An oxide with a calcium iron oxide structure, an electrolytic cell cathode material and its preparation method

Abstract

This invention discloses a calcium-iron-type oxide, an electrolytic cell cathode material, and a method for preparing the same, belonging to the field of solid oxide electrolytic cells. The calcium-iron-type oxide has the following structural composition: CaFe 2‑x Cr x O 4‑δ In the formula, 0 ≤ x ≤ 1, and δ represents the number of oxygen vacancies. When the above solid oxide is prepared into a cathode material for use in the field of carbon dioxide electroreduction, the cathode material exhibits good electrochemical performance.

Description

Technical Field

[0001] This invention belongs to the field of solid oxide electrolytic cells, specifically relating to an oxide with a calcium iron stone structure, an electrolytic cell cathode material, and a method for preparing the same. Background Technology

[0002] The excessive consumption of fossil fuels has led to massive CO2 emissions into the atmosphere, causing a series of problems such as global warming, which has attracted widespread global attention. In this context, there is an urgent need to effectively capture CO2 and convert it into valuable chemicals (carbon monoxide, methane, ethylene, etc.) to achieve a carbon-neutral cycle.

[0003] Solid oxide electrolysis (SOEC) technology, as a method for carbon dioxide conversion and utilization, has attracted widespread attention due to its advantages such as fast reaction rate, high product selectivity, and high Faraday efficiency. Metal-ceramic materials, such as Ni-GDC, have advantages such as inexpensive and readily available raw materials and excellent electroreduction performance. However, the drawbacks of nickel-based materials, such as easy sintering and carbon deposition at high temperatures, limit their widespread application. Perovskite-based oxides exhibit mixed ionic and electronic conductivity. Fe-based perovskite materials, as cathodes, have advantages such as low cost, high catalytic activity, and strong resistance to coking. Therefore, researchers have developed a series of iron-based perovskite materials with excellent electrochemical performance, such as La... 0.6 Sr 0.4 Fe 0.8 Ni 0.2 However, when Sr-containing perovskite oxides are used as cathode materials for SOECs, SrCO3 easily forms on the electrode surface, creating an insulating layer that leads to an irreversible decline in electrochemical performance. Therefore, the search for high-performance cathode catalysts remains a hot topic in this research field.

[0004] Enhancing the CO2 adsorption capacity of SOEC cathodes is one way to improve CO2 electroreduction performance. Introducing oxygen vacancies on the cathode surface can promote the chemisorption of CO2. Furthermore, calcium carbonate decomposes into calcium oxide (CaO) at temperatures above 820℃. CaO is a common carbon dioxide adsorbent, and its presence can further promote CO2 adsorption by the electrode material, thus improving the electrode's electrochemical performance. In conclusion, developing a calcium-containing iron-based oxide that maintains structural stability at 1000℃ and applying it to the field of electrolytic cells is of great significance. Summary of the Invention

[0005] To address the aforementioned problems in the prior art, this invention provides an iron-based oxide and its preparation method that maintain a calcium-iron-type structure at temperatures above 1000°C by controlling the B-site doping element in the calcium-iron-type oxide. The key lies in maintaining the calcium-iron-type structure of the oxide under the aforementioned temperature conditions when different amounts of the metal element Cr are doped at the B-site. Furthermore, this invention applies the above-mentioned solid oxide to the preparation of cathode materials for electrolytic cells and the field of carbon dioxide electroreduction. This cathode material is low in cost and exhibits good electrochemical performance and excellent stability.

[0006] The technical solution of the present invention is as follows:

[0007] In a first aspect, the present invention provides a calcium-iron-type oxide with Cr doping at the B site, which maintains its calcium-iron-type structure at temperatures above 1000°C, and its structural characteristic composition is: CaFe 2-x Cr x O 4-δ In the formula, 0≤x≤1, and δ represents the number of oxygen vacancies, 0≤δ<1.

[0008] In its structural composition expression, it is preferable that 0 ≤ x ≤ 0.5.

[0009] Secondly, the present invention provides a method for preparing the above-mentioned calcium iron oxide, comprising the following steps:

[0010] a. Based on the structural composition expression: CaFe 2-x Cr x O 4-δ Weigh calcium nitrate, ferric nitrate, and chromium nitrate according to their stoichiometric ratios, and dissolve them in 500 mL of aqueous solution.

[0011] b. Weigh out citric acid and ethylenediaminetetraacetic acid separately and add them to the above nitrate solution. The molar ratio of citric acid to the total number of metal cations is 1.5:1-2.0:1, and the molar ratio of ethylenediaminetetraacetic acid to the total number of metal cations is 1:1-1.5:1.

[0012] c. Add ammonia water dropwise to adjust the pH of the above mixture to between 7 and 8;

[0013] d. After stirring at 120–180°C for 2–5 hours, heat at 200–300°C until a gel is formed;

[0014] e. Heat the gel to spontaneous combustion, collect the powder, calcine it, and obtain a calcium-iron-type oxide structure.

[0015] Furthermore, in the above technical solution, the calcination temperature in step e is 800–1200℃, and the time is 2–10 hours.

[0016] Thirdly, the present invention provides an electrolytic cell cathode material, which is prepared using the above-mentioned calcium iron oxide structure.

[0017] Fourthly, the present invention provides a method for preparing the above-mentioned cathode material, comprising the following steps:

[0018] After thoroughly grinding the B-site Cr-doped calcium iron oxide structure prepared in the above ae step, an electrode slurry containing 6-10 wt.% ethyl cellulose terpineol solution is added. The electrode slurry is then uniformly coated onto a strontium and magnesium co-doped lanthanum gallate electrolyte sheet coated with a lanthanum-doped cerium oxide transition layer and calcined at 1000-1200℃.

[0019] Furthermore, in the above technical solution, the mass ratio of the terpineol solution of ethyl cellulose to the calcium iron oxide is 1 to 2:1.

[0020] Furthermore, in the above technical solution, the calcination time is 2 to 5 hours.

[0021] Fifthly, the present invention provides an electrolytic cell system comprising the above-described electrolytic cell cathode material.

[0022] Sixthly, the present invention provides an electrochemical testing method that utilizes the aforementioned electrolytic cell system for testing.

[0023] Beneficial effects:

[0024] 1. This invention provides an iron-based calcium-iron oxide with Cr doping at the B site, which can maintain the calcium-iron structure at temperatures above 1000°C. When the above solid oxide is prepared as a cathode material and applied in the field of carbon dioxide electroreduction, the cathode material exhibits good electrochemical performance and excellent stability.

[0025] 2. This invention provides a series of calcium-iron-type oxides suitable for use as cathodes in solid oxide electrolytic cells by doping different amounts of Cr at the B-site in calcium-iron-type oxides, and applies them to the CO2 electroreduction reaction. Experimental results show that this type of catalyst exhibits excellent catalytic performance and good stability, outperforming some cathode materials in the prior art. Attached Figure Description

[0026] Figure 1 It is the CaFe2O prepared in Example 1 4-δ The X-ray diffraction (XRD) pattern.

[0027] Figure 2 It is the CaFe prepared in Example 3 1.5 Cr 0.5 O 4-δThe X-ray diffraction (XRD) pattern.

[0028] Figure 3 It is the CaFeCrO ​​prepared in Example 5 4-δ The X-ray diffraction (XRD) pattern.

[0029] Figure 4 It is the CaFe2O prepared in Example 1 4-δ Polarization curves of CO2 electrolysis.

[0030] Figure 5 It is the CaFe prepared in Example 2 1.5 Cr 0.5 O 4-δ Polarization curves of CO2 electrolysis. Detailed Implementation

[0031] The following provides a detailed description of specific embodiments of the present invention. These specific embodiments are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0032] Example 1

[0033] CaFe2O 4-δ Preparation

[0034] According to CaFe2O 4-δ The chemical formula is as follows: Calcium nitrate (23.615 g) and ferric nitrate (80.800 g) were accurately weighed according to stoichiometry and dissolved in 500 mL of deionized water. After the nitrates were completely dissolved, citric acid and ethylenediaminediacetic acid were weighed according to the same molar ratios of 1.5:1 and 1:1 with the total metal cations, respectively. Ammonia water was added dropwise to adjust the pH of the solution to 7-8. The solution was heated and stirred at 80℃ for 1 h, then the temperature was increased to 220℃ and the mixture was heated and stirred to evaporate the water until a gel was formed. The gel was then transferred to a ceramic bowl and heated to self-ignite. The powder was collected and calcined in a muffle furnace at 1000℃ for 5 h to obtain the composite oxide. Its XRD pattern is shown below. Figure 1 As shown, analysis of the spectrum reveals that the CaFe2O2 after high-temperature calcination... 4-δ It has a calcium-iron oxide structure, which is a pure phase calcium-iron oxide structure, and no impurity diffraction peaks were observed.

[0035] The 0.5g CaFe2O prepared above 4-δ The oxides were thoroughly ground and homogenized, and 0.5g of a 6wt.% terpineol solution of ethyl cellulose was added to prepare an electrode slurry. The electrode slurry was then coated onto a strontium and magnesium co-doped lanthanum gallate electrolyte sheet coated with a lanthanum-doped cerium oxide transition layer. The slurry was then sintered at 1100℃ for 2 hours to a thickness of ~15μm.

[0036] This material was used for CO2 electroreduction tests, with pure carbon dioxide introduced into the cathode side at a flow rate of 50 mL / min. -1 Air is introduced into the anode at a flow rate of 100 mL / min. -1 The test temperature was 850℃; under an applied voltage of 1.4V, the polarization current reached 1.02A cm⁻¹. -2 .

[0037] Example 2

[0038] CaFe 1.8 Cr 0.2 O 4-δ Preparation

[0039] According to CaFe 1.8 Cr 0.2 O 4-δ The chemical formula is obtained by accurately weighing calcium nitrate (23.615 g), ferric nitrate (72.720 g), and chromium nitrate (8.003 g) in stoichiometric ratios and dissolving them in 500 mL of deionized water. After the nitrates are completely dissolved, citric acid and ethylenediamine diacetic acid are weighed at a molar ratio of 1.5:1 and 1:1 to the total metal cations, respectively. Ammonia water is added dropwise to adjust the pH of the solution to 7-8. The solution is heated and stirred at 80 °C for 1 h, and then the temperature is increased to 220 °C and heated and stirred to evaporate the water until a gel is formed. The gel is then transferred to a ceramic bowl and heated to self-ignite. The powder is collected and placed in a muffle furnace and calcined at 1000 °C for 5 h to obtain a composite oxide with a calcium-iron-type structure.

[0040] The 0.5g CaFe prepared above 1.8 Cr 0.2 O 4-δ The oxides were thoroughly ground and homogenized, and 0.5g of a 6wt.% terpineol solution of ethyl cellulose was added to prepare an electrode slurry. The electrode slurry was then coated onto a strontium and magnesium co-doped lanthanum gallate electrolyte sheet coated with a lanthanum-doped cerium oxide transition layer. The slurry was then sintered at 1100℃ for 2 hours to a thickness of ~15μm.

[0041] This material was used for CO2 electroreduction tests, with pure carbon dioxide introduced into the cathode side at a flow rate of 50 mL / min. -1 Air is introduced into the anode at a flow rate of 100 mL / min. -1 The test temperature was 850℃; under an applied voltage of 1.4V, the polarization current reached 0.96A cm⁻¹. -2 .

[0042] Example 3

[0043] CaFe 1.5 Cr 0.5 O 4-δ Preparation

[0044] According to CaFe 1.5 Cr 0.5 O 4-δ The chemical formula is as follows: Calcium nitrate (23.615 g), ferric nitrate (60.600 g), and chromium nitrate (20.008 g) were accurately weighed according to stoichiometry and dissolved in 500 mL of deionized water. After the nitrates were completely dissolved, citric acid and ethylenediaminediacetic acid were weighed at a molar ratio of 1.5:1 and 1:1 to the total metal cations, respectively. Ammonia water was added dropwise to adjust the pH of the solution to 7-8. The solution was heated and stirred at 80℃ for 1 h, then the temperature was increased to 220℃ and heated and stirred to evaporate the water until a gel was formed. The gel was then transferred to a ceramic bowl and heated for self-ignition. The powder was collected and calcined in a muffle furnace at 1000℃ for 5 h to obtain the composite oxide. Its XRD pattern is shown below. Figure 2 As shown, the oxide has a calcium-iron-type structure, which is a pure phase calcium-iron-type structure, and no impurity diffraction peaks were observed.

[0045] The 0.5g CaFe prepared above 1.5 Cr 0.5 O 4-δ The oxides were thoroughly ground and homogenized, and 0.5g of a 6wt.% terpineol solution of ethyl cellulose was added to prepare an electrode slurry. The electrode slurry was then coated onto a strontium and magnesium co-doped lanthanum gallate electrolyte sheet coated with a lanthanum-doped cerium oxide transition layer. The slurry was then sintered at 1100℃ for 2 hours to a thickness of ~15μm.

[0046] This material was used for CO2 electroreduction tests, with pure carbon dioxide introduced into the cathode side at a flow rate of 50 mL / min. -1 Air is introduced into the anode at a flow rate of 100 mL / min. -1 The test temperature was 850℃; under an applied voltage of 1.4V, the polarization current reached 0.92A cm⁻¹. -2 .

[0047] Example 4

[0048] CaFe 1.3 Cr 0.7 O 4-δ Preparation

[0049] According to CaFe 1.3 Cr 0.7 O 4-δThe chemical formula is obtained by accurately weighing calcium nitrate (23.615 g), ferric nitrate (52.520 g), and chromium nitrate (28.011 g) in stoichiometric ratios and dissolving them in 500 mL of deionized water. After the nitrates are completely dissolved, citric acid and ethylenediamine diacetic acid are weighed at molar ratios of 1.5:1 and 1:1 with the total metal cations, respectively. Ammonia water is added dropwise to adjust the pH of the solution to 7-8. The solution is heated and stirred at 80 °C for 1 h, then the temperature is increased to 220 °C and heated and stirred to evaporate the water until a gel is formed. The gel is then transferred to a ceramic bowl and heated to self-ignite. The powder is collected and calcined in a muffle furnace at 1000 °C for 5 h to obtain the calcium-iron-type oxide CaFe. 1.3 Cr 0.7 O 4-δ XRD pattern analysis shows that the CaFe after high-temperature calcination... 1.3 Cr 0.7 O 4-δ It has a calcium-iron-stone structure.

[0050] Example 5

[0051] CaFeCrO 4-δ Preparation

[0052] According to CaFeCrO 4-δ The chemical formula is as follows: Calcium nitrate (23.615 g), ferric nitrate (52.520 g), and chromium nitrate (28.011 g) were accurately weighed according to stoichiometry and dissolved in 500 mL of deionized water. After the nitrates were completely dissolved, citric acid and ethylenediaminediacetic acid were weighed at a molar ratio of 1.5:1 and 1:1 to the total metal cations, respectively. Ammonia water was added dropwise to adjust the pH of the solution to 7-8. The solution was heated and stirred at 80℃ for 1 h, then the temperature was increased to 220℃ and heated and stirred to evaporate the water until a gel was formed. The gel was then transferred to a ceramic bowl and heated for self-ignition. The powder was collected and calcined in a muffle furnace at 1000℃ for 5 h. The XRD pattern is shown below. Figure 3 As shown, analysis of the spectrum reveals that the CaFeCrO2 after high-temperature calcination... 4-δ Pure phase. A calcium-iron-type oxide, CaFeCrO, was obtained. 4-δ It has a pure phase calcium-iron-type structure, and no impurity diffraction peaks were observed.

[0053] Example 6

[0054] This embodiment lists a performance comparison between other prior art electrodes and the electrode described in this application, as shown in Table 1.

[0055] Table 1 Comparison of CO2 electrolysis performance of various electrode materials

[0056]

[0057] Reference

[0058] [1]S.Park,Y.Kim,Y.Noh,T.Kim,H.Han,W.Yoon,J.Choi,SHYi,WJLee andW.B.Kim,A sulfur-tolerant cathode catalyst fabricated with in situ exsolvedCoNi alloy nanoparticles anchored on a Ruddlesden–Popper support for CO2electrolysis,J.Mater.Chem.A 2020,8,138-148.

[0059] [2]H.Lv,Y.Zhou,X.Zhang,Y.Song,Q.Liu,G.Wang and X.Bao,Infiltration ofCe 0.8 Gd 0.2 O 1.9 nanoparticles on Sr2Fe 1.5 Mo 0.5 O 6-δ cathode for CO2 electroreduction in solid oxide electrolysis cell,J.Energy Chem.2019,35,71-78.

[0060] [3]S.Lee,M.Kim,KTLee,JTSIrvine and THShin,EnhancingElectrochemical CO2 Reduction using Ce(Mn,Fe)O2 with La(Sr)Cr(Mn)O3 Cathode for High-Temperature Solid Oxide Electrolysis Cells,Adv.Energy Mater.2021,11.

[0061] For any person skilled in the art, any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention should still fall within the protection scope of the present invention.

Claims

1. The application of an electrolytic cell cathode material in the electroreduction of carbon dioxide, characterized in that, The cathode material is prepared using a calcium-iron oxide with a calcium-iron structure; the calcium-iron oxide has a CaFe composition. 2-x Cr x O 4-δ In the formula, 0.5≤x≤1, δ represents the number of oxygen vacancies, 0≤δ<1; The method for preparing the aforementioned calcium-iron-type oxide includes the following steps: a. Based on the structural composition expression: CaFe 2-x Cr x O 4-δ Weigh calcium nitrate, ferric nitrate, and chromium nitrate according to their stoichiometric ratios and dissolve them in an aqueous solution. b. Weigh out citric acid and ethylenediaminetetraacetic acid separately and add them to the above nitrate solution. The molar ratio of citric acid to the total number of metal cations is 1.5:1-2.0:1, and the molar ratio of ethylenediaminetetraacetic acid to the total number of metal cations is 1:1-1.5:

1. c. Add ammonia water dropwise to adjust the pH of the above mixture to between 7 and 8; d. After stirring at 120~180℃ for 2~5h, heat at 200~300℃ until a gel is formed; e. Heat the gel to spontaneous combustion, collect the powder, calcine it, and obtain a calcium-iron oxide structure.

2. The application according to claim 1, characterized in that, The calcination temperature in step e is 800~1200℃, and the time is 2~10 h; The method for preparing the cathode material of the electrolytic cell includes the following steps: After grinding the calcium iron oxide structure according to claim 1, an electrode slurry is prepared by adding a terpineol solution containing 6-10 wt.% ethyl cellulose; the electrode slurry is coated onto a strontium and magnesium co-doped lanthanum gallate electrolyte sheet coated with a lanthanum-doped cerium oxide transition layer, and then calcined at 1000-1200℃. The mass ratio of the terpineol solution of ethyl cellulose to the calcium iron oxide is 1~2:1.

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