BEST MODE FOR CARRYING OUT THE INVENTION

[0057] The invention will be described in more detail with reference to the embodiments thereof.

[0058] In the first production process pertaining to the present invention, the physical vapor deposition mentioned above should preferably be sputtering which employs a target composed of the noble metal and additive material mentioned above. Sputtering permits easy production with high productivity and exhibits good film-forming performance.

[0059] The physical vapor deposition mentioned above may also be pulsed laser deposition in place of sputtering. Pulsed laser deposition permits easy control in film formation and exhibits good film-forming performance,

[0060] The conventional chemical process does not introduce the solid-insoluble additive material into the noble metal material. Therefore, it does not give the catalytic material based on the alloy. By contrast, the first process pertaining to the present invention consists of coating the surface of the conductive powder with the noble metal and the additive material which is thermally solid-insoluble in the noble metal all together by physical vapor deposition. Therefore, it can compulsorily introduce the solid-insoluble additive material which originally forms no alloy with the noble metal material even when heated into the crystal lattice of the noble metal material. Thus, the process yields the conductive catalytic particles having the catalytic material (which is an alloy of the noble metal material and the additive material) adhering to the surface of the conductive powder. The conductive catalytic particles are incorporated into the first gas-diffusing catalytic electrode pertaining to the present invention, in which sintering hardly occurs because the additive material prevents the noble metal material from internal self-diffusion in the crystal lattice.

[0061] The first conductive catalytic particles pertaining to the present invention are produced by coating the surface of the conductive powder with the noble metal and the additive material which is thermally solid-insoluble in the noble metal all together by physical vapor deposition. This process prevents the noble metal material from growing in grain size at the time of deposition and the resulting product has an outstanding catalytic activity.

[0062] Moreover, the sputtering or pulsed laser deposition permits the catalytic material with good crystallinity to be deposited at a low temperature on the surface of the conductive powder. Therefore, the thus obtained first conductive catalytic particles pertaining to the present invention produce a good catalytic activity with a less amount of the catalytic material. In addition, they ensure the catalytic material to have a sufficiently large area for contact with gas, and hence the catalytic material has a large specific surface area contributing to reaction. This leads to an improved catalytic activity.

[0063] Incidentally, the first process pertaining to the present invention, which consists of coating the surface of a conductive powder with the catalytic material, has the advantage over the process of forming noble metal film on a carbon sheet by sputtering, which is disclosed in Japanese Translations of PCT for Patent No. Hei 11-510311. The former process makes the catalytic substance have a larger specific surface area contributing to reaction than the latter process, and this leads to an improved catalytic performance.

[0064] The amount of the solid-insoluble additive material to be added to the noble metal material should preferably 2-70 mol % or at % for effective prevention of sintering. If the amount of the additive material is less than 2 mol % or at % which is too small amount, the effect of preventing sintering will be poor. If the amount of the additive material is more than 70 mol % or at % which is too large amount, catalytic activity will be poor.

[0065] The solid-insoluble additive material should preferably be ceramics, whose typical examples include B (boron), silicon oxide (SiO and SiO ₂ ), gallium oxide (Ga ₂ O ₃ ), vanadium oxide (V ₂ O ₅ ), and tungsten oxide (WO ₃ ) At least one them should be used.

[0066] When the physical vapor deposition (such as sputtering) is carried out to coat the surface of the conductive powder with the noble metal material and the additive material which is thermally solid-insoluble in the noble metal material, it is desirable to vibrate the conductive powder. It is also desirable to coat the surface of the conductive material with the noble metal material and the additive material by the physical vapor deposition while vibrating the conductive material and vibrating amplifying means on a vibrating plane. Thus, the conductive powder is sufficiently vibrated and mixed, without staying at one place on the vibrating plane. Therefore, the conductive powder moves such that not only those particles in the outer layer but also those particles in the inner layer are exposed, and the conductive powder is uniformly coated with the catalytic material composed of the noble metal material and the additive material.

[0067] FIGS. 1A and 1B are schematic sectional views showing an example of the apparatus for production of the first conductive catalytic particles pertaining to the present invention.

[0068] The apparatus shown in FIG. 1A is used for the physical vapor deposition (such as sputtering) which employs a target 4 consisting of a noble metal material 2 and an additive material 3 to coat the surface of a conductive powder 1 with the catalytic material. This apparatus employs smoothly surfaced balls 5 as the vibration amplifying means. A mixture of the conductive powder 1 and the balls 5 is placed on the vibrating plane 7 in the container 6 . The mixture should preferably be vibrated by means of the vibrator 8 of electromagnetic type or supersonic horn type. The vibrating device 9 constructed as mentioned above causes the conductive powder 1 and the balls 5 to collide and mix with each other and also causes the mixture to flow without staying at one place on the vibrating plane 7 . Vibration causes the particles of the conductive powder 1 to be exposed regardless of whether they are in the upper layer or the inner layer in the container 6 . Sputtering in this manner causes the catalytic material to adhere uniformly to all the particles of the conductive powder 1 .

[0069] The balls 5 should preferably be ceramic or metallic balls 1-15 mm in diameter.

[0070] The target 4 as shown in FIG. 1B should preferably be composed of the noble metal material 2 and the additive material 3 incorporated thereinto. The additive material is any of B (boron), silicon oxide (SiO and SiO ₂ ), gallium oxide (Ga ₂ O ₃ ), vanadium oxide (V ₂ O ₅ ), and tungsten oxide (WO ₃ ). With the help of this target 4 , the physical vapor deposition such as sputtering can compulsorily introduce the additive material 3 into the crystal lattice of the noble metal material 2 .

[0071] The first conductive catalytic particles pertaining to the present invention have the catalytic material 10 (which is an alloy of the noble metal material and the additive material) adhering to the surface of the conductive powder 1 , as shown in FIG. 2A . The first gas-diffusing catalytic electrode pertaining to the present invention, which contains the conductive catalytic particles, has the advantage that the additive material effectively prevents the internal self-diffusion in the crystal lattice of the noble metal material. Thus, the occurrence of sintering can be inhibited more effectively.

[0072] Moreover, the additive material prevents the grain growth of the noble metal material at the time of deposition on the surface of the conductive powder; therefore, the first conductive catalytic particles pertaining to the present invention exhibit an outstanding catalytic activity.

[0073] Moreover, the catalytic material 10 achieves a good catalytic action in a less amount and provides a sufficient area for contact with gas, and hence provides a large specific surface area contributing to reaction. This leads to an improved catalytic performance.

[0074] Also, the catalytic material 10 which is an alloy of the noble metal material and the additive material may adhere unevenly to the surface of the conductive powder 1 , as shown in FIG. 2B . In this case, too, the resulting product has the same outstanding characteristic properties as the first conductive catalytic particles constructed as shown in FIG. 2A .

[0075] The process may be modified such that the surface of the conductive powder 1 is coated with an ionic conductor 11 and then the surface of the ionic conductor 11 undergoes the physical vapor deposition for deposition thereon of the catalytic material 10 which is an alloy of the noble metal material and the additive material, as shown in FIG. 2C . Unlike the conventional process, this process does not need thermal treatment to improve the crystallinity of the catalyst, and hence it permits the catalytic material 10 to be deposited without adverse effect on the performance of the ionic conductor 11 .

[0076] Any of the first conductive catalytic particles pertaining to the present invention as shown in FIGS. 2A to 2 C should preferably be prepared such that the catalytic material 10 is deposited in an amount of 10-1000 wt % of the conductive powder 1 from the standpoint of good catalytic performance and good electrical conductivity. The noble metal material is exemplified by Pt, Ir, Rh, etc.

[0077] On the other hand, the physical vapor deposition used in the second process pertaining to the present invention should preferably be sputtering that employs a target composed of the MI and MII. The sputtering process permits easy production with high productivity and is superior in film-forming performance.

[0078] Also, the physical vapor deposition may include pulsed laser deposition as well as the sputtering. The pulsed laser deposition process permits easy production with high productivity and is superior in film-forming performance.

[0079] Deposition by the conventional chemical process mentioned above resorts to diffusion by heating in order to introduce the MII into the MI. Heating increases the particle diameter owing to sintering. In contrast to the conventional chemical process, the second process pertaining to the present invention can compulsorily introduce the MII into the crystal lattice of the MI without heating, because it causes the MI and MII to adhere all together to the surface of the conductive powder by the physical vapor deposition such as sputtering. In this way it is possible to obtain the conductive catalytic particles having the catalytic material (which is an alloy of the MI and MII) adhering to the surface of the conductive powder. The second gas-diffusing catalytic electrode pertaining to the present invention, which contains the conductive catalytic particles, is by far less vulnerable to sintering because the MII prevents the internal self-diffusion of the crystal lattice of the MI.

[0080] Moreover, the sputtering or pulsed laser deposition permits the catalytic material with good crystallinity to adhere to the surface of the conductive powder at a low temperature. Therefore, the thus obtained second conductive catalytic particles pertaining to the present invention exhibit a good catalytic activity with a less amount of the catalytic material. They also permit the catalytic material to have a sufficiently large area for contact with gas. Thus, the catalytic material has a large specific surface area contributing to reaction. This leads to an improved catalytic performance.

[0081] The second process pertaining to the present invention, which causes the catalytic material to adhere to the surface of a conductive powder, is advantageous over the process disclosed in Japanese Translations of PCT for Patent No. Hei 11-510311 which is designed to form a film of noble metal on a carbon sheet by sputtering, because the catalytic material has a large specific surface area contributing to reaction. This lead to an improved catalytic performance.

[0082] The catalytic material may be an alloy represented by MI-MII′-MII″ (where MI is at least one species selected from noble metal elements such as Pt, Ir, Pd, Rh, Au, and Ru; MII′ is at least one species selected from Fe, Co, Ni, Cr, Al, Sn, Cu, Mo, W, O, N, F and C; and MII″ is at least one species selected from Hf, Zr, Ti, V, Nb, Ta, Ga, Ge, Si, Re, Os, Pb, Bi, Sb, Mn, and rare earth elements). The alloy may have a composition represented by MI _a -MII′ _b -MII″ _c (where a+b+c=100 at %, 0.5 at %≦b+c≦60 at %, b≦60 at %, c≦20 at %) so that it effectively prevents sintering and exhibits good catalytic performance.

[0083] If the value of b+c is less than 0.5 at %, the amount of MII′ and MII″ added is too small to prevent sintering. If the value of b+c is more than 60 at %, the amount of MII′ and MII″ is too large for the adequate catalytic action. The second gas-diffusing catalytic electrode pertaining to the present invention which is used for a fuel cell will decrease the output of the fuel cell if it contains the conductive catalytic particles having an excessively large value of b+c.

[0084] It is desirable that the amount of the MII′ (at least one species selected from Fe, Co, Ni, Cr, Al, Sn, Mn, Cu, W, O, N, F and C) as the MII should be less than 60 at %, so that the MII″ produces a good catalytic performance and effectively prevents sintering, thereby improving the catalytic activity. With an amount exceeding 60 at %, the catalytic performance and output are lowered because of too much addition of the MII′.

[0085] It is also desirable that the amount of the MII″ (at least one species selected from Hf, Zr, Ti, V, Nb, Ta, B, Ga, Si, Re, Os, Pb, Bi, Sb, Mn, and rare earth elements) as the MII should be less than 20 at %, so that the MII″ produces a good catalytic performance and effectively prevents sintering. With an amount exceeding 20 at %, the catalytic performance and output are lowered because of too much addition of the MII.

[0086] It is desirable that the conductive powder should be vibrated when the MI and MII are deposited on the surface of the conductive powder by the physical vapor deposition such as sputtering. It is also desirable that the MI and MII should be deposited on the surface of the conductive powder by the physical vapor deposition while vibrating the conductive powder together with vibration amplifying means on a vibrating plane. In this way the conductive powder is thoroughly mixed by vibration without staying at one place on the vibrating plane. Therefore, the conductive powder moves such that not only those particles in the outer layer but also those particles in the inner layer are exposed, and all of the catalytic material which is an alloy of the MI and MII is uniformly deposited on the conductive powder.

[0087] FIGS. 3A and 3B are schematic sectional views showing one example of the apparatus for producing the second conductive catalytic particles pertaining to the present invention.

[0088] As shown in FIG. 3 A, the apparatus is designed for sputtering as the physical vapor deposition process to cause the catalytic material to adhere to the surface of the conductive powder 1 by using the target 4 composed of MI 12 and MII 13 . To achieve deposition with the catalytic material, it is desirable that the conductive powder 1 should be mixed with the balls 5 which are smoothly surfaced balls as the vibration amplifying means, and the resulting mixture should be placed on the vibrating plane 7 in the container 6 . It is desirable that the vibration should be accomplished by means of the vibrator 8 which is of electromagnetic coil type or supersonic horn type. The vibrating device 9 constructed as mentioned above causes the conductive powder 1 and the balls 5 to collide each other and to flow without staying at one place on the Vibrating plane 7 . Vibration in this manner causes the layers of the conductive powder 1 to move such that not only those particles in the outer layer but also those particles in the inner layer are exposed in the container 6 , so that the catalytic material is uniformly deposited on all of the conductive powder 1 by the sputtering.

[0089] The balls 5 should preferably be ceramic or metallic balls 1-10 mm in diameter.

[0090] The target 4 as shown in FIG. 3B should preferably be constructed such that the MII 13 is introduced into the MI 12 . With the help of this target 4 , the physical vapor deposition such as sputtering can compulsorily introduce the MII 13 into the crystal lattice of the MI 12 without heating.

[0091] The second conductive catalytic particles pertaining to the present invention have the catalytic material 14 (which is an alloy of the MI and MII) adhering to the surface of the conductive powder 1 , as shown in FIG. 4A . The second gas-diffusing catalytic electrode pertaining to the present invention, which contains the conductive catalytic particles, has the advantage that the MII effectively prevents the internal self-diffusion in the crystal lattice of the MI. Thus, the occurrence of sintering can be inhibited more effectively.

[0092] They also exhibit a good catalytic activity with a less amount of the catalytic material 14 . They also permit the catalytic material 14 to have a sufficiently large area for contact with gas. Thus, the catalytic material 14 has a large specific surface area contributing to reaction. This leads to an improved catalytic performance.

[0093] Also, the catalytic material 14 (which is an alloy of the MI and MII) may adhere unevenly to the surface of the conductive powder 1 , as shown in FIG. 4B . In this case, too, the resulting product has the same outstanding characteristic properties as the second conductive catalytic particles constructed as shown in FIG. 4A .

[0094] The process may be modified such that the surface of the conductive powder 1 is coated with an ionic conductor 11 and then the surface of the ionic conductor 11 undergoes the physical vapor deposition for deposition thereon of the catalytic material 14 which is an alloy of the MI and MII, as shown in FIG. 4C . Unlike the conventional process, this process does not need thermal treatment to improve the crystallinity of the catalyst, and hence it permits the catalytic material 14 to be deposited without adverse effect on the performance of the ionic conductor 11 .

[0095] Any of the second conductive catalytic particles pertaining to the present invention as shown in FIGS. 4A to 4 C should preferably be prepared such that the catalytic material 14 is deposited in an amount of 10-1000 wt % of the conductive powder 1 from the standpoint of good catalytic performance and good electrical conductivity.

[0096] FIG. 5 is a schematic diagram showing the container 6 containing the conductive powder 1 and the balls 5 as the vibration amplifying means. This container is used for production of the first or second conductive catalytic particles pertaining to the present invention.

[0097] As shown in FIG. 5 , the conductive powder 1 and the balls 5 should be mixed together such that the total area A of the balls account for 30-80% of the area S in which the conductive powder 1 is distributed. If this ratio is excessively small, satisfactory mixing is not achieved. Conversely, if this ratio is excessively large with a small proportion of the conductive powder 1 , sputtering for adhesion of the catalytic material is poor in efficiency, which leads to a low productivity of the catalyst particles carrying the catalytic material.

[0098] FIG. 6 is a partly enlarged schematic sectional view showing the container 6 which holds the conductive powder 1 and the balls 5 as the vibration amplifying means. As shown in FIG. 6 , the balls 5 as the vibration amplifying means should preferably have a diameter (R) which is equivalent to 10-70% of the layer thickness (t) of the conductive powder 1 . The balls 5 with a diameter outside this range are undesirable as in the case of the surface ratio mentioned above.

[0099] The vibrator 8 should apply vibration to the conductive powder 1 and the balls 5 as the vibration amplifying means at a frequency of 5-200 Hz and an amplitude of 0.5-20 mm for their thorough mixing. (This applies to other embodiments mentioned later.)

[0100] Under the preferable condition as described above, sputtering, for example, in combination with vibration permits the catalytic material to adhere more uniformly to the surface of the conductive powder than sputtering without vibration. With the ball diameter smaller than 1 mm or larger than 15 mm, the frequency less than 5 Hz or more than 200 Hz, or the amplitude less than +0.5 mm, vibration does not shake the conductive powder effectively but permits it to stay on the bottom of the container. In this situation, uniform film formation cannot be achieved. Moreover, vibration with an amplitude in excess of 20 mm may force out the conductive powder, which leads to a decreased yield.

[0101] The first or second production process pertaining to the present invention may be modified such that the balls as vibration-amplifying means are replaced by an approximately flat gadget formed in an approximately spiral, concentric, or turned-around pattern. This gadget is fixed to the container, with at least part thereof remaining unfixed, such that the gadget itself is capable of free three-dimensional movement. The conductive powder may be placed on this gadget so that it undergoes vibration.

[0102] FIG. 7 is a schematic sectional view showing the vibrating device that can be used for the first or second production process pertaining to the present invention. The vibrating device is provided with the gadget 15 (as the vibration-amplifying means) which is approximately flat and is formed in an approximately spiral pattern.

[0103] FIG. 8 is a schematic sectional view showing the vibrating device that can be used for the first or second production process pertaining to the present invention. The vibrating device is provided with the gadget 16 as the vibration-amplifying means which is approximately flat and is formed in an approximately concentric pattern (with all the segments connected in the radial direction).

[0104] FIG. 9 is a schematic sectional view showing the vibrating device that can be used for the first or second production process pertaining to the present invention. The vibrating device is provided with the gadget 17 as the vibration-amplifying means which is approximately flat and is formed in an approximately turned-around pattern.

[0105] In all the cases shown in FIGS. 7 to 9 , the gadget 15 , 16 , or 17 is installed in the container 6 , with at least a part thereof unfixed. On the gadget 15 , 16 , or 17 is placed the conductive powder 1 . When the container vibrates, the gadget 15 , 16 , or 17 also vibrates while keeping its shape. The vibrating gadget in turn causes the conductive powder 1 to fully vibrate and flow. During vibration, the conductive powder 1 in the container 6 undergoes the physical vapor deposition such as sputtering, so that the catalytic material is deposited on the surface thereof. In this way, the catalytic material is uniformly deposited on the entire conductive powder in both the upper and inner layers.

[0106] For the gadget formed in a spiral, concentric, or turned-around pattern to produce the desired effect, it should be made of a metal wire 1 to 10 mm in diameter and it should have an outside diameter smaller by about 5 mm than the inside diameter of the container. In addition, the pattern should be such that adjacent wires are 5-15 mm apart. The gadget not meeting these conditions does not achieve the thorough mixing of the conductive powder 1 and hence reduces the deposition of the catalytic material.

[0107] The gadget, which is approximately flat and is formed in an approximately spiral, concentric, or turned-around pattern, should preferably have a thickness equivalent to 10-70% of the thickness of the layer of the conductive powder for the same reason as in the case where the balls are used.

[0108] The conductive powder 1 should preferably have an electrical resistance lower than 10 ⁻³ Ω·mm. It may be at least any one selected from carbon, ITO, and SnO ₂ . (ITO stands for Indium Tin Oxide; it is a conductive oxide composed of tin and indium oxide doped therein.) Carbon as the conductive powder 1 should preferably have a specific surface area larger than 300 m ² /g. Any carbon not meeting this requirement would impair the characteristic properties of the conductive catalytic particles.

[0109] The first or second gas-diffusing catalytic electrode pertaining to the present invention, which is prepared from the first or second conductive catalytic particles pertaining to the present invention, depends heavily on gas permeability for its performance. The desirable gas permeability of carbon as the conductive powder 1 is indicated by an oil absorption value higher than 200 mL/100 g.

[0110] The first or second conductive catalytic particles pertaining to the present invention may be formed alone into a catalyst layer by pressing or the like. However, it may also be formed into a film by binding with a resin. The resulting film is composed of a porous gas-permeable current collector and the conductive catalytic powder firmly adhering thereto. Such a film is desirable for production of the first or second gas-diffusing catalytic electrode pertaining to the present invention.

[0111] The first or second gas-diffusing catalytic electrode pertaining to the present invention may be composed substantially of the first or second conductive catalytic particles pertaining to the present invention. Alternatively, it may contain, in addition to the conductive catalytic particles, auxiliary components such as resin to bind them. In the latter case, the auxiliary components include a water-repellent resin such as fluorocarbon resin which contributes to binding performance and water drainage, a pore-forming agent such as CaCO ₃ which contributes to gas permeability, and an ionic conductor which contributes to the mobility of protons and the like. Moreover, the first or second conductive catalytic particles should preferably be supported on a porous gas-diffusing current collector (such as carbon sheet).

[0112] The first or second gas-diffusing catalytic electrode pertaining to the present invention may be applied to electrochemical devices such as fuel cells and hydrogen generating apparatus.

[0113] In the case of an electrochemical device which is composed basically of a first electrode, a second electrode, and an ionic conductor held between these electrodes, the first or second gas-diffusing catalytic electrode pertaining to the present invention may be applied to at least the first one of the two electrodes.

[0114] To be more specific, the first or second gas-diffusing catalytic electrode may be suitably applied to an electrochemical device in which at least either of the first and second electrodes is a gas electrode.

[0115] FIG. 10 shows a typical example of fuel cells in which is used the first gas-diffusing catalytic electrode pertaining to the present invention. The catalyst layer 18 in FIG. 10 is formed from a mixture of the first conductive catalytic particles pertaining to the present invention and an optional ionic conductor, water-repellent resin (fluorocarbon resin), and pore-forming agent (CaCO ₃ ). The first conductive catalytic particles pertaining to the present invention are composed of a conductive powder (such as carbon powder) and the catalytic material which is an alloy of the noble metal material such as Pt and the additive material such as B adhering to the surface thereof. The first gas-diffusing catalytic electrode pertaining to the present invention is a porous gas-diffusing catalytic electrode which is composed of a catalyst layer 18 and a carbon sheet 19 as a porous gas-diffusing current collector. In a narrow sense, only the catalyst layer 18 may be called the gas-diffusing catalytic electrode. Moreover, an ionic conductive portion 20 is held between the first and second electrodes, at least one of which is the first gas-diffusing catalytic electrode pertaining to the present invention.

[0116] This fuel cell has a negative electrode (fuel or hydrogen electrode) 22 connected to a terminal 21 , and a positive electrode (oxygen electrode) 24 connected to a terminal 23 , with an ionic conductive portion 20 held between them. The negative electrode (and optionally the positive electrode also) is the first gas-diffusing catalytic electrode pertaining to the present invention. When the fuel cell is in operation, hydrogen passes through the hydrogen passage 25 adjacent to the negative electrode 22 . While passing through the passage 25 , hydrogen (fuel) gives rise to hydrogen ions. These hydrogen ions, together with hydrogen ions generated by the negative electrode 22 and the ionic conductive portion 20 , migrate to the positive electrode 24 , at which they react with oxygen (air) passing through the oxygen passage 26 . Thus, there is obtained an electromotive force as desired.

[0117] This fuel cell, which has the first gas-diffusing catalytic electrode pertaining to the present invention as the first and second electrodes, is hardly subject to sintering and is superior in catalytic activity. Moreover, it ensures the catalytic material a sufficiently large area for contact with gas (hydrogen). Thus, the catalytic material has a large specific surface area contributing reaction, and this leads to improved catalytic performance and good output properties. Another advantage is a high hydrogen ion conductivity, which results from the fact that dissociation of hydrogen ions takes place in the negative electrode 22 and the hydrogen ions supplied from the negative electrode 22 migrate to the positive electrode 24 while dissociation of hydrogen ions is taking place in the ionic conductive portion 20 .

[0118] FIG. 11 shows a typical example of hydrogen producing apparatus in which the first and second electrodes are based on the first gas-diffusing electrode pertaining to the present invention.

[0119] Reactions at each electrode take place as follows.

at positive electrode: H ₂ O ⁺ H ⁺ +{fraction (1/2)}O ₂ ⁺ 2 e ⁻

at negative electrode: 2H ⁺ +2 e ⁺ →H ₂ ↑

[0120] The necessary theoretical voltage is higher than 1.23 V.

[0121] The catalyst layer 18 ′ in FIG. 11 is formed from the first conductive catalytic particles pertaining to the present invention, optionally in combination with an ionic conductor, a water-repellent resin (such as fluorocarbon resin), and a pore-forming agent (such as CaCO ₃ ). The first conductive catalytic particles pertaining to the present invention are composed of the conductive powder (such as carbon powder) and an alloy of the noble metal material (such as Pt) and the additive material (such as B) which adheres in the form of film to the surface of the conductive powder. The first gas-diffusing catalytic electrode pertaining to the present invention is a porous gas-diffusing catalytic electrode which is composed of a catalyst layer 18 ′ and a carbon sheet 19 ′ as a porous gas-diffusing current collector. An ionic conductive portion 20 ′ is held between the first and second electrodes which are the first gas-diffusing catalytic electrode pertaining to the present invention.

[0122] This hydrogen producing apparatus operates in such an way that the positive electrode 24 ′ is supplied with steam or steam-containing air, which, upon decomposition at the positive electrode 24 ′, gives rise to electrons and protons (hydrogen ions). The thus generated electrons and protons migrate to the negative electrode 22 ′ for conversion into hydrogen gas. In this way there is obtained hydrogen gas as desired.

[0123] Since the hydrogen producing apparatus is constructed such that at least one of the first and second electrodes is the first gas-diffusing catalytic electrode pertaining to the present invention, it is hardly subject to sintering and permits protons and electrons necessary for hydrogen generation to move smoothly in the negative electrode 22 ′.

[0124] The first or second gas-diffusing catalytic electrode pertaining to the present invention is provided with an ionic conductive portion, or the electrochemical device has an ionic conductive portion held between the first and second electrodes. This ionic conductor includes well-known Nafion (perfluorosulfonic acid resin made by DuPont) and fullerene derivative such as fullerenol (or polyfullerene hydroxide).

[0125] Fullerenol is fullerene having hydroxyl groups attached thereto, as shown in FIGS. 12A and 12B . The first synthesis of this compound was reported in 1992 by Chiang et al. (Chiang, L. Y.; Swirczewski, J. W.; Hsu, C. S.; Chowdhury, S. K.; Cameron, S.; and Creegan, K., J. Chem. Soc, Chem. Commun. 1992, 1791)

[0126] The present inventors formed fullerenol into an aggregate so that hydroxyl groups in adjacent fullerenol molecules react with each other as shown in FIG. 13A (in which a circle denotes a fullerene molecule). They became the first to find that the resulting aggregate as a macroscopic aggregate exhibits outstanding proton conducting characteristics (or dissociation of H ⁺ from the phenolic hydroxyl group in the fullerenol molecule).

[0127] Moreover, the fullerenol as the ionic conductor may be replaced by an aggregate of fullerene having more than one OSO ₃ H group. This fullerene derivative in which OH groups are replaced by OSO ₃ H groups, is hydrogensulfate-esterified fullerenol, as shown in FIG. 13B . It was also reported in 1994 by Chiang et al. (Chiang, L. Y.; Wang, L. Y.; Swirczewski, J. W.; Soled, S.; and Cameron, S., J. Org. Chem. 1994, 59, 3960). The hydrogensulfate-esterified fullerenol may have OSO ₃ H groups alone in one molecule or both OSO ₃ H groups and hydroxyl groups in one molecule.

[0128] An aggregate formed from a large number of molecules of fullerenol or hydrogensulfate-esterified fullerenol exhibits proton conductivity as the property of a bulk material. This proton conductivity directly involves migration of protons derived from a large number of hydroxyl groups which originally exist in molecules and OSO ₃ H groups. Therefore, this proton conductivity does not need to rely on hydrogen or protons originating from steam molecules supplied from the atmosphere. In other words, the proton conductivity manifests itself without supply of water from the outside or absorption of moisture from the air. This permits continuous use even in a dry atmosphere regardless of the environment.

[0129] A probable reason for the significant proton conductivity of the fullerene derivatives mentioned above is that fullerene as the base shows conspicuous electrophilicity which greatly promotes the electrolytic dissociation of hydrogen ions from the hydroxyl groups as well as from the highly acidic OSO ₃ H groups. In addition, the proton conductivity can be effectively increased because each fullerene molecule can accept a considerable number of hydroxyl groups and OSO ₃ H groups, so that the number of protons involved in conduction is very large per unit volume of the conductor.

[0130] The fullerenol and hydrogensulfate-esterified fullerenol mentioned above are composed mainly of carbon atoms arising from fullerene. Therefore, they are light in weight, stable in quality, and free of contaminants. In addition, fullerene is rapidly decreasing in production cost. The foregoing makes fullerene a nearly ideal carbonaceous material standing above other materials from the standpoint of resource, environment, and economy.

[0131] Other fullerene derivatives than mentioned above may also be used, which have any of —COOH, —SO ₃ H, and OPO(OH) ₂ in place of —OH and —OSO ₃ H.

[0132] The fullerenol or fullerene derivative mentioned above may be obtained by treating fullerene powder with an acid or hydrolyzing fullerene. Any known process can attach desired groups to carbon atoms constituting fullerene molecules.

[0133] The ionic conductor which constitute the ionic conductive portion of the fullerene derivative may be in the form of simple body composed substantially of fullerene derivative alone or in the form of lump solidified with a binder.

[0134] The fullerene derivative may be made into a film by press-forming, so that the resulting film serves as the ionic conductor held between the first and second electrodes. This ionic conductor in film form may be replaced by the one ( 20 or 20 ′) which is obtained from a lump of fullerene derivative solidified with a binder. In this case, the ionic conductor has a sufficient strength.

[0135] The binder mentioned above may be one or more than one kind of any known polymeric material capable of forming film. It should be used in an amount less than 20 wt % of the ionic conductive portion; it will deteriorate the conductivity of hydrogen ions if used in an amount more than 20 wt %.

[0136] The ionic conductive portion composed of the fullerene derivative as an ionic conductor and a binder permits conduction of hydrogen ions in the same way as that composed of the fullerene derivative alone.

[0137] In addition, owing to the film-forming polymeric material contained therein, the former is stronger than the latter which is formed by compression from the fullerene derivative in powder form. It is a flexible ion-conducting thin film (usually thinner than 300 μm) capable of blocking gas permeation.

[0138] The polymeric material mentioned above is not specifically restricted so long as it forms a film without inhibiting the hydrogen ion conductivity (by reaction with the fullerene derivative). It should preferably be one which is stable without electron conductivity. It includes, for example, polyfluoroethylene, polyvinylidene fluoride, and polyvinyl alcohol, which are desirable for reasons given below.

[0139] Polyfluoroethylene is desirable because it permits the fullerene derivative to be formed into a strong thin film more easily with a less amount than other polymeric materials. It produces its effect only with a small amount of 3 wt %, preferably 0.5-1.5 wt % in the ionic conductive portion. It gives a thin film ranging from 100 μm down to 1 μm in thickness.

[0140] Polyvinylidene fluoride and polyvinyl alcohol are desirable because they give an ion-conducting thin film with a remarkable ability to block gas permeation. They should be used in an amount of 5-15 wt % in the ionic conductive portion.

[0141] Any of the polyfluoroethylene, polyvinylidene fluoride, and polyvinyl alcohol would adversely affect its film-forming performance if it is used in an amount less than the lower limit of the range mentioned above.

[0142] The thin film for the ionic conductive portion composed of the fullerene derivative and the binder may be obtained by any known film-forming process such as compression molding and extrusion molding.

EXAMPLES

[0143] The invention will be described in more detail with reference to the following examples. Examples 1 to 5 demonstrate the first aspect of the present invention, and Examples 6 to 12 demonstrate the second aspect of the present invention.

Example 1

[0144] An apparatus shown in FIG. 1 was assembled from a sputtering target, a vibrator, and a container. The container was charged with a conductive powder and balls. The sputtering target (shown in FIG. 1B ) is a platinum disk 100 mm in diameter, which is incorporated with boron (B) in such an amount that the film formed by sputtering contains as much boron as shown in Table 1 giver below. The balls are stainless steel balls 3 mm in diameter. The conductive powder is a carbon powder having a surface area of 800 m ² /g and an oil absorption value of 360 mL/100 g. Sputtering is conducted with the vibrator generating vibration with an amplitude of 1 mm and a frequency of 36 Hz.

[0145] The container was charged with the carbon powder (1 g) and the stainless steel balls (35 g). Sputtering was carried out for 30 minutes while the carbon powder and stainless steel balls were being vibrated by the vibrator, with the vacuum chamber supplied with argon (at 1 Pa) and the target activated by 400 W RF. After sputtering, it was found that the carbon powder increased in weight to 1.66 g owing to deposition of a Pt/B alloy (0.66 g) thereon. This implies that the treated carbon powder carries the Pt/B alloy as much as 40 wt %.

[0146] A carbon sheet was coated with a mixture of teflon binder and carbon (not carrying platinum) dispersed in a solvent such that the coating layer was 20 μm thick after drying. This coating functions as a layer to prevent spreading.

[0147] The Pt/B alloy-carrying carbon powder, which was obtained as mentioned above, was mixed with perfluorosulfonic acid resin (as a binder) and n-propyl alcohol (as an organic solvent). The resulting mixture was applied to that side of the carbon sheet on which the layer to prevent spreading was formed. After drying, the coating layer was 10 μm thick. The thus obtained sheet was used in this example as the gas-diffusing catalytic electrode. A fuel cell as shown in FIG. 10 was made, in which the gas-diffusing catalytic electrode was placed on both sides of the ion-exchange membrane (of perfluorosulfonic acid resin). The resulting fuel cell was tested for initial output and output after operation for 200 hours. Several samples were prepared, in which the gas-diffusing catalytic electrode varies in the amount of boron. The results of measurements of output of each fuel cell are shown in Table 1 and FIG. 14 given below. Incidentally, the initial output (in terms of mW/cm ² ) generated by the fuel cell which employs the gas-diffusing catalytic electrode containing no boron is regarded as the standard (100%) for relative values. 1

[0148] It is apparently shown that while Pt as the noble metal material and B as the additive material cannot be made into an alloy by chemical heating because B is solid-insoluble in Pt, they can be made into an alloy by the physical vapor deposition such as sputtering. It is also shown that the first gas-diffusing catalytic electrode pertaining to the present invention, which contains the first conductive catalytic particles pertaining to the present invention which are the conductive powder on the surface of which is deposited by sputtering the catalytic material which is an alloy of Pt as the noble metal material and B as the additive material, prevents the internal self-diffusion of Pt crystal lattice in the catalytic material and hence is hardly subject to sintering. Therefore, it is superior in catalytic activity and output characteristics to the one containing Pt alone.

[0149] In this Example, the carbon powder as the conductive powder and the balls as the vibration-amplifying means are placed on the vibrating plane, and the catalytic material is made to adhere to the surface of the carbon powder while they are being vibrated. Therefore, the carbon powder thoroughly vibrates, without staying at one place on the vibrating plane. Thus, it is possible to make the catalytic material adhere uniformly to all of the carbon powder placed in the container.

[0150] In addition, it is apparent from Table 1 and FIG. 14 that sintering is effectively prevented if B as the additive material is added in a specific amount of 2-70 mol % or at %. This in turn leads to a good catalytic activity and a high output over a long period of time.

Example 2

[0151] The same procedure as in Example 1 was repeated to prepare a fuel cell as shown in FIG. 10 , except that B was replaced by SiO ₂ and the amount of SiO ₂ was varied as shown in Table 2. The resulting fuel cells were tested for initial output and output after operation for 200 hours. The results are shown in Table 2 and FIG. 15 . Incidentally, the initial output (in terms of mW/cm ² ) generated by the fuel cell which employs the gas-diffusing catalytic electrode containing no SiO ₂ is regarded as the standard (100%) for relative values. 2

[0152] It is apparently shown that while Pt as the noble metal material and SiO ₂ as the additive material cannot be made into an alloy by chemical heating because SiO ₂ is solid-insoluble in Pt, they can be made into an alloy by the physical vapor deposition such as sputtering. It is also shown that the first gas-diffusing catalytic electrode pertaining to the present invention, which contains the first conductive catalytic particles pertaining to the present invention which are the conductive powder on the surface of which is deposited by sputtering the catalytic material which is an alloy of Pt as the noble metal material and SiO ₂ as the additive material, prevents the internal self-diffusion of Pt crystal lattice in the catalytic material and hence is hardly subject to sintering. Therefore, it is superior in catalytic activity and output characteristics to the one containing Pt alone.

[0153] In this Example, the carbon powder as the conductive powder and the balls as the vibration-amplifying means are placed on the vibrating plane, and the catalytic material is made to adhere to the surface of the carbon powder while they are being vibrated. Therefore, the carbon powder thoroughly vibrates, without staying at one place on the vibrating plane. Thus, it is possible to make the catalytic material adhere uniformly to all of the carbon powder placed in the container.

[0154] In addition, it is apparent from Table 2 and FIG. 15 that sintering is effectively prevented if SiO ₂ as the additive material is added in a specific amount of 2-70 mol % or at %. This in turn leads to a good catalytic activity and a high output over a long period of time.

[0155] The same effect as mentioned above was produced when SiO ₂ (as the additive material) was replaced by SiO. Also, the same effect as mentioned above was produced when SiO ₂ was partly replaced by B.

Example 3

[0156] The same procedure as in Example 1 was repeated to prepare a fuel cell as shown in FIG. 10 , except that B was replaced by Ga ₂ O ₃ and the amount of Ga ₂ O ₃ was varied as shown in Table 3. The resulting fuel cells were tested for initial output and output after operation for 200 hours. The results are shown in Table 3 and FIG. 16 . Incidentally, the initial output (in terms of mW/cm ² ) generated by the fuel cell which employs the gas-diffusing catalytic electrode containing no Ga ₂ O ₃ is regarded as the standard (100%) for relative values. 3

Example 4

[0157] The same procedure as in Example 1 was repeated to prepare a fuel cell as shown in FIG. 10 , except that B was replaced by V ₂ O ₅ and the amount of V ₂ O ₅ was varied as shown in Table 4. The resulting fuel cells were tested for initial output and output after operation for 200 hours. The results are shown in Table 4 and FIG. 17 . Incidentally, the initial output (in terms of mW/cm ² ) generated by the fuel cell which employs the gas-diffusing catalytic electrode containing no V ₂ O ₅ is regarded as the standard (100%) for relative values. 4

Example 5

[0158] The same procedure as in Example 1 was repeated to prepare a fuel cell as shown in FIG. 10 , except that B was replaced by WO ₃ and the amount of WO ₃ was varied as shown in Table 5. The resulting fuel cells were tested for initial output and output after ope