Oxygen-rich thiomolybdate compound, preparation method and application of oxygen-rich thiomolybdate compound in ion conduction

Abstract

The invention discloses an oxygen-rich thiomolybdate compound, a preparation method and application of the oxygen-rich thiomolybdate compound in ion conduction, and belongs to the field of synthesis of multi-metal oxygen clusters. The oxygen-rich thiomolybdate compound is synthesized by adopting a one-pot method, and ionic conductivity tests are carried out on the synthesized oxygen-rich thiomolybdate compound at different temperatures and humidity, so that the oxygen-rich thiomolybdate compound is found to have relatively high ionic conductivity in a wide temperature range; moreover, typical temperature and humidity dependent ionic conductivity is presented, and the conductivity is increased along with the increase of the temperature and increased along with the increase of the humidity. The ionic conductivity can reach 8.6 * 10 <-3 > S cm <-1 > under the conditions that the humidity is 80% and the temperature is 85 DEG C, so that the compound has a good prospect of serving as an efficient ionic conductor. The preparation method disclosed by the invention is simple in process, the product is easy to crystallize, the reaction time is short, the synthesis yield is high, and the prepared oxygen-rich thiomolybdate compound has good ionic conductivity and can be widely applied to ionic conduction materials.

Description

Technical Field

[0001] The invention belongs to the field of polymetallic oxygen cluster synthesis, and in particular relates to a polyoxysulfuric molybdate compound, a preparation method and application thereof in ion conduction. Background Art

[0002] Ion-conducting materials play a vital role in modern energy conversion and storage technologies. Especially in the field of fuel cells, efficient ion conductors are the key to achieving efficient energy conversion. The traditional Nafion series membranes are limited in their wide application due to their high cost and unclear structural characteristics. Therefore, the development of new ion-conducting materials with clear structures and excellent conductive properties has become a hot topic in current research.

[0003] Polyoxometalates (POMs) have shown great potential in improving ion conductivity due to their unique structures and properties. Through a large number of screenings, we noticed that [Mo2O2S2] 2+ It can maintain stable configuration in a wide pH range. The introduction of S and the formation of Mo-Mo metal bonds affect the overall electronic structure and chemical properties of the compound. We can use [Mo2O2S2] 2+ The unit tends to form a ring structure, and the ion carrier is attached to the inner and outer surfaces of the ring through coordination bonds to increase the concentration and specific surface area of ​​the ion carrier. The present invention imitates the process of LEGO building, designs and assembles functional molecular compounds and applies them to ion conduction technology. Summary of the invention

[0004] The purpose of the present invention is to provide a polyoxysulfur molybdate compound, a preparation method and its application in ion conduction. The preparation method of the present invention has simple process, easy crystallization of the product, short reaction time and high synthesis yield. The prepared polyoxysulfur molybdate compound has good ion conductivity and can be widely used in ion conduction materials.

[0005] The present invention adopts a one-pot method to synthesize the polyoxysulfur molybdate compound. The clear and definite structure of the polyoxysulfur molybdate compound enables it to be used for the study of ion conductivity. By testing the ion conductivity of the synthesized polyoxysulfur molybdate compound at different temperatures and humidities, it is found that the polyoxysulfur molybdate compound has high ion conductivity in a wide temperature range and exhibits typical temperature and humidity dependent ion conductivity. The conductivity increases with increasing temperature and increases with increasing humidity. Under the conditions of 80% humidity (RH) and 85°C, the ion conductivity can reach 8.6×10 -3 S cm -1 , indicating that the compound has good prospects as an efficient ion conductor.

[0006] The first object of the present invention is to provide a method for preparing a polyoxysulfur molybdate compound, which comprises dissolving 0.02-0.03 g of potassium dihydrogen arsenate and 0.08-0.12 g of succinic acid in 15-30 mL of deionized water, stirring for 3-10 minutes, and adding 5-8 mL of [Mo2O2S2] 2+ The solution (synthesized according to the literature: Cadot E., Salignac B., Halut S., Sécheresse F., Angew. Chem. Int. Ed. Eng., 1998, 37 (5), 611-613) is orange and transparent; after continuing to stir for 3 to 10 minutes, 1.0M K2CO3 is added to adjust the pH of the reaction system to 4 to 5, and then the mixture is stirred at room temperature for 1.0 to 2.0 hours and filtered. The obtained filtrate is slowly evaporated at room temperature for 5 to 8 days to obtain orange rhombus crystals, i.e., the polyoxythiomolybdate compound, whose chemical formula is H6K 12 I4[(AsO5)4(Mo2O2S2) 10 O4(C4H4O4)2]·[(Mo2O2S2)4(OH)8(MoO6)]·18H2O, whose crystallographic data are shown in Table 1:

[0007] Table 1: Crystallographic data of the obtained compounds

[0008]

[0009] The second object of the present invention is to provide a polyoxysulfuric molybdate compound, which is prepared by the above method.

[0010] The third object of the present invention is to provide the use of the above-mentioned polyoxysulfide molybdate compound in ion conduction.

[0011] Beneficial Effects

[0012] 1. The present invention can successfully prepare polyoxysulfuric molybdate compounds, and has the characteristics of simple and easy preparation method;

[0013] 2. The polyoxythiomolybdate compound synthesized by the present invention is a crystal with high crystallinity and clear structure. The presence of a large number of terminal oxygen, bridging oxygen, free water molecules and arsenic acid groups on the surface of the structure makes it have excellent ion conductivity; these groups act as ion transition sites and establish a wide range of hydrogen bond networks with adsorbed water molecules, thereby enhancing ion conductivity;

[0014] 3. The test results under different temperatures and humidities show that the synthesized polyoxysulfuric molybdate exhibits typical temperature and humidity dependent ionic conductivity, and the conductivity increases with increasing temperature and increases with increasing humidity. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 The H6K synthesized by the present invention 12 I4[(AsO5)4(Mo2O2S2) 10 O4(C4H4O4)2]·[(Mo2O2S2)4

[0016] Crystal structure diagram of (OH)8(MoO6)]·18H2O;

[0017] Figure 2 H6K synthesized by the present invention 12 I4[(AsO5)4(Mo2O2S2) 10 PXRD pattern of O4(C4H4O4)2]·[(Mo2O2S2)4(OH)8(MoO6)]·18H2O;

[0018] Figure 3 H6K synthesized by the present invention 12 I4[(AsO5)4(Mo2O2S2) 10 FT-IR pattern of O4(C4H4O4)2]·[(Mo2O2S2)4(OH)8(MoO6)]·18H2O;

[0019] Figure 4 H6K synthesized by the present invention 12 I4[(AsO5)4(Mo2O2S2) 10 O4(C4H4O4)2]·[(Mo2O2S2)4(OH)8(MoO6)]·18H2O Nyquist plot of humidity at 30°C;

[0020] Figure 5 H6K synthesized by the present invention 12 I4[(AsO5)4(Mo2O2S2) 10 O4(C4H4O4)2]·[(Mo2O2S2)4(OH)8(MoO6)]·18H2O Humidity-dependent ionic conductivity image at 30°C;

[0021] Figure 6 H6K synthesized by the present invention 12 I4[(AsO5)4(Mo2O2S2) 10 Nyquist plot of O4(C4H4O4)2]·[(Mo2O2S2)4(OH)8(MoO6)]·18H2O as a function of temperature at 80% RH;

[0022] Figure 7 H6K synthesized by the present invention 12 I4[(AsO5)4(Mo2O2S2) 10Arrhenius curve of [(Mo2O2S2)4(OH)8(MoO6)]·18H2O at 80% RH. DETAILED DESCRIPTION

[0023] Example 1

[0024] Synthetic H6K 12 I4[(AsO5)4(Mo2O2S2) 10 O4(C4H4O4)2]·[(Mo2O2S2)4(OH)8(MoO6)]·18H2O, where C4H4O4 is deprotonated succinic acid. Dissolve 0.03g potassium dihydrogen arsenate and 0.1g succinic acid in 20mL deionized water, stir for 5 minutes, and add 5mL of [Mo2O2S2] 2+ The solution (the raw materials were synthesized according to the literature, Cadot E., Salignac B., Halut S., Sécheresse F., Angew. Chem. Int. Ed. Eng., 1998, 37 (5), 611-613) was orange and transparent; after stirring for 5 minutes, 1.0 M K2CO3 was added to adjust the pH to 4.5; after stirring at room temperature for 1 hour, the solution was filtered, and the filtrate was slowly evaporated at room temperature for 7 days to obtain orange rhombus crystals (product mass: 0.06 g).

[0025] The crystal structure of the compound is shown in Figure 1 As shown. The compound is a 3D framework structure composed of cubic cages and Mo9 rings arranged in an alternating pattern. Specifically: [AsO5] 5- As a building block with four [Mo2O2S2] 2+ The units are connected to form a unique Mo8 ring supported by succinic acid. 2+ The unit and two K2 atoms connect the two identical Mo8 rings above and below to build a cubic cage As4Mo 20 (L)2, (L=C4H4O4). In addition, in this structure, there is also [Mo2O2S2] 2+ The unit self-condenses into a Mo9 ring structure, and the Mo9 ring and the cubic cage are connected by K1 and K3 to form an ordered 3D framework structure.

[0026] The prepared materials were basically characterized:

[0027] Powder X-ray diffraction (PXRD) measurements were recorded on an X-ray diffractometer with Mo Kα (λ=0.071073 nm) in the range of 5° to 50° at room temperature. Figure 2 The H6K synthesized by the present invention12 I4[(AsO5)4(Mo2O2S2) 10 From the PXRD spectrum of [(Mo2O2S2)4(OH)8(MoO6)]·18H2O, it can be seen that the experimental spectrum (As-synthesized) matches well with the simulated spectrum (Simulated), proving that the crystal has a crystalline structure and is pure without impurities.

[0028] The compound was tested by infrared. The infrared spectrum of the crystal is as follows Figure 3 As shown, the test wavelength range is 4000cm -1 ~500cm -1 In the compound, 510cm -1 、624cm -1 and 938cm -1 The absorption peaks observed at 738 cm-1 are attributed to ν(Mo-S-Mo), ν(Mo-OH-Mo) and ν(Mo=O). -1 The absorption peak is attributed to the stretching vibration of As-O at 1410 cm -1 、1550cm -1 The absorption peak observed at 1615 cm is attributed to the stretching vibration of CC and CO. -1 and 3416cm -1 The peaks at are attributed to the bending vibration and stretching of hydroxyl groups.

[0029] Study on ion conductivity of compounds:

[0030] The obtained crystal particles were ground into powder, and the obtained powder sample was placed in a powder tableting mold with an inner diameter of 5 mm, and a pressure of 20 MPa was applied for 30 seconds to obtain a small disc of compound with a thickness of 0.091 cm and a smooth surface. Subsequently, the small disc of compound with a certain thickness and a smooth surface was sandwiched between two gold-plated electrodes, and the thickness of the electrode was about 1.0 mm. The temperature and relative humidity were controlled by a Sanwood constant temperature and humidity chamber (SC-80-CC-3). The alternating current (AC) impedance method of the Solartron SI1260 impedance / gain phase analyzer was used to determine the ionic conductivity of the compound. For the electrochemical impedance spectroscopy (EIS) test with variable temperature and humidity, each test point was tested after 30 minutes and 12 hours of equilibrium.

[0031] Zview software was used to fit the impedance data. The ionic conductivity (σ) was calculated from the resistance value (R) using the following formula:

[0032]

[0033] Where σ is the ionic conductivity (S cm-1 d is the particle thickness of the powder sample after tableting (cm); A is the cross-sectional area of ​​the disc sample (cm 2 );R is the resistance (Ω).

[0034] The activation energy (E a ), the formula is as follows:

[0035]

[0036] Where T is the absolute temperature (K); σ0 is the pre-exponential factor (rewrite the Arrhenius equation as lnσT = lnσ0-E a / k B T, and then by plotting lnσT against 1 / T, the slope of the straight line is -E a / k B , the intercept is lnσ0, so we can find E a and the value of σ0); E a is the activation energy (eV); k B is the Boltzmann constant, which is 1.38×10 -23 J / K.

[0037] The ionic conductivity of the compounds was measured by the electrochemical impedance spectroscopy technique under different humidity and temperature conditions. At a temperature of 30°C, the ionic conductivity of the compounds was studied as a function of relative humidity (RH). Figure 4 The resistance of the powder sample was determined based on the semicircle of the Nyquist plot, and it was found that as the humidity increased, the resistance of the compound became smaller and smaller. Figure 5 This is the ionic conductivity graph of the compound obtained from the measured resistance data when it was tested at 30°C. As the RH increases from 50%, 60% to 70%, 80%, the σ value gradually increases from 6.63×10 -5 S cm -1 ,7.51×10 -5 S cm -1 Increased to 1.17×10 -4 Scm -1 , 3.39×10 -4 S cm -1 . This phenomenon shows that the sample is highly dependent on humidity, and also indicates that water molecules play a very important role in the conduction process. This obvious enhancement in ionic conductivity is attributed to the abundant bridging oxygen, terminal oxygen and arsenic acid groups on the surface of the structure. These groups act as proton transition sites and establish extensive hydrogen bond networks with adsorbed water molecules, thereby enhancing ionic conductivity. In addition, temperature changes are also an important factor affecting ionic conductivity. Variable temperature impedance tests were carried out under conditions of 80% RH and temperatures of 30 to 85°C. Figure 6As the temperature increases from 30°C to 85°C, the ionic conductivity of the compound increases from 3.38×10 -4 S cm -1 Increased to 8.60×10 -3 S cm -1 , showing typical temperature-dependent ionic conductivity, which is attributed to the acceleration of ion migration rate due to increased temperature.

[0038] In order to study the ion conduction mechanism, the activation energy of ion transfer in the compound was determined according to the Arrhenius equation by using the ln(σT) curve plotted on 1000 / T, as Figure 7 As shown, the calculated activation energy is 0.53 eV. The results show that the ion migration path of the compound is consistent with the vehicle mechanism. The observation of high ionic conductivity can be attributed to the presence of a large number of free water molecules and polyoxyanion groups in the compound. Ions are transferred from free water molecules to cooperatively coordinated water molecules, and then further transferred to the terminal oxygen atoms of POMs through the hydrogen bond network, establishing a fast and efficient transport pathway, ultimately leading to the vehicle mechanism.

[0039] In summary, the present invention synthesizes a novel multi-nuclear multi-metal sulfur cluster crystalline material based on the ion conduction function and function orientation. 12 I4[(AsO5)4(Mo2O2S2) 10 O4(C4H4O4)2]·[(Mo2O2S2)4(OH)8(MoO6)]·18H2O material, the presence of a large number of terminal oxygen, bridge oxygen and free water molecules in its structure makes it have excellent ion conductivity. At 80% RH and 85℃, its ion conductivity can reach 8.6×10 -3 S cm -1 , indicating that the compound has the potential to be a highly efficient ion conductor. The research results have reference value for the in-depth exploration of the structure-activity relationship between the structure and properties of polymetallic oxosulfates.

Claims

1. A method for preparing a polyoxysulfur molybdate compound, comprising dissolving 0.02-0.03 g potassium dihydrogen arsenate and 0.08-0.12 g succinic acid in 15-30 mL deionized water, stirring for 3-10 minutes, and adding 5-8 mL of [Mo2O2S2] to the solution. 2+ The solution is orange and transparent; after continuing to stir for 3 to 10 minutes, 1.0M K2CO3 is added to adjust the pH of the reaction system to 4 to 5, and then stirred at room temperature for 1.0 to 2.0 hours and filtered. The obtained filtrate is slowly evaporated at room temperature for 5 to 8 days to obtain orange rhombus crystals, namely the polyoxythiomolybdate compound, whose chemical formula is H6K 12 I4[(AsO5)4(Mo2O2S2) 10 O4(C4H4O4)2]·[(Mo2O2S2)4(OH)8(MoO6)]·18H2O.

2. A polyoxysulfur molybdate compound, characterized in that: The method is prepared by the method of claim 1.

3. Use of the polyoxysulfuric molybdate compound according to claim 2 in ion conduction.

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