in a drying oven to obtain the black C-carried Pt-W-Sn three-element catalyst. The catalyst has the advantages of favorable methanol catalytic activity and low price. Besides, the catalyst can greatly reduce the cost of direct methanol fuel batteries and enhance the performance cost ratio and the market competitive capability of batteries.

Description

Preparation method of anode catalyst of direct methanol fuel cell

Technical Field

The invention relates to a fuel cell, in particular to a preparation method of an anode catalyst of a direct methanol fuel cell.

Background

The direct methanol fuel cell is a chemical power source with anode directly adopting liquid methanol as fuel and cathode adopting pure oxygen or air as electrode active material. With gaseous H at the anode₂Compared with a fuel cell with a cathode adopting pure oxygen or air as an electrode active substance as a fuel, the direct methanol fuel cell has the advantages of small volume, light weight, simple structure, high reliability, convenient fuel carrying and supplement and the like. In addition, the direct methanol fuel cell also has the performance of quick starting function and quick response load speed. Therefore, the direct methanol fuel cell is an ideal power supply, can be used as a household small-sized power station, a portable electronic and electric appliance mobile power supply, a power supply of an electric vehicle and the like, and has wide application prospect and huge market. Currently, the anode catalyst of the direct methanol fuel cell is mainly a binary platinum alloy with a high noble metal content, and mainly includes platinum-molybdenum (Pt-Mo), platinum-tungsten (Pt-W), platinum-ruthenium (Pt-Ru), and the like, which use carbon (C) as a carrier. Among them, Pt-Ru/C is recognized as the anode catalyst of the direct methanol fuel cell with the best performance at present, and commercial mass production is realized. However, the Pt-Ru/C catalyst currently used in the direct methanol fuel cell has the following disadvantages:

(1) the content (i.e., the amount of supported material per unit area) of Pt and Ru is high.

(2) The resource of Pt is limited, and the resource of Ru is more rare, so that the price of the catalyst is extremely high, and the catalyst becomes a bottleneck problem of the development and popularization of direct methanol fuel cells.

(3) The performance-price ratio is low, and the market competitiveness is lacked.

Therefore, in order to realize the practical use and industrialization of the direct methanol fuel cell, an anode catalyst with abundant resources, low price and high catalytic activity is required.

Disclosure of Invention

The invention aims to find a preparation method of a novel platinum catalyst with a very low anode concentration for a direct methanol fuel cell, and the obtained catalyst has the advantages of high methanol electrocatalytic activity, high CO poisoning resistance, low price and the like.

The direct methanol fuel cell anode catalyst of the invention takes carbon (C) as a carrier and consists of Pt and WO_xAnd a Pt-W-Sn/C ternary anode low platinum catalyst consisting of three effective components of Sn.

The preparation method of the catalyst is that the carrier carbon is firstly used for adsorbing metal ions, and is characterized in that the carrier carbon is added into water to form suspension, chloroplatinic acid, tin salt and tungstate solution are added under the acidic environment with the pH value less than 5 to prepare mixed solution, and then reducer KBH is added₄、NaBH₄And formaldehyde or formic acid to prepare the catalyst. The atomic molar ratio of the metal elements Pt, W and Sn is 3: X: Y, wherein X, Y is a natural number less than or equal to 3.

The specific preparation method comprises the following steps: adding carbon black into water, stirring to form a suspension, then adding chloroplatinic acid, tin salt and tungstate into the suspension under an acidic environment with the pH value of less than 5 to prepare a mixed solution, and adding a reducing agent into the mixed solution after stirring; the reducing agent is KBH₄、NaBH₄Formaldehyde or formic acid. The atomic mole parts of the raw materials are as follows:

chloroplatinic acid: 1 to 3 portions of

Tin salt: the mole fraction of tin atoms is 0.3-3 times of that of platinum atoms;

tungstate: the mole fraction of tungsten atoms is 0.3-3 times of that of platinum atoms;

carbon black: the atomic mole fraction of the platinum is 80-325 times of that of the platinum;

water: the molar fraction of which corresponds to the molar fraction of platinum atoms of 2.7X 10⁴～1.35×10⁵Doubling;

reducing agent: KBH₄、NaBH₄Or the molar part of the formaldehyde is 1-4 times of that of the platinum atom; the mole fraction of formic acid is 2-8 times of the mole fraction of platinum atoms.

More specifically, the method comprises the following steps:

(1) adding carbon black into distilled water, and continuously stirring for 10-60 min at 60-100 ℃ to obtain a suspension;

(2) mixing chloroplatinic acid, tungstate, tin salt and hydrochloric acid, adding into a reaction container, stirring for 10-90 min, and dropwise adding a reducing agent KBH₄、NaBH₄Formaldehyde or formic acid, hydrochloric acid is added to adjust and controlthe pH value of the system solution to be less than 5, and the mixture is stirred and reacted for 1 to 4 hours after the reducing agent is added;

(3) washing the reactant with distilled water, carrying out suction filtration until the washing liquid is neutral, and then placing the reactant in a drying oven to dry for 2-12 hours at 100-130 ℃.

The catalytic mechanism of the catalyst of the invention used as the anode catalyst of the direct methanol fuel cell is generally as follows:

methanol is first dehydrogenated and oxidized by Pt in the catalyst to release electrons and protons, forming carbon monoxide in an adsorbed state, i.e., (CO)_ads(ads is an English abbreviation for adsorption state), and formed on the Pt surface layer_COThe adsorption layer of (1). The adsorption layer isolates Pt and CH₃Contact of OH, thereby "deactivating" the Pt. And W in the system is WO₃And WO₂Exist in the form of (1). The added Sn can change the state and the adsorption performance of Pt surface electrons, so that the concentration of Pt surface positions is reduced, and the probability of Pt poisoning is favorably reduced. This is achieved byIn addition, electrons in the d orbital of Sn atom are shared with electrons in the d orbital of W atom, thereby facilitating the redox couple W (VI)/W (IV) (e.g., WO)₃/WO₂) Is performed. The redox couple has rapid valence transition function, and can decompose water at low potential to form an oxygen-containing species (OH) on the surface of W_ads. The (OH)_adsCan adsorb (CO) on the surface of Pt_adsOxidation to stable CO at low potential₂Thereby desorbing Pt to "revitalize". So that Pt can adsorb new CH again₃And (5) OH. The Pt-W-Sn/C catalyst is thus on CH₃OH is subjected to repeated catalytic oxidation reaction. The specific catalytic reaction process is represented by the formula as follows:

the Pt-W-Sn/C ternary anode catalyst of the direct methanol fuel cell of the invention is prepared by the following more specific preparation operation steps:

(1) adding carbon black into distilled water, and continuously stirring for 10-60 min at 60-100 ℃ to obtain a suspension;

(2) using a Pt loading amount which is 5-10 percent of the total weight of the catalyst, mixing chloroplatinic acid, tungstate, tin salt and hydrochloric acid according to the atomic mole ratio of Pt, W and Sn which is 3: X and Y, wherein X, Y is a natural number which is less than or equal to 3, adding the mixture into a reaction container, stirring for 10-90 min, and dropwise adding a reducing agent KBH₄、NaBH₄Formaldehyde or formic acid, hydrochloric acid is added to adjust and control the pH value of the system solution to be less than 5, and the mixture is stirred and reacted for 1 to 4 hours after the reducing agent is added;

(3) the reaction was washed with distilled water and filtered with suction until the washings were neutral. And then the reactant is placed in a drying oven to be dried for 2-12 hours at the temperature of 100-130 ℃.

The catalyst prepared in the way is a carbon-supported platinum, tungsten and tin three-way catalyst Pt-W-Sn/C.

The catalytic performance of the catalyst was tested using a three-electrode system: at 0.5M H₂SO₄And 0.5M CH₃Under the OH condition, the catalyst is mixed with Polytetrafluoroethylene (PTFE) emulsion with the solid content of 5 percent, and then the mixture is coated on a glassy carbon electrode to be used as a research electrode, a pure platinum sheet is used as a counter electrode, a Saturated Calomel Electrode (SCE) is used as a reference electrode, and the catalyst is tested at 8 DEGCurrent-voltage polarization curve of oxidized methanol at 0 ℃.

The catalytic activity of the Pt-W-Sn/C catalyst of the invention as the anode catalyst of the direct methanol fuel cell is evaluated by a method for testing the current-voltage polarization curve of a single direct methanol fuel cell with the Pt-W-Sn/C catalyst of the invention as the anode catalyst. The cathode adopts Pt/C as a catalyst, the working temperature is 80 ℃, the working pressure is normal, the feeding concentration of methanol is 2.5M, and a liquid feeding mode is directly adopted. The specific test results are shown in fig. 1.

Compared with the prior art, the invention has the following advantages:

(1) the electrocatalytic activity of the three-way catalyst Pt-W-Sn/C of the invention to methanol is basically equivalent to that of the commercial Pt-Ru/C catalyst.

(2) The Pt-W-Sn/C catalyst adopts tungsten and tin which are rich in resources, and the cost of the catalyst is much lower than that of the Pt-Ru/C catalyst.

(3) The preparation method of the catalyst is simple and easy to implement, the quality is easier to control, and the catalyst is suitable for large-scale industrial production.

Drawings

FIG. 1 shows the current-voltage polarization curve of the Pt-W-Sn/C catalyst prepared by the invention for a direct methanol fuel cell.

FIG. 2 shows the current-voltage polarization curves of electrodes in different atomic molar ratios in the Pt-W-Sn/C catalyst.

FIG. 3 shows the current-voltage polarization curves of Pt-W-Sn/C electrocatalysts prepared under different temperature conditions.

Detailed Description

Example 1

Weighing carbon black with the atomic mole fraction being 300 times of that of platinum atom, adding the carbon black into the mixture at the temperature of 80 DEG CCorresponding to a mole fraction of 1.0X 10 of platinum atoms⁵Stirring in distilled water for 30min to obtain suspension. Respectively preparing H with the concentration of 0.1M₂PtCl₆、Na₂WO₄And SnCl₄Adding the solution into dispersed carbon black suspension in sequence in an acid environment according to the atomic mol ratio of Pt, W and Sn of 3 to 2 to 1, strongly stirring for 40min, and dropwise adding KBH with the mol ratio of 3 times that of platinum atoms₄Reducing agent, adjusting pH value of the system solution to be less than 5 by hydrochloric acid, and reacting for 3 hours. The reaction was washed with distilled water, filtered with suction until the washings were neutral, and then dried in a drying cabinet at 100 ℃ for 9 hours.

The catalyst is dispersed on carbon paper and used as an anode catalyst of a direct methanol fuel cell, Pt/C is used as a catalyst for a cathode, a Nafion117 membrane is used as a proton exchange membrane, a direct methanol fuel cell monomer is assembled, a direct methanol fuel cell feeding mode is adopted, the feeding concentration of methanol is 2.5M, the working temperature is 80 ℃, the normal pressure is realized, and the current-voltage polarization curve of the single cell is tested. The results of the experiment are shown in FIG. 1. FIG. 1 shows that the catalyst prepared by the invention has good catalytic activity on methanol. The catalytic activity of the catalyst is basically equivalent to that of a Pt-Ru/C catalyst under the same condition, but is obviously higher than that of the Pt/C catalyst under the same condition.

Example 2

Weighing carbon black with the atomic mole fraction being 80 times of that of platinum atom, adding the carbon black into the mixture at 60 ℃ until the atomic mole fraction being 2.7 multiplied by 1O⁴Stirring in distilled water for 10min to obtain suspension. Respectively preparing H with the concentration of 0.1M₂PtCl₆、Na₂WO₄And SnCl₄Solution according toThe atomic mol ratio of Pt, W and Sn is 3: 2, the materials are added into the dispersed carbon black suspension in sequence in an acid environment, the mixture is stirred for 90min by force, formaldehyde reducing agent with the mol ratio being 4 times of that of platinum atom is added dropwise, hydrochloric acid is used for adjusting the pH value of the system solution to be less than 5, and the reaction is carried out for 4 hours. Washing the reaction product with distilled water, filtering and dryingUntil the washing solution is neutral, the solution is dried in a drying oven at 130 ℃ for 2 hours.

Weighing a certain mass of the catalyst, mixing the catalyst with PTFE emulsion with the solid content of 5%, coating the mixture on a glassy carbon electrode, airing the glassy carbon electrode at room temperature to prepare a research electrode of a three-electrode system, and placing the research electrode in a position of 0.5M H₂SO₄And 0.5M CH₃In an electrolytic cell of OH electrolyte, a platinum electrode is taken as a counter electrode, SCE is taken as a reference electrode, and a current-voltage polarization curve of the electrode at 80 ℃ and normal pressure is tested and researched. The results are shown in FIG. 2 by the curve "Pt: W: Sn ═ 3: 2". The results of fig. 2 show that the catalyst prepared by the invention has better methanol catalytic activity.

Example 3

Weighing carbon black with 325 times of atomic mole fraction equivalent to platinum atom mole fraction, adding into carbon black with 5.4 × 10 atomic mole fraction equivalent to platinum atom mole fraction at 100 deg.C⁴Stirring in distilled water for 20min to obtain suspension. Respectively preparing H with the concentration of 0.1M₂PtCl₆、Na₂WO₄And SnCl₄Adding the solution into dispersed carbon black suspension in sequence in an acid environment according to the atomic mol ratio of Pt, W and Sn of 3, 2 and 3, strongly stirring for 10min, and dropwise adding NaBH of which the mol portion is 1 time of that of platinum atoms₄Reducing agent, adjusting pH value of system solution to be less than 5 by hydrochloric acid, and reacting for 1 hour. The reaction was washed with distilled water, filtered with suction until the washings were neutral, and then dried in a drying cabinet at 100 ℃ for 12 hours.

Weighing a certain mass of the catalyst, mixing the catalyst with PTFE emulsion with the solid content of 5%, coating the mixture on a glassy carbon electrode, airing the glassy carbon electrode at room temperature to prepare a research electrode of a three-electrode system, and then mixing the catalyst with the PTFE emulsion to obtain a three-electrode systemIt was placed at 0.5M H₂SO₄And 0.5M CH₃In an electrolytic cell of OH electrolyte, a platinum electrode is taken as a counter electrode, SCE is taken as a reference electrode, and a current-voltage polarization curve of the electrode at 80 ℃ and normal pressure is tested and researched. The results are shown in FIG. 2 by the curve "Pt: W: Sn ═ 3: 2: 3". The results of FIG. 2 show that the invention is usefulThe prepared catalyst has better methanol catalytic activity.

Example 4

Weighing carbon black with the atomic mole fraction equivalent to 290 times of the platinum atomic mole fraction, adding the carbon black to the mixture at the temperature of 80 ℃ with the atomic mole fraction equivalent to 1.0 multiplied by 10⁵Stirring in distilled water for 30min to obtain suspension. Respectively preparing H with the concentration of 0.1M₂PtCl₆、Na₂WO₄And SnCl₄Adding the solution into dispersed carbon black suspension in sequence in an acid environment according to the atomic mol ratio of Pt, W and Sn of 3 to 2 to 1, strongly stirring for 60min, and dropwise adding KBH with the mol ratio of 3 times that of platinum atoms₄Reducing agent, adjusting pH value of the system solution to be less than 5 by hydrochloric acid, and reacting for 3 hours. The reaction was washed with distilled water, filtered with suction until the washings were neutral, and then dried in a drying cabinet at 110 ℃ for 8 hours.

Weighing a certain mass of the catalyst, mixing the catalyst with PTFE emulsion with the solid content of 5%, coating the mixture on a glassy carbon electrode, airing the glassy carbon electrode at room temperature to prepare a research electrode of a three-electrode system, and placing the research electrode in a position of 0.5M H₂SO₄And 0.5M CH₃In an electrolytic cell of OH electrolyte, a platinum electrode is taken as a counter electrode, SCE is taken as a reference electrode, and a current-voltage polarization curve of the electrode at 80 ℃ and normal pressure is tested and researched. The results are shown in FIG. 2 by thecurve "Pt: W: Sn ═ 3: 2: 1". The results of fig. 2 show that the catalyst prepared by the present invention has good methanol catalytic activity. Among them, the catalyst having an atomic ratio of Pt: W: Sn of 3: 2: 1 has the best catalytic activity, i.e., the maximum polarization current, under the same voltage condition.

Example 5

Weighing carbon black with the atomic mole fraction being 200 times of that of platinum atom, adding the carbon black into the mixture at the temperature of 60 DEG CThe molar fraction corresponds to the molar fraction of platinum atoms of 1.35X 10⁵Stirring in distilled water for 30min to obtain suspension. Respectively preparing H with the concentration of 0.1M₂PtCl₆、Na₂WO₄And SnCl₄Solution in terms of atomic molThe mixture is added into dispersed carbon black suspension in an acid environment in a molar ratio of Pt to W to Sn of 3 to 2 to 1, strongly stirred for 60min, added with formaldehyde reducing agent with a molar part 2 times that of platinum atoms dropwise, and adjusted with hydrochloric acid to have a pH value of less than 5, and reacted for 2 hours. The reaction was washed with distilled water, filtered with suction until the washings were neutral, and then dried in a drying cabinet at 120 ℃ for 10 hours.

Weighing a certain mass of the catalyst, mixing the catalyst with PTFE emulsion with the solid content of 5%, coating the mixture on a glassy carbon electrode, airing the glassy carbon electrode at room temperature to prepare a research electrode of a three-electrode system, and placing the research electrode in a position of 0.5M H₂SO₄And 0.5M CH₃In an electrolytic cell of OH electrolyte, a platinum electrode is taken as a counter electrode, SCE is taken as a reference electrode, and a current-voltage polarization curve of the electrode at 80 ℃and normal pressure is tested and researched. The results of the experiment are shown in the curve "60 ℃ preparation" of FIG. 3. The results of fig. 3 show that the catalyst prepared by the invention has better methanol catalytic activity.

Example 6

Weighing carbon black with 325 times of atomic mole fraction equivalent to platinum atom mole fraction, adding into carbon black with 100 deg.C mole fraction equivalent to platinum atom mole fraction of 1.0 × 10⁵Stirring in distilled water for 40min to obtain suspension. Respectively preparing H with the concentration of 0.1M₂PtCl₆、Na₂WO₄And SnCl₄The solution is added into dispersed carbon black suspension in sequence in an acid environment according to the atomic mol ratio of Pt to W to Sn of 3 to 2 to 1, strongly stirred for 60min, and then formic acid reducing agent with the mol ratio of 8 times of that of platinum atom is added dropwise, hydrochloric acid is used for adjusting the pH value of the system solution to be less than 5, and the reaction lasts for 3 hours. The reaction was washed with distilled water, filtered with suction until the washings were neutral, and then dried in a drying cabinet at 100 ℃ for 9 hours.

Weighing a certain mass of the catalyst, mixing the catalyst with PTFE emulsion with the solid content of 5%, coating the mixture on a glassy carbon electrode, airing the glassy carbon electrode at room temperature to prepare a research electrode of a three-electrode system, and then placing the research electrode of the three-electrode systemIs set at 0.5M H₂SO₄And 0.5M CH₃In an electrolytic cell of OH electrolyte, a platinum electrode is taken as a counter electrode, SCE is taken as a reference electrode, and a current-voltage polarization curve of the electrode at 80 ℃ and normal pressure is tested and researched. The results of the experiment are shown in the curve "100 ℃ preparation" of FIG. 3. The results of fig. 3 show that the catalyst prepared by the present invention has good methanol catalytic activity.

Example 7

Weighing carbon black with the atomic mole fraction being 310 times of that of platinum atom, adding the carbon black to the mixture at 80 ℃ with the atomic mole fraction being 1.0 multiplied by 10⁵Stirring in distilled water for 50min to obtain suspension. Respectively preparing H with the concentration of 0.1M₂PtCl₆、Na₂WO₄And SnCl₄Adding the solution into dispersed carbon black suspension in sequence in an acid environment according to the atomic mol ratio of Pt, W and Sn of 3 to 2 to 1, strongly stirring for 60min, and dropwise adding KBH with the mol ratio of 3 times that of platinum atoms₄Reducing agent, adjusting pH value of the system solution to be less than 5 by hydrochloric acid, and reacting for 3 hours. The reaction was washed with distilled water, filtered with suction until the washings were neutral, and then dried in a drying cabinet at 120 ℃ for 10 hours.

Weighing a certain mass of the catalyst, mixing the catalyst with PTFE liquid with solid content of 5%, coating the mixture on a glassy carbon electrode, airing the glassy carbon electrode at room temperature to prepare a research electrode of a three-electrode system, and placing the research electrode in a position of 0.5M H₂SO₄And 0.5M CH₃In an electrolytic cell of OH electrolyte, a platinum electrode is taken as a counter electrode, SCE is taken as a reference electrode, and a current-voltage polarization curve of the electrode at 80 ℃ and normal pressure is tested and researched. The results of the experiment are shown in the curve "80 ℃ preparation" of FIG. 3. The results of fig. 3 show that the catalystprepared by the present invention has good methanol catalytic activity. Among them, the catalyst preparation temperature of 80 ℃ is the best under the same voltage condition.

Claims (2)

1. Preparation of direct methanol fuel cell anode catalystThe method is characterized in that carbon black is added into water and stirred into suspension, then chloroplatinic acid, tin salt and tungstate are added into the suspension under the acidic environment with the pH value less than 5 to prepare mixed solution, and reducing agent is added into the mixed solution after stirring; the reducing agent is KBH₄、NaBH₄Formaldehyde or formic acid; the atomic mole parts of the raw materials are as follows:

chloroplatinic acid: 1 to 3 portions of

Tin salt: the mole fraction of tin atoms is 0.3-3 times of that of platinum atoms;

tungstate: the mole fraction of tungsten atoms is 0.3-3 times of that of platinum atoms;

carbon black: the atomic mole fraction of the platinum is 80-325 times of that of the platinum;

water: the molar fraction of which corresponds to the molar fraction of platinum atoms of 2.7X 10⁴～1.35×

10⁵Doubling;

reducing agent: KBH₄、NaBH₄Or the molar fraction of formaldehyde corresponds to the molar fraction of platinum atoms

1-4 times of the total weight of the composition; the mole fraction of formic acid is 2-8 times of the mole fraction of platinum atoms.

2. The method of claim 1, comprising the steps of:

(1) adding carbon black into distilled water, and continuously stirring for 10-60 min at 60-100 ℃ to obtain a suspension;

(2) mixing chloroplatinic acid, tungstate, tin salt and hydrochloric acid, adding into a reaction container, stirring for 10-90 min, and dropwise adding a reducing agent KBH₄、NaBH₄Formaldehyde or formic acid, hydrochloric acid is added to adjust and control the pH value of the system solution to be less than 5, and the reducing agent is stirred to react for 1-4 hours after the addition is finished;

(3) washing the reactant with distilled water, carrying out suction filtration until the washing liquid is neutral, and then placing the reactant in a drying oven to dry for 2-12 hours at 100-130 ℃.