Photochromic polyoxomolybdate and preparation method and application thereof

Abstract

The application discloses a photochromic polyoxymolybdate and a preparation method and application thereof, and the photochromic polyoxymolybdate has a molecular formula of C 24 H 28 N4O 26 Mo8, a structural general formula of MV2[β-Mo8O 26 ], wherein MV is a methyl viologen radical cation; the photochromic polyoxymolybdate has electron transfer from O to Mo under ultraviolet irradiation, and is accompanied by crystal color change from colorless to gray; the colored state of the photochromic polyoxymolybdate has a super-stable charge separation state for more than one year under normal temperature environmental conditions; the photochromic polyoxymolybdate has a high-stable charge separation state, can be applied to an oxygen evolution reaction in a neutral electrolyte as a catalyst, realizes efficient electrocatalytic oxygen evolution, and has extremely important significance for designing various renewable energy storage and conversion devices.

Description

Technical Field

[0001] This invention belongs to the field of chemical material synthesis and electrocatalysis technology, specifically relating to a photochromic polyoxomolybdate, its preparation method, and its application. Background Technology

[0002] Electrolysis for hydrogen production is a promising energy storage technology widely used for storing intermittent energy sources such as wind and solar power. Of the two reactions involved, the oxygen evolution reaction (OER) is significantly more complex. This reaction requires the slow oxidation of two water molecules with four electrons, while simultaneously removing four protons. The efficiency of the proton-coupled electron transfer process remains fundamentally hampered by its potentially limiting step (i.e., O-O coupling), considered one of the bottlenecks in the development of water oxidation catalysts (WOCs). However, the cost of storing renewable energy remains prohibitively high due to the corrosion and environmental issues associated with the strong acids or bases used in electrolyzers. Furthermore, only a very small number of WOCs can operate effectively in neutral water under ambient conditions due to low ion concentrations and high ohmic losses. Although there are reports of RuO2... x and IrO x While some high-cost noble metal oxides exhibit high OER activity in neutral solutions, developing a non-noble metal WOC that can operate at low overpotential in neutral electrolytes remains an urgent need.

[0003] Nature provides the blueprint for designing photosystems (WOCs), where photosystem II (PS-II), with its reactive oxygen evolution center (OEC), is composed of Mn4CaO5 clusters that exhibit remarkable efficiency in catalyzing water splitting to produce oxygen in neutral media. Based on the structural characteristics of the OEC, various metal oxides have been designed to mimic the chemical functions of PS-II. In fact, the main step in natural photosynthesis—absorbing sunlight and converting it into spatially separated electron / hole pairs—is often overlooked. Therefore, generating an intrinsically stable charge-separated state within the WOC is crucial for achieving artificial photosynthesis. Electron transfer (ET) photochromic materials, in particular, can form long-lived charge-separated states.

[0004] Inspired by the structural features of metal-oxygen clusters and the stable charge separation behavior of OEC observed in PS-II, polyoxygen metal salts (POMs), as metal-oxygen clusters with well-defined structures and ET photochromic redox activity, are excellent candidate materials for developing artificial light systems. In addition, it is worth mentioning that since most reported WOCs are amine-phase composite catalysts without well-defined crystal structures, it remains a challenge to gain a deeper understanding of their charge separation processes and catalytic mechanisms at the atomic level. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a photochromic polyoxomolybdate, its preparation method, and its applications. This photochromic polyoxomolybdate exhibits a highly stable charge-separated state and can be used as a catalyst in the oxygen evolution reaction in neutral electrolytes, achieving highly efficient electrocatalytic oxygen evolution. This is of great significance for the design of various renewable energy storage and conversion devices.

[0006] The present invention adopts the following technical solution:

[0007] A photochromic polyoxymolybdate with the molecular formula C 24 H 28 N4O 26 Mo8 has the general structural formula MV2[β-Mo8O] 26 ], wherein MV is a methyl viologen cation; the photochromic polyoxomolybdate undergoes electron transfer from O to Mo under ultraviolet irradiation, accompanied by a change in crystal color from colorless to gray; the colored state of the photochromic polyoxomolybdate has an ultra-stable charge separation state for more than one year under normal temperature conditions.

[0008] A method for preparing photochromic polyoxomolybdate specifically includes the following steps:

[0009] S1. Add 151 mg of 0.625 mM Na2MoO4·2H2O and 10.8 mg of 0.042 mM MV to 8 mL of water, stir at room temperature for 1 hour, and obtain a clear initial solution.

[0010] S2. The pH of the primary solution was adjusted to 6 using 1M HCl to obtain a turbid secondary solution.

[0011] S3. After stirring at room temperature for 1 hour, the secondary solution is placed in a 25 mL Teflon-lined stainless steel autoclave and sterilized at 140°C for 72 hours to obtain colorless blocky crystals, which are photochromic polyoxymolybdate.

[0012] An application of a photochromic polyoxomolybdate, wherein the photochromic polyoxomolybdate is used as a catalyst in the oxygen evolution reaction in a neutral electrolyte and in a renewable energy storage and conversion device.

[0013] After adopting the above technical solution, the present invention has the following advantages compared with the prior art: The photochromic polyoxomolybdate POMo of the present invention can form an ultra-stable charge-separated state under ultraviolet irradiation. The π-conjugated organic catalyst has a strong polarization effect on the anionic POM, which can effectively stabilize the charge-separated state. This photochromic polyoxomolybdate can be used as a highly active non-noble metal catalyst for the oxygen evolution reaction (OER) in neutral electrolytes, which is of great significance for the design of various renewable energy storage and conversion devices. This photochromic material has a switchable special OER activity in the neutral electrolyte before and after photochromism. The well-defined structure allows for a deeper understanding of the charge separation process and catalytic mechanism at the atomic level, and is applicable to different [β-Mo8O]... 26 ] 4- Studies of the salt structure show that the delocalized π-cation structure in MV enables the colored photochromic polyoxomolybdate to possess an ultrastable charge-separated state through intermolecular polarization. Furthermore, studies of the colored electronic structure indicate that [β-Mo8O] 26 ] 4- The presence of oxygen vacancies within the clusters serves as sites for direct O-O coupling, thereby effectively promoting OER. Experimental and theoretical calculations demonstrate that the enhanced OER activity of colored photochromic polyoxymolybdates stems from the lower Fermi level of their charge-separated states, which effectively activates the O-O coupling process. Their OER activity even surpasses that of ordinary RuO2, providing a forward-looking direction and design concept for the development of non-noble metal OER arrays in artificial photosynthetic devices. Attached Figure Description

[0014] Figure 1 This is a crystal structure diagram of the photochromic polyoxymolybdate of the present invention;

[0015] Figure 2 The powder diffraction pattern of the photochromic polyoxomolybdate of the present invention is shown below.

[0016] Figure 3 The infrared spectrum of the photochromic polyoxomolybdate of the present invention is shown below.

[0017] Figure 4 The ultraviolet absorption spectrum of the photochromic polyoxomolybdate of this invention is shown.

[0018] Figure 5 This is a graph showing the electrochemical performance of the photochromic polyoxomolybdate of the present invention;

[0019] Figure 6 This is the crystal structure and color-changing test diagram of the photochromic polyoxymolybdate of the present invention. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0021] See Figures 1 to 6 A method for preparing photochromic polyoxomolybdate specifically includes the following steps:

[0022] S1. Add 151 mg of 0.625 mM Na2MoO4·2H2O and 10.8 mg of 0.042 mM MV to 8 mL of water, stir at room temperature for 1 hour, and obtain a clear initial solution.

[0023] S2. The pH of the primary solution was adjusted to 6 using 1M HCl to obtain a turbid secondary solution.

[0024] S3. After stirring at room temperature for 1 hour, the secondary solution is placed in a 25 mL Teflon-lined stainless steel autoclave and sterilized at 140°C for 72 hours to obtain colorless blocky crystals, which are photochromic polyoxymolybdate.

[0025] The photochromic polyoxomolybdate crystals prepared above were characterized and their properties were tested.

[0026] (1) Crystal structure determination

[0027] Select a single crystal of suitable size, regular shape, and transparency under a microscope. Then, using a Bruker APEX II CCD diffractometer, monochromate the Mo-Kα rays at 175(2)K using a graphite monochromator. The incident light source was used to collect crystal diffraction data. In the structural analysis, the Shelextl-97 program was used to directly analyze and refine the crystal structure. Simultaneously, non-hydrogen atoms and their anisotropic treatment parameters were corrected using the full-matrix least squares method. All hydrogen atoms were obtained through theoretical hydrogenation. The resulting crystal structure diagram is shown below. Figure 1 As shown. Some crystallographic data and refinement parameters are shown in Table 1.

[0028] Table 1: Crystal parameters of the compounds

[0029]

[0030]

[0031] (2) Powder diffraction characterization:

[0032] Take an appropriate amount of the single crystal prepared by the above method, grind it thoroughly into powder, and measure the powder diffraction pattern of the conductive material at room temperature, as shown below. Figure 2 As shown, the experimental results, compared with those simulated based on single-crystal diffraction data, agree well with the results fitted by Mercury software, indicating that the compound is a pure phase. The anisotropy of the crystal leads to differences in the intensity of some diffraction peaks.

[0033] (3) Infrared spectroscopy characterization:

[0034] like Figure 3 As shown, Fourier transform infrared spectrum (KBr, 4000-400cm) -1 ), 3101(w), 3050(m), 1637(s), 1560(w), 1498(w), 1441(m), 1329(w), 1267(w), 1206(w), 11 79(w), 949(s), 903(s), 846(s), 821(s), 707(s), 671(s), 559(m), 512(w), 466(w), 441(w).

[0035] (4) Ultraviolet absorption spectroscopy characterization:

[0036] The ultraviolet absorption spectrum of photochromic polyoxomolybdate is as follows: Figure 4 As shown.

[0037] (5) Neutral electrolyte electrocatalytic OER test of photochromic polyoxymolybdate:

[0038] The neutral electrolyte electrocatalytic OER test results of photochromic polyoxymolybdate are as follows: Figure 5 As shown.

[0039] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A photochromic polyoxymolybdate, characterized in that: Its molecular formula C 24 H 28 N4O 26 Mo8 has the structural formula MV2[β-Mo8O] 26 ], where MV is methyl viologen cation.

2. A method for preparing photochromic polyoxomolybdate as described in claim 1, characterized in that, Specifically, the following steps are included: S1. Add 151 mg of Na2MoO4·2H2O and 10.8 mg of MV to 8 mL of water and stir for 1 hour at room temperature to obtain a clear initial solution. S2. The pH of the primary solution was adjusted to 6 using 1M HCl to obtain a turbid secondary solution. S3. After stirring at room temperature for 1 hour, the secondary solution is placed in a 25 mL Teflon-lined stainless steel high-pressure reactor and reacted at 140°C for 72 hours to obtain colorless blocky crystals, which are photochromic polyoxymolybdate.

3. An application of the photochromic polyoxomolybdate as described in claim 1, characterized in that: The photochromic polyoxomolybdate is used as a catalyst in the oxygen evolution reaction in a neutral electrolyte.

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