CN1571200A

CN1571200A - Ammonium bicarbonate pore-forming material and process for preparing membrane electrode

Info

Publication number: CN1571200A
Application number: CNA2004100192277A
Authority: CN
Inventors: 田建华; 单忠强; 刘邦卫; 朱科; 陈延禧
Original assignee: Tianjin University
Current assignee: Tianjin University
Priority date: 2004-05-12
Filing date: 2004-05-12
Publication date: 2005-01-26
Anticipated expiration: 2024-05-12
Also published as: CN1259744C

Abstract

The invention relates to an ammonium bicarbonate hole-making agent and its film electrode preparing method. The novel hole-making agent provided by the invention for film electrode is ammonium bicarbonate. The film electrode preparing method by ammonium bicarbonate as follows: mixing Pt/C electric catalyst and solid ammonium bicarbonate with water and isopropyl alcohol, making supersonic vibration for 10-20 minutes, adding in Nafion solution at 8-10mu Nafion solution per mg Pt/C electric catalyst, then continuing supersonic vibration for 20-40 minutes; vacuum-drying the above pulp at 35 deg.C-45 deg.C into conjee, then uniformly coating the pulp on carbon paper; coating a layer of Nafion solution on the front surface of electrode at 8-12 mul per sq cm electrode, then vacuum-drying under the protection of nitrogen gas at 35deg.C-45deg.C for 1-2 hours; after the electrode dry, obtaining the film electrode. Place the made film electrode in a proton exchange film monomer battery, and measure voltage-current curve of the battery on the condition of H2/O2 or H2/air. The result shows that the battery performance can be remarkably improved.

Description

Ammonium bicarbonate pore-forming agent and preparation method of membrane electrode thereof

Technical Field

The invention relates to the technical field of proton exchange membrane fuel cells, and provides an ammonium bicarbonate pore-forming agent and a preparation method of a membrane electrode thereof.

Background

Proton Exchange Membrane Fuel Cells (PEMFCs) have a series of advantages of high energy conversion efficiency, large specific energy, rapid start-up, environmental friendliness, etc., and are one of the most efficient and clean power generation technologies. In the early 90s, fuel cell technologies, represented by PEMFCs, have made significant progress. Through the development of the last decade, PEMFCs have attracted attention from laboratory research to demonstration operations (electric vehicle power supply, small electronic devices, and field power generation), and have made the world recognize their great market potential and application prospects. Currently, the worldwide environmental and resource issues are increasingly prominent, which further makes PEMFCs a hot spot for the disputed development of countries in the world.

A pem fuel cell, like other types of fuel cells, is a continuously operating electrochemical reactor in which reactant fuel andoxidant are not stored in the cell during the manufacture of the cell, but are continuously supplied from the outside during operation to cause electrochemical reactions within the cell, thereby enabling continuous operation. Thermodynamically, a fuel cell is a device that converts chemical energy directly into electrical energy without passing through thermal energy. Because the device is not limited by the Carnot cycle of converting heat into work, the energy consumption is undoubtedly reduced, and the energy conversion efficiency is greatly improved.

The core component of a PEMFC is the Membrane electrode (Membrane)&Electrode Assembly, MEA). The membrane electrode consists of a gas diffusion layer, a catalyst layer and a proton exchange membrane. The gas diffusion layer is generally made of carbon paper or carbon cloth treated by Polytetrafluoroethylene (PTFE), or carbon paper or carbon cloth treated by PTFE is pressed with a layer of carbon powder bonded by PTFE to form a porous structure, and the function of the gas diffusion layer is to provide stable and quick electrode reactionThe gas transmission channel is fast, and the strength of the electrode is ensured to meet the requirement. The electrocatalyst uses supported platinum/carbon (Pt/C) or platinum-ruthenium/carbon (Pt-Ru/C), which is currently hydrogen/oxygen (H)₂/O₂) Or hydrogen/air (H)₂/air) the preferred high activity electrocatalyst for PEMFC. Proton exchange membranes are generally used with high H⁺Conductive perfluorosulfonic acid proton exchange membranes (e.g., Nafion series membranes from dupont, usa). Proton exchange membranes, as solid electrolytes for PEMFCs, directly affect cell performance and lifetime.

When hydrogen or purified reformed gas is used as fuel and air or pure oxygen is used as oxidant, H2 in the anode catalyst layer on the PEMFC membrane electrode generates electrode reaction under the action of electrocatalyst:

the electrons generated by the electrode reaction reach the cathode through an external circuit, and the hydrogen ions reach the cathode through the proton exchange membrane. Oxygen reacts with hydrogen ions and electrons in the cathode catalyst layer to generate water:

the overall cell reaction:

the membrane electrode is the core of the PEMFC electrochemical reaction that can proceed efficiently. The membrane electrode preparation process and technology are the technical key of PEMFC research, which not only directly affect the performance of the cell, but also are important for reducing the cost of the cell and improving the specific power and specific energy of the cell.

The preparation technology of the membrane electrode comprises a pretreatment process of the proton exchange membrane, a coating process of the electro-catalytic layer, a forming process of combining the diffusion layer, the electro-catalytic layer and the proton exchange membrane into a whole and the like. The membrane electrode is generally formed by hot pressing. Under normal conditions, the porosity of the membrane electrode catalyst layer after hot press molding is relatively low, and a certain diffusion resistance is formed to reactant gas. Particularly at the cathode when takingThe problem of electrode polarization caused by unfavorable mass transfer of the oxidant is particularly prominent when air is used as a reactant. In order to reduce the diffusion mass transfer resistance of the gas reactant and ensure the smooth removal of the product water, thereby improving the performance of the PEMFC, a method of adding a proper amount of pore-forming agent to improve the pore structure of the gas diffusion layer in the membrane electrode preparation process can be adopted. Reported pore formers include ammonium oxalate [ (NH)₄)₂C₂O₄]Ammonium carbonate [ (NH)₄)₂CO₃]Ammonium Nitrate (NH)₄NO₃) Lithium carbonate (Li)₂CO₃) And sodium chloride (NaCl), wherein (NH)₄)₂C₂O₄The effect of (2) is preliminarily confirmed. However, in order to significantly improve the performance of the membrane electrode, development of a novel and more efficient pore-forming agent is required.

Disclosure of Invention

In order to prepare a high-performance membrane electrode, the invention provides a novel pore-forming agent and a membrane electrode preparation method relating to the novel pore-forming agent.

The novel pore-forming agent of the membrane electrode provided by the invention is ammonium bicarbonate (NH)₄HCO₃). Ammonium bicarbonate has a low thermal decomposition temperature and moderate solubility. The membrane electrode is prepared by using ammonium bicarbonate to replace other pore-forming agents, so that the performance of the cell can be obviously improved.

The method for preparing the membrane electrode by using the ammonium bicarbonate pore-forming agent comprises the following steps:

(1) mixing a platinum/carbon electrocatalyst, solid ammonium bicarbonate, water and isopropanol, wherein the addition amount of the ammonium bicarbonate is 0.5-2 times of the weight of the platinum/carbon electrocatalyst; adding water and isopropanol in equal amount, wherein the adding amount is 0.06-0.10 ml per milligram of platinum/carbon electrocatalyst; and (5) ultrasonically oscillating for 10-20 minutes.

(2) Adding Nafion solution, wherein the adding amount of the Nafion solution is 8-10 mu l per mg of platinum/carbon electrocatalyst, and continuing ultrasonic oscillation for 20-40 minutes;

(3) vacuum drying the slurry at 35-45 deg.c to form porridge, and painting carbon paper to form electrode;

(4) brushing a layer of Nafion solution on the front surface of the electrode, wherein the brushing amount of the Nafion solution is 8-12 mu l per square centimeter of the electrode, and then carrying out vacuum drying for 1-2 h at 35-45 ℃ under the protection of nitrogen;

(5) and after the electrodes are dried, hot-pressing the two electrodes and the treated proton exchange membrane for 60-90 s at 130-135 ℃ under 0.3-0.4 MPa to obtain the membrane electrode.

Wherein the platinum content in the platinum/carbon electrocatalyst is 20 to 40 weight percent.

Wherein the Nafion solution is 5% Nafion solution by weight of DuPont, USA.

Wherein the proton exchange membrane is Nafion1135 or Nafion115 of DuPont, USA.

The membrane electrode prepared according to the technical scheme is arranged in a proton exchange membrane monomer battery. The cells were fabricated according to the usual method and measured for hydrogen/oxygen (H)₂/O₂) Or hydrogen/air (H)₂/air) condition. The result shows that the membrane electrode prepared by the method can obviously improve the performance of the battery.

Drawings

FIG. 1: working effect diagram of the membrane electrode of embodiment 1 of the invention;

FIG. 2: the working effect diagram of the membrane electrode in the embodiment 2 of the invention.

Wherein ▲ is NH₄HCO₃A pore-forming agent;

■ is (NH)₄)₂C₂O₄A pore-forming agent;

□ contains no pore former.

Detailed Description

Example 1:

(1) 8mg of Pt/C electrocatalyst (platinum content 20 wt%, UK JM company), 8mg of solid ammonium bicarbonate was mixed with 0.6ml of water and 0.6ml of isopropyl alcohol, and ultrasonically shaken for 20 minutes;

(2) adding 0.074ml of Nafion solution (5 wt%, DuPont, USA), and continuing ultrasonic oscillation for 30 minutes;

(3) vacuum drying the above ink-like slurry at 35 deg.C to obtain porridge, and uniformly coating on 2 × 2cm²On the carbon paper;

(4) coating 40 μ l Nafion solution (5 wt%, DuPont, USA) on the front surface of the electrode, and drying at 40 deg.C under nitrogen protection for 1.5 h;

(5) after the electrodes are dried, the two electrodes and the treated proton exchange membrane (Nafion115, DuPont, USA) are hot-pressed for 90s under 0.35MPa and 132 □, and then the membrane electrode is prepared.

The membrane electrode prepared according to the technical scheme is arranged in a proton exchange membrane monomer battery. The size of the electrode plate of the battery is 4 multiplied by 0.3cm³The effective area of the membrane electrode is 4cm². The battery adopts a nonporous graphite polar plate and a stainless steel end plate. First, a two-stage forced activation process is performed: adjusting hydrogen pressure and oxygen pressure to 0.10MPa and 0.12MPa, respectively, H₂And O₂The humidification temperatures of (1) were 60 □ and 55 □, respectively, and the current was slowly adjusted to 300mA/cm²The cell temperature rose to 50 □. Under the condition, after the battery continuously works for 8 hours, the hydrogen pressure and the oxygen pressure are respectively adjusted to be 0.28MPa and 0.30MPa, and H₂And O₂The humidification temperature is respectively adjusted to 80 ℃ and 75 ℃, the battery temperature is increased to 70 □, and the current is adjusted to 500mA/cm²And after continuously running for 4 hours, the external power supply is cut off. Connecting the single battery with the electronic load, and adjusting H₂And air pressure of 0.28MPa and 0.30MPa, respectively, and battery temperature of 70 deg.C,measuring cell in hydrogen/air (H)₂/air) condition. As shown in fig. 1. The test results show that NH is added₄HCO₃The membrane electrode performance of the pore-forming agent is obviously improved and is better than that of (NH)₄)₂C₂O₄The performance of the membrane electrode of the pore-forming agent.

Example 2:

(1) 8mg of Pt/C electrocatalyst (platinum content 20 wt%, UK JM company), 4mg of solid ammonium bicarbonate were mixed with 0.5ml of water and 0.5ml of isopropanol and ultrasonically shaken for 15 minutes;

(2) adding 0.065ml Nafion solution (5 wt%, DuPont, USA), and continuing ultrasonic oscillation for 20 minutes;

(3) vacuum drying the above ink-like slurry at 40 deg.C to obtain porridge, and uniformly coating on 2 × 2cm²On the carbon paper;

(4) coating 35 μ l Nafion solution (5 wt%, DuPont, USA) on the front surface of the electrode, and drying at 35 deg.C under nitrogen protection for 1 h;

(5) after the electrodes are dried, the two electrodes and the treated proton exchange membrane (Nafion115, DuPont, USA) are hot-pressed for 80s under 0.30MPa and 134 □, and then the membrane electrode is prepared.

After forced activation according to the method described in example 1, the cells were measured for H under the same conditions as described in example 1₂Voltage-current curves in the/air system are shown in fig. 2. The test results show that NH is added₄HCO₃The membrane electrode performance of the pore-forming agent is obviously improved and is better than that of (NH)₄)₂C₂O₄The performance of the membrane electrode of the pore-forming agent.

Claims

1. The pore-forming agent is characterized in that the pore-forming agent of the electro-catalytic layer of the membrane electrode is ammonium bicarbonate.

2. A preparation method of a membrane electrode taking ammonium bicarbonate as a pore-forming agent comprises the following steps: the method comprises the following steps:

(1) mixing a platinum/carbon electrocatalyst, solid ammonium bicarbonate, water and isopropanol, wherein the addition amount of the ammonium bicarbonate is 0.5-2 times of the weight of the platinum/carbon electrocatalyst; adding water and isopropanol in equal amount, wherein the adding amount is 0.06-0.10 ml per milligram of platinum/carbon electrocatalyst; carrying out ultrasonic oscillation for 10-20 minutes;

(3) vacuum drying the slurry (2) at 35-45 ℃ to form porridge, and then coating the porridge on carbon paper to form an electrode;

3. The method of claim 2, wherein the Nafion solution is 5 wt% Nafion solution from dupont, usa.

4. The method for preparing a membrane electrode using ammonium bicarbonate as a pore-forming agent according to claim 2, wherein the proton exchange membrane is Nafion1135 or Nafion115, dupont.