JP5397241B2 - Catalyst for polymer electrolyte fuel cell and electrode for polymer electrolyte fuel cell using the same - Google Patents

Description

  The present invention relates to a polymer electrolyte fuel cell catalyst and a polymer electrolyte fuel cell electrode using the same.

  The polymer electrolyte fuel cell is being developed as a clean power source using hydrogen as a fuel, a driving power source for an electric vehicle, and a stationary power source using both power generation and heat supply. In addition, solid polymer fuel cells are characterized by a high energy density compared to secondary batteries such as lithium ion batteries, and power sources for portable computers or mobile communication devices that require high energy density. Is also being developed.

  A typical single cell of a polymer electrolyte fuel cell has a basic configuration of an anode (fuel electrode), a cathode (air electrode), and a proton-conducting solid polymer electrolyte membrane disposed between both electrodes. The anode and the cathode are usually used as a thin film electrode comprising a catalyst supporting a noble metal such as platinum, a pore forming agent such as a fluororesin powder, and a solid polymer electrolyte.

  Although the polymer electrolyte fuel cell is a high energy density power source as described above, further improvement in output per unit electrode area is required. One of the most effective solutions for this purpose is to improve the catalytic activity of the electrochemical reaction that occurs in the electrocatalyst constituting the anode and cathode. An anode using hydrogen as a fuel is an electrochemical reaction in which hydrogen molecules are oxidized to hydrogen cations (protons), which is an improvement in the catalytic activity. On the other hand, the cathode is an electrochemical reaction in which protons coming from the solid polymer electrolyte and oxygen react to reduce oxygen to water, which is an improvement in its catalytic activity. A noble metal such as platinum is used for the anode and cathode electrode catalyst of such a polymer electrolyte fuel cell. However, since noble metals are expensive, in order to accelerate the practical use and spread of solid polymer fuel cells, it is required to reduce the amount used per unit area of the electrode. To that end, further improvement in catalytic activity is essential. is there.

  Furthermore, when used as a fuel cell, it is known that metals such as platinum as a catalyst component are eluted or the carbon material used for the carrier is corroded due to start-stop and high-load operation. Durability technology that prevents elution of metals such as platinum and carbon corrosion is also very important.

As measures for preventing the corrosion of the carbon material used as the catalyst support, the following techniques have been disclosed so far. For example, in Patent Document 1, by performing heat treatment or the like, a peak intensity ( _ID ) in a range of 1300 to 1400 cm ⁻¹ called a D-band obtained from a Raman spectroscopic spectrum, and a 1500 to 1600 cm ⁻ called a G-band ⁻ It is disclosed that a carbon material having a relative intensity ratio (I _D / I _G ) with a peak intensity (I _G ) in the range of ¹ adjusted to 0.9 to 1.2 is used as a catalyst support.

In Patent Document 2, the specific surface area of the carbon material used as the catalyst carrier is set to 800 m ² / g or more and 900 m ² / g or less, so that power generation performance is high, and high potential durability and fuel shortage durability are excellent. An electrode structure of a polymer electrolyte fuel cell is disclosed.
In Patent Document 3, the anode electrode is composed of a catalyst layer, a water decomposition layer, and a gas diffusion layer, and the carrier used for the catalyst layer has a water adsorption amount of 100 cc / g or less under a saturated water vapor pressure of 60 ° C. It is disclosed that the carrier used for the water splitting layer has a water adsorption amount of 150 cc / g or more under a saturated water vapor pressure of 60 ° C.

JP 2008-41253 JP JP 2006-318707 A JP 2006-134629 A

  As described above, measures for preventing the corrosion of the carbon material used as the catalyst carrier include controlling the graphitization degree and surface area of the carbon material, as described in Patent Documents 1 and 2. However, if the degree of graphitization is increased or the specific surface area is reduced, there is no doubt that the resistance to oxidation consumption is improved. However, even if the degree of graphitization and the specific surface area are the same, the resistance to oxidation consumption is high. In order to obtain a carbon material that is low and has a high resistance to oxidation exhaustion, it was necessary to clarify what caused it. Further, it has been known that increasing the degree of graphitization or reducing the specific surface area not only lowers the dispersibility of the catalyst particles but also reduces the moisture retention and the fuel cell performance.

  In addition, as in Patent Document 3, the performance is improved by stacking and combining a carrier having a large amount of water adsorption and a carrier having a small amount of water adsorption, but a product with sufficient resistance to oxidation consumption has not been obtained. .

  In view of the above problems, an object of the present invention is to provide a catalyst having high resistance to oxidation consumption and capable of exhibiting high battery performance, and an electrode for a polymer electrolyte fuel cell using the catalyst.

In order to solve the above problems, the present inventors have intensively investigated the degree of graphitization, oxygen concentration, specific surface area, water vapor adsorption amount, etc. of the carbon material. It was found that the trends were in agreement, that is, when the two kinds of water vapor adsorption amounts at different relative humidity were specific values, it was found that excellent battery performance was exhibited with excellent oxidation consumption resistance, and the present invention was achieved. . That is, the present invention has the following gist.
(1) A catalyst in which a catalytic component having oxygen reduction activity is supported on a carbon material, the water vapor adsorption amount (V ₁₀ ) at 25 ° C. and a relative humidity of 10% of the carbon material is 2 ml / g or less, and A solid polymer fuel cell catalyst, wherein the carbon material has a water vapor adsorption amount (V ₉₀ ) of at least 400 ml / g at 25 ° C. and a relative humidity of 90%.
(2) Ratio V ₁₀ / V ₉₀ of water vapor adsorption amount V ₁₀ at 25 ° C. and relative humidity 10% of the carbon material and water vapor adsorption amount V ₉₀ at 25 ° C. and relative humidity 90% is 0.002 or less (1) 2. A catalyst for a polymer electrolyte fuel cell according to 1.
(3) A polymer electrolyte fuel cell electrode comprising at least the catalyst according to (1) or (2).

  The solid polymer fuel cell catalyst of the present invention has an effect that it has higher oxidation consumption resistance and higher battery performance than conventional catalysts. When an electrode using the catalyst is used for a polymer electrolyte fuel cell, durability of an automobile fuel cell, a stationary fuel cell, etc. can be improved, and high cell performance can be obtained. Can be reduced, the cost can be significantly reduced, and commercialization of the polymer electrolyte fuel cell can be accelerated.

  The catalyst for a polymer electrolyte fuel cell of the present invention is obtained by examining the water vapor adsorption amount of a carbon material used as a catalyst carrier, and setting the water vapor adsorption amount at a relative humidity of 10% and 90% within a specific range.

It is known that when the fuel electrode is partially depleted of hydrogen due to the presence of air or the like when the fuel cell is started or stopped, the potential of the air electrode increases and the carbon material as the catalyst carrier is oxidized and consumed. and has, but the carbon material used as a catalyst carrier, 25 ° C., the amount of adsorbed water vapor V ₁₀ at a relative humidity of 10% or less 2 ml / g, the oxidation loss is suppressed, and excellent catalytic oxidation exhaustion resistance can do. If the carbon material used as the catalyst support has a water vapor adsorption amount of more than 2 ml / g at 25 ° C. and 10% relative humidity, the above oxidation consumption occurs remarkably, and the hydrophilicity of the catalyst support becomes too high, resulting in a decrease in drainage capacity. In addition, the fuel cell performance is reduced, or the catalyst that has been carried along with the oxidation consumption is dropped or eluted, so that the amount of catalyst is reduced and the fuel cell performance is lowered. Therefore, it is more preferable that there is a margin of about 10%, and it is preferable that the amount be 1.8 ml / g or less.

  The amount of water vapor adsorption at a relative humidity as low as 10% relative humidity depends on the functional group species constituting the surface of the carbon material and its density, not on the aggregate structure or pore structure of the carbon material aggregate. Conceivable. When the water vapor adsorption amount at a relative humidity of 10% of the present invention is 2 ml / g or less, the absolute amount of functional groups on the surface of the carbon material is small, and therefore, oxidative consumption due to oxidative decomposition of the functional groups is suppressed. It is guessed.

The amount of water vapor adsorption V _{10 at} 25 ° C. and 10% relative humidity of the carbon material used as the catalyst support is better if only considering the resistance to oxidation consumption, but the dispersibility when supporting the catalyst is functional groups. Since it may be possible to improve the presence by the presence, the lower limit is preferably 0.05 ml / g or more.

When the water vapor adsorption amount V ₉₀ at a temperature of 25 ° C. and a relative humidity of 90% of the carbon material used as the catalyst support is 400 ml / g or more, the electrolyte in the vicinity of the catalyst component is kept in a suitable wet state, and the proton conductivity is high. Since the decrease can be prevented, it is possible to minimize the decrease in fuel cell performance even when it is necessary to operate with low humidification as in a fuel cell for automobiles. More preferably, there should be a margin of about 10%, and it is preferably 440 ml / g or more.

If the water vapor adsorption amount V _{90 at} 25 ° C and 90% relative humidity of the carbon material used as the catalyst support is too high, the discharge of produced water will be delayed during high load operation, and the fuel cell performance will be reduced. The upper limit is preferably 2000 ml / g or less. More preferably, it is 1200 ml / g or less. It is inferred that the dominant factor of the water vapor adsorption amount at 90% relative humidity is the pore structure of the carbon material surface. That is, since the water vapor adsorption amount at a relative humidity of 90% according to the present invention is 400 ml / g or more, it is presumed that corresponding pores exist on the surface of the carbon material.

In the present invention, the water vapor adsorption amount V ₉₀ at 25 ° C. and a relative humidity of 90%, which is an index corresponding to the moisture retention capacity of the catalyst, has a high value, and at the same time, it corresponds to the high oxidation consumption resistance of the catalyst support carbon material. Having a small value of the water vapor adsorption amount V ₁₀ at 25 ° C. and a relative humidity of 10%, which is an index, is essential for achieving both durability and high catalyst activity. Result of further study, 25 ° C., and the water vapor adsorption amount V ₁₀ at a relative humidity of _{10% 25 ℃, V 10 /} V 90 is the ratio of the water vapor adsorption amount V ₉₀ at a relative humidity of 90% is 0.002 or less And it was found that it is suitable for achieving both high durability (oxidation wear resistance) and high moisturizing ability. When V ₁₀ / V ₉₀ exceeds 0.002, the durability or the moisture retention performance is deteriorated. Therefore, more preferably, V ₁₀ / V ₉₀ is preferably 0.0018 or less.

  The amount of water vapor adsorbed at 25 ° C. and relative humidity of 10% and 90% as an index in the present invention is shown by converting the amount of water vapor adsorbed per 1 g of carbon material placed in an environment of 25 ° C. into the water vapor volume in the standard state. Index. The measurement of the water vapor adsorption amount at 25 ° C. and relative humidity of 10% and 90% of the carbon material can be performed using a commercially available water vapor adsorption amount measuring device. The water vapor adsorption amount in the present invention is an adsorption amount when the water vapor is gradually adsorbed on the carbon material by starting the adsorption from a vacuum state where the vapor pressure of the water vapor is zero, and gradually increasing the relative pressure of the water vapor. Relative humidity values of 10% and 90% are used. Alternatively, the dried carbon material can be allowed to stand in a constant temperature and humidity chamber at 25 ° C. and 10% and 90% relative humidity for a sufficient period of time, and the change can be measured from the mass change. That is, the dried carbon material is placed in a constant temperature and humidity chamber at 25 ° C. and a relative humidity of 10% and a constant temperature and humidity chamber at 25 ° C. and a relative humidity of 90%. Thus, the water vapor adsorption amount at 25 ° C., relative humidity of 10% and 90%, which is an index in the present invention, can be obtained. If the value obtained by any one of the above-described measurement methods is within the scope of the present invention, this effect can be obtained.

  Examples of the types of carbon materials used as the catalyst carrier include coke, various artificial graphites made from resin as raw materials, natural graphite, carbon black, char, so-called carbon fibers, carbon nanotubes, carbon nanohorns, fullerenes and the like. Further, for example, so-called template carbon, which is produced by dissolving a template after carbonizing the carbon source after filling the pores of the porous body with a porous material such as silica as a template, is also preferably used. Is possible. Further, these two or more kinds of complexes may be used.

  The above-mentioned types of carbon materials having the water vapor adsorption amount specified in the present invention can be selected. For example, activation treatment such as alkali activation, water vapor activation, carbon dioxide gas activation, zinc chloride activation or the like can be performed. The water vapor adsorption amount can also be controlled by performing heat treatment in an active atmosphere, a reducing gas atmosphere, or an atmosphere containing an oxidizing gas.

  The particle size of the carbon material used as the catalyst is more preferably 10 nm or more and 5 μm or less. A carbon material larger than this range can be used after being pulverized, and is preferably pulverized. If the particle size is more than 5 μm, there is a high risk of disrupting the gas diffusion path and proton conduction path, and the amount of the catalyst component used is limited particularly for economic reasons.For example, a catalyst layer with a thickness of about 10 μm When it is desired to exhibit performance, the distribution of the catalyst-carrying carbon material in the catalyst layer tends to be nonuniform, which may not be preferable. On the other hand, if the particle size is less than 10 nm, the electron conductivity is lowered, which is not preferable. In order to obtain more stable performance, the particle diameter of the carbon material is preferably 15 nm or more and 4.5 μm or less.

  Examples of catalyst components having oxygen reduction activity include noble metals such as platinum, palladium, ruthenium, gold, rhodium, osmium, iridium, composites and alloys of noble metals obtained by combining two or more of these noble metals, and noble metals and organic compounds. And a complex with an inorganic compound, a transition metal, a complex of a transition metal with an organic compound or an inorganic compound, a metal oxide, and the like. Also, a combination of two or more of these can be used.

  The amount of the metal supported as the catalyst component is preferably in the range of 10% by mass to 80% by mass in terms of metal with respect to the total mass of the carbon support supporting the catalyst component. If the amount is less than 10% by mass, the supported catalyst component is reduced, and thus the output per unit thickness of the catalyst layer may decrease. Therefore, it is necessary to make the catalyst layer thicker in order to obtain a high output, which makes it difficult to remove the generated water, which not only lowers the battery performance but also increases the amount of water contained in the catalyst layer during operation, resulting in durability. May also decrease. On the other hand, if it exceeds 80% by mass, it may be difficult to disperse the catalytically active component at a high density and the catalytic activity may be lowered, and the catalyst particles may be easily aggregated and the durability may be lowered. More preferably, it is 15 mass%-80 mass%, More preferably, it is 15 mass%-70 mass%.

  The particle diameter of the catalyst particles is preferably in the range of 2.0 nm to 10.0 nm. More preferably, it is the range of 3.0 nm-7.0 nm.

  The method for producing the solid polymer fuel cell catalyst of the present invention is not particularly limited, but a reducing agent is obtained after dissolving a metal chloride such as chloroplatinic acid, a metal nitrate, or a metal complex in a solvent such as water or an organic solvent. A production method in which a catalytically active component containing platinum is supported on a carbon support (liquid phase adsorption) is preferable. Examples of the reducing agent include alcohols, phenols, citric acids, ketones, aldehydes, carboxylic acids, ethers, and the like. At that time, sodium hydroxide, hydrochloric acid or the like may be added to adjust the pH, and a surfactant such as polyvinylpyrrolidone may be added to prevent aggregation of particles. The catalyst supported on the carbon support may be further subjected to re-reduction treatment. As the re-reduction treatment method, heat treatment is performed at a temperature of 500 ° C. or lower in a reducing atmosphere or an inert atmosphere. Alternatively, it can be dispersed in distilled water and reduced with a reducing agent selected from alcohols, phenols, citric acids, ketones, aldehydes, carboxylic acids and ethers.

  The electrode for a polymer electrolyte fuel cell of the present invention includes a catalyst layer including a catalyst in which the catalyst component having the oxygen reduction activity is supported on at least the carbon material. In addition to the catalyst, the catalyst layer includes an electrolyte material having proton conductivity, and exhibits the effect of the catalyst regardless of the type and form of the electrolyte material and the type and structure of the binder material required for the electrode configuration. Thus, these electrode constituent materials are not particularly limited. Examples of the electrolyte material having proton conductivity include polymers introduced with phosphoric acid groups, sulfonic acid groups, and the like, for example, polymers containing perfluorosulfonic acid polymer and benzenesulfonic acid.

  The method for producing the polymer electrolyte fuel cell electrode of the present invention is not particularly limited as long as it contains the catalyst for the polymer electrolyte fuel cell of the present invention, but the catalyst for the polymer electrolyte fuel cell of the present invention is not limited. And a catalyst layer slurry comprising a solvent containing the electrolyte material having proton conductivity and applying to a polymer material such as a Teflon (registered trademark) sheet, a gas diffusion layer, or an electrolyte membrane and drying. As mentioned. When applied to a polymer material such as a Teflon (registered trademark) sheet, the electrolyte membrane is sandwiched between two polymer materials such as a Teflon (registered trademark) sheet so that the catalyst layer and the electrolyte membrane are in contact with each other. As an example, the catalyst layer can be fixed to the electrolyte membrane in step 2 and then hot pressed by sandwiching it between two gas diffusion layers to produce a membrane / electrode assembly (MEA). . In addition, when applied to the gas diffusion layer, the MEA is applied by sandwiching the electrolyte membrane between the two gas diffusion layers so that the catalyst layer and the electrolyte membrane are in contact, and pressing the catalyst layer to the electrolyte membrane, such as hot pressing. Can be produced. When the catalyst layer is applied to the electrolyte membrane, the MEA can be produced by sandwiching the gas diffusion layer between the two gas diffusion layers so that the catalyst layer and the gas diffusion layer are in contact with each other. it can.

  Examples of the solvent used for the catalyst layer slurry include methanol, ethanol, isopropanol, hexane, toluene, benzene, ethyl acetate, butyl acetate and the like.

  As a function of the gas diffusion layer, a function of uniformly diffusing gas from the gas flow path formed in the separator to the catalyst layer and a function of conducting electrons between the catalyst layer and the separator are required. If it has, it will not specifically limit. As a general example, a carbon material such as carbon cloth or carbon paper is used as a main constituent material.

Various artificial graphite, natural graphite, carbon black, char, so-called carbon fibers, carbon nanotubes, carbon nanohorns, fullerenes, and other carbon materials made from coke and resin, alkali activation, water vapor activation, carbon dioxide activation, zinc chloride activation Table 1 shows the values of water vapor adsorption V ₁₀ , V ₉₀ , and V ₁₀ / V ₉₀ by heat treatment in an inert atmosphere, reducing gas atmosphere, or atmosphere containing oxidizing gas. 14 types of carbon materials from A to N shown in Table 1 were prepared. The particle diameters of these carbon materials were in the range of 10 nm to 5 μm.

  A chloroplatinic acid aqueous solution and polyvinylpyrrolidone are placed in distilled water. While stirring at 90 ° C., sodium borohydride is dissolved in distilled water and poured to reduce chloroplatinic acid. The catalyst support carbon material was added to the aqueous solution and stirred for 60 minutes, followed by filtration and washing. The obtained solid was vacuum-dried at 90 ° C., pulverized, and heat-treated at 250 ° C. for 1 hour in a hydrogen atmosphere to prepare Catalyst Nos. 1 to 14. The catalyst was prepared so that the amount of platinum supported was 50% by mass.

  The amount of water vapor adsorbed on the carbon material was measured using a constant capacity water vapor adsorption device (BELSORP18, manufactured by Nippon Bell Co., Ltd.). The water vapor was gradually supplied from the vacuum state to the saturated vapor pressure of water vapor at 25 ° C. to gradually change the relative humidity, and the water vapor adsorption amount was measured. The same value was obtained even when the same measurement was performed using a constant capacity water vapor adsorption apparatus (BELSORP-aqua3, manufactured by Nippon Bell). An adsorption isotherm was drawn from the obtained measurement results, and the water vapor adsorption amount at relative humidity of 10% and 90% was read from the figure. In Table 1, the read water vapor amount is shown in terms of the water vapor volume in the standard state adsorbed per 1 g of the sample.

  The particle diameter of the platinum particles was estimated by the Scherrer equation from the half-value width of the platinum (111) peak of the powder X-ray diffraction spectrum of the catalyst obtained using an X-ray diffractometer (manufactured by Rigaku Corporation).

  Each of the catalysts No. 1 to 14 was added to a 5% Nafion solution (manufactured by Aldrich) in an argon stream so that the mass of Nafion solids was tripled with respect to the mass of the catalyst. The catalyst was pulverized and butyl acetate was added with stirring so that the solid content concentration of the platinum catalyst and Nafion was 2% by mass to prepare each catalyst layer slurry.

The catalyst layer slurry was applied to each side of a Teflon (registered trademark) sheet by a spray method, and dried in an argon stream at 80 ° C. for 10 minutes and then in an argon stream at 120 ° C. for 1 hour. A solid polymer fuel cell electrode contained in the catalyst layer was obtained. The conditions of spraying and the like were set so that the amount of platinum used for each electrode was 0.10 mg / cm ² . The amount of platinum used was determined by measuring the dry mass of a Teflon (registered trademark) sheet before and after spray coating and calculating the difference.

In addition, two 2.5 cm square pieces were cut from the obtained polymer electrolyte fuel cell electrode, and the electrolyte membrane (Nafion 112) was cut with two electrodes of the same type so that the catalyst layer was in contact with the electrolyte membrane. Hot pressing was performed for 10 minutes at 130 ° C. and 90 kg / cm ² . After cooling to room temperature, only the Teflon (registered trademark) sheet was carefully peeled off to fix the anode and cathode catalyst layers to the Nafion membrane. Further, two commercially available carbon cloths (EC-CC1-060 manufactured by ElectroChem) were cut into 2.5 cm square pieces, and the anode and cathode fixed to the Nafion membrane were sandwiched between 130 ° C and 50 kg / cm ² at 10 ° C. 14 minutes of membrane / electrode assemblies (Membrane Electrode Assembly, MEA) were produced by hot pressing for 5 minutes.

  Each of the produced MEAs was incorporated into a fuel cell measurement device, and battery performance was measured. In the battery performance measurement, the voltage between the cell terminals was changed stepwise from the open voltage (usually about 0.9 to 1.0 V) to 0.2 V, and the current density flowing when the cell terminal voltage was 0.8 V was measured. In addition, as a durability test, a cycle of holding the open voltage for 15 seconds and holding the cell terminal voltage at 0.5 V for 15 seconds was performed 4000 times, and then the battery performance was measured in the same manner as before the durability test. As the gas, air was supplied to the cathode and pure hydrogen was supplied to the anode so that the utilization rates would be 50% and 80%, respectively, and each gas pressure was adjusted to 0.1 MPa with a back pressure valve provided downstream of the cell. . The cell temperature was set to 70 ° C., and the supplied air and pure hydrogen were bubbled in distilled water kept at 50 ° C. and humidified.

  Table 2 shows the battery performance results of each MEA and the battery performance after the endurance test. MEA using catalyst Nos. 1, 4, 6, 7, 9, 10, 12, 13, 14 of the present invention exhibits excellent initial battery performance and at the same time maintains high battery performance after endurance testing. doing. It can be seen that the MEA using Comparative Catalyst Nos. 2 and 8 has excellent initial battery performance, but the battery performance after the durability test is low and the durability is inferior. In addition, the MEA using the catalyst Nos. 3 and 5 of the comparative example has a low deterioration rate indicating a difference between the initial battery performance and the battery performance after the durability test, and is excellent in durability, but the initial battery performance is the present invention. It is inferior to MEA using No. 1, 4, 6, 7, 9, 10, 12, 13, 14 Note that the MEA using the catalyst No. 11 of the comparative example is an MEA using the catalyst No. 1, 4, 6, 7, 9, 10, 12, 13, 14 of the present invention in both initial battery performance and durability performance. Is inferior to According to the present invention, both the excellent initial battery performance and the durability performance can be exhibited at the same time because the water vapor adsorption amount is high at a relative humidity of 90%. High battery performance is exhibited even under the above conditions, and furthermore, the water vapor adsorption amount at 10% relative humidity is low, and the adsorption amount of functional groups that promote the oxidative consumption of the carbon material is small, so it exhibits high durability performance. Because.

Claims (3)

A catalyst in which a catalyst component having oxygen reduction activity is supported on a carbon material, the water vapor adsorption amount (V ₁₀ ) at 25 ° C. and a relative humidity of 10% of the carbon material is 2 ml / g or less, and the carbon material The solid polymer fuel cell catalyst characterized in that the water vapor adsorption amount (V ₉₀ ) at 25 ° C. and 90% relative humidity is 400 ml / g or more. 25 ° C. of the carbon material, a water vapor adsorption amount V ₁₀ at a relative humidity of 10%, 25 ° C., the ratio V ₁₀ / V ₉₀ of the water vapor adsorption amount V ₉₀ at a relative humidity of 90% according to claim 1 is 0.002 or less Catalyst for polymer electrolyte fuel cell.   3. An electrode for a polymer electrolyte fuel cell, comprising at least the catalyst according to claim 1.