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). In the 31P MAS NMR spectrum using 85% phosphoric acid aqueous solution as the reference substance, the ratio of the peak area of a second peak having a chemical shift in the range of -20 ppm or more and 10 ppm or less to the peak area of a first peak having a chemical shift in the range of -60 ppm or more and -20 ppm or less is 0.05 or more.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 a proton-conductive material by the method described in Patent Document 1 many times, the proton conductivity sometimes decreased.

[0006] Therefore, the present inventors investigated the cause of the decrease in proton conductivity and found that: 31 We obtained a new finding that the peak area ratio of the second peak area having a chemical shift value in the range of -20 ppm to 10 ppm inclusive to the first peak area having a chemical shift value in the range of -60 ppm to -20 ppm inclusive in the P MAS NMR spectrum affects the proton conductivity.

[0007] 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. [Means for solving the problem]

[0008] The proton conductive material according to the present invention is Sn 1-x Al x It 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 31 In a P MAS NMR spectrum, when an 85% aqueous phosphoric acid solution is used as a reference substance, the peak area ratio of a second peak area having a chemical shift value in the range of −20 ppm to 10 ppm to a first peak area having a chemical shift value in the range of −60 ppm to −20 ppm is 0.05 or more. Effect of the Invention

[0009] According to the present invention, it is possible to provide a proton-conducting material having high proton conductivity. [Brief description of the drawings]

[0010] [Figure 1] 1 is an example of a 31P MASNMR spectrum of a proton conducting material. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] (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.

[0012] 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.

[0013] Sn 1-x Al x P2O7…(1)

[0014] 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.

[0015] 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.

[0016] [NMR spectrum] FIG. 1 shows a proton conductive material according to this embodiment. 31 1 is an example of a P MAS NMR spectrum (hereinafter abbreviated as "NMR spectrum").

[0017] The NMR spectrum is 31 The measurement is performed by P-MAS (Magic Angle Spinning)-NMR (Nuclear Magnetic Resonance) spectroscopy. The measurement conditions for NMR spectroscopy may be ordinary measurement conditions, but may be, for example, the following conditions.

[0018] Equipment: Agilent Technologies NMR spectrometer, model Agilent NMR System 400WB Probe: 4.0mmφ -Sample rotation speed: 15kHz ·Measurement environment temperature: 25℃ Sample: Place 100 mg of the measurement sample (proton conductive material) in a sample tube with a diameter of 4.0 mm. ·Measurement nuclear frequency: 162.12MHz Reference substance: 85% phosphoric acid aqueous solution (external standard: 0 ppm) Observation width: 50kHz Pulse width: 2.0μsec Measurement time: 3.6 hours Repeat time: 800 seconds Number of times: 16

[0019] The NMR spectrum is a composite waveform obtained by peak separation using curve fitting to minimize the difference between the composite waveform of the separated waveforms of orthophosphate, condensed phosphoric acid, pyrophosphate, and polycondensed phosphate and the observed waveform. ALICE2 (registered trademark), an NMR data processing software made by JEOL, is used for curve fitting.

[0020] The baseline of an NMR spectrum can be determined by a normal method, as described below. First, the FID signal acquired in the NMR measurement is Fourier transformed, and the horizontal axis is converted into a spectrum of frequency (ppm), after which the spectrum is observed and phase correction is performed. Next, since the baseline of the spectrum still has a large distortion even after phase correction, the baseline is automatically corrected using data processing software. After that, the spectrum is enlarged and observed, and if there is an obvious singular point on the baseline automatically corrected by the data processing software, it may be manually corrected at the discretion of the analyst.

[0021] In addition, FIG. 1 shows the approximate observation ranges of orthophosphate, condensed phosphoric acid, pyrophosphate, and polycondensed phosphate.

[0022] [Chemical shift] The resonance position in an NMR spectrum is called the chemical shift, and if it is divided by the frequency of a reference substance and converted to ppm as shown in the following equation (2), the chemical shift becomes a number that is independent of an external magnetic field.

[0023] Chemical shift = [(resonance frequency of sample - resonance frequency of reference substance) / resonance frequency of reference substance] x 10 6 …(2)

[0024] [Peak area ratio] As shown in Figure 1, the NMR spectrum shows a first peak in the chemical shift range of -60 ppm to -20 ppm, and a second peak in the chemical shift range of -20 ppm to 10 ppm. The first peak mainly contains pyrophosphate, and the second peak mainly contains orthophosphate.

[0025] In the NMR spectrum, when an 85% phosphoric acid aqueous solution is used as a reference material, the ratio of the area of ​​the second peak in the chemical shift range of -20 ppm to 10 ppm to the area of ​​the first peak in the chemical shift range of -60 ppm to -20 ppm (hereinafter referred to as "peak area ratio") is 0.05 or more. This can increase the proton conductivity of the proton conductive material. The mechanism by which high proton conductivity can be obtained by making the peak area ratio 0.05 or more is not necessarily clear, but it is thought to be related to the fact that the proton conductive material contains orthophosphoric acid, which can improve the hygroscopicity of the proton conductive material.

[0026] The peak area ratio is preferably 0.09 or more, which can further increase the proton conductivity of the proton-conducting material.

[0027] The first peak area is represented by the first integral value in the range of -60 ppm to -20 ppm in the NMR spectrum. The second peak area is represented by the second integral value in the range of -20 ppm to 10 ppm in the NMR spectrum. The peak area ratio is the value obtained by dividing the second integral value by the first integral value.

[0028] The peak area ratio is preferably 0.12 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 believed to be related to the formation of voids in the process of evaporating excess moisture absorbed water.

[0029] (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.

[0030] 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 peak area ratio described above can be adjusted by the molar ratio P / (Sn+Al) of the Sn, P, and Al elements. The molar ratio P / (Sn+Al) can be adjusted by the amount of SnO2, (NH4)2HPO4, and Al(OH)3 charged. The value of the molar ratio P / (Sn+Al) is not particularly limited, but can be, for example, 2.5 to 4.0. The suffix X in the above formula (1) can be adjusted by the molar ratio Al / (Sn+Al) of the Sn and Al elements charged. The molar ratio Al / (Sn+Al) can be appropriately adjusted by the amount of SnO2 and Al(OH)3 charged.

[0031] 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

[0032] The following describes examples of the present invention. In these examples, the effect of the peak area ratio in the NMR spectrum of a proton-conducting material on the proton conductivity is examined. However, the present invention is not limited to the examples described below.

[0033] (Preparation of Samples No. 1 to 14) The proton conductive materials according to Samples No. 1 to 14 were prepared by solid phase synthesis.

[0034] 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 placed in 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 peak area ratio was adjusted for each sample, as shown in Table 1. In addition, SnO 2、 By changing the amount of Al(OH)3 added, the molar ratio Al / (Sn+Al) of the Sn and Al elements added was adjusted as shown in Table 1. As a result, the subscript X in formula (1) was adjusted for each sample as shown in Table 1.

[0035] The powder mixture was then calcined at 650°C for 2.5 hours to synthesize the proton-conducting material.

[0036] (Peak area ratio) In the NMR spectra of the proton conductive materials of Samples No. 1 to 14, when an 85% aqueous phosphoric acid solution was used as a reference substance, the peak area ratio of the second peak area in the chemical shift range of -20 ppm or more and 10 ppm or less to the first peak area in the chemical shift range of -60 ppm or more and -20 ppm or less was calculated.

[0037] The NMR spectrum was obtained under the measurement conditions described in the above embodiment. The peak area ratio was calculated by dividing the second peak area by the first peak area. The calculation results are summarized in Table 1.

[0038] (Proton Conductivity) The proton conductivity of the proton conductive materials according to Samples No. 1 to 14 was measured by the following method.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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 value of less than S / cm were rated as x.

[0043] (composition formula) By performing ICP emission spectroscopy on the proton conductive materials of Samples No. 1 to 14, the composition formula of the proton conductive materials was Sn 1-x Al x The subscript X in P2O7 was determined.

[0044] 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.

[0045] (Gas barrier properties) The proton conductive materials according to Samples No. 1 to 14 were formed into membranes, and the gas barrier properties of the resulting proton conductive membranes were evaluated.

[0046] 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.

[0047] 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.

[0048] 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 ×.

[0049] [Table 1]

[0050] As shown in Table 1, high proton conductivity was obtained in Samples No. 4 to No. 14, which had a peak area ratio of 0.05 or more. It is believed that such results were obtained because the proton conductive material contained orthophosphoric acid, which improved the hygroscopicity of the proton conductive material.

[0051] Moreover, in Samples Nos. 6 to 14, which had a peak area ratio of 0.09 or more, higher proton conductivity was obtained.

[0052] Furthermore, among samples Nos. 4 to 14, samples Nos. 4 to 9, which had a peak area ratio of 0.12 or less, were able to obtain high gas barrier properties. It is believed that such results were obtained because the formation of pores in the proton conductive membrane was suppressed.

Claims

1. Sn １－ｘ A ｘ P ２ O ７ (x is 0.00 or more and 0.15 or less), ３１ In a P MAS NMR spectrum, when an 85% aqueous phosphoric acid solution is used as a reference substance, a peak area ratio of a second peak area having a chemical shift in the range of -20 ppm or more and 10 ppm or less to a first peak area having a chemical shift in the range of -60 ppm or more and -20 ppm or less is 0.05 or more. Proton conducting materials.

2. The peak area ratio is 0.12 or less. The proton conducting material of claim 1 .

3. The peak area ratio is 0.09 or more. The proton conducting material according to claim 1 or 2.

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