Proton-conductive material

Abstract

To provide a proton-conductive material having high proton conductivity.SOLUTION: A proton-conductive material is composed of a metal phosphate represented by Sn1-xAlxP2O7 (where x is 0.00 or more and 0.15 or less). When being allowed to stand for 60 minutes in an atmosphere at 25°C and 50% RH, the moisture absorption rate of the proton-conductive material is 2.5% or more and 4.5% or less.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a proton conducting material. [Background technology]

[0002] Proton-conducting materials are widely used in electrochemical devices such as fuel cells, electrolysis cells, electrochromic display devices, and sensors.

[0003] Patent Document 1 discloses that tin pyrophosphate (SnP2O7), obtained by adding phosphoric acid (H3PO4) to tin oxide (SnO2) and heating the mixture, exhibits proton conductivity. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2005-294245 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, when the present inventors attempted to synthesize tin pyrophosphate by the method described in Patent Document 1 many times, the proton conductivity sometimes decreased. The present inventors then investigated the cause of the decrease in proton conductivity and discovered a new finding that the moisture absorption rate of a proton-conductive material made of a metal phosphate affects the proton conductivity and gas barrier properties.

[0006] The present invention has been made based on the above-mentioned new findings, and an object of the present invention is to provide a proton-conducting material having high proton conductivity and gas barrier properties. [Means for solving the problem]

[0007] The proton conductive material according to the present invention is Sn 1-x Alx The proton conductive material is composed of a metal phosphate represented by P2O7 (x is 0.00 or more and 0.15 or less). The proton conductive material is composed of a metal phosphate. When the proton conductive material is left standing for 60 minutes in an atmosphere of 25°C and 50% RH, the moisture absorption rate is 2.5% or more and 4.5% or less. Effect of the Invention

[0008] According to the present invention, it is possible to provide a proton conductive material having high proton conductivity and gas barrier properties. [Brief description of the drawings]

[0009] [Figure 1] 1 is a graph showing the relationship between moisture absorption rate and proton conductivity of a proton-conducting material according to an example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] (Proton Conductive Materials) The proton conductive material according to the present embodiment can be used as a constituent material of a proton conductive membrane in electrochemical elements such as fuel cells, electrolytic cells, electrochromic display elements, sensors, etc. In particular, the proton conductive material according to the present embodiment is suitable as a material for a solid electrolyte used in fuel cells, electrolytic cells, etc.

[0011] The proton conductive material according to this embodiment is composed of a metal phosphate represented by the following formula (1): The metal phosphate is in particulate form.

[0012] Sn 1-x Al x P2O7…(1)

[0013] In formula (1), x is a value in the range of 0.00 to 0.15, and is preferably 0.15 or less since it exhibits higher proton conductivity.

[0014] The composition formula represented by formula (1) is obtained from the contents of Sn and Al measured by ICP (Inductively Coupled Plasma) optical emission spectroscopy. As the ICP optical emission spectroscopy analyzer, for example, PS3520UV-DD (sequential type) manufactured by Hitachi High-Tech Corporation can be used.

[0015] Here, the moisture absorption rate of the proton conductive material according to this embodiment is 2.5% or more. This can improve the proton conductivity of the proton conductive material. The mechanism by which the proton conductivity can be improved by making the moisture absorption rate of the proton conductive material 2.5% or more is not necessarily clear, but it is thought to be related to the fact that protons can be conducted not only through the proton conductive material itself but also through absorbed water.

[0016] In addition, the moisture absorption rate of the proton conductive material is 4.5% or less. This makes it possible to suppress the formation of voids in the membrane when the proton conductive material is made into a membrane. This makes it possible to improve the gas barrier properties of the proton conductive membrane made of the proton conductive material. The mechanism by which the formation of voids in the membrane can be suppressed is not entirely clear, but it is thought to be related to the generation of voids in the process of evaporating excess moisture-absorbed water.

[0017] The moisture absorption rate of the proton conductive material is measured according to the method described in JIS Z0701:1977. Specifically, the method is as follows. First, 0.5 g of the proton conductive material (powder) is weighed, placed in a flat weighing bottle, and dried at 120°C for 30 minutes. Next, the flat weighing bottle is covered and cooled to room temperature, and the dry weight of the powder is measured. Next, the flat weighing bottle with the cover removed is left to stand for 60 minutes in a thermostatic and hygroscopic chamber adjusted to an atmosphere of 25°C and 50% RH. Next, the flat weighing bottle is covered and removed from the thermostatic and hygroscopic chamber, and the moisture absorption weight of the powder is measured. At this time, in order to suppress moisture absorption or drying of the powder, the moisture absorption weight is measured within 1 minute after removing the flat weighing bottle. Then, the moisture absorption rate is calculated according to the following formula (2).

[0018] Moisture absorption rate (%) = 100 × (moisture absorption weight - dry weight) / dry weight … (2)

[0019] (Method of manufacturing proton conductive material) A method for producing the proton conductive material according to this embodiment will be described below. The method includes a step of mixing a metal (Sn) source, a P source, and an Al source, and a step of firing the mixture.

[0020] First, SnO2, (NH4)2HPO4, and Al(OH)3 are put into a ball mill (Ar gas atmosphere) and dry mixed to prepare a powdery mixture. The mixing time can be, for example, 12 hours to 48 hours. The moisture absorption rate described above can be adjusted by the molar ratio P / (Sn+Al) of the Sn element, P element, and Al element. The molar ratio P / (Sn+Al) of the feed can be adjusted by the amount of SnO2, (NH4)2HPO4, and Al(OH)3 respectively. The value of the molar ratio P / (Sn+Al) of the feed is not particularly limited, but can be, for example, 2.8 or more and 3.1 or less. The suffix X in the above formula (1) can be adjusted by the molar ratio Al / (Sn+Al) of the Sn element and Al element. The molar ratio Al / (Sn+Al) of the feed can be appropriately adjusted by the amount of SnO2 and Al(OH)3.

[0021] Next, the powder mixture is calcined to synthesize the proton conductive material in a solid phase. The calcination temperature can be, for example, 500° C. to 700° C. The calcination time can be, for example, 2 hours to 3 hours. EXAMPLES

[0022] Examples of the present invention will be described below. In these examples, the effect of the moisture absorption rate of a proton conductive material on the proton conductivity and gas barrier properties will be examined. However, the present invention is not limited to the examples described below.

[0023] (Preparation of Samples No. 1 to 17) The proton conductive materials according to Samples No. 1 to 17 were prepared by a solid phase synthesis method.

[0024] First, SnO2 (manufactured by FUJIFILM Wako Pure Chemical Industries), (NH4)2HPO4 (manufactured by Taihei Chemical Industries), and Al(OH)3 (manufactured by FUJIFILM Wako Pure Chemical Industries) were put into a ball mill (Ar gas atmosphere) and dry mixed (24 hours) to prepare a powdery mixture. At this time, the molar ratio P / (Sn+Al) of the charged Sn element, P element, and Al element was adjusted as shown in Table 1 by the charged amounts of SnO2, (NH4)2HPO4, and Al(OH)3, respectively. As a result, the moisture absorption rate was adjusted for each sample as shown in Table 1. In addition, the molar ratio Al / (Sn+Al) of the charged Sn element and Al element was adjusted as shown in Table 1 by the charged amounts of SnO2 and Al(OH)3. As a result, the suffix X in formula (1) was adjusted as shown in Table 1.

[0025] The powder mixture was then calcined at 650°C for 2.5 hours to synthesize the proton-conducting material.

[0026] (moisture absorption rate) First, 0.5 g of the proton conductive material (powder) of each sample was weighed out, placed in a flat weighing bottle and dried for 30 minutes at 120° C. Next, the flat weighing bottle was covered and cooled to room temperature, and then the dry weight of the powder was measured.

[0027] Next, the flat weighing bottle with the lid removed was left to stand for 60 minutes in a thermostatic chamber adjusted to an atmosphere of 25°C and 50% RH. Next, the flat weighing bottle was capped and removed from the thermostatic chamber, and the moisture absorption weight of the powder was measured within 1 minute.

[0028] The moisture absorption rate was calculated using the above formula (2). The calculation results are shown in Table 1.

[0029] (Proton Conductivity) The proton conductivity of the proton conductive materials according to Samples No. 1 to 17 was measured by the following method.

[0030] First, the proton conductive material was filled into a mold and uniaxially molded, and then pressurized at 300 MPa using a cold isostatic press (CIP) to produce circular pellets with a diameter of 10 mm and a thickness of 1 mm.

[0031] Next, platinum paste was applied to each of the two main surfaces of the circular pellet to form electrodes on each of the two main surfaces of the circular pellet.

[0032] Next, the proton conductivity was measured using a 4-probe conductivity measuring device under the conditions of a frequency of 1 MHz to 0.1 Hz and a voltage of 10 mV. The circular pellet was placed in a thermo-hygrostat and measured under the conditions of 120°C and 20% RH.

[0033] The measurement results are summarized in Table 1. In Table 1, the proton conductivity is 5×10 -3 Samples with proton conductivity of 1×10 S / cm or more were rated as ◎. -3 S / cm or more 5×10 -3 Samples with proton conductivity of less than 10 S / cm were evaluated as ◯. -3 Samples with a thickness of less than S / cm were rated as x.

[0034] (composition formula) By performing ICP emission spectroscopy on the proton conductive materials of Samples No. 1 to 17, the composition formula of the proton conductive materials was Sn 1-x Al x The subscript X in P2O7 was determined.

[0035] In the ICP emission spectroscopic analysis, the contents of Sn and Al were measured under the measurement conditions described in the above embodiment. The measurement results are summarized in Table 1.

[0036] (Gas barrier properties) The proton conductive materials according to Samples No. 1 to 17 were formed into membranes, and the gas barrier properties of the resulting proton conductive membranes were evaluated.

[0037] The proton conductive membrane was fabricated by the following method. First, each proton conductive material was mixed with an organic solvent (such as N-methyl-2-pyrrolidone). Next, a mixture was prepared by dissolving an organic polymer (such as polyvinylidene fluoride) as a binder. The mixture ratio of proton conductive material, organic solvent, and binder was 3.5 vol%:3.5 vol%:93 vol%. Then, the mixture was formed into a film on a substrate and dried to obtain an intermediate. This intermediate was densified by a roll press method to obtain a proton conductive membrane.

[0038] Next, the gas barrier properties were evaluated by flowing helium gas at a pressure of 10 kPa through one main surface of the proton conductive membrane and measuring the amount of helium gas leaking to the other main surface.

[0039] The evaluation results are summarized in Table 1. In Table 1, samples with a gas leakage rate of 1 ml / min or less were evaluated as ◯, and samples with a gas leakage rate of more than 1 ml / min were evaluated as ×.

[0040] [Table 1]

[0041] Fig. 1 is a graph showing the relationship between moisture absorption rate and proton conductivity of the proton conductive materials according to Samples No. 2 to 17. Note that, since the proton conductivity of the proton conductive material according to Sample No. 1 was below the measurement limit, Sample No. 1 is not shown in Fig. 1.

[0042] As shown in Figure 1, samples No. 7 to No. 12, which had a moisture absorption rate of 2.5% or more and 4.5% or less, were able to achieve both high proton conductivity and gas barrier properties. It is believed that high proton conductivity was achieved because protons were conducted not only through the proton conductive material itself but also through absorbed water. It is believed that high gas barrier properties were achieved because the formation of pores in the proton conductive membrane was suppressed.

Claims

[Claim 1] Sn １－ｘ A ｘ P ２ O ７ (x is 0.00 or more and 0.15 or less), The moisture absorption rate is 2.5% or more and 4.5% or less when left standing for 60 minutes in an atmosphere of 25°C and 50% RH. Proton conducting materials.

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