Fuel cell in which proton conductive gel is used and manufacturing method thereof, and electric power generation method

This is a continuation application under U.S.C 111(a) of pending prior International application No. PCT/JP2009/003793, filed on Aug. 7, 2009, which in turn claims the benefit of Japanese Application No. 2009-114288 filed on May 11, 2009, the disclosures of which Application are incorporated by reference herein.

The present invention relates to a fuel cell which is operable in a temperature range of not lower than 100° C., and in particular, relates to a fuel cell in which a homogenous solid electrolyte material is used that is superior in weight stability and proton conductivity in a temperature range of not lower than 100° C., and a method for manufacturing the same and an electric power generation method.

In recent years, fuel cells have been put into practical applications as electric power generation means accompanied by less CO 2 emission. Although several types of fuel cells have been proposed, fuel cells which are generally referred to as PEFC (polymer electrolyte fuel cell), have been extensively developed as a typical type among them.

PEFC has a structure which includes a polymer electrolyte membrane sandwiched between electrodes (an anode and a cathode) supporting a catalyst such as Pt. By supplying a gas that contains hydrogen to the anode, and a gas that contains oxygen to the cathode, hydrogen is separated on the anode into a proton and an electron by an action of the catalyst.

Thus generated proton is transferred together with H 2 O in the form of an oxonium ion H 3 O + , and supplied to the polymer electrolyte membrane. In the polymer electrolyte membrane, only the protons migrate, the protons, oxygen and electrons form a so-called three-phase interface, on the catalyst of the cathode. Accordingly, a reaction that produces water from oxygen and the proton is caused, and thus electric power generation by the fuel cell is executed. Namely, it is important for electric power generation by fuel cells that only the protons migrate in the polymer electrolyte membrane, and that hydrogen, oxygen, and electrons are not transmitted to the opposite electrode.

Thus, in fuel cells typified by PEFC, in which electric power generation is executed by proton transfer, proton conductor plays an important role in proton transfer at the electrode and the electrolyte membrane. Therefore, proton conductors have been extensively developed, along with the development of fuel cells.

However, the electric power generation efficiency of PEFC is still so low. Therefore, improvement of the reaction efficiency of the catalyst in the electrode, and improvement of the proton conduction in the polymer electrolyte membrane are important for improving the electric power generation efficiency of PEFCs. In particular, since the reaction efficiency of the catalyst greatly depends on the reaction temperature, the most effective means for increasing electric power generation efficiency is elevation of the reaction temperature of the catalyst of PEFC, namely elevation of the operation temperature of PEFC.

However, since mechanisms of proton transfer in the polymer electrolyte membranes involve oxonium (H 3 O + ) conduction via H 2 O that is present in the polymer chain, it is difficult to allow PEFC to generate electric power under an ambient pressure at not lower than 100° C. This is because water vaporizes under an ambient pressure at 100° C., and it is difficult to permit stable presence of H 2 O in the polymer electrolyte membrane at not lower than 100° C.

On the other hand, some of phosphoric acid type fuel cells (PAFCs) have been put into practical applications. Since the PAFCs use phosphoric acid as an electrolyte, electric power generation at around 200° C. is enabled. However, PAFC involves a specific problem of necessity for measures against corrosion and leakage of liquids since phosphoric acid that is an acidic liquid is used.

Accordingly, operation of fuel cells within a temperature range of approximately 100° C. to 300° C., which is referred to as middle temperature range, is advantageous. However, there still exists a problem of absence of a proton conductor which is most suited for such fuel cells.

Proton conductors are broadly classified into proton conductors intermediated by H 2 O (i.e., proton conductors in which conduction of H 3 O + is utilized), and proton conductors that conduct H + without intermediation of water. According to the proton conductors intermediated by H 2 O, it is difficult to allow H 2 O that serves as a conducting medium to be stably present at a temperature within the range of not lower than 100° C. On the other hand, as the proton conductor that conducts only H + , perovskite type oxides such as SrZr 1-x Y x O 3 based conductors have been known. However, in the case of the proton conductors composed of perovskite type oxides, the temperature at which proton can be conducted is not lower than 400° C.; therefore, operation temperature is likely to be too high.

As described above, there hardly exist proton conductors without intermediating H 2 O which are stably present within a temperature range of not higher than 300° C. Particularly, for realizing fuel cells that are operable in a temperature range of 100° C. to 200° C., the most crucial point is as to how stably H 2 O is allowed to exist in a proton conductor.

Transmission of fuels (H 2 , O 2 ) in the fuel cells may lead to deterioration of electric power generation efficiency. Therefore, proton conductors desirably have low gas permeability such as, for example, compact membranes and gels. Similarly, also in light of affinity and adhesiveness with an electrode, membranes or gels being compact are desired.

Conventionally, a variety of materials that exhibit proton conductivity at a temperature of not lower than 100° C. have been proposed.

For example, according to Nonpatent Document 1, tin oxide hydrates (SnO 2 .nH 2 O) have favorable proton conductivity. SnCl 4 that is a water soluble substance is dissolved in water, and then an equal amount of NH 4 OH is added thereto to allow Sn(OH) 4 to be formed. Thus obtained precipitates, Sn(OH) 4 are sufficiently washed with water to remove NH 4 + and Cl − ions, and then heated to 110° C. to obtain SnO 2 .nH 2 O powders.

In Nonpatent Document 1, SnCl 4 is used as a water soluble Sn compound and neutralized with NH 4 OH to form Sn(OH) 4 , which is a hydrozide salt. It is to be noted that Sn(OH) 4 and SnO 2 .nH 2 O are insoluble in water.

The SnO 2 .nH 2 O powders include both adsorbed water and bound water. Nonpatent Document 1 reports that when weight variation from room temperature to 500° C. is studied, the adsorbed water desorbs in a temperature range of 25° C. to 130° C., and then the bound water desorbs in a temperature range of 150° C. to 350° C. On the basis of the weight when the temperature is elevated to 350° C., desorption of water of not less than 50% occurs through elevating the temperature by 200° C.

SnO 2 .nH 2 O disclosed in Nonpatent Document 1 is powdery. When adsorbed water more likely to be desorbed is removed, the amount of H 2 O relative to the entire powder is approximately 20% by weight in the case of n=2.

Patent Document 1 has proposed tin oxide hydrate, namely a complex of SnO 2 .nH 2 O obtained by conjugation with ceramic porous particles in order to maintain a water holding capacity in a temperature range of not lower than 100° C. Patent Document 1 discloses that ceramics porous particles are dispersed in, for example, a SnO 2 .nH 2 O matrix to provide the hydrate with moisture supplied from pores of ceramics particles, and thus water holding capacity is improved as compared with the case of SnO 2 .nH 2 O alone even in a temperature range of not lower than 100° C.

Therefore, the conductors disclosed in Patent Document 1 are powders and molded products thereof, and the proportion of H 2 O adsorbed in the porous particles relative to the H 2 O content similar to that of Nonpatent Document 1 will account for the proportion of the adsorbed H 2 O amount relative to the entire H 2 O.

Patent Document 2 discloses a solid electrolyte membrane that is a layered phosphoric acid compound (Sn(HPO 4 ) 2 .nH 2 O etc.), which is characterized by having a molar ratio of Sn/P of 0.3 to 0.8 . Patent Document 2 discloses that crystalline tin phosphate results in a high proton conductivity of approximately 10 −2 to 10 −3 S/cm at 150° C.

According to Patent Document 2, the layered phosphoric acid compound is powdery.

The Nonpatent Document 2 discloses that a mixture of nanoparticles SnO 2 and phosphoric acid (H 3 PO 4 ) is superior in thermal stability. Furthermore, Nonpatent Document 2 also discloses that mixing of nanoparticles SnO 2 with phosphoric acid improves water holding capacity. Namely, network between SnO 2 and H 3 PO 4 is disclosed to provide high water holding capacity.

Patent Document 3 discloses a proton conductor having a P 2 O 5 or phosphoric acid group on the fine pore surface or inside the fine pore structure of a nano porous material of one metal oxide selected from tin oxide, vanadium oxide, tungsten oxide and manganese oxide. According to Patent Document 3, by forming P 2 O 5 or phosphoric acid groups in fine pores, the P 2 O 5 or phosphoric acid groups reportedly bind to water by a binding force that is greater than van der Waals attraction.

The proton conductor disclosed in Patent Document 3 is powdery. Thus, in order to improve water holding capacity, doping of nano porous fine pores with P 2 O 5 or phosphoric acid groups is carried out. Construction of a network consisting of fine pores of oxides, P 2 O 5 or phosphoric acid groups, and H 2 O improves the water holding capacity. Patent Document 3 describes that the network disclosed in Patent Document 3 is superior in water holding capacity as compared with the SnO 2 —H 3 PO 4 network disclosed in Nonpatent Document 2.

As gelatinous substances in which SnO 2 is used, Patent Document 4 discloses a gel in which SnO 2 , Sb, and NH 3 are used. According to Patent Document 4, the gel is produced in the step of preparing a material having electron conductivity of SnO 2 .

As in the foregoing, a large number of proton conductors for operating fuel cells at temperatures of not lower than 100° C. have been proposed.

As an example of a practically applied fuel cell operated in a temperature range of approximately 200° C., PAFC in which liquid H 3 PO 4 is used has already put into practical applications (Nonpatent Document 3).

[Citation List]

[Patent Documents]

Patent Document 1: Japanese Patent Laid-Open Publication No. 2007-273286

Patent Document 2: Japanese Patent Laid-Open Publication No. 2005-285426

Patent Document 3: Japanese Patent Laid-Open Publication No. 2007-66668

Patent Document 4: Japanese Patent Laid-Open Publication No. 1-257129

Patent Document 5: Japanese Patent Laid-Open Publication No. 2008-243688 (in particular, paragraph No. 0034)

Patent Document 6: Japanese Patent Laid-Open Publication No. 2008-020411 (in particular, paragraph Nos. 0013 to 0017)

[nonpatent documents]

Nonpatent Document 1: Shinji Hara et. al. Solid state Ionics 154-155 (2002) 679-685.

Nonpatent Document 2: Colloids and Surfaces A: Physicochem. Eng. Aspects 268 (2005) 147-154.

Nonpatent Document 3: Fuji Jihou Vol. 75 No. 5 (2002) 285.

Technical Problem

However, conventionally disclosed fuel cells have the following problems.

In fuel cells such as PEFCs etc., in which electric power is generated by proton transfer, a proton conductor should not permit the transmission of hydrogen, which had been supplied to the anode side, to the cathode side. Therefore, the proton conductor must have high ability to prevent the transmission of hydrogen. Thus, it is not desired that this type of proton conductor is composed of particles having pores, or a solid having air holes.

Furthermore, in order to enhance the electric power generation efficiency of fuel cells, the proton conductor should have high proton conductivity. Since substantial proton conductivity is improved as the proton conductor has a smaller thickness, particulate forms can be problematic in terms of practical applications.

In order to use a proton conductor in fuel cells, it is important that the proton conductor has thermal stability, in light of achievement of high proton conductivity, and retainment of structural stability of the fuel cell. Namely, when a large amount of H 2 O that involves in proton conduction at not lower than 100° C. moves in and out, deterioration of shape stability as a proton conductor, as well as stability of the proton conductivity may raise problems.

According to the powdery proton conductors disclosed in Nonpatent Document 1, and Patent Document 1 and Patent Document 2, desorption of the adsorbed water are obliged at approximately 100° C., and thus the state with less water on the surface of the powder occurs, leading to problems such as low proton conductivity, and formation of pores among particles.

Nonpatent Document 2 discloses that when SnO 2 is mixed with H 3 PO 4 to provide a proton conductor, thermal stability is improved. However, when the present inventors carried out a supplementary examination, it was proven that a mixture of SnO 2 colloid particles with phosphoric acid is in the form of a liquid, and SnO 2 particles are aggregated and precipitated when left to stand for a long period of time to cause separation in the solution. In addition, the composition of the layered phosphoric acid compound is represented by Sn(HPO 4 ) 2 .nH 2 O, which forms a different crystal system from SnO 2 .

Also according to the powdery proton conductor disclosed in Patent Document 3, film thinning is similarly difficult, leading to problems in forming a minute region, such as conjugation with an electrode. The proportion of H 2 O occupying the particles is estimated to be approximately 20% by weight similarly to Patent Document 1, Patent Document 2 and Nonpatent Document 1. When the water content is higher than 20% by weight, phase separation is caused between oxide particles and water. Therefore, it is difficult, in principle, to increase the amount of H 2 O and allow many proton conduction paths to exist.

Patent Document 4 discloses formation of an electron conductive membrane by obtaining a gel composed of SnO 2 , Sb and NH 3 , and thereafter applying an aqueous solution in which the gel is dissolved. However, Patent Document 4 does not disclose properties, characteristics and moisture retention capacity of the gel. In addition, the disclosed gel has a weight ratio of SnO 2 being 32.1% and NH 3 being 0.38%, which can be converted into a molar ratio of SnO 2 :NH 3 being 213:22.

Namely, the molar ratio represented by NH 3 /SnO 2 is 0.10, revealing an intermediate product formed as a gel in a region including more SnO 2 than NH 3 . It is impossible for the gel having such a composition region to have properties satisfactory as a proton conductive gel.

The foregoing problems in prior arts can be summarized as in the following.

For ensuring shape thermal stability and proton conductivity of a proton conductor at 100° C., it is necessary that the conductor is composed of a material which has a high proportion of water occupying the entire material, and exhibits less desorption of water at a temperature in the range of not lower than 100° C. Furthermore, it is necessary that binding of the material and water in the material forms a network in the proton conductor, forming a structure having fewer pores such that water is not easily desorbed. However, the proton conductors according to the aforementioned prior arts do not satisfy these requirements. Therefore, construction of a network superior in water holding capacity has been a key point in proton conductors.

The present inventors discovered that a gel having superior water holding capacity, thermal stability and shape stability, not accompanied by phase separation can be produced on the basis of a state formed by dispersing SnO 2 particles and NH 4 + , and adding H 3 PO 4 thereto to form a network of the binding of the constituents with water.

Namely, the present inventors discovered that by providing a proton conductor in a cluster state in which ions of the constituents strongly interact with one another, desorption of H 2 O due to heat can be prevented, and thus a gelatinous state not accompanied by fluidity like a liquid can be formed even in a minute region.

Furthermore, such a gelatinous state is distinct from a state in which a plurality of constituents forms a compound, and mixed with H 2 O. It is assumed that SnO 2 particles cause an electrostatic interaction with ions of other constituents to forma stable cluster region as a whole gel, rendering to be in a state having water holding capacity, thermal stability and shape stability expressed therein. Additionally, the present inventors also discovered that it is important for the proton conductive material to have a specific composition in order to form such a gelatinous state.

In addition, the present inventors succeeded in forming a binding state with a higher H 2 O content and favorable thermal stability by setting the component materials of the proton conductor in a specified proportion, and revealed that such a binding state depends on how the constituting elements can form a network.

Fuel cells in which the proton conductive material as described above is used are operable in a temperature range of not lower than 100° C., and a fuel cell system enabling stable operation even though a slight change occurs in the operation temperature can be put into practice.

Accordingly, the present invention provides a fuel cell in which a proton conductive gel having a composition that allows the water content in the material to be stably present even in a temperature range of not lower than 100° C. is used, and a method for manufacturing such a fuel cell.

Solution to Problems

The fuel cell of the present invention in which a proton conductive gel is used for solving the foregoing problems is characterized by use of a proton conductive gel prepared by mixing H 3 PO 4 with a dispersion solution composed of SnO 2 , NH 3 and H 2 O as a proton conductor to form a network of the constituents.

Since the proton conductive gel of the present invention is a gel having a high water content, and having a network structure of SnO 2 , NH 3 and H 3 PO 4 with each other, it has a high water content at a temperature of not lower than 100° C. and has a superior water holding capacity, also with superior thermal stability and proton conductivity. In addition, the gel is homogeneous without being accompanied by phase separation.

The network state refers to a state in which each of the constituents electrically assemble to result in stabilization, and this state is believed to involve potent interactions. Such interactions enable H 2 O to be stably present for a long period of time in a temperature range of not lower than 100° C.

Therefore, use of such a gel as a proton conductor enables a fuel cell to be operated in a temperature range of not lower than 100° C.

Specifically, according to an aspect of the present invention, a fuel cell is provided having

a proton conductive gel,

an anode electrode, and

a cathode electrode,

the proton conductive gel being sandwiched between the anode electrode and the cathode electrode, wherein

the proton conductive gel is composed of SnO 2 , NH 3 , H 2 O, and H 3 PO 4 ,

and provided that the molar ratio represented by NH 3 /SnO 2 is X, and the molar ratio represented by P/Sn is Y,

X is not less than 0.2 and not greater than 5, and Y is not less than 1.6 and not greater than 3.

In the fuel cell of the present invention, by making the composition of the proton conductive gel have a molar ratio X represented by NH 3 /SnO 2 in the range of not less than 0.2 and not greater than 5, a homogenous gel can be obtained without causing cloudiness and precipitation.

Moreover, setting a molar ratio Y represented by P/Sn to fall within the range of not less than 1.6 and not greater than 3 enables a homogenous gel without precipitation and cloudiness to be obtained, and the gel exhibits a weight loss percentage of not greater than 6% in a temperature range of 100° C. to 200° C.

Furthermore, the proton conductive gel produced to exhibit the molar ratios X and Y in the range described above is superior in the water holding capacity even at a temperature of not lower than 100° C., and has favorable proton conductivity.

Constructing a fuel cell by sandwiching the proton conductive gel that exhibits the molar ratios X and Y described above between electrodes having a catalyst supported enables the fuel cell to be stably operated even at a temperature of not lower than 100° C.

The aforementioned proton conductive gel preferably has a conductivity of not less than 10 −3 S/cm in the temperature range of not lower than 100° C. and not higher than 200° C.

Another aspect of the present invention relates to a method for manufacturing a fuel cell having

a proton conductive gel, an anode electrode, and a cathode electrode,

the method comprising the steps of: mixing H 3 PO 4 with a solution composed of SnO 2 , NH 3 , and H 2 O to obtain the proton conductive gel, in which

provided that the molar ratio represented by NH 3 /SnO 2 is X, the molar ratio represented by P/Sn is Y, X is not less than 0.2 and not greater than 5, and Y is not less than 1.6 and not greater than 3; and

sandwiching the proton conductive gel between the anode electrode and the cathode electrode, in this order.

In the method for manufacturing the fuel cell of the present invention, H 3 PO 4 is mixed with a solution in which SnO 2 particles, NH 4 and H 2 O are dispersed, and the molar ratios of NH 3 /SnO 2 and P/Sn are adjusted in a specified range to produce a proton conductive gel. Since this proton conductive gel has a state that enables interaction of all the constituents including H 2 O, construction of a network that is superior in the water holding capacity is enabled.

In addition, still another aspect of the present invention relates to a method for generating an electric power by a fuel cell,

the fuel cell having

a proton conductive gel,

an anode electrode, and

a cathode electrode,

the proton conductive gel being sandwiched between the anode electrode and the cathode electrode, wherein

the proton conductive gel is composed of SnO 2 , NH 3 , H 2 O, and H 3 PO 4 ,

provided that the molar ratio represented by NH 3 /SnO 2 is X, and the molar ratio represented by P/Sn is Y,

X is not less than 0.2 and not greater than 5, and Y is not less than 1.6 and not greater than 3, and wherein

the method includes the step of:

supplying hydrogen to the anode electrode and supplying oxygen to the cathode electrode while maintaining the fuel cell in a temperature range of not lower than 100° C. and not higher than 200° C. to generate a potential difference between the anode electrode and the cathode electrode.

The above objects, other objects, features and advantages of the present invention will be apparent from the following detailed description of preferred embodiments with reference to attached drawings.

Advantageous Effects of Invention

According to the present invention, by using a homogenous proton conductive gel that is superior in water holding capacity in a temperature range of 100° C. to 200° C., a fuel cell operable at a temperature of not lower than 100° C. can be realized.

FIG. 1 shows a schematic configuration view illustrating a fuel cell in which a proton conductive gel is used according to Embodiment 1 of the present invention.

FIG. 2 shows a photograph illustrating an external view of the proton conductive gel according to Embodiment 1 of the present invention.

FIG. 3 shows a flow chart illustrating a production procedure of the proton conductive gel of the present invention.

FIG. 4 shows a flow chart illustrating a production procedure of a SnO 2 solution with NH 3 dispersion.

FIG. 5 shows a X-ray diffraction graph obtained after elevating the temperature of the proton conductive gel (X=0.2, Y=3) in the present invention to 200° C.

FIG. 6 shows a graph demonstrating a proton conducting characteristic of the proton conductive gel (X=0.2, Y=3) in the present invention.

FIG. 7 shows a schematic configuration view of a sample piece upon measurement of the proton conductivity of the proton conductive gel in the present invention.

FIG. 8 shows an X-ray diffraction graph when X is 200, and Y is 5.

FIG. 9 shows a graph demonstrating results of a thermal analysis of the proton conductive gel (X=0.2, Y=3) in the present invention.

FIG. 10 shows a graph demonstrating proton conducting characteristics when X is 0.2 and Y is 3, and X is 20 and Y is 3.

FIG. 11 shows a schematic configuration view illustrating a sample piece upon evaluation of electric power generation characteristics of the fuel cell in which a proton conductive gel of the present invention is used.

Hereinafter, embodiments of the present invention are explained with reference to drawings.

FIG. 1 shows a schematic configuration view of the fuel cell in the present invention.

FIG. 1 shows only the elements required for description of the function. In addition, FIG. 2 shows an external view of the proton conductive gel in the fuel cell of the present invention in which a proton conductive gel is used.

In FIG. 1 , the numeral “11” indicates a proton conductive gel, “12” indicates an anode electrode, “13” indicates a cathode electrode, and “14” and “15” indicate an insulator.

As shown in FIG. 1 , the fuel cell of the present invention has a structure in which the proton conductive gel 11 is sandwiched between the anode electrode 12 and the cathode electrode 13 . The anode electrode 12 and the cathode electrode 13 support a catalyst of fine particles in a nanometer size such as Pt fine particles (not shown in the Figure). The insulators 14 and 15 insulate electrons and ions to prevent conduction of ions and electrical short between the anode electrode 12 and the cathode electrode 13 . The proton conductive gel 11 is obtained by mixing H 3 PO 4 with a solution composed of NH 3 , SnO 2 and H 2 O to form a network of these components.

Herein, provided that the molar ratio represented by NH 3 /SnO 2 is X, and the molar ratio represented by P/Sn is Y, X and Y satisfy the formulae of : 0.2≦X≦5, and 1.6≦Y≦3, respectively. In mixing H 3 PO 4 , the solution is preferably heated. The fuel cell of the present invention is characterized by use of this proton conductive gel 11 .

The fuel cell having the structure as described above has favorable proton conductivity even in a temperature range of not lower than 100° C. since the proton conductive gel 11 has a water holding capacity. Thus, electric power generation at a temperature which is not lower than 100° C. (preferably not higher than 200° C.) can be realized.

In the fuel cell of the present invention, by supplying a gas containing hydrogen to the anode electrode 12 , and a gas containing oxygen to the cathode electrode 13 , electrons and protons are produced by virtue of the catalyst supported on the anode electrode (not shown in the Figure). Thus produced protons reach the cathode electrode 13 after conducting through the proton conductive gel 11 , and binding to oxygen on the catalyst inside the cathode electrode 13 results in achievement of operation of the fuel cell. In this operation, the electrons are supplied to the cathode electrode 13 via the external circuit.

It should be noted that the fuel cell of the present invention is not limited to the structure shown in FIG. 1 , and the functions are performed as long as the proton conductive gel 11 having proton conductivity is provided between the anode electrode 12 that separates a gas containing hydrogen into electrons and protons, and the cathode electrode 13 for allowing the gas containing oxygen to bind to the protons.

Next, features of the proton conductive gel 11 in the fuel cell shown in FIG. 1 are described in detail.

The proton conductive gel 11 shown in FIG. 1 is produced by mixing H 3 PO 4 with a solution composed of SnO 2 particles, NH 3 and H 2 O, followed by heating. The proton conductive gel 11 in the present invention is a homogenous gelatinous substance being accompanied by no phase separation as shown in FIG. 2 , and has a network structure of the SnO 2 particles, NH 3 , H 2 O and H 3 PO 4 in the gel.

The state of forming a network refers to a state in which constituents of the proton conductive gel are present stably while keeping their interaction, without producing any compound. When the proton conductive gel in such a state is subjected to crystal evaluation by an X-ray diffraction, only diffraction peak of SnO 2 particles is detected.

The proton conductive gel is in a gelatinous state not exhibiting fluidity. The gelatinous state not exhibiting fluidity as referred to herein is defined as a state of a gel, when pushed out from a glass tube having a diameter of 1 cm to place on a glass substrate and thereafter left to stand for 1 hour, has the profile area changed within the range of four times the diameter of the glass tube.

In addition, when the molar ratio X represented by NH 3 /SnO 2 is in the range of not less than 0.2 and not greater than 5, and the molar ratio Y represented by P/Sn is in the range of not less than 1.6 and not greater than 3, a stable gelatinous state forming a network as described above can be maintained without causing phase separation and precipitation. Such a proton conductive gel has superior water holding capacity and proton conductivity even in a temperature range of not lower than 100° C.

By sandwiching the proton conductive gel having the features as described above between an anode electrode and a cathode electrode, operation of a fuel cell at a temperature which is not lower than 100° C. is enabled. Since the proton conductor has a gelatinous state, diffusion of the gas can be prevented, liquid dripping which may be problematic when a liquid such as H 3 PO 4 is used does not occur, leading to simplification of the mechanisms for maintaining the shape of the proton conductor.

According to the fuel cell of the present invention, since the proton conductive gel is advantageous in high proton conductivity as well as homogeneity, thermal weight stability and high water content, it is operable at not lower than 100° C. by utilizing proton conduction via H 2 O.

11 proton conductive gel

12 anode electrode

13 cathode electrode

14 insulator

15 insulator

21 proton conductive gel

22 electrode sheet

23 electrode sheet

24 insulator

25 insulator

31 proton conductive gel

32 electrode sheet

33 electrode sheet

34 insulator

35 insulator