CN105567325A - Spinel compound-carbonate mixture system for solar energy photo-thermal chemical conversion, preparation and application thereof - Google Patents

Abstract

The present invention relates to a method for producing _H2 and CO2 by splitting water or _CO2 through a multi-step thermochemical cycle using carbonate and spinel-like compounds as cycle active materials. The main steps are as follows: 1) Synthesize the active material and mix the two materials; 2) Heat the mixed material to a certain temperature and feed H ₂ O or CO ₂ to generate H ₂ and CO; 3) Treat 2) The finished active material is dispersed in deionized water, passed through CO ₂ for hydrolysis, and the hydrolyzed active species is separated; 4) The active material after 3) is heated to a certain temperature for oxygen evolution reaction. The invention utilizes the hydrolysis reaction for the first time to process the active species after _H2 production, so that the oxygen production reaction can be carried out more smoothly, and the feasibility of the circulation system is improved. The circulation system has a low reaction temperature, uses solar energy as a heat source, and uses H ₂ O and CO ₂ as raw materials, which is clean and pollution-free.

Description

A mixture system of spinel compounds and carbonates for photothermal chemical conversion of solar energy and its preparation and application

technical field

The present invention relates to a multi-step thermochemical cycle for splitting water and carbon dioxide. It specifically involves using a mixture system composed of spinel compounds and alkali metal or alkaline earth metal carbonates as an active material system to decompose water and carbon dioxide through a multi-step thermochemical cycle to produce hydrogen and carbon monoxide. The system uses solar energy as a heat source to decompose water and carbon dioxide at low temperature (500-1000° C.), and has very broad application prospects in energy saving, emission reduction and environmental protection.

Background technique

Under the background of energy crisis and environmental crisis, the unsustainability of fossil energy is becoming more and more obvious, and the greenhouse effect and environmental pollution caused by excessive use of fossil energy are becoming more and more prominent. A renewable energy system is imminent. China is currently the second largest country in terms of CO ₂ emissions, and the CO ₂ emissions are growing rapidly, which is under increasing pressure from environmental protection and the international community. Solar energy has many advantages such as clean, non-polluting, inexhaustible, and renewable. Using solar energy to convert water into hydrogen and oxygen avoids pollution problems from the source. In addition, using solar energy to convert greenhouse gas _CO2 into chemical fuels that are easy to store Can reduce the greenhouse effect. In recent years, the development and application of this kind of science and technology has received extensive attention from the international community.

The multi-step thermochemical cycle decomposition of H ₂ O/CO ₂ technology is a key technology integrating solar energy conversion and chemical fuel production, and is one of the hotspots in the field of new energy development and research. Compared with the reaction temperature of the two-step thermochemical cycle above 1000 °C, the multi-step thermochemical cycle has the obvious advantage of low reaction temperature, that is, most multi-step thermochemical cycles can be completed below 1000 °C. A more common multi-step loop pattern is as follows:

H ₂ O+A→0.5H ₂ +AO

AO+B→0.5O ₂ +AB

AB→A+B

Substance A reduces H ₂ O to produce hydrogen and oxide AO; substance B oxidizes AO to produce oxygen and compound AB; in the third step, compound AB undergoes metathesis reaction under certain conditions to produce A and B; through three reaction steps The cycle is complete. H ₂ O is decomposed into O ₂ and H ₂ through this cycle, in which H ₂ O is the only input material and O ₂ and H ₂ are output species. The mixed system of spinel oxides and carbonates is a type of multi-step thermochemical cycle designed based on the above design ideas. But multi-step cycles are diverse and not limited to the above-mentioned cycle models. Classical multi-step cycles include non-metallic compound cycle, metal/metal oxide and halogen or acid cycle, and metal oxide and basic compound cycle, among which SI cycle, Fe-Cl cycle and Cu-Cl cycle are typical multi-step cycles cycle.

Beghi, GE first proposed the SI cycle (Int.J.HydrogenEnergy, 1986, 11(12):761-771), the main reaction steps of this cycle are shown in the figure below. The reaction temperature is significantly lower than that of the two-step cycle, and the highest reaction temperature is only 850 °C. However, the acidic system is very corrosive to the material, and the separation of HI and H ₂ SO ₄ is also very energy-consuming. Zhang, Y. et al. (Industrial & Engineering Chemistry Research, 2014, 53, 3021-3028) recently conducted an in-depth study on the BunsenReaction involved in the SI cycle. Mainly studied the influence of SO ₂ flow rate, mole fraction; I ₂ content; water content on the liquid-liquid separation process. The experimental results showed that when the mole fraction of SO ₂ exceeds 0.12 and the molar ratio of I ₂ /H ₂ O exceeds 0.284 Can get the best HI and H ₂ SO ₄ separation effect and minimal side reaction.

TolgaBalta. et al. (Energy, 2010, 35, 3263-3272) studied in detail the influence of the four reaction steps of the Cu-Cl cycle on the performance of the entire cycle system under reaction conditions such as different temperatures, and calculated the production capacity and energy release efficiency. The biggest problem faced by this cycle is the corrosiveness of the acid to the material.

Tamaura, Y. et al. (SolarEnergy, 1999, 65, 55-57) first studied the multi-step cycle of MnFe ₂ O ₄ and Na ₂ CO ₃ , which can be completed in three steps. The main problem faced by this system is that the kinetics of the oxygen generation reaction is unfavorable and the reaction rate is too slow. Seralessandri, L. et al. (Journal of Solid State Chemistry, 2008, 181, 1992-1997; Scripta Materialia, 2006, 55, 875-877) studied the cyclic oxygen production reaction and found the crystal structure of the reaction product after hydrogen production and the partial pressure of CO ₂ It has a particularly large impact on the reduction reaction. The results of our repeated experiments also show that the oxygen generation reaction is very unfavorable, it is difficult to observe the generation of _O2 under normal conditions, and the cycle mode needs to be improved. Varsano, F. et al. (SolidStateIonics, 2011, 187, 19-26) used XRD technology to analyze the various species generated during the reaction process. They proposed that the mechanism of oxygen generation proceeds in two steps, that is, CO ₂ first combines with sodium ions to form Na ₂ CO ₃ , and the sodium ions are partially separated, causing the structure of the original compound to collapse, thereby enabling the oxygen generation reaction to proceed smoothly. In short, the separation of sodium ions is the key to complete the oxygen production reaction. Kaneko, H. et al. (Journal of Physics and Chemistry of Solids, 2001, 62, 1341-1347; Energy, 2001, 26, 919-929) accelerated the extraction of sodium ions by adding Fe ₂ O ₃ . This method obviously promotes the oxygen production reaction, but how to separate the residual _Fe2O3 after the _cycle is completed is another problem.

In recent years, Xu, B. et al. (ProcNatlAcadSci, 2012, 109(24):9260-9264) reported the Mn ₃ O ₄ -Na ₂ CO ₃ multi-step cycle system. Compared with the previous similar cycle, replacing NaOH with Na ₂ CO ₃ reduces the corrosion strength of the system and reduces the requirements for materials. In summary, the cycle of metal oxides and basic compounds is a kind of low-temperature multi-step cycle with wide application potential.

Contents of the invention

The present invention aims to provide the application of the mixed active material of carbonate (A _x CO ₃ ) and spinel compound (MN ₂ O ₄ ) in the multi-step thermochemical cycle decomposition of H ₂ O or CO ₂ . The hybrid materials composed of different carbonates and different spinel compounds can selectively decompose one or both of _H2O or _CO2 , and simultaneously produce _H2 and CO.

The object of the present invention is also based on improving and optimizing the circulation mode of the system, thereby improving the feasibility of this type of circulation reaction system. Another object of the present invention is to optimize the reaction parameters of the mixed material of carbonate and spinel compound to decompose water or CO ₂ and provide optimal reaction conditions.

To achieve the above object, the present invention provides the following aspects:

The mixed system of carbonate (A _x CO ₃ ) and spinel compound MN ₂ O ₄ of the present invention is characterized in that A in the carbonate A _x CO ₃ is Li, Na, K, Be, Mg , Ca, Sr, Ba, or one or two or more of them, M and N in MN ₂ O ₄ are one or two or more of Mn, Fe, and Co. Take carbonate and spinel compound according to the molar ratio of 3:2, and mix them by direct mechanical grinding until they are fully mixed.

The preparation method of the spinel compound is one of co-precipitation hydrothermal method, high-temperature solid reaction, microemulsion reaction and egg white sol-gel method.

The specific steps of the co-precipitation hydrothermal method are as follows: Weigh the salt of M MCl _x or M(NO ₃ ) _x 0.01-50 mmol, and weigh the salt of N NCl _y or N( NO ₃ ) _y , dissolved in 50-300mL deionized water, added 30mL NaOH solution with a concentration of 0.1-10mol/L, stirred evenly; 3-28h; after the completion of the hydrothermal reaction, cool to room temperature, filter and wash, then vacuum dry for 6-12h, the temperature of vacuum drying is 50-80°C;

The specific steps of the high-temperature solid reaction are as follows: Weigh the M carbonate M(CO ₃ ) _x 0.01-50mmol, weigh the N oxide N _y O _z according to the molar ratio N:M=2:1, in the total The flow rate is 200mL/min, and the gas volume ratio is: heated to 1100°C in a mixed atmosphere of air (0-100%) and CO ₂ (100-0%), kept for 7 hours, and cooled down to room temperature under the protection of the original atmosphere;

The specific steps of the microemulsion reaction are as follows: Weigh the salt of M MCl _x or M(NO ₃ ) _x 0.01-50 mmol, and weigh the salt of N NCl _y or N(NO ₃ ) according to the molar ratio N:M=2:1 ) _y , dissolved in 50-300mL deionized water, stirred evenly; then added 60mL 0.4M NaDBS solution; 2mol/L NaOH solution, continue stirring for 2h; aging at 60-100°C for 1.5h under Ar protection; filtering and washing, drying at 50-80°C for 6-12h; roasting at 320-600°C for 1-2h to obtain spinel compound in oxidized state .

The specific steps of the egg white sol-gel method are as follows: Take 30-120mL of egg white liquid that has been stirred evenly, and add 50-200mL of deionized water to dilute the egg white liquid, weigh the salt of M MCl _x or M(NO ₃ ) _x 0.01 -50mmol, weigh N salt NCl _y or N(NO ₃ ) _y according to the molar ratio N:M=2:1, add the metal salt to the diluted egg white, stir and evaporate until gelatinous, transfer to muffle Calcined in a furnace at 500°C for 5 hours to obtain the spinel compound in the oxidized state.

The described mixed system of carbonate and spinel compounds can be applied to the multi-step decomposition of _H2O and _CO2 , which consists of the following multiple reaction steps:

a. Synthesize the spinel compound MN ₂ O ₄ , and use grinding and other methods to mix the two materials of carbonate and spinel compound together;

b. Heating the mixed active material system to 500-1000°C under an Ar atmosphere, and after constant temperature treatment for 2-3 hours, one or both of H ₂ O or CO ₂ is brought into by Ar; or brought into by CO ₂ H ₂ O; or feed CO ₂ alone; generate H ₂ and CO;

c. Dispersing the active material treated in b in water to obtain a mixed solution with an active material content of 1-10 wt%, stirring continuously and introducing _CO2 for hydrolysis reaction, separating and drying to obtain the hydrolyzed active species;

d. Heating the active species treated in c to 500-1000° C. under an Ar atmosphere to perform an oxygen evolution reaction and complete the cycle of oxygen and hydrogen production.

The hydrogen production and oxygen production reaction of the cycle reaction is carried out in a fixed bed reactor.

The composition and structure of the fixed bed reactor is as follows: comprising a quartz tube, a corundum crucible with an upper end opening and a hole in the bottom is provided in the quartz tube, a supporting quartz tube is arranged below the corundum crucible, and the corundum crucible is positioned on the At a special position inside the outer quartz tube, quartz wool is placed above the inner bottom hole of the corundum crucible, and Al ₂ O ₃ fillers are laid on the quartz wool, and active materials are filled on the Al ₂ O ₃ fillers, followed by Al ₂ O ₃ fillers. , Quartz wool storage.

The present invention has the following advantages:

1. For the first time, the present invention utilizes hydrolysis reaction to treat active species after producing H ₂ , which improves the kinetic properties of oxygen production reaction, greatly increases the rate of oxygen production reaction, makes oxygen production reaction proceed more smoothly, and improves the circulation system feasibility.

2. The active material system of the present invention can complete the oxygen generation reaction at a relatively low reduction temperature (500-1000° C.).

3. The active material system provided by the present invention can use high-temperature heat generated by concentrated solar energy as an energy source, and use H ₂ O or CO ₂ as a reaction raw material to generate H ₂ and CO without any other by-products, which is sustainable and clean Pollution-free energy conversion system.

Description of drawings

Figure 1 is a schematic diagram of the structure of a fixed-bed reactor, where 1: quartz tube; 2: supporting quartz tube; 3: sealing joint; 4: corundum crucible; 5: active material.

Figure 2 is the XRD pattern of MnFe ₂ O ₄ synthesized at different hydrothermal times, and the XRD diffraction peaks show that the synthesized MnFe ₂ O ₄ has a typical spinel structure.

Figure 3 is the hydrogen production rate-time curve of MnFe ₂ O ₄ &Na ₂ CO ₃ , and the hydrogen production is 34.9mlH ₂ /gMnFe ₂ O ₄ by integration.

Fig. 4 is the oxygen production rate-time curve of the hydrolyzate, and the oxygen production is 16.2mlO ₂ /g hydrolyzate by integration.

Figure 5 is the XRD pattern of the cycle product, and the XRD diffraction peaks confirm that MnFe ₂ O ₄ is regenerated after the cycle reaction of hydrogen production and oxygen production.

Figure 6 is the oxygen production curve of the active material MnFe ₂ O ₄ &Na ₂ CO ₃ hydrolyzate. After integration, the oxygen production is 17.1mlO ₂ /g hydrolyzate.

detailed description

A schematic diagram of the structure of the fixed-bed reactor is shown in Figure 1. During application, about 0.2g of the mixed active material is placed in a corundum crucible, the sample filling method is as described above, the material of the reactor is a quartz tube, and the inner diameter of the reaction tube (quartz tube) is 17mm, and the reaction product is analyzed online by gas chromatography. Example 1

Weigh 1.9791g manganese chloride (10mmol), 5.4058g ferric chloride (20mmol) and dissolve in 200ml deionized water, stir at room temperature for 30min; weigh 4.8gNaOH and dissolve in 30ml deionized water; add NaOH solution dropwise under continuous stirring Add to the metal salt solution, continue to stir for 30 minutes until uniform; transfer to a 300ml hydrothermal kettle for hydrothermal reaction at 180°C for 3h; filter and wash, and vacuum dry at 60°C for 6h to obtain the spinel compound MnFe ₂ O ₄ . The hydrothermal treatment time was set to 5h, 6h, 8h, 12h, 14h, 18h, 24h, 28h to obtain the MnFe ₂ O ₄ materials hydrothermally synthesized at different times. The XRD pattern shows that this series of MnFe ₂ O ₄ materials have typical spinel Stone structure (figure 2). According to the molar ratio of 3:2, Na ₂ CO ₃ and 6h hydrothermally synthesized MnFe ₂ O ₄ materials were weighed, mixed by direct mechanical grinding mixing method, and ground several times until fully mixed and uniform.

Example 2

Weigh 1.9791g manganese chloride (10mmol), 5.4058g ferric chloride (20mmol) and dissolve in 200ml deionized water, stir at room temperature for 30min; weigh 3.2gNaOH, dissolve in 30ml deionized water; drop NaOH solution under continuous stirring Add it to the metal salt solution, and continue to stir for 30 minutes until uniform; transfer it to a 300ml hydrothermal kettle for 6 hours at 180°C; filter and wash, and vacuum dry at 60°C for 6 hours to obtain the spinel compound MnFe ₂ O ₄ . Change the amount of NaOH, weigh 4.8g, 6.4g, 8.0g, and 9.6g NaOH respectively, and treat them according to the above method to obtain MnFe ₂ O ₄ materials hydrothermally synthesized with different alkali concentrations. According to the molar ratio of 3:2, Na ₂ CO ₃ and MnFe ₂ O ₄ materials synthesized by adding 3.2g of NaOH were weighed, mixed by direct mechanical grinding mixing method, and ground several times until fully mixed and uniform.

Example 3

Weigh 1.9791g manganese chloride (10mmol), 5.4058g ferric chloride (20mmol) and dissolve in 200ml deionized water, stir at room temperature for 30min; weigh 4.8gNaOH, dissolve in 30ml deionized water; drop the NaOH solution under continuous stirring Add it to the metal salt solution, and continue to stir for 30 minutes until uniform; transfer it to a 300ml hydrothermal kettle, and react at 160°C for 6h; filter and wash, and vacuum dry at 60°C for 6h to obtain the spinel compound MnFe ₂ O ₄ . Change the hydrothermal treatment temperature and set it to 80°C, 100°C, 120°C, 140°C, 180°C, 200°C respectively, and obtain MnFe ₂ O ₄ materials hydrothermally synthesized at different temperatures after treatment according to the above method. According to the molar ratio of 3:2, Na ₂ CO ₃ and 160°C hydrothermally synthesized MnFe ₂ O ₄ materials were weighed, mixed by direct mechanical grinding, and ground several times until fully mixed.

Example 4

Weigh 1.1495g MnCO ₃ (10mmol) and 1.5969g Fe ₂ O ₃ (10mmol), mix them uniformly with a mortar, and grind them thoroughly. In an atmosphere of 25% air & 75% CO ₂ , it was heated to 1100°C at a heating rate of 20°C/min, kept for 7 hours, and cooled down to room temperature under the protection of the original atmosphere. The obtained product is ground uniformly to obtain MnFe ₂ O ₄ material. By changing the volume ratio of air (0-100%) and CO ₂ (100-0%), a series of MnFe ₂ O ₄ materials synthesized under different atmospheres are obtained. Weigh Na ₂ CO ₃ and MnFe ₂ O ₄ materials synthesized under the atmosphere of 25% air & 75% CO ₂ according to the molar ratio of 3:2, and mix them by direct mechanical grinding mixing method, and grind them several times until they are fully mixed and uniform .

Example 5

Take 30ml of evenly stirred egg white, add 50ml of deionized water to dilute the egg white, weigh 3.579g of manganese nitrate (20mmol) and 16.16g of ferric nitrate (40mmol) according to the molar ratio of 1:2, add the metal salt after stirring Egg white liquid, stirred evenly, evaporated to gel, transferred to a muffle furnace at 500°C and baked for 5 hours to obtain a spongy spinel compound MnFe ₂ O ₄ material. Weigh the Na ₂ CO ₃ and MnFe ₂ O ₄ materials according to the molar ratio of 3:2, mix them by direct mechanical grinding, and grind them several times until they are fully mixed.

Example 6

Weigh 1.7895g of manganese nitrate (10mmol) and 8.080g of ferric nitrate (20mmol) according to the molar ratio of 1:2, dissolve them in 50ml of deionized water, stir well; then add 60ml of 0.4M NaDBS solution; add 500ml of toluene solution , continuously stirred for 24 hours to form a uniform microemulsion system; added 80ml of NaOH solution with a concentration of 1mol/L, and continued to stir for 2h; aged at 100°C for 1.5h under the protection of Ar; filtered, washed and dried; roasted at 500°C to obtain oxidized spinels Petroleum compound MnFe ₂ O ₄ material. Weigh the Na ₂ CO ₃ and MnFe ₂ O ₄ materials according to the molar ratio of 3:2, mix them by direct mechanical grinding, and grind them several times until they are fully mixed.

Example 7

Weigh about 0.2 g of the mechanically ground mixed material of MnFe ₂ O ₄ and Na ₂ CO ₃ hydrothermally synthesized in Example 1 for 6 hours, and place the sample in the reaction tube after loading. Heated from room temperature to 800°C at a rate of 20°C/min under Ar atmosphere, and after constant temperature treatment for 2.5 hours, water vapor was introduced to keep the reaction temperature at 800°C, and the hydrogen production reaction ended within 3 hours. Accompanying drawing 3 is the rate-time variation curve of the hydrogen production reaction of MnFe ₂ O ₄ synthesized by hydrothermal 6h in Example 1. The reaction product after hydrogen production was taken out, ground uniformly, and then dispersed in deionized water, wherein the solid powder content was 2 wt%. The mixture was heated to 80° C., continuously stirred and hydrolyzed for 3 h under the condition of introducing CO ₂ , and the solid product obtained by hydrolysis was separated and dried in vacuo. Weigh 0.4 g of the active species obtained by hydrolysis, put the sample into the reaction tube, and heat it from room temperature to 800 °C at a rate of 20 °C/min under Ar atmosphere to carry out the oxygen generation reaction. The oxygen generation reaction is completed after constant temperature treatment for 30 minutes. Accompanying drawing 4 is the oxygen production reaction rate-time variation curve of the hydrolyzed product after hydrothermal synthesis of MnFe ₂ O ₄ hydrogen production reaction in Example 1 for 6 hours. The active material is regenerated through hydrogen production and oxygen production cycles, and the regenerated MnFe ₂ O ₄ undergoes hydrogen production and oxygen production cycle reactions in turn. The XRD pattern of the cycled reaction product indicated that the active material was regenerated after the cycle (Fig. 5).

Example 8

Weigh about 0.2 g of the mixed material obtained in Example 5, and place it in the reaction tube after loading the sample. Heated to 800°C at a heating rate of 20°C/min under Ar atmosphere, and cooled to room temperature after constant temperature treatment for 2.5h. The reaction product was taken out and ground, dispersed in 50 ml of deionized water, introduced with CO ₂ , hydrolyzed at 80° C. for 3 h, separated and dried to obtain the hydrolyzed product. The hydrolyzate was put back into the original reaction tube, and heated to 800° C. under an Ar atmosphere at a heating rate of 20° C./min to carry out an oxygen generation reaction, and the oxygen generation reaction was completed after 30 minutes of constant temperature treatment (Fig. 6). The product after oxygen generation was treated in the same way as in Example 7, and the cycle reaction of hydrogen and oxygen generation was carried out.

In summary, the present invention synthesized a series of spinel-type (MN ₂ O ₄ ) compounds, which can be mixed with carbonate (A _x CO ₃ ) to convert H ₂ O or CO into ₂ decomposes into _H2 and CO. The patent of the present invention further improves and develops the multi-step thermochemical cycle mode of the carbonate (A _x CO ₃ ) and spinel compound (MN ₂ O ₄ ) system, and uses hydrolysis reaction for the first time to treat the active species after H ₂ production , making the oxygen production reaction proceed more smoothly and improving the feasibility of the cycle system. The multi-step thermochemical cycle system of the present invention has a low reaction temperature (500-1000°C), can use high-temperature heat generated by focused solar energy as an energy source, and use _H2O and _CO2 as input materials to produce _H2 and CO , clean and pollution-free, it is expected to become an effective technology for the reduction of H ₂ O and CO ₂ by solar energy to prepare chemical fuel (synthesis gas).

Claims (6)

1. A mixture system of spinel compounds and carbonates for photothermal chemical conversion of solar energy, characterized in that: the mixture system is composed of carbonates A _x CO ₃ and spinel compounds MN ₂ O ₄ composition. 2. The mixed system according to claim 1, characterized in that: in the carbonate A _x CO ₃ , A is one or both of Li, Na, K, Be, Mg, Ca, Sr, Ba more than one species; in the spinel compound MN ₂ O ₄ , M and N are one or more than two transition metals Mn, Fe and Co. 3. The mixing system according to claim 1 or ₂ , characterized in that: the preparation method of the spinel compound _MN2O4 is co-precipitation hydrothermal method, high temperature solid reaction, microemulsion reaction, egg white sol - one of the gel methods; The cothermal precipitation hydrothermal method consists of the following steps: Weigh M salt MCl _x or M(NO ₃ ) _x 0.01-50mmol, weigh N salt NCl _y or N(NO ₃ ) _y according to the molar ratio N:M=2:1, dissolve in 50-300mL deionized Add 30mL of NaOH solution with a concentration of 0.1-10mol/L to the water, stir evenly; transfer to a 300mL hydrothermal kettle, the reaction temperature range is 80°C-200°C, and the reaction time is 3-28h; after the hydrothermal reaction is completed, cool to At room temperature, vacuum dry for 6-12 hours after filtering and washing, and the temperature of vacuum drying is 50-80°C; The specific steps of high temperature solid reaction are as follows: Weigh M carbonate M(CO ₃ ) _x 0.01-50mmol, weigh N oxide N _y O _z according to the molar ratio N:M=2:1, when the total flow rate is 200mL/min, the gas volume ratio is : Heating to 1100°C in a mixed atmosphere of air (0-100%) and CO ₂ (100-0%), keeping it for 7 hours, cooling down to room temperature under the protection of the original atmosphere; The specific reaction of microemulsion reaction is as follows: Weigh M salt MCl _x or M(NO ₃ ) _x 0.01-50mmol, weigh N salt NCl _y or N(NO ₃ ) _y according to the molar ratio N:M=2:1, dissolve in 50-300mL deionized In water, stir evenly; then add 60mL of 0.4M NaDBS solution; add 300-500mL of toluene solution, and stir continuously for 12-24h to form a uniform microemulsion system; add 80mL of NaOH solution with a concentration of 0.1-2mol/L, and continue stirring for 2h ;Aging at 60-100°C for 1.5h under the protection of Ar; filtering and washing, drying at 50-80°C for 6-12h; roasting at 320-600°C for 1-2h to obtain spinel compounds in oxidized state; The specific steps of the egg white sol-gel method are as follows: Take 30-120mL of evenly stirred egg white liquid, add 50-200mL of deionized water to dilute the egg white liquid, weigh M salt MCl _x or M(NO ₃ ) _x 0.01-50mmol, according to the molar ratio N:M=2:1 Weigh the N salt NCl _y or N(NO ₃ ) _y , add the metal salt to the diluted egg white liquid, stir and evaporate until gelatinous, transfer to a muffle furnace and roast at 500°C for 5 hours to obtain oxidized spinel compound. 4. a preparation method of the spinel compound and carbonate mixed system described in claim 1, 2 or 3, characterized in that: the mixing method adopted is a direct mechanical grinding mixing method, i.e. according to a molar ratio of 3 : 2 Weigh the carbonate and spinel compound, fully mix them in a mortar, grind them several times until fully ground evenly, or use a ball mill to grind evenly. 5. The application of a mixed system of spinel compounds and carbonates according to claim 1, 2 or 3, characterized in that: said mixed system can be used for multi-step thermochemical cycle decomposition of H ₂ O or CO ₂ , the cycle consists of the following multistep reactions: a. Synthesize the spinel compound MN ₂ O ₄ , and use grinding and other methods to mix the two materials of carbonate and spinel compound together; b. Heating the mixed active material system to 500-1000°C under an Ar atmosphere, and after constant temperature treatment for 2-3 hours, one or both of H ₂ O or CO ₂ is brought into by Ar; or brought into by CO ₂ H ₂ O; or feed CO ₂ alone; generate H ₂ and CO; c. Dispersing the active material treated in b in water to obtain a mixed solution with an active material content of 1-10 wt%, stirring continuously and introducing _CO2 for hydrolysis reaction, separating and drying to obtain the hydrolyzed active species; d. Heating the active species treated in c to 500-1000° C. under an Ar atmosphere to perform an oxygen evolution reaction and complete the cycle of oxygen and hydrogen production. 6. The application according to claim 5, characterized in that: In the described circulation reaction, the reactions of hydrogen production and oxygen production, that is, step b and step d in claim 5, are carried out in a fixed bed reactor; the composition structure of the fixed bed reactor is: comprising a quartz tube , the quartz tube is provided with a corundum crucible with an upper end opening and a hole in the bottom, a supporting quartz tube is provided below the corundum crucible, and the corundum crucible is positioned at a specific position in the outer quartz tube through the supporting quartz tube below it, and the inner bottom hole of the corundum crucible is Quartz wool is arranged above the , and Al ₂ O ₃ filler is laid on the quartz wool, and the Al ₂ O ₃ filler is filled with active materials, which are sealed with Al ₂ O ₃ filler and quartz wool in turn.