HK1083025B - Solid electrolyte and electrochemical system using the solid electrolyte - Google Patents

Description

Solid electrolyte and electrochemical system using the same

Technical Field

The present invention relates to a proton (hydrogen ion) highly conductive solid electrolyte or a hydroxide ion highly conductive solid electrolyte which is applicable to a fuel cell or the like, and a fuel cell and other electrochemical systems using the solid electrolyte.

Background

In the past, an electrolysis apparatus having a proton conductive solid electrolyte, such as a fuel cell, a dehumidifier, or an electrolytic hydrogen generator, was put to practical use. In particular, proton-conductive solid electrolytes operating at normal temperatures have been used for various purposes. For example, in the case of a polymer electrolyte fuel cell, electric current and electric energy are generated by an electrochemical oxidation reaction of hydrogen supplied to the anode, as shown in the following reaction formula (1), and an electrochemical reduction reaction of oxygen supplied to the cathode, as shown in (2), and transfer of protons in the electrolyte between the anode and the cathode.

H₂→2H⁺+2e^- (1)

1/2O₂+2H⁺+2e^-→H₂O (2)

In a direct methanol fuel cell, fuel is electrochemically oxidized at the negative electrode, releasing protons, with methanol being provided as fuel; and in other fuel cells, substances other than hydrogen or methanol are used as fuel. They can also operate with proton conductive solid electrolytes.

For example, electrolytic hydrogen generators have been put to practical use as electrolytic devices. This electrolytic hydrogen generator generates hydrogen by the reverse reaction of the aforementioned reaction formulae (1) and (2) of the fuel cell. By using it, high-purity hydrogen can be obtained even with water and electric energy in the device area, and the device has the advantage of no need of a hydrogen cylinder. In addition, when a solid electrolyte is used, electrolysis can be easily performed by merely supplying pure water containing no electrolyte. The paper industry also attempts to produce hydrogen peroxide for bleaching by using the following formula (3) under a similar system (see non-patent reference 1).

O₂+H₂O+2e^-→HO₂ ^-+OH^- (3)

The dehumidifier has a structure similar to that of a fuel cell and a hydrogen generator, in which a proton-conductive solid electrolyte is sandwiched between positive and negative electrodes, and when a voltage is applied between the positive and negative electrodes, a reaction represented by the following formula (4) occurs at the positive electrode, water is decomposed into oxygen and protons, and the protons move toward the negative electrode through the solid electrolyte, and are combined with oxygen in the air again to generate water by a reaction represented by the formula (5).

H₂O→1/2O₂+2H⁺+2e^- (4)

1/2O₂+2H⁺+2e^-→H₂O (5)

An operating principle similar to that of an electrolytic hydrogen generator can also decompose water to remove moisture, and therefore, an air conditioner combined with a moisture evaporation cold blast cooler has been proposed (see non-patent reference 2).

In any of the systems that have been used as described above, a perfluorosulfonic acid ion-exchange membrane represented by a solid electrolyte Nafion membrane is used. In addition, various sensors, electrochromic display elements, and the like also basically operate based on the same principle as described above, that is, they operate on a principle in which protons are transferred in an electrolyte between two different redox pairs of a positive electrode and a negative electrode. Therefore, a proton conductive solid electrolyte can be applied. At present, experimental studies on systems having these proton-conductive solid electrolytes are also being conducted.

For the hydrogen sensor, the change in electrode potential caused by the change in hydrogen concentration at the time of introducing hydrogen, for example, caused by the above-described equations (4) and (5), is utilized. Further, the proton conductive electrolyte may also be applied to a humidity sensor in which electrode potential change or ion conductivity change is used.

For example, in the case of an electrochromic display element, an electric field is applied to cause the reaction of the following formula (6) to produce WO on the negative electrode₃And (4) color generation. The applications include display devices and light-shielding glasses. This system also works by proton transfer back and forth at the negative electrode, so proton conductive solid electrolytes can also be applied.

WO₃+xH⁺+xe^-→HxWO₃(color generation) (6)

Further, a primary battery, a secondary battery, a light converter, an electrolytic water generator, and the like can also be considered as an electrochemical system that operates using a proton-conductive solid electrolyte. A nickel-metal hydride battery, which is an example of a storage battery, uses a hydrogen-adsorbing alloy for a negative electrode, nickel hydroxide for a positive electrode, and an alkaline electrolyte solution as an electrolyte. As shown in the following formulas (7) and (8), proton electrochemical oxidation-reduction occurs in the negative electrode and hydrogen is absorbed into the hydrogen absorbing alloy during charge and discharge.

[ charging]H₂O+e^-→ H (storage) + OH^- (7)

[ discharge of electric energy]H (storage) + OH^-→H₂O+e^- (8)

An electrochemical redox reaction of nickel hydroxide represented by the following formulas (9) and (10) occurs at the positive electrode.

[ charging]Ni(OH)₂+OH^-→NiOOH+H₂O+e^-(9)

[ discharge of electric energy]NiOOH+H₂O+e^-→Ni(OH)₂+OH^-(10)

The charge-discharge reaction of this battery is formed by the transfer of protons or hydroxide ions in the electrolyte, and the principle is to use a proton-conductive electrolyte. However, not a solid electrolyte but an alkaline electrolyte solution has been used.

For example, a light conversion system using yttrium in the negative electrode has been proposed (see non-patent reference 3). When an electric field is applied, yttrium is oxidized by hydrogen as shown in the following formula (11) and transmits light. Thus, the transmission and non-transmission of light can be switched by an electric field. The principle of this system is also to use a proton conductive solid electrolyte, but an alkaline electrolyte solution has been generally used.

Y+3/2H₂O+3e^-→YH₃+3OH (11)

The electrolyzed water is water subjected to an electrolytic reaction, and its function differs depending on the reducing side and the oxidizing side. It is beneficial for health, and has antibacterial, cleaning, and crop growth promoting effects. Has multiple uses such as drinking water, food water, cooking water, washing water, agricultural water and the like. The electrolysis reaction is promoted by the electrolyte contained in the water. However, in the case where the electrolyte is dissolved in water, it is necessary to remove the electrolyte when the water is used. When a solid electrolyte is used, the electrolyte does not need to be removed.

The proton conductive electrolyte of normal temperature operation type used in the above electrochemical system has been mostly used in the pastThe membrane is a typical perfluorosulfonic acid polymer ion exchange membrane. But perfluorosulfonic acid electrolytes are expensive due primarily to the complexity of the manufacturing process. Big (a)The economic benefits of mass production of these electrolytes have helped to reduce their price to some extent, but there is still a desire for alternative materials at low prices.

In view of the above, a composite compound of an organic polymer having a hydroxyl group and various inorganic compounds has been proposed as an electrolyte material having a low price and high ion conductivity instead of a perfluorosulfonic acid electrolyte. This is based, for example, on trace levels of the following complex compounds: polyvinyl alcohol and silicic acid compounds (refer to patent document 1), polyvinyl alcohol and tungstic acid compounds (refer to patent document 2), polyvinyl alcohol and molybdic acid compounds (refer to patent document 2), polyvinyl alcohol and stannic acid compounds (refer to patent document 3), polyvinyl alcohol and zincic acid compounds (refer to patent documents 4, 5). As for the other components, at least one of phosphorus, boron, aluminum, titanium, calcium, strontium and barium compounds is added. Thus, they can be produced by a simple process of neutralizing the raw material salt of the inorganic compound in a solution in which polyvinyl alcohol coexists, and are characterized by low cost. The polyvinyl alcohol side is provided with water resistance, strength, and electrical conductivity by being combined with an inorganic compound. On the other hand, flexibility is imparted to the inorganic compound side by the combination with polyvinyl alcohol. As a result, a high-performance solid electrolyte is produced. These materials are treated with an aldehyde, which acetylates the hydroxyl groups of the polyvinyl alcohol moiety and also suppresses excessive swelling due to water absorption.

[ patent document 1] Japanese patent application laid-open No. 2003-007133

[ patent document 2] Japanese patent application laid-open No. 2003-138084

[ patent document 3] Japanese patent application laid-open No. 2003-208814 and No. 2002-4151

[ patent document 4] Japanese patent application No. 2002-35832

[ patent document 5] Japanese patent application No. 2002 and 310093

[ patent document 6] Japanese patent application No. 2003-86442

[ Nonpatent document 1] electrochemistry, 69, No.3, 154-

[ Nonpatent document 2] the Collection of lectures from the national congress of the Electrical society in 12 years, P3373(2000)

[ non-patent document 3] J.electrochem.Soc., Vol.143, No.10, 3348-3353(1996)

Disclosure of Invention

The present invention is intended to improve the energy conversion efficiency of the aforementioned fuel cell, and it is desirable to operate at a higher temperature. Operating at high temperatures reduces the amount of platinum used as an electrode catalyst, which is advantageous in terms of cost. In particular for fuel cells using modified carbohydrate fuels and direct methanol type fuel cells, it is also advantageous to operate at high temperatures in order to mitigate poisoning of the platinum catalyst by carbon monoxide.

In addition, in order to improve the energy conversion efficiency of various electrolytic devices such as an electrolytic hydrogen generator, it is also desired to use the electrolytic device at a higher temperature. However, the proton conductivity of the novel solid electrolyte composed of the above-mentioned composite compound of the organic polymer having a hydroxyl group and the inorganic compound gradually decreases at a temperature of 100 ℃ or more. The operating temperature cannot be too high for use in electrochemical systems such as fuel cells, electrolyzers, etc. Further, the problem of the decrease in conductivity due to high temperature is more significant in an environment with insufficient humidity. Therefore, in the case of operation at a temperature of 100 ℃ or higher, in order to increase the relative humidity, it is necessary to operate in a pressurized state, which in turn makes the system bulky. Since the decrease in conductivity at high temperatures is particularly significant in dry environments, the system becomes complicated by the need to control the humidity at the start of operation and at the time of shutdown for various electrochemical systems.

Solid electrolytes composed of a composite compound of polyvinyl alcohol and an inorganic compound as proposed in the above-mentioned patent documents 1 to 5 suffer from performance degradation at a temperature of 100 ℃ or higher. The main reason for this reduction is, for example, hydrophobization, hardening, which occurs as a result of partial degradation of the polyvinyl alcohol. The polyvinyl alcohol degradation reaction includes an intramolecular dehydration reaction of polyvinyl alcohol shown in FIG. 1(a), an intramolecular or intermolecular dehydration condensation reaction of polyvinyl alcohol shown in FIG. 1(b), and the like. These reactions are dehydration reactions, which are particularly prone to occur under low humidity conditions, or in the dry state. In the case where polyvinyl alcohol is used alone, these reactions occur at 300 ℃ or higher, but in the case of the above-mentioned composite compound of polyvinyl alcohol and an inorganic compound, the composite inorganic compound acts as a catalyst, and the reactions shown in fig. 1(a) and (b) can be produced even at a relatively low temperature.

After the above reaction, the hydrophilicity of polyvinyl alcohol decreases, and the proton transfer promoting effect of water molecules decreases, thereby causing a decrease in proton conductivity. In addition, since the amount of water having a lubricant effect is reduced, the material is entirely hardened, and molecular motion of the polyvinyl alcohol portion is suppressed, whereby proton conductivity is lowered. In addition, the degradation of the polyvinyl alcohol moiety at high temperatures may also be caused by oxidation reactions of the polyvinyl alcohol by oxygen. In this case, too, material hardening occurs, resulting in a decrease in proton conductivity.

Further, the solid electrolyte formed from the above-mentioned composite compound of polyvinyl alcohol and an inorganic compound is characterized in that an electrolyte membrane is produced by a simple method of forming a membrane from a composite compound solution by casting by complexing through neutralization reaction in an aqueous solution. When an electrolyte membrane is produced by such a production method, in order to produce an electrolyte membrane having sufficient water resistance and strength, the electrolyte membrane is subjected to heat treatment. The heating is performed in a dry state because the water resistance and strength are improved by the dehydration condensation reaction of the inorganic compound or between the inorganic compound and polyvinyl alcohol by heating.

In order to promote the above reaction to proceed efficiently, the heat treatment is performed at 100 ℃ or higher, but if the heating is excessively performed in a dry environment, the dehydration reaction as shown in fig. 1(a) and (b) excessively proceeds, and the proton conductivity of the resulting electrolyte membrane becomes low. In addition, when hydrochloric acid is used for the neutralization reaction and the hydrochloric acid is excessively present in the system, substitution of chlorine with the hydroxyl group of polyvinyl alcohol occurs as shown in fig. 1(c), and in this case, hydrophilicity of the polyvinyl alcohol portion is also lowered and hardening is also caused, so that the polyvinyl alcohol conductivity is lowered. Therefore, the solid electrolyte formed from the above-mentioned composite compound of polyvinyl alcohol and an inorganic compound must be temperature-controlled to avoid excessive heating when processed into a film.

The proton conductivity is improved by impregnating the solid electrolyte with a solution containing sulfuric acid, or the like, to bond sulfuric acid to the hydroxyl group part of polyvinyl alcohol in the solid electrolyte formed from the composite compound of polyvinyl alcohol and an inorganic compound in the form of hydrogen bond, sulfuric ester, and sulfonic acid group. However, after this method is applied, the contained sulfuric acid component functions as the aforementioned reaction catalyst that partially degrades polyvinyl alcohol, giving rise to a problem of promoting deterioration of performance at high temperatures.

With the above solid electrolyte formed from a composite compound of polyvinyl alcohol and an inorganic compound, acetylation of the hydroxyl group of the polyvinyl alcohol moiety by treatment with an aldehyde can suppress excessive swelling due to water absorption, and problems such as strength decrease in a humid environment. However, when the solid electrolyte subjected to the above-mentioned treatment is used at a high temperature, the hydrophilicity of the solid electrolyte is lowered by the pretreatment, and as a result, the performance deterioration at a high temperature as described above is likely to occur at an early stage. The problems described above apply not only to polyvinyl alcohol but also to solid electrolytes composed of a composite compound of an organic polymer having hydroxyl groups and an inorganic compound. The stability of the material at higher temperatures is improved, and the life of the solid electrolyte can be prolonged both in the case of using the fuel cell or the like at high temperatures and in the case of using the solid electrolyte at normal temperatures.

The object of the invention is therefore: a solid electrolyte having high ionic conductivity, which contains a composite compound formed from an inorganic compound such as a silicic acid compound, a tungstic acid compound, a molybdic acid compound, a stannic acid compound, or a zincic acid compound, which has been conventionally provided as described above, and an organic compound of an organic polymer having a hydroxyl group such as polyvinyl alcohol, and which is less degraded not only at 100 ℃ or more but also with less performance degradation while maintaining high performance, and an electrochemical system using the solid electrolyte.

In order to achieve the above object, the present invention provides a hybrid compound (hybrid compound) containing an organic polymer having a hydroxyl group, an inorganic compound and water. The composite compound is immersed in or coated with a liquid containing at least one of phosphoric acid and boric acid. Specifically, the present invention provides a solid electrolyte comprising the composite compound, wherein a part or all of the hydroxyl groups in the hydroxyl group-containing organic polymer are bonded to at least one of phosphoric acid and boric acid. The present invention also provides various electrochemical systems using the solid electrolyte.

The inorganic compound comprises at least one of silicic acid compound, tungstic acid compound, molybdic acid compound, stannic acid compound and zincic acid compound. The composite compound is produced by neutralizing an inorganic salt with an acid or an alkali in a raw material solution in which an organic compound containing an organic polymer having a hydroxyl group coexists, and removing the solvent. As the salt of the inorganic compound, a metal salt of at least one of silicic acid, tungstic acid, molybdic acid, stannic acid is used; or using zirconium halide and/or zirconium oxyhalide.

In the case of producing a complex compound by a neutralization reaction, the solution after neutralization contains at least one of phosphoric acid and boric acid, and a part or all of the hydroxyl groups in the hydroxyl group-containing organic polymer are bonded to at least one of phosphoric acid and boric acid. Further, a part or all of the hydroxyl groups in the hydroxyl group-containing organic polymer are bonded to at least one of phosphoric acid and boric acid to form at least one form of hydrogen bond, phosphate ester or borate ester.

Polyvinyl alcohol is used as the organic polymer having hydroxyl groups. When the composite compound is produced by the neutralization reaction, the raw material solution before neutralization may contain at least one metal salt selected from phosphoric acid and boric acid, or at least one of aluminum salt, titanium salt, calcium salt, strontium salt, barium salt, and boric acid, whereby the composite compound contained in the solid electrolyte may contain at least one of phosphorus, boron, aluminum, titanium, calcium, strontium, and barium compounds. In addition, the hydroxyl group of the organic polymer is impregnated in a liquid containing at least one of phosphoric acid and boric acid, or the application of the liquid is carried out by heating at 60 ℃ or more than 60 ℃.

In order to ensure bonding with at least one of phosphoric acid and boric acid, the solution after neutralization is subjected to a heat treatment at 40 ℃ or more, preferably 100 ℃ or more, in a state where the solution contains at least one of phosphoric acid and boric acid.

Part or all of the hydroxyl groups in the hydroxyl group-containing organic polymer are bonded to sulfuric acid in such a manner that a hydrogen bond is formed, or a sulfate ester or a sulfonic acid group is formed. In order to combine a part of the hydroxyl groups in the hydroxyl group-containing organic polymer with sulfuric acid, the composite compound is immersed in a sulfuric acid-containing liquid, or coated with the liquid, or exposed to a sulfuric acid-containing vapor under heating at 60 ℃ or more than 60 ℃.

In the above-mentioned organic polymer having hydroxyl groups, a part of the hydroxyl groups is bonded to an aldehyde, and the bonding is carried out by acetylation.

In order to bind a part of the hydroxyl groups in the hydroxyl group-containing organic polymer to aldehydes, the complex compound is immersed in or coated with a liquid containing aldehydes and acids, or exposed to a vapor containing aldehydes and acids. In addition, when the complex compound is produced by the neutralization reaction, at least one metal salt of silicic acid, tungstic acid, molybdic acid, and stannic acid is used. Further, zirconium chloride or zirconium oxychloride is used as the zirconium halide or the zirconium oxyhalide.

It can be applied to the following electrochemical systems: fuel cell, vapor pump, dehumidifier, air conditioner, electrochromic display element, electrolyzer, electrolytic hydrogen generator, electrolytic hydrogen peroxide generator, electrolytic water generator, humidity sensor, hydrogen sensor, galvanic cell, accumulator, light conversion system or novel battery system using polyvalent metal.

According to the invention: a basic method for producing a solid electrolyte comprising a composite compound, wherein a part or all of the hydroxyl groups in the hydroxyl group-bearing organic polymer are combined with at least one of phosphoric acid and boric acid. For this purpose, a composite compound composed of an organic compound containing an organic polymer having a hydroxyl group, an inorganic compound, and water is immersed in or coated with a liquid containing at least one of phosphoric acid and boric acid; and

a basic method for producing a solid electrolyte comprising a composite compound, wherein a part or all of the hydroxyl groups in the hydroxyl group-bearing organic polymer are combined with at least one of phosphoric acid and boric acid. For this purpose, the complex compound is prepared by neutralizing an inorganic salt with an acid or a base in a raw material solution in which an organic compound containing an organic polymer having a hydroxyl group coexists, and removing the solvent. In this treatment, the solution after the neutralization treatment contains at least one of phosphoric acid and boric acid. Accordingly, the present invention can provide an inexpensive solid electrolyte that is less likely to suffer deterioration in performance even when used at a temperature of 100 ℃ or higher, and an electrochemical system using the solid electrolyte.

Drawings

Referring now to the drawings wherein:

[ FIG. 1] (a), (b) and (c) are equations for the reaction of the hydroxyl groups of the polyvinyl alcohol moiety.

Fig. 2 shows the change in ion conductivity when samples 1, 2 and 3 were placed in saturated water vapor.

Fig. 3 shows the change in ion conductivity when samples 4, 5, 6, which had been previously subjected to immersion treatment in sulfuric acid, were placed in saturated water vapor.

FIG. 4 shows equations for hydroxyl groups in an organic polymer to form a phosphate ester (a) and a borate ester (b).

FIG. 5 shows equations for forming sulfate ester (a) and sulfonic acid group (b) from hydroxyl group of organic polymer.

Fig. 6 shows the change in ion conductivity when samples 7, 8 were placed in saturated water vapor.

Fig. 7 shows the change in ion conductivity when samples 1, 3, and 7 were left in the atmosphere.

Fig. 8 shows the change in ion conductivity when samples 1, 3, 7 were placed in saturated water vapor.

FIG. 9 shows equations of phosphoric ester (a) of condensed phosphoric acid and boric ester (b) of condensed boric acid formed by hydroxyl groups of an organic polymer.

Detailed Description

Embodiments related to the solid electrolyte and the electrochemical system having the solid electrolyte of the present invention are explained below. The present invention relates to a composite compound composed of an organic compound containing an organic polymer having hydroxyl groups, an inorganic compound, and water, characterized by a solid electrolyte containing the composite compound, wherein a part or all of the hydroxyl groups in the organic polymer having hydroxyl groups are bonded to at least one of phosphoric acid and boric acid. For this purpose, the composite compound is immersed in a liquid containing at least one of phosphoric acid and boric acid, or coated with the above liquid. Further, the present invention is characterized by a solid electrolyte comprising the composite compound, wherein a part or all of the hydroxyl groups in the hydroxyl group-containing organic polymer are bonded to at least one of phosphoric acid and boric acid. For this purpose, the complex compound is prepared by neutralizing an inorganic salt with an acid or a base in a raw material solution in which an organic compound containing an organic polymer having a hydroxyl group coexists, and removing the solvent. The solution after the neutralization treatment contains at least one of phosphoric acid and boric acid.

The following examples of the present invention will explain the preparation method of the solid electrolyte. The present invention is not limited to the description of these embodiments.

Example 1

To prepare a solid electrolyte membrane, first, 7.5% by weight of sodium tungstate dihydrate (Na) was added to 100cc of a 10% by weight aqueous solution of polyvinyl alcohol having an average polymerization degree of 3100 to 3900 and a saponification degree of 86 to 90%₂WO₄·2H₂O) and 3% by weight trisodium phosphate (Na)₃PO₄·12H₂O) 23cc of mixed aqueous solution, and 24cc of 3 wt% sodium silicate aqueous solution. While this raw material aqueous solution was stirred, 12cc of 2.4M hydrochloric acid was added dropwise thereto to neutralize the solution, thereby preparing a viscous precursor aqueous solution. The aqueous solution of the precursor is put into a closed container, evacuated by a vacuum pump to remove bubbles, and then placed at 40 ℃ for 1 hour and at normal temperature for 15 hours to promote the compositing.

The polyester film was then spread on a smooth base of a coating apparatus (manufactured by PKPrint Coat Instruments ltd., K Control Coater 202) with a doctor blade having an adjustable base gap. The aqueous solution of the defoaming precursor was cast thereon. At this point, the base was heated at 50 ℃ under control.

Immediately after the precursor aqueous solution was poured onto the base, the doctor blade gap was adjusted to 0.6mm and the doctor blade was swept over the precursor aqueous solution at a certain speed to smooth it to a certain thickness. Then heating at 50 deg.C to evaporate water, pouring the precursor aqueous solution on it again when the fluidity almost disappears, and immediately sweeping the precursor aqueous solution at a certain speed by a scraper again to smooth it to obtain a certain thickness. After repeating this operation three times, the temperature of the susceptor was raised to 105 to 110 ℃ and the heat treatment was carried out for 2 hours while maintaining this state. Then the film on the base was peeled off, washed with water and dried.

The solid electrolyte membrane thus prepared was cut out to a diameter of 30mm, and first subjected to immersion treatment in a 10% by weight aqueous phosphoric acid solution and 100ml of water containing 6g of boric acid powder. The solid electrolyte membrane sample was immersed in each reaction solution, left at 60 to 100 ℃ for 1 hour while stirring the reaction solution, washed with water, and dried. The sample which was not subjected to any treatment was sample 1, and the samples subjected to the above-mentioned treatment were sample 2 and sample 3, respectively. The above-cut solid electrolyte was then immersed in 1.8M sulfuric acid at a temperature of 60 to 100 ℃ for 1 hour, and washed with water to obtain sample 4. Samples 2 and 3 were further treated with sulfuric acid and then immersed in aqueous phosphoric acid and boric acid solutions under similar conditions, and the samples obtained were sample 5 and sample 6, respectively.

Each of these samples was placed in a constant temperature and humidity cell, and the ionic conductivity was measured by adjusting the temperature to 60 ℃ and the relative humidity to 90%. The ionic conductivity was measured as follows. The solid electrolyte membrane sample was first clamped with 2 platinum disks having a diameter of 28mm and a brass disk placed on the outer side of the platinum disks, and then clamped with an insulating clamp to be fixed. The current and phase angle responses were measured by applying an alternating voltage of 10mV to a wire attached to a brass disk using an LCR meter, with the frequency being varied from 5MHz to 50 Hz. The ion conductivity was determined from the intercept of the real number axis of the known Cole-Cole diagram.

After the ionic conductivity was measured, each sample was placed in a 44ml capacity container made of tetrafluoroethylene tetrafluoride resin to which 10cc of pure water was added, and the container was placed in a stainless pressure container and stored in a thermostatic bath at 120 ℃. At this time, the solid electrolyte sample in the container made of tetrafluoroethylene resin was not directly immersed in water, and the sample was placed in the vapor portion. After a predetermined period of time, a sample of solid electrolyte was taken. The ionic conductivity was measured at a temperature of 60 ℃ and a relative humidity of 90% by a similar method as described above. The change in ionic conductivity of each sample corresponding to the incubation time in the thermostatic bath at 120 ℃ is shown in FIGS. 2 and 3.

It is also clear from FIG. 2 that the conductivity of the sample (sample 1) without any treatment is greatly reduced when it is kept at a high temperature of 120 ℃. In contrast, the samples (samples 2 and 3) immersed in the aqueous solution containing phosphoric acid or boric acid had a small decrease in conductivity. Particularly, the ionic conductivity was maintained better in the boric acid treatment. The conductivity decreases when kept at 100 ℃ or higher, mainly because degradation occurs in association with the hydroxyl group of the polyvinyl alcohol moiety as shown in the aforementioned fig. 1(a) and (b). The decrease in conductivity was suppressed after the immersion treatment in an aqueous solution containing phosphoric acid or boric acid, which indicates that the hydroxyl group was changed. Possible changes of the hydroxyl group caused by the immersion treatment in the aqueous solution containing phosphoric acid or boric acid are that phosphoric acid or boric acid is hydrogen-bonded to the hydroxyl group, or that phosphoric acid or boric acid is bonded to the hydroxyl group in the form of forming a phosphate or borate (as shown in fig. 4(a) and (b)). These combinations occur to prevent degradation associated with the hydroxyl groups of the polyvinyl alcohol moiety as shown in fig. 1(a) and (b).

As further shown in fig. 3, the initial ionic conductivity was increased by immersion in sulfuric acid. But the conductivity of the sample (sample 4) without any treatment decreased significantly with time. In addition, the samples (samples 5 and 6) which had been subjected to the immersion treatment in phosphoric acid or boric acid had a low degree of decrease in conductivity with time even if the sulfuric acid immersion treatment was performed in advance. In this case, the treated sample in boric acid maintained better ionic conductivity. By performing the sulfuric acid impregnation treatment, sulfuric acid is bonded to the hydroxyl moiety of polyvinyl alcohol in the form of forming a hydrogen bond, or in the form of forming a sulfuric ester or a sulfonic acid group (see fig. 5(a) and (b)). As a result, sulfuric acid is introduced into the solid electrolyte.

Since the proton dissociation degree of the introduced sulfuric acid is high, the initial ion conductivity is increased, but the sulfuric acid acts as a catalyst for the degradation reaction and the oxidation reaction of the polyvinyl alcohol moiety as shown in fig. 1(a) and (b), and promotes the decrease of the ion conductivity at a high temperature. The dipping treatment in an aqueous solution containing phosphoric acid or boric acid is performed, and the phosphoric acid or boric acid is bound to a hydroxyl group with a hydrogen bond, or forms a phosphoric ester or a boric ester (see fig. 4(a) and (b)), which can suppress a degradation reaction or an oxidation reaction of such polyvinyl alcohol.

Example 2

Polyethylene having an average degree of polymerization of 3100 to 3900 and a degree of saponification of 86 to 90% at 100ccTo a 10 wt% aqueous solution of an enol was added sodium tungstate dihydrate (Na) containing 7.5 wt% of₂WO₄·2H₂O), 3% by weight of trisodium phosphate (Na)₃PO₄·12H₂O) 23cc of mixed aqueous solution and 24cc of 3 wt% sodium silicate aqueous solution to prepare a raw material aqueous solution. While stirring the raw material aqueous solution, 11cc of hydrochloric acid having a concentration of 2.4M and 13cc of phosphoric acid having a concentration of 30% by weight were added dropwise for neutralization, thereby preparing a viscous precursor aqueous solution. In addition, similarly to this operation, 5cc of a 6.7 wt% aqueous solution of boric acid was added in addition to hydrochloric acid and phosphoric acid, thereby preparing an aqueous precursor solution.

These aqueous precursor solutions were subjected to defoaming treatment and then heated at 40 ℃ for 24 hours to promote complexing and bonding of phosphoric acid and boric acid to the hydroxyl groups of the polyvinyl alcohol moiety. Thereafter, a film was formed by a method similar to that of example 1. For the sample in which phosphoric acid was added to the raw material at the time of neutralization treatment, phosphoric acid in liquid form remained in the film even after heating at 105 ℃ to 110 ℃ to evaporate water. From this, it is clear that the precursor aqueous solution of the film contains phosphoric acid. Such phosphoric acid exists in the form of an acid, showing that the acid is added in excess beyond the neutralization point during the neutralization operation. It is thus also shown that the aqueous solution of the boric acid-added precursor also contains boric acid in the form of boric acid.

Of the two samples, the solid electrolyte membrane made of the precursor aqueous solution to which hydrochloric acid and phosphoric acid were added at the time of neutralization was sample 7. On the other hand, a solid electrolyte membrane prepared by adding an aqueous solution of a precursor of hydrochloric acid, phosphoric acid, boric acid at the time of neutralization was sample 8. These samples were examined for changes in ionic conductivity by the same method as in example 1, with the ionic conductivity being maintained at 120 ℃. The results are shown in FIG. 6. Both samples showed a reduction in conductivity compared to the sample containing no phosphoric acid or boric acid in the aqueous precursor solution after the neutralization operation (sample 1 in fig. 2). From these results, it was found that the neutralized precursor aqueous solution containing phosphoric acid and boric acid can prevent the resulting solid electrolyte from deteriorating at high temperatures. The reason for this effect is that, as in the case of example 1 (as shown in fig. 4(a) and (b)), the neutralized precursor aqueous solution contains phosphoric acid or boric acid, and the phosphoric acid or boric acid is bound to the hydroxyl group of the polyvinyl alcohol moiety by hydrogen bonding or bound in the form of forming a phosphoric ester or a boric ester. By creating these combinations, degradation of the polyvinyl alcohol moiety associated with the hydroxyl group as shown in fig. 1(a) and (b) can be prevented.

In addition, as shown in example 1, if only hydrochloric acid is used at the time of neutralization, the resultant film is hardened by heating at 100 ℃ or more for a long time during film formation, and the water absorption rate is reduced. Therefore, it is necessary to strictly control the heating time, but as in this example, when the neutralized precursor aqueous solution contains phosphoric acid or boric acid, the degradation of the film is small even if the film is heated at 100 ℃ or higher for a long time at the time of film formation, so that it is not necessary to strictly control the heating time, and the variation in product production can be easily reduced. As in example 1, in the case of using only hydrochloric acid at the time of neutralization, a chlorine substitution reaction of the hydroxyl group of the polyvinyl alcohol portion as shown in fig. 1(c) is generated at the time of heating, thereby causing a decrease in hydrophilicity and hardening. On the other hand, as in example 2, when the amount of hydrochloric acid at the time of neutralization is reduced and phosphoric acid or boric acid is contained in the aqueous precursor solution after neutralization, the chlorine substitution reaction of the hydroxyl group of the polyvinyl alcohol moiety can be suppressed, and thus degradation can be prevented.

Example 3

Samples 1, 3 of example 1 and sample 7 of example 2 were kept at 120 ℃ in a dry state (under the atmosphere) to examine the change in ion conductivity with time. The conductivity was measured under the same conditions as in examples 1 and 2, at a temperature of 60 ℃ and a relative humidity of 90%. The results are shown in FIG. 7. The neutralized aqueous precursor solution contained no phosphoric acid or boric acid, and sample 1, which had not been subjected to any treatment, had a drastic decrease in conductivity in the dry state, as compared with the wet state of example 1. However, even when sample 3 subjected to the immersion treatment in the solution containing boric acid and sample 7 containing phosphoric acid in the aqueous solution of the precursor after the neutralization operation were left at a high temperature under drying, the decrease in the conductivity was remarkably small.

Example 4

The solid electrolytes of samples 1, 3 of example 1 and sample 7 of example 2 were subjected to aldehyde treatment. For the aldehyde treatment, the solid electrolyte membrane was first immersed in 1.2M hydrochloric acid at room temperature for 1 hour, and then immersed in 100cc of 1.2M hydrochloric acid containing 10cc of isobutyraldehyde for 2 hours while stirring at room temperature. Then, after rinsing in hot water at 70 to 100 ℃, it was kept in saturated water vapor at 120 ℃ to detect the change in ion conductivity with time. The results are shown in FIG. 8.

From the results shown in fig. 8, it is understood that the precursor aqueous solution after the neutralization operation does not contain phosphoric acid or boric acid, and that the treatment with aldehyde of sample 1, which has not been subjected to any treatment, results in early deterioration of conductivity at high temperature. However, sample 3 in which the immersion treatment was performed in the aqueous solution containing boric acid and sample 7 in which phosphoric acid was contained in the precursor aqueous solution after the neutralization operation were less susceptible to a decrease in conductivity at high temperatures. The hydrophilicity of the solid electrolyte has been reduced at the time of aldehyde treatment, and thus the conductivity decrease time caused by the degradation reaction of polyvinyl alcohol is advanced at high temperature as in fig. 1(a) and (b). On the other hand, in samples 3 and 7 in which the hydroxyl group of the polyvinyl alcohol moiety was bonded to boric acid or phosphoric acid, the degradation reaction of polyvinyl alcohol hardly occurred, and even if the hydrophilicity was lowered by the aldehyde treatment, the conductivity at high temperature did not decrease.

In each of the above examples, in order to bond phosphoric acid or boric acid to the hydroxyl group of the organic polymer, the liquid containing at least one of phosphoric acid and boric acid is immersed or coated in the liquid. However, any liquid may be used as long as the desired combination of phosphoric acid or boric acid can occur, and thus phosphoric acid or boric acid does not necessarily have to be dissolved. The phosphoric or boric acid is bound to the hydroxyl groups of the organic polymer in the form of hydrogen bonds and/or as phosphate and/or borate esters as shown in figure 4. These types and patterns of bonding may also be present in a mixture. When phosphoric acid or boric acid is combined, two or more phosphoric acid molecules or boric acid molecules can be combined to form condensed phosphoric acid (shown in FIG. 9(a)) or condensed boric acid (shown in FIG. 9 (b)); alternatively, the phosphoric acid molecules and/or boric acid molecules are bound to the hydroxyl groups of the organic polymer in a mixed-condensed form. In the dipping or coating treatment in the liquid containing phosphoric acid and/or boric acid, it is preferable that the sample is heat-treated at 60 ℃ or more. The higher the temperature, the higher the solubility of the compound, thereby promoting the binding reaction with the solid electrolyte. It is also effective to apply a pressure-resistant vessel and perform the treatment at a temperature higher than the boiling point of the treatment solution.

The examples are based on the fact that phosphoric acid and/or boric acid is bonded to hydroxyl groups of an organic polymer to improve durability at high temperatures. Therefore, the electrolyte is effective for all solid electrolytes containing a composite compound of an organic compound having a hydroxyl group and an inorganic compound. In the present invention, the organic polymer having hydroxyl groups is polyvinyl alcohol, various celluloses, polyethylene glycol, various organic polymers into which hydroxyl groups are introduced, or an organic polymer copolymerized or graft-polymerized with the organic polymer having hydroxyl groups. For example, polyvinyl alcohol is the most representative of the present invention, but it is not necessarily completely polyvinyl alcohol, and it can be used as long as it has a function of polyvinyl alcohol in nature. For example, a substance in which a part of the hydroxyl groups is replaced with another group, or another part is copolymerized or graft-polymerized with another polymer may have the function of polyvinyl alcohol. Since the intermediate polyvinyl alcohol in the reaction process can also provide the same effect, polyvinyl acetate, which is a raw material of polyvinyl alcohol, can be used as a starting material.

In addition, in each example, other polymers such as polyolefin polymers such as polyethylene and polypropylene; polyesters such as polyethylene terephthalate and polybutylene terephthalate; fluorinated polymers such as polytetrafluoroethylene and polyvinylidene fluoride; polyvinyl acetate polymers, polystyrene polymers, polycarbonate polymers, epoxy resin polymers, and other organic/inorganic additives.

In each example, a salt of an inorganic compound is neutralized with an acid or a base in a raw material solution in which an organic compound containing an organic polymer having a hydroxyl group coexists, and a solvent is removed to prepare a composite compound composed of the organic compound, the inorganic compound, and water. Representative examples of the salt of the inorganic compound herein are oxoacid salts of metals, such as metal salts of at least one of silicic acid, tungstic acid, molybdic acid, stannic acid, can be used. Here neutralized with an acid. Any kind of metal salts of silicic acid, tungstic acid, molybdic acid, stannic acid may be used as long as they are soluble in the solvent used. The kind of metal ion, the oxygen/cation ratio or the water content may be arbitrary.

In addition, another representative example of the salt of the inorganic compound is a halide or oxyhalide of a metal, for example, a zirconium halide or oxyhalide may be used, in which case it is neutralized with a base. Any type of zirconium salt and zirconium oxide salt may be used, mainly soluble in the solvent used. Further, the ratio of oxygen/anion, water content may be arbitrary. Any solvent of the raw material solution can be used as long as the metal salt and the organic polymer as the raw materials can be dissolved. However, water is preferred in view of high solubility of the metal salt. In addition, the starting material is a metal salt of silicic acid, tungstic acid, molybdic acid, stannic acid, and alkali metal salts are preferable in terms of solubility.

When the solid electrolyte is prepared by the neutralization method as described above, the solution after neutralization contains at least one of phosphoric acid and boric acid, and thus the hydroxyl group of the organic polymer can be bonded to phosphoric acid or boric acid. To ensure that phosphoric acid or boric acid is contained, the neutralized solution must be acidic, and therefore, the oxometalate of the metal is mainly used here as the salt of the inorganic compound, which is neutralized with an acid. In this case, in order to make the neutralized solution acidic, the acid must be added in excess over the neutralization point. The most representative methods for ensuring that the neutralized solution contains phosphoric acid and/or boric acid are: in the neutralization, the acid containing phosphoric acid and/or boric acid is added in excess over the neutralization point, or the phosphoric acid and/or boric acid is added after the acid is added in excess over the neutralization point. The neutralized solution contains phosphoric acid and/or boric acid, and thus the phosphoric acid and/or boric acid is bound to the hydroxyl groups of the hydroxyl group-containing organic polymer in the form of hydrogen bonds or phosphate or borate esters as shown in fig. 4. These types or patterns of bonding may also be present in a mixture. The solution after neutralization is allowed to contain at least one of phosphoric acid and boric acid to bond phosphoric acid and/or boric acid to the hydroxyl group of the organic polymer, and in any process after neutralization, heat treatment may be performed at 40 ℃ or more than 40 ℃ to promote bonding. In addition, if the neutralized solution contains phosphoric acid, the phosphoric acid remains in the film in a liquid form even after processing into, for example, a shape of the film after the solvent is removed by heating. In this state, the bonding can be promoted by the heat treatment at 100 ℃ or more than 100 ℃.

In the composite compound constituting the solid electrolyte, at least one of phosphorus, boron, aluminum, titanium, calcium, strontium, and barium compounds may be contained. In the case of the neutralization method, these are added by a method in which the raw material solution before neutralization contains at least one metal salt selected from phosphoric acid and boric acid; or at least one selected from aluminum salt, titanium salt, calcium salt, strontium salt, barium salt and boric acid. Any metal salt of phosphoric acid or boric acid may be used as long as it is soluble in the solvent used. The kind of metal ion, the oxygen/cation ratio and the water content may be arbitrary. However, the alkali metal salt is preferably used in terms of solubility of the metal salt. An aluminum salt, a titanium salt, a calcium salt, a strontium salt, or a barium salt may be optionally used as long as it is soluble in the solvent used. The kind and water content of the anion can be arbitrary. In addition, when phosphorus, boron, or silicon is added, tungstic acid or molybdic acid may be chemically combined with phosphoric acid, silicic acid, or boric acid to form heteropoly acids such as tungstophosphoric acid, molybdophosphoric acid, silicotungstic acid, silicomolybdic acid, tungstophosphoric acid, and molybdoboric acid, and these heteropoly acids or salts thereof may be used as the raw material.

When prepared by neutralization, any acid or base for neutralization may be used as long as it can neutralize the metal salts of silicic acid, tungstic acid, molybdic acid, stannic acid; or it may neutralize a zirconium salt or a zirconium oxide salt. Hydrochloric acid, sulfuric acid, phosphoric acid, sodium hydroxide, lithium hydroxide, and the like may also be used.

The solid electrolyte of the present invention can promote the bonding of inorganic compounds and organic compounds by heat treatment at 100 ℃ or higher, and increase strength, water resistance, and high-temperature stability. If the treatment is not carried out, problems such as strength reduction in high-temperature water occur. The heat treatment may be carried out in air, in an inert gas, or in vacuum.

When an acid-type proton-conductive solid electrolyte is obtained, the ion conductivity can be improved by immersing the resulting complex compound in an acid and by completely protonating the proton sites in the material to increase the proton concentration. The acid for impregnation may be arbitrarily selected, and hydrochloric acid, sulfuric acid, etc. may be used as long as protonation can be performed. Particularly, when sulfuric acid is used, the sulfuric acid is combined with the hydroxyl group of the polyvinyl alcohol moiety in the form of hydrogen bond formation, or formation of sulfuric ester or sulfonic acid group as shown in fig. 5, thereby improving proton conductivity.

The acid impregnation treatment is particularly effective for electrolytes containing tungstic acid compounds. It is advantageous to carry out the acid impregnation treatment before the impregnation or coating treatment in the liquid containing phosphoric and/or boric acid. In addition, when the acid immersion treatment is performed, phosphoric acid and/or boric acid may be added to the treatment liquid in advance.

The solid electrolyte obtained by the invention is based on cheap raw materials and simple preparation process, and has greatly reduced price compared with the existing perfluorosulfonic acid electrolyte. Further, the solid electrolyte of the present invention has the same function as a conventionally used solid electrolyte composed of a composite compound of polyvinyl alcohol and an inorganic compound, and can be used for the same purpose, and therefore, it is suitable for electrochemical systems including fuel cells, vapor pumps, dehumidifiers, air conditioners, electrochromic elements, electrolyzers, electrolytic hydrogen generators, electrolytic hydrogen peroxide generators, electrolytic water generators, humidity sensors, hydrogen sensors, galvanic cells, secondary batteries, light conversion systems, or novel battery systems using polyvalent metals.

As described above, the present invention relates to a composite compound of an organic polymer having a hydroxyl group, an inorganic compound and water. In particular, it relates to a solid electrolyte comprising the composite compound, wherein a part or all of hydroxyl groups in an organic polymer are bonded to at least one of phosphoric acid and boric acid by dipping in or coating with a liquid containing at least one of phosphoric acid and boric acid. And a solid electrolyte comprising the composite compound, wherein a part or all of the hydroxyl groups of the organic polymer having hydroxyl groups are bonded to at least one of phosphoric acid and boric acid because the solution contains at least one of phosphoric acid or boric acid after neutralization. Specifically, the compound is a compound composed of an organic compound containing an organic polymer having a hydroxyl group, an inorganic compound, and water, which is prepared by neutralizing a salt of the inorganic compound with an acid in a raw material solution in which the organic compound coexists, and removing the solvent. Therefore, the solid electrolyte provided by the invention is less subject to degradation and performance deterioration even if placed at a temperature of 100 ℃ or higher, and is inexpensive and high in performance. In addition, the present invention can provide various electrochemical systems using the solid electrolyte. As an electrochemical system, it can be applied to a fuel cell, a vapor pump, a dehumidifier, an air conditioner, an electrochromic display element, an electrolysis device, an electrolytic hydrogen generator, an electrolytic hydrogen peroxide generator, an electrolytic water generator, a humidity sensor, a hydrogen sensor, a primary cell, a secondary cell, a light conversion system, or a novel battery system using a polyvalent metal.

Claims (20)

1. A solid electrolyte characterized by comprising a composite compound composed of an organic compound containing polyvinyl alcohol, an inorganic compound and water, wherein the inorganic compound comprises at least one of a silicic acid compound, a tungstic acid compound, a molybdic acid compound, a stannic acid compound and a zincic acid compound, and a part or all of hydroxyl groups of polyvinyl alcohol in the composite compound are bonded to at least one of phosphoric acid and boric acid by a treatment of immersing in or coating with a liquid containing at least one of phosphoric acid and boric acid.

2. A solid electrolyte characterized by comprising a composite compound composed of an organic compound containing polyvinyl alcohol, an inorganic compound and water, wherein the inorganic compound contains at least one of a silicic acid compound, a tungstic acid compound, a molybdic acid compound, a stannic acid compound and a zincic acid compound, the composite compound is prepared by neutralizing a salt of the inorganic compound with an acid or a base and removing a solvent in a solution containing polyvinyl alcohol, and a part or all of hydroxyl groups of polyvinyl alcohol in the composite compound are bonded to at least one of phosphoric acid and boric acid by a treatment of immersing in, or coating with, a liquid containing at least one of phosphoric acid and boric acid.

3. The solid electrolyte as claimed in claim 2, wherein the salt of the inorganic compound is a metal salt of at least one of silicic acid, tungstic acid, molybdic acid and stannic acid, or is a zirconium halide and/or a zirconium oxyhalide.

4. A solid electrolyte characterized by comprising a composite compound composed of an organic compound containing polyvinyl alcohol, an inorganic compound and water, wherein the inorganic compound contains at least one of a silicic acid compound, a tungstic acid compound, a molybdic acid compound, a stannic acid compound and a zincic acid compound, the composite compound is prepared by neutralizing a salt of the inorganic compound with an acid or a base and removing a solvent in a solution containing polyvinyl alcohol, and the solution after neutralization contains at least one of phosphoric acid and boric acid, and a part or all of hydroxyl groups of polyvinyl alcohol in the composite compound is bonded to at least one of phosphoric acid and boric acid.

5. The solid electrolyte as claimed in claim 4, wherein the salt of the inorganic compound is a metal salt of at least one of silicic acid, tungstic acid, molybdic acid and stannic acid.

6. The solid electrolyte according to claim 1, 2, 3, 4 or 5, wherein a part or all of hydroxyl groups of polyvinyl alcohol in the composite compound are bonded to at least one of phosphoric acid and boric acid, and wherein the bonding is in the form of forming a hydrogen bond, and/or in the form of forming at least one of a phosphate ester and a borate ester.

7. The solid electrolyte according to claim 2, wherein the solution before neutralization contains at least one selected from the group consisting of metal salts of phosphoric acid and boric acid, or at least one selected from the group consisting of aluminum salts, titanium salts, calcium salts, strontium salts, barium salts, and boric acid, and the complex compound in the solid electrolyte contains at least one selected from the group consisting of phosphorus, boron, aluminum, titanium, calcium, strontium, and barium compounds.

8. The solid electrolyte as claimed in claim 1, wherein the solid electrolyte is immersed in a liquid containing at least one of phosphoric acid and boric acid, which is performed by heating at a temperature in the range of 60 ℃ to 100 ℃.

9. The solid electrolyte according to claim 4, wherein in the case where the solution of the complex compound after neutralization contains phosphoric acid, heat treatment is performed at a temperature in the range of 105 ℃ to 110 ℃.

10. The solid electrolyte according to claim 1, wherein a part of hydroxyl groups of polyvinyl alcohol in the composite compound is bonded to sulfuric acid.

11. The solid electrolyte according to claim 10, wherein a part of the hydroxyl groups of the polyvinyl alcohol in the composite compound is bonded to sulfuric acid in the form of forming a hydrogen bond, a sulfuric acid ester and/or a sulfonic acid group.

12. The solid electrolyte as claimed in claim 10, wherein a part of the hydroxyl groups of the polyvinyl alcohol in the composite compound is combined with sulfuric acid by immersion in a sulfuric acid-containing liquid, or coating of the liquid, or exposure to a vapor containing sulfuric acid.

13. The solid electrolyte as claimed in claim 12, wherein the solid electrolyte is impregnated in a sulfuric acid-containing liquid, which is performed by heating at a temperature in the range of 60 ℃ to 100 ℃.

14. The solid electrolyte according to claim 1, wherein a part of hydroxyl groups of the polyvinyl alcohol in the composite compound is bonded to an aldehyde.

15. The solid electrolyte according to claim 14, wherein a part of hydroxyl groups of polyvinyl alcohol in the composite compound is bonded to aldehyde by acetylation reaction.

16. The solid electrolyte according to claim 15, wherein a part of the hydroxyl groups of the polyvinyl alcohol in the composite compound is bonded to the aldehyde by immersion in a solution containing the aldehyde and the acid, or coating the solution, or exposure to a vapor containing the aldehyde and the acid.

17. The solid electrolyte as claimed in claim 3, wherein the metal salt of at least one of silicic acid, tungstic acid, molybdic acid and stannic acid is an alkali metal salt.

18. The solid electrolyte of claim 3, wherein the zirconium halide or oxyhalide is zirconium chloride or zirconium oxychloride.

19. An electrochemical system using a solid electrolyte, characterized by using the solid electrolyte according to any one of claims 1 to 18.

20. The electrochemical system of claim 19, wherein the electrochemical system is a fuel cell, a vapor pump, a dehumidifier, an air conditioner, an electrochromic element, an electrolysis device, an electrolytic hydrogen generator, an electrolytic hydrogen peroxide generator, an electrolytic water generator, a humidity sensor, a hydrogen sensor, a galvanic cell, a battery, or a light conversion system.