JP3446064B2 - Electrode catalyst materials for polymer electrolyte fuel cells - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a material for an electrode catalyst used in a solid polymer electrolyte fuel cell.

[0002]

2. Description of the Related Art Fuel cells have been attracting attention as a highly efficient power generation system in harmony with the environment. In particular, solid polymer electrolyte fuel cells that use a fluorine-based ion exchange membrane as an electrolyte can operate at room temperature and have a high output density, so they are exhaust gas-free power sources for electric vehicles and household use. Widespread practical application is expected as a power source for the combined heat and power system. However, even higher performance is required for its practical application and widespread use. That is, in solid polymer electrolyte fuel cells, there is a strong demand for the realization of an electrode catalyst having a high oxygen reduction activity, especially because the loss of voltage at the positive electrode is large.

In the solid polymer electrolyte fuel cell, the electrode catalyst is arranged between the electrode and the electrolyte. As such an electrode catalyst, conductive carbon black on which platinum fine particles are highly dispersed and supported has been generally used.
However, since this type of electrode catalyst does not exhibit satisfactory catalytic performance, further improvement is required.

For example, US Patent No. 6,074,773 describes that in order to improve the electrocatalyst activity, an inorganic acid such as H ₃ PO ₄ , HNO ₃ or CF ₃ is added to carbon black carrying a catalytically active component (platinum). It has been proposed to support organic acids such as COOH and CF ₃ SO ₃ H. However, the improvement of the catalytic activity is not yet sufficient, and further improvement is demanded in that the increase of the cell voltage is small especially in the high potential region.

[0005]

Therefore, the present invention enhances the activity of the electrocatalyst used in a solid polymer electrolyte fuel cell, and increases the cell potential in a wide range from a high potential region to a low potential region. Its main purpose is to provide technology.

[0006]

The present inventor has conducted extensive research and research in view of the current state of the art as described above. As described above, conventionally, conductive carbon black particles in which platinum particles are highly dispersed and supported are generally used for the electrode catalyst of the solid polymer electrolyte fuel cell. In order to improve the catalytic activity, it is effective to increase the specific surface area of the platinum fine particles, and for that purpose, it is naturally considered that activated carbon having a large specific surface area is used as a carrier. However,
Until now, activated carbon has rarely been used as a carrier. This is because activated carbon is inferior in conductivity to carbon black, and in activated carbon having a well-developed pore structure, mass transfer of gas, ions and the like is slowed down, resulting in low catalytic activity.

However, as a result of further research by the present inventors, in a solid polymer electrolyte fuel cell, a specific fluorine-containing organic acid is impregnated or impregnated into activated carbon as a carrier carrying a catalytically active component (platinum). In addition, when using an electrode catalyst that uses a conductive agent and a fluorine-containing ion exchange resin together, the catalytic activity is significantly improved, and the cell voltage is significantly increased in a wide range from the high potential region to the low potential region. The present invention has been completed and the present invention has been completed.

That is, the present invention provides the following material for an electrode catalyst of a solid polymer electrolyte fuel cell, a catalyst electrode using this material, and a solid polymer electrolyte fuel cell provided with this catalyst electrode. is there. 1. A material for an electrode catalyst of a solid polymer electrolyte fuel cell, which comprises activated carbon supporting platinum and impregnated with a fluorine-containing organic acid, a conductive agent, and a fluorine-containing ion exchange resin. 2. An electrode catalyst for a solid polymer electrolyte fuel cell, comprising an ion-exchange membrane surface provided with a coating layer comprising the electrode catalyst material according to item 1. 3. A solid polymer electrolyte fuel cell comprising the electrode catalyst according to item 2.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The electrode catalyst for polymer electrolyte fuel cells according to the present invention can be manufactured as follows.

Activated carbon is used as the base material of the electrocatalyst according to the present invention. The activated carbon is not particularly limited, but usually has a particle size of 100 μm or less (more preferably about 50 μm), pore volume of micropores and mesopores 0.1 to 2 ml / g.
Degree (more preferably about 0.3-1 ml / g), specific surface area 500 m ² /
A material of g or more (more preferably about 700 to 3000 m ² / g) is used.

A catalytically active component is supported on the activated carbon carrier according to a conventional method. As the catalytically active component, any one can be used as long as it can exhibit catalytic activity in the oxidation reaction of fuel such as hydrogen or the reduction reaction of oxygen which is an oxidant, and specifically, platinum, palladium, iridium, rhodium. , Ruthenium, osmium, gold, silver, etc .; alloys containing these elements and at least one selected from chromium, vanadium, titanium, aluminum, tungsten, silicon, carbon, silver, iron, nickel, molybdenum, selenium and sulfur, or An oxide is illustrated. More specifically,
As the alloy, Pt- (alloy with at least one of Ru, Ir, Pd, Rh and Au), Pt-Cr, Pt-V, Pt-Ti, Pt-Al, Pt-
W, Pt-Si, Pt-C, Pt-Ag, Pt-Fe, Pt-Ni and the like are exemplified, and as the oxide, (Ru _1-x Mo _x ) _y SeO _z , Mo _x Ru _y S _z , Mo _x
Rh _y S _{z and the} like are exemplified. Among these, platinum and its alloys are preferable, and platinum and at least platinum and ruthenium, iridium, palladium, rhodium and gold.
Alloys with one are more preferred.

Supporting of the catalytically active component on the activated carbon carrier can be carried out by a conventional method. For example, when platinum is used as a catalytically active component, a desired electrode catalyst can be obtained by immersing activated carbon particles in an ethanol solution of chloroplatinic acid and then subjecting it to reduction treatment. The loading amount of platinum is usually 1 based on the total weight of platinum and activated carbon.
It is about 90%, more preferably about 5-80%.

Then, activated carbon carrying platinum is immersed in a solution of a fluorine-containing organic acid or a salt thereof as a predetermined ion conductive material to impregnate the fluorine-containing organic acid or a salt thereof. Examples of the fluorine-containing organic acid or its salt include potassium trifluoromethanesulfonate (CF ₃ SO ₃ K), trifluoromethanesulfonimide ((CF ₃ SO ₂ ) ₂ NH, trifluoromethanecarboxylic acid (CF ₃ COOH), and perfluoroethylene. -1,2-bis-phosphonic acid ((OH) ₂ OPCF ₂ CF ₂ PO (OH) ₂ ) etc. The solution of the fluorine-containing organic acid or its salt may be an aqueous solution or an organic solvent. It may be a solution. At the time of impregnation, it is preferable to carry out a stirring operation such as ultrasonic vibration stirring in order to uniformly disperse the activated carbon particles in the solution. ,Normal
It is about 5 to 50%, more preferably about 10 to 40%.

Next, a solution of a known conductive agent (such as carbon black) and a known polymer electrolyte (such as a fluorine-containing ion exchange resin) is added to the activated carbon carrying platinum and impregnated with a fluorine-containing organic acid according to a conventional method. Is added to prepare an electrode catalyst layer forming material (paste). The paste is prepared by adding a conductive agent and a polymer electrolyte solution to activated carbon carrying platinum and impregnated with a fluorine-containing organic acid and uniformly mixing them. In order to obtain a paste having a uniform composition, it is preferable to carry out a stirring operation such as ultrasonic vibration stirring. As the polymer electrolyte solution, for example, a known solution in which a fluorine-containing ion exchange resin is dissolved in alcohol / water as a solvent can be used. Carbon black as a conductive agent varies depending on the properties of activated carbon,
The average particle size is usually 70 nm or less (more preferably about 10 to 60 nm), and the amount used is usually 10 based on the weight of activated carbon.
It is about 200%, more preferably about 100%.

Next, the paste obtained above is directly applied to the polymer electrolyte (ion exchange membrane) and the applied layer is dried to form an electrode catalyst. Alternatively, the paste may be applied onto a sheet-shaped base material such as carbon paper and dried to form a catalyst layer, and then the sheet-shaped base material may be bonded to an ion exchange membrane to form an electrode catalyst. Alternatively, the catalyst layer on the sheet-shaped substrate may be transferred to the ion exchange membrane side to form the electrode catalyst. When using a salt of a fluorine-containing organic acid as a precursor of an ion-conducting substance, in order to convert the fluorine-containing organic acid salt impregnated on the platinum-supported activated carbon into a fluorine-containing organic acid, a K ion or the like is changed by a hydrogen ion. Replace. This ion replacement operation is
It is carried out by immersing in a perchloric acid aqueous solution, an acid aqueous solution such as sulfuric acid. Thus, the desired electrocatalyst is obtained.

The electrocatalyst according to the present invention is prepared by a conventional method.
It can be used as a constituent element of a polymer electrolyte fuel cell.

[0017]

According to the present invention, the catalytic activity of a solid polymer electrolyte fuel cell can be remarkably improved. Therefore, the present invention, which can significantly improve the performance of the solid polymer electrolyte fuel cell, is extremely useful in practice.

[0018]

EXAMPLES The features of the present invention will be further clarified by the following examples.

The evaluation of the catalytic activity is effective for the evaluation of the catalytic activity of the solid polymer electrolyte fuel cell and is reported to have a good correlation with the fuel cell performance (J. Electrochem). Soc., 145, 3713 (1998), J. Ele
ctrochem. Soc., 146, 1296 (1999)). Example 1 Platinum loaded with 10 wt% of activated carbon powder (average particle size 22 μm,
Specific surface area 718 m ² / g, pore volume 0.473 ml / g) 11 mg 0.2 M potassium trifluoromethanesulfonate (CF ₃ SO ₃ K) aqueous solution
It was put in 0.5 ml and dispersed by ultrasonic waves to impregnate CF ₃ SO ₃ K onto platinum-supported activated carbon. Thereafter, 10 wt% perfluorosulfonic acid resin solution (prepared by concentrating a 5 wt% solution manufactured by Aldrich) 0.5 ml and carbon black (trade name: VulcanXC-72R, manufactured by Cabot) 10 mg were added,
The mixture was again dispersed by ultrasonic waves to prepare a catalyst paste.

Next, 1 μl of catalyst paste (microliter
Torr) was applied to a rotating glassy carbon disk electrode (coating area = 0.071 cm ² ) and dried sufficiently to fix the catalyst precursor layer to the rotating electrode. Then, the catalyst precursor layer is added to 0.1
It was immersed in an aqueous solution of M 2 perchloric acid, and potassium ions in the catalyst precursor layer were replaced with hydrogen ions to form a desired catalyst layer.

Next, the rotating electrode with the catalyst layer fixed was immersed in a 0.1 M perchloric acid aqueous solution saturated with oxygen, and the reversible hydrogen electrode (RHE) was used as a reference electrode to measure the relationship between the oxygen reduction current and the electrode potential. .

Example 2 and Example 2 and Comparative Example 1
The results obtained for ~ 2 are shown in FIG. Example 2 Instead of the 0.2 M CF ₃ SO ₃ K aqueous solution used in Example 1,
0.1 M trifluoromethanesulfonimide ((CF ₃ SO ₂ ) ₂ N
H) A catalyst paste was prepared in the same manner as in Example 1 except that the aqueous solution was used.

Then, 1 μl of the catalyst paste (microliter
By applying it to a rotating glassy carbon disk electrode (application area = 0.071 cm ² ) and thoroughly drying it.
The desired catalyst layer was formed.

Then, the rotary electrode having the catalyst layer fixed thereon was immersed in a 0.1 M perchloric acid aqueous solution saturated with oxygen, and the relationship between the oxygen reduction current and the electrode potential was measured. Comparative Example 1 A catalyst layer was formed by the same method as in Example 1 except that carbon black was not added, and the relationship between oxygen reduction current and electrode potential was measured by the same method. Comparative Example 2 11 mg of carbon black carrying 10 wt% of platinum (same as in Example 1) was put in 1 ml of 5 wt% perfluorosulfonic acid resin solution (manufactured by Aldrich) and dispersed by ultrasonic waves to prepare a catalyst paste, A catalyst layer was formed, and the relationship between oxygen reduction current and electrode potential was measured by the same method. Evaluation of Results Obtained in Examples and Comparative Examples As is clear from the results shown in FIG. 1, the electrode catalyst according to the present invention is excellent in catalytic activity and significantly improves the fuel cell performance of the solid polymer electrolyte fuel cell. Can be improved.

[Brief description of drawings]

FIG. 1 is a graph showing a relationship between a current I _K, which is an index of catalyst activity, and an electrode potential E in an electrode catalyst according to the present invention and a comparative electrode catalyst.

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H01M 4/86-4/98 H01M 8/00-8/24 CAPLUS (STN) REGISTRY (STN)

Claims (3)

(57) [Claims] 1. Platinum-loaded and trifluoromethane
Rufonic acid, trifluoromethanesulfonimide, trif
Luoromethanecarboxylic acid and perfluoroethylene-1,2
Of a solid polymer electrolyte type fuel cell characterized by containing activated carbon impregnated with one kind of a fluorine-containing organic acid selected from -bis-phosphonic acid , a conductive agent and a fluorine-containing ion exchange resin. Electrode catalyst material. 2. An electrode catalyst for a solid polymer electrolyte fuel cell comprising a coating layer made of the electrode catalyst material according to claim 1 on the surface of an ion exchange membrane. 3. A solid polymer electrolyte fuel cell provided with the electrode catalyst according to claim 2.