A high entropy oxide oxygen carrier and its preparation method and application

Abstract

The present invention provides a high entropy oxide oxygen carrier and its preparation method and application. The chemical formula of the high entropy oxide oxygen carrier of the present invention is (Co x Ca y Cu z Al r Mg s )Fe2O4, which is a high-entropy oxide spinel-type oxygen carrier, addresses the three major problems of the current spinel-type chemical looping hydrogen production technology: low lattice oxygen activity and low hydrogen production at low temperatures; oxygen carriers are easily sintered and deactivated at high temperatures and cannot be effectively recycled; they cannot be regenerated in an H2O atmosphere and require the addition of an oxygen reactor, which makes the equipment complex. The high-entropy oxide oxygen carrier provided by the present invention has achieved good results, producing 99.9% pure hydrogen at 800°C, and no obvious attenuation was observed in 30 cycles of CO2 decomposition experiments. (In chemical looping technology, traditional CoFe2O4 spinel has lower hydrogen yield and output under the same conditions, and the oxygen carrying capacity was reduced by more than 50% in 10 CO2 decomposition cycle experiments).

Description

Technical Field

[0001] The present invention belongs to the technical field of hydrogen preparation, and in particular relates to a high-entropy oxide oxygen carrier and a preparation method and application thereof. Background Art

[0002] Current chemical looping water / CO2 splitting technologies face the following common technical challenges: low lattice oxygen activity at low temperatures leads to low fuel conversion rates; and oxygen carriers easily sinter and deactivate at high temperatures, making them ineffective for recycling. Although doping and modification have improved oxygen activity and stability to some extent, industrial application still faces challenges such as high reaction temperatures, resulting in high energy consumption and large equipment investments.

[0003] As a new type of oxide system that has just developed in recent years, high entropy oxides (HEOs) have broken the design concept of traditional doped oxides and have attracted widespread attention from the scientific community. On the one hand, due to the high configuration entropy of this system, it is easy to form a simple solid solution structure; on the other hand, the main elements tend to be arranged chaotically, and their chemical composition is in a disordered state, resulting in various performances that are different from traditional doped oxides, often showing unexpected performance, which is called the cocktail effect. At present, many studies have shown that it has high strength, high toughness, good high / low temperature stability, excellent catalytic performance, etc. In particular, it has great application prospects in energy preparation and storage and catalytic materials.

[0004] However, current high-entropy oxides still have defects such as low lattice oxygen activity at low temperatures, resulting in low fuel conversion rate. Therefore, it is necessary to improve this. Summary of the Invention

[0005] In view of this, the present invention proposes a high entropy oxide oxygen carrier and a preparation method and application thereof to solve the technical problems existing in the prior art.

[0006] In the first aspect, the present invention provides a high entropy oxide oxygen carrier, the chemical formula of which is (Co x Ca y Cu z Al r Mg s )Fe2O4, wherein x:y:z:r:s is (0.1~0.25):(0.1~0.25):(0.1~0.25):(0.1~0.25):(0.1~0.5).

[0007] In a second aspect, the present invention further provides a method for preparing the high entropy oxide oxygen carrier, characterized in that it comprises the following steps:

[0008] Adding Co source, Ca source, Cu source, Al source, Mg source and Fe source to citric acid, and then adding polyethylene glycol and water, stirring to obtain a gel;

[0009] The gel is dried and then calcined to obtain a high entropy oxide oxygen carrier.

[0010] Preferably, in the preparation method of the high entropy oxide oxygen carrier, the calcination temperature is 900-1100° C. and the calcination time is 8-12 hours.

[0011] Preferably, the preparation method of the high entropy oxide oxygen carrier is to add Co source, Ca source, Cu source, Al source, Mg source, and Fe source to citric acid, and then add polyethylene glycol and water, and stir at 90-100° C. to obtain a gel.

[0012] Preferably, in the method for preparing the high entropy oxide oxygen carrier, the gel is dried at 100-110° C. and then calcined to obtain the high entropy oxide oxygen carrier.

[0013] Preferably, in the method for preparing the high entropy oxide oxygen carrier, the Co source comprises at least one of cobalt nitrate, cobalt sulfate, and cobalt chloride;

[0014] The Ca source includes at least one of calcium nitrate, calcium sulfate, and calcium chloride;

[0015] The Cu source includes at least one of copper nitrate, copper sulfate, and copper chloride;

[0016] The Al source includes at least one of aluminum nitrate, aluminum sulfate, and aluminum chloride;

[0017] The Mg source includes at least one of magnesium nitrate, magnesium sulfate, and magnesium chloride;

[0018] The Fe source includes at least one of ferric nitrate, ferric sulfate, and ferric chloride.

[0019] Preferably, in the method for preparing the high entropy oxide oxygen carrier, the molar ratio of Co ions in the Co source, Ca ions in the Ca source, Cu ions in the Cu source, Al ions in the Al source, Mg ions in the Mg source, Fe ions in the Fe source, citric acid, and polyethylene glycol is (0.1-0.25):(0.1-0.25):(0.1-0.25):(0.1-0.25):(0.1-0.5):2:(0.5-2):(0.5-1).

[0020] In a third aspect, the present invention also provides an application of the high-entropy oxide oxygen carrier or the high-entropy oxide oxygen carrier prepared by the preparation method to prepare synthesis gas and hydrogen through chemical looping reforming.

[0021] Preferably, the application comprises: placing the high entropy oxide oxygen carrier in a reactor, heating the reactor, introducing fuel into the reactor, and obtaining synthesis gas through reaction;

[0022] After the reaction is completed, water vapor is continued to be introduced into the reactor to obtain H2 through the reaction.

[0023] Preferably, the application heats the reactor to a temperature of 600-900° C.; the flow rate of the fuel is controlled to be 0.03-0.07 mL / min, and the flow rate of the water vapor is controlled to be 0.03-0.07 mL / min.

[0024] The high entropy oxide oxygen carrier of the present invention and its preparation method and application have the following beneficial effects compared with the prior art:

[0025] The chemical formula of the high entropy oxide oxygen carrier of the present invention is (Co x Ca y Cu z Al r Mg s )Fe2O4, which is a high-entropy oxide spinel-type oxygen carrier, addresses the three major problems of the current spinel-type chemical looping hydrogen production technology: low lattice oxygen activity and low hydrogen production at low temperatures; oxygen carriers are easily sintered and deactivated at high temperatures and cannot be effectively recycled; they cannot be regenerated in an H2O atmosphere and require the addition of an oxygen reactor, which makes the equipment complex. The high-entropy oxide oxygen carrier provided by the present invention has achieved good results, producing 99.9% pure hydrogen at 800°C and showing no obvious attenuation in 30 cycles of CO2 decomposition experiments. (In chemical looping technology, traditional CoFe2O4 spinel has lower hydrogen yield and output under the same conditions, and the oxygen carrying capacity is reduced by more than 50% in 10 CO2 decomposition cycle experiments). BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0027] Figure 1 This is the experimental principle diagram of the application of the high entropy oxide oxygen carrier of the present invention

[0028] Figure 2 The XRD patterns of the high entropy oxide oxygen carrier (HEO) and CoFe2O4 prepared in Example 1, as well as the XRD patterns of the high entropy oxide oxygen carrier (HEO) and CoFe2O4 after one cycle;

[0029] Figure 3 The gas yields during the synthesis of gases and the H2 yield during the hydrogen production process at different reaction temperatures (600°C, 800°C) for the high entropy oxide oxygen carrier and ordinary CoFe2O4 spinel prepared in Example 1;

[0030] Figure 4 This is the thermogravimetric diagram of 10 cycles of ordinary CoFe2O4 spinel under H2 reduction, CO2 oxidation, and O2 oxidation atmosphere;

[0031] Figure 5 This is the thermogravimetric diagram of the high entropy oxide oxygen carrier in Example 1 after 30 cycles under H2 reduction, CO2 oxidation, and O2 oxidation atmospheres. DETAILED DESCRIPTION

[0032] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0033] For a better understanding of the present invention and not to limit the scope of the present invention, all numbers used in this application to express amounts, percentages, and other numerical values ​​should be understood as modified by the word "about" in all cases. Therefore, unless otherwise specified, the numerical parameters listed in the specification and the appended claims are approximate values, which may vary depending on the desired properties to be obtained. Each numerical parameter should at least be regarded as obtained based on the reported significant figures and by conventional rounding methods.

[0034] It should be noted that the order of description of the following embodiments is not intended to limit the preferred order of the embodiments. In addition, in the description of this application, the term "including" means "including but not limited to". Various embodiments of the present invention may be presented in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be understood as a rigid limitation on the scope of the invention; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within the range. For example, the range description from 1 to 6 should be considered to have specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the range, such as 1, 2, 3, 4, 5 and 6, regardless of the range. In addition, whenever a numerical range is indicated herein, it is meant to include any cited number (fractional or integer) within the indicated range.

[0035] The present invention provides a high entropy oxide oxygen carrier, the chemical formula of which is (Co x Ca y Cu z Al r Mg s )Fe2O4, wherein x:y:z:r:s is (0.1~0.25):(0.1~0.25):(0.1~0.25):(0.1~0.25):(0.1~0.5).

[0036] The chemical formula of the high entropy oxide oxygen carrier of the present invention is (Co x Ca y Cu z Al r Mg s )Fe2O4, which is a high-entropy oxide spinel-type oxygen carrier, addresses the three major problems of the current spinel-type chemical looping hydrogen production technology: low lattice oxygen activity and low hydrogen production at low temperatures; oxygen carriers are easily sintered and deactivated at high temperatures and cannot be effectively recycled; they cannot be regenerated in an H2O atmosphere and require the addition of an oxygen reactor, which makes the equipment complex. The high-entropy oxide oxygen carrier provided by the present invention has achieved good results, producing 99.9% pure hydrogen at 800°C, and no obvious attenuation was observed in 30 cycles of CO2 decomposition experiments. (In chemical looping technology, traditional CoFe2O4 spinel has lower hydrogen yield and output under the same conditions, and the oxygen carrying capacity was reduced by more than 50% in 10 CO2 decomposition cycle experiments).

[0037] Based on the same inventive concept, the present invention also provides a method for preparing the above-mentioned high entropy oxide oxygen carrier, comprising the following steps:

[0038] S1. Add Co source, Ca source, Cu source, Al source, Mg source, and Fe source to citric acid, and then add polyethylene glycol and water, and stir to obtain a gel;

[0039] S2. Drying the gel and then calcining it to obtain a high entropy oxide oxygen carrier.

[0040] In some embodiments, the calcination temperature is 900-1100° C., and the calcination time is 8-12 hours.

[0041] In some embodiments, a Co source, a Ca source, a Cu source, an Al source, a Mg source, and a Fe source are added to citric acid, and then polyethylene glycol and water are added, and the mixture is stirred at 90-100° C. to obtain a gel.

[0042] In some embodiments, the gel is dried at 100-110° C. and then calcined to obtain a high entropy oxide oxygen carrier.

[0043] In some embodiments, the Co source includes at least one of cobalt nitrate, cobalt sulfate, and cobalt chloride; preferably, the Co source is Co(NO3)2·6H2O.

[0044] In some embodiments, the Ca source includes at least one of calcium nitrate, calcium sulfate, and calcium chloride; preferably, the Ca source is Ca(NO3)2·4H2O.

[0045] In some embodiments, the Cu source includes at least one of copper nitrate, copper sulfate, and copper chloride; preferably, the Cu source is Cu(NO3)2·3H2O.

[0046] In some embodiments, the Al source includes at least one of aluminum nitrate, aluminum sulfate, and aluminum chloride; preferably, the Al source is Al(NO 3 ) 3 ·9H 2 O.

[0047] In some embodiments, the Mg source includes at least one of magnesium nitrate, magnesium sulfate, and magnesium chloride; preferably, the Mg source is Mg(NO3)2·6H2O.

[0048] In some embodiments, the Fe source includes at least one of ferric nitrate, ferric sulfate, and ferric chloride; preferably, the Fe source is Fe(NO3)3·9H2O.

[0049] In some embodiments, the molar ratio of Co ions in the Co source, Ca ions in the Ca source, Cu ions in the Cu source, Al ions in the Al source, Mg ions in the Mg source, Fe ions in the Fe source, citric acid, and polyethylene glycol is (0.1-0.25):(0.1-0.25):(0.1-0.25):(0.1-0.25):(0.1-0.5):2:(0.5-2):(0.5-1).

[0050] Based on the same inventive concept, an embodiment of the present application also provides an application of the above-mentioned high-entropy oxide oxygen carrier or the high-entropy oxide oxygen carrier prepared by the above-mentioned preparation method to chemically loop reforming to prepare synthesis gas and hydrogen.

[0051] In some embodiments, the above application includes: placing a high entropy oxide oxygen carrier in a reactor, heating the reactor, introducing fuel (ethanol or toluene) into the reactor, and generating synthesis gas through reaction;

[0052] After the reaction is completed, water vapor is continued to be introduced into the reactor to obtain H2 through the reaction.

[0053] In some embodiments, for the above application, the reactor is heated to a temperature of 600-900° C.; the flow rate of the fuel is controlled to be 0.03-0.07 mL / min, and the flow rate of the water vapor is controlled to be 0.03-0.07 mL / min.

[0054] In some embodiments, for the aforementioned applications, a high-entropy oxide oxygen carrier (1-5 g) was placed in a reactor, an electric furnace was turned on, and the reactor was heated to 600-900°C. Ethanol was then introduced at a flow rate of 0.05 ml / min for 20 minutes. After the reaction was complete, the ethanol was turned off and water vapor was introduced until the hydrogen concentration dropped below 0.5%. The experiment was then terminated. Gas concentrations were measured using an online gas analyzer and the data were calculated.

[0055] For further information, please refer to Figure 1 As shown, a high-entropy oxide oxygen carrier is placed in a fuel reactor, an electric furnace is turned on, and the reactor is heated to a preset temperature (600-900°C). After the temperature stabilizes, nitrogen is introduced into the reactor to purge for 10 minutes, and then fuel (ethanol or toluene) is introduced at a flow rate of 0.03-0.07 mL / min. During this process, the fuel reacts with the high-entropy oxide oxygen carrier to generate synthesis gas; in the process of preparing the synthesis gas, the high-entropy oxide oxygen carrier loses lattice oxygen and is reduced to generate a reduced oxygen carrier; then the reduced oxygen carrier is placed in a water vapor reactor, and the reduced oxygen carrier reacts with water vapor to generate hydrogen. During the reaction, the temperature of the water vapor reactor is controlled at 600-900°C, and the flow rate of water vapor is 0.03-0.07 mL / min; at the same time, the reduced oxygen carrier is oxidized and regenerated to obtain the original high-entropy oxide oxygen carrier, that is, the high-entropy oxide oxygen carrier is regenerated.

[0056] The following further illustrates the high-entropy oxide oxygen carrier of the present application, its preparation method, and application with specific examples. This section further illustrates the content of the present invention in conjunction with specific examples, but should not be construed as limiting the present invention. Unless otherwise specified, the technical means used in the examples are conventional means well known to those skilled in the art. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in the art.

[0057] Example 1

[0058] The present invention provides a method for preparing a high entropy oxide oxygen carrier, comprising the following steps:

[0059] S1. Co(NO3)2·6H2O, Ca(NO3)2·4H2O, Mg(NO3)2·6H2O, Cu(NO3)2, Al(NO3)2·9H2O, and Fe(NO3)2·9H2O were added to citric acid, and then polyethylene glycol and water were added, and the mixture was stirred at 95°C to obtain a gel;

[0060] S2, transfer the gel to a drying oven at 105°C for drying;

[0061] S3, calcining the dried sample in a muffle furnace at 1000°C for 10 h, grinding and sieving to a size range of less than 212 μm (70 mesh) after cooling, thereby obtaining a high entropy oxide oxygen carrier (denoted as HEO);

[0062] The molar ratio of Co(NO3)2·6H2O, Ca(NO3)2·4H2O, Mg(NO3)2·6H2O, Cu(NO3)2, Al(NO3)2·9H2O, Fe(NO3)2·9H2O, citric acid, and polyethylene glycol is 0.1:0.1:0.5:0.1:0.1:2:1:0.5; the molar ratio of Co(NO3)2·6H2O to water is 1:50; the chemical formula of the obtained high entropy oxide oxygen carrier is (Co 0.1 Ca 0.1 Cu 0.1 Al 0.1 Mg 0.5 )Fe2O4. Example 2

[0063] The present application provides an application of the high entropy oxide oxygen carrier prepared in Example 1 in chemical looping hydrogen and synthesis gas, specifically including:

[0064] 3g of a high-entropy oxide oxygen carrier was placed in a reactor. An electric furnace was turned on and the reactor was heated to the preset reaction temperature. After the temperature stabilized, nitrogen was purged into the reactor for 10 minutes. Toluene was then introduced at a flow rate of 0.05ml / min for 20 minutes. After the reaction was complete, the toluene was turned off and water vapor was introduced at a flow rate of 0.05ml / min until the hydrogen concentration dropped below 0.5%. The experiment was then terminated. Gas concentrations were measured and calculated using an online gas analyzer.

[0065] Experimental results

[0066] Figure 2 The XRD patterns of the high entropy oxide oxygen carrier (HEO) and CoFe2O4 prepared in Example 1, as well as the XRD patterns of the high entropy oxide oxygen carrier (HEO) and CoFe2O4 after one cycle; wherein, after one cycle specifically refers to: the high entropy oxide oxygen carrier (HEO) or CoFe2O4 in Figure 1 After the reaction in the fuel reactor, it enters the steam reactor for the post-reaction regeneration process.

[0067] from Figure 2 It can be seen that both fresh cobalt iron spinel and high entropy oxide show typical spinel peaks. After one fixed bed experiment, the CoFe2O4 sample shows a stray peak at 45 degrees, while the high entropy oxide does not show a stray peak. This means that the CoFe2O4 sample undergoes a phase change after one cycle, while the high entropy oxide still maintains its original phase.

[0068] Hydrogen production and synthesis gas effects

[0069] According to the method in Example 2, the high entropy oxide oxygen carrier prepared in Example 1 and the ordinary CoFe2O4 spinel were studied. The yield of each gas and the yield of synthesis gas (CO and H2) during the synthesis gas process at different reaction temperatures (600℃, 800℃) were studied. The results are as follows: Figure 3 ( Figure 3 The upper portion of the vertical axis (i.e., 0.0 to 0.3) indicates the H2 yield. The H2 yield refers to the amount of H2 obtained from 1 kg of oxygen carrier or CoFe2O4 spinel after chemical looping reforming. The CO yield refers to the amount of CO obtained from 1 kg of oxygen carrier or CoFe2O4 spinel after chemical looping reforming. The CO2 yield refers to the amount of CO2 obtained from 1 kg of oxygen carrier or CoFe2O4 spinel after chemical looping reforming. The CH4 yield refers to the amount of CH4 obtained from 1 kg of oxygen carrier or CoFe2O4 spinel after chemical looping reforming. Figure 3 The lower middle part shows the process of high-entropy oxide oxygen carriers and ordinary CoFe2O4 spinel reacting with water vapor to produce H2 at different reaction temperatures (600℃, 800℃) after the synthesis gas reaction is completed. The amount of H2 obtained by reacting 1 kg of oxygen carrier or CoFe2O4 spinel.

[0070] from Figure 3 It can be seen that at 800℃, the high-entropy oxide oxygen carrier is superior to CoFe2O4 in both hydrogen production and synthesis gas production. Even at 600℃, the hydrogen production performance of high-entropy oxide is comparable to that of CoFe2O4, and the synthesis gas production performance is significantly better than CoFe2O4.

[0071] Figure 4 This is the thermogravimetric analysis of ordinary CoFe2O4 spinel under H2 reduction, CO2 oxidation, and O2 oxidation atmospheres for 10 cycles.

[0072] Figure 5 This is the thermogravimetric diagram of the high entropy oxide oxygen carrier in Example 1 after 30 cycles under H2 reduction, CO2 oxidation, and O2 oxidation atmospheres.

[0073] Thermogravimetry was used to study the ability of various samples to release lattice oxygen under the reducing atmosphere H2 and to reversibly store lattice oxygen under the oxidizing atmosphere CO2 and O2. The temperature was set to 800 degrees to eliminate the possible effects of the production of carbon oxides such as CaCO3. After the introduction of H2, each sample immediately showed a significant weight loss phenomenon, that is, the lattice oxygen [O] in the oxygen carrier was taken away by H2 ([O]+H2→H2O), and the weight loss rate showed a trend of first fast, then slow, and then leveling off. The reaction time of 60 minutes in each stage ensured that the oxygen carrier was completely reduced and oxidized, and the oxygen loading capacity R O (R O =mO / (m O –m R )) is used to measure the limit of the amount of bulk lattice oxygen that can participate in the reaction. Figure 4 It can be seen that CoFe2O4 has poor cycling and sintering resistance, losing 53% of its oxygen carrying capacity after only 5 cycles and only 7.4% after 10 cycles.

[0074] Figures 4-5 It can be seen that the high-entropy oxide oxygen carrier has excellent cycling and anti-sintering properties. There is no obvious attenuation of oxygen carrying capacity after 30 cycles, and the oxygen carrying capacity is still maintained at 23% after 5000 minutes of high-temperature experiment.

[0075] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. Application of a high entropy oxide oxygen carrier in chemical looping reforming to produce synthesis gas and hydrogen; The applications include: A high entropy oxide oxygen carrier is placed in a reactor, the reactor is heated, fuel is introduced into the reactor, and synthesis gas is obtained through reaction; After the reaction is completed, water vapor is continuously introduced into the reactor to obtain H2 through the reaction; The reactor was heated to 600°C; the fuel flow rate was controlled to 0.03-0.07 mL / min, and the water vapor flow rate was controlled to 0.03-0.07 mL / min; The fuel is toluene; The chemical formula of high entropy oxide oxygen carrier is (Co x Ca y Cu z Al r Mg s )Fe2O4, wherein x:y:z:r:s is 0.1:0.1:0.1:0.1:0.5; The method for preparing the high entropy oxide oxygen carrier comprises the following steps: Adding Co source, Ca source, Cu source, Al source, Mg source and Fe source to citric acid, and then adding polyethylene glycol and water, stirring to obtain a gel; The gel is dried and then calcined to obtain a high entropy oxide oxygen carrier; The calcination temperature is 1000°C and the calcination time is 10h; The Co source includes at least one of cobalt nitrate, cobalt sulfate, and cobalt chloride; The Ca source includes at least one of calcium nitrate, calcium sulfate, and calcium chloride; The Cu source includes at least one of copper nitrate, copper sulfate, and copper chloride; The Al source includes at least one of aluminum nitrate, aluminum sulfate, and aluminum chloride; The Mg source includes at least one of magnesium nitrate, magnesium sulfate, and magnesium chloride; The Fe source includes at least one of ferric nitrate, ferric sulfate, and ferric chloride; The molar ratio of Co ions in the Co source, Ca ions in the Ca source, Cu ions in the Cu source, Al ions in the Al source, Mg ions in the Mg source, Fe ions in the Fe source, citric acid, and polyethylene glycol is 0.1:0.1:0.1:0.1:0.5:2:(0.5~2):(0.5~1).

2. The use according to claim 1, characterized in that A Co source, a Ca source, a Cu source, an Al source, a Mg source, and a Fe source are added to citric acid, and then polyethylene glycol and water are added, and the mixture is stirred at 90-100° C. to obtain a gel.

3. The use according to claim 1, characterized in that The gel is dried at 100-110°C and then calcined to obtain a high entropy oxide oxygen carrier.

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