Electrolyte material of solid oxide electrolytic cell and preparation method of electrolyte material

Abstract

The invention provides an electrolyte material of a solid oxide electrolytic cell and a preparation method of the electrolyte material. The preparation method of the material specifically comprises the following steps: preparing a solution by taking nitrate of Ce and Gd as raw materials according to a certain stoichiometric ratio, adding urea, polymer gel related raw materials and an initiator, heating to form gel, freeze-drying, calcining the obtained dry gel step by step, calcining for 1-2 hours at 300-400 DEG C under the protection of inert gas, and calcining for 2-4 hours at 650 DEG C in air to obtain the material. Through the method, product looseness caused by a deflagration phenomenon in raw material calcination can be prevented, gel agglomeration is prevented, the product powder has better conductivity and controllable specific surface area, and the product powder is more suitable for being used as an electrolyte material of a solid oxide electrolytic cell. The material and the preparation method thereof have important application in the development of a solid oxide electrolytic cell technology.

Description

Technical Field

[0001] The present invention relates to the technical field of fuel cells, and particularly to an electrolyte material for a solid oxide electrolyzer and a preparation method thereof. Background Art

[0002] For traditional water electrolysis or thermochemical conversion devices, solid oxide electrolyzers (SOECs) have become a research hotspot in the field of energy conversion due to their advantages such as high-efficiency energy conversion, potential for large-scale storage of renewable energy, low carbon emissions, and adaptability to multiple raw materials (such as co-electrolysis of H2O and CO2). Through the high-temperature electrolysis mode, SOECs can efficiently convert electrical energy into chemical energy (such as hydrogen and syngas), showing broad prospects in the fields of green hydrogen production, carbon cycle utilization, and industrial waste heat coupling.

[0003] As the core component of SOECs, the ionic conductivity and chemical stability of the electrolyte material directly determine the electrolysis efficiency and long-term durability. Yttria-stabilized zirconia (YSZ) is the currently commonly used oxygen ion conductor electrolyte, which has excellent ionic conduction performance (about 0.1 S / cm) at high temperatures (>800 °C), but its conductivity significantly decreases (<0.03 S / cm) when operating at medium and low temperatures (600 - 750 °C), and it is easily affected by oxidation-reduction cycle stress at high current densities, resulting in interface delamination and performance degradation. In contrast, gadolinium-doped ceria (GDC) exhibits higher oxygen ionic conductivity (such as up to 0.1 S / cm at 800 °C), better chemical compatibility (reducing the reaction with electrode materials), and stronger antioxidant ability in the medium and low temperature range (600 - 800 °C), and is particularly suitable for the high-pressure and high-humidity operating environment of SOECs. In addition, the low-temperature processability of GDC helps to reduce the system thermal stress and enhance the large-scale integration potential of the electrolyzer stack, making it an important candidate for medium and low temperature SOEC electrolyte materials.

[0004] Since the performance of electrolyte materials is directly affected by the microscopic morphology of particles and the types of raw materials, a large number of studies have shown that there are also significant differences in the performance of materials prepared by different synthesis processes. Currently, the methods for synthesizing GDC include sol-gel method, solid-state reaction method, co-precipitation method, spray pyrolysis method, etc. Although the solid-state reaction method has a simple process, the prepared powder has poor uniformity and low sintering activity; CN117023647A uses spray pyrolysis method to prepare nano-powders, and the obtained products have high purity, complete crystal lattice and uniform particle size distribution, but the equipment requirements and costs are relatively high, and there are problems with product recovery and capture; CN105130426B and others use sol-gel method and co-precipitation method. Although these methods have the advantages of small product particles, high uniformity and high sintering activity, they also have low yield, long production cycle, and large influence of process variable factors (such as pH value, temperature, reactant concentration, etc.) on the physical and chemical properties of products, and are difficult to be used for large-scale production. CN100447090C shows that the rapid curing of high-molecular organic matter can also be applied to the preparation of nano-powders. The high-molecular gel method is a method that uses in-situ polymerization reaction of organic monomers to quickly form gels. Due to its characteristics of low-temperature synthesis and controllable composition, it has gradually become an effective means for preparing nano-scale electrolytes, porous electrodes and composite materials.

[0005] However, for the powders synthesized by the high-molecular gel method, due to the violent decomposition (200 - 400 °C) of organic matter and nitrate in the same temperature range, a large amount of heat and oxygen are released, triggering an uncontrollable combustion reaction. The obtained powder is extremely loose and porous, with a low true density. The electrolyte layer prepared has more pores and cannot be practically applied. If chloride salts are used as raw materials instead, the conductivity will decrease due to the fact that chloride salts are likely to form colloids under certain conditions, which destroys the solution uniformity, and the residual chloride ions occupy the oxidation sites during the sintering process, not meeting the requirements of electrolyte materials. Summary of the Invention

[0006] The present invention provides an electrolyte material for a solid oxide electrolytic cell and a preparation method thereof, aiming to solve the defect that the explosion combustion of nitrate raw materials and organic matter in the existing high-molecular gel method leads to loose and porous products, and to achieve the controllability of high conductivity and specific surface area of GDC powders.

[0007] In a first aspect, the present invention provides a preparation method for an electrolyte material of a solid oxide electrolytic cell, including the following steps: (1) Mix nitrate raw materials, organic monomers, cross-linking agents and urea and dissolve them in water, and add an initiator to initiate a cross-linking reaction to obtain a gel; (2) Freeze-dry the gel until the mass is constant to obtain a dry gel; (3) Heat the dry gel to a first temperature under inert gas protection and calcine it, and after the calcination is completed, heat it to a second temperature in air and calcine it to obtain the product.

[0008] The present invention aims at nitrate raw materials widely used in the market and develops a sintering process in a locally oxygen-deficient microenvironment under an inert atmosphere. First, in the temperature range of nitrate and organic matter decomposition, an inert gas is used to slowly raise the temperature to inhibit the combustion reaction. Secondly, urea is introduced, and the NH 3 / HNCO gas layer dilutes the oxygen concentration decomposed from nitrate at the molecular level, blocks combustion, and solves the problem of synchronous and intense heat release of nitrate and organic matter. Finally, air is used for full sintering at high temperature to complete the reconstruction of the oxide lattice and the full oxidation of residual carbon. The powder prepared by this method not only has high activity, small and concentrated particle size, appropriate specific surface area, but also is easy to pulverize, has a high yield, and a short synthesis cycle.

[0009] Preferably, in the above preparation method, the nitrate raw material in step (1) is a mixture of at least two of cerium nitrate, gadolinium nitrate, samarium nitrate, lanthanum nitrate, yttrium nitrate, strontium nitrate, and calcium nitrate, and at least contains cerium nitrate. The concentration of the nitrate dissolved in water is 0.5 - 1 mol / L.

[0010] The above preparation method is generally applicable to CeO2-based electrolyte materials with high requirements for electrical conductivity.

[0011] Preferably, in the above preparation method, the organic monomer in step (1) is acrylamide (AM), the crosslinking agent is N,N'-methylenebisacrylamide (MBAM), and the initiator is ammonium persulfate (APS).

[0012] The preparation method provided by the present invention constructs a polymer network by in-situ polymerization reaction of monomers to fix ions. During the gel drying and heat treatment processes, it can maintain the uniform mixing of multiple components, avoid agglomeration, and control the chemical composition of the synthesized product. Compared with the traditional sol-gel method, it does not require metal alkoxides as raw materials, has less consumption of organic matter, simple process, low equipment requirements, easy process control, short synthesis cycle, and is suitable for large-scale industrial production.

[0013] Further preferably, in the above preparation method, the addition amount of the organic monomer is 5 - 40% of the mass of water, the mass ratio of the organic monomer to the crosslinking agent is 3:1 - 10:1, the addition amount of the initiator is 1 - 2% of the mass of the organic monomer, and the addition amount of urea accounts for 2 - 5 wt% of the total system.

[0014] Preferably, after adding the initiator in step (1) of the above preparation method, it further includes heating in a water bath at 60 - 80 °C for 2 - 30 min.

[0015] The present invention realizes the rapid formation of a gel through a polymerization reaction by selecting appropriate cerium sources, gadolinium sources, and certain proportions of organic monomers, crosslinking agents, and initiators to form a solution, and simultaneously achieves the uniform mixing of raw materials at the molecular level. Moreover, the reactant solution is absorbed into its micron-scale pore structure, thereby preventing the occurrence of gel agglomeration.

[0016] Preferably, in step (3) of the above preparation method, the temperature of the first temperature is 300 - 400 °C, the calcination time is 1 - 2 h, and the heating rate is 0.5 - 1 °C / min; and / or, the temperature of the second temperature is 600 - 700 °C, and the calcination time is 2 - 4 h.

[0017] Slowly heating to the first temperature can slow down the decomposition rate of nitrate and prevent the rapid decomposition of nitrate to release oxygen and cause deflagration.

[0018] More preferably, the inert gas in step (3) of the above preparation method is a mixed gas of N2 and CO2, and the ratio of N2 to CO2 is 3 - 10:1.

[0019] The inert gas is selected as a mixed gas of N2 and CO2 because CO2 has a higher cost but can play a role in inhibiting oxidation, while N2 has a low cost but only acts as a protective gas. This gas ratio can minimize the cost while meeting the process requirements.

[0020] Preferably, the preparation method of the electrolyte material of the above solid oxide electrolytic cell includes: Prepare an aqueous solution of nitrate, acrylamide, N,N'-methylenebisacrylamide, and urea according to the required stoichiometric ratio, where the nitrate concentration is 0.5 - 1 mol / L, the acrylamide addition amount is 5 - 40% of the water mass, the mass ratio of acrylamide to N,N'-methylenebisacrylamide is 3:1 - 10:1, and the urea addition amount accounts for 2 - 5 wt% of the total system; Add ammonium persulfate to the aqueous solution, place it in a water bath at 60 - 80 °C and heat for 2 - 30 min to obtain a gel. The addition amount of ammonium persulfate is 1 - 2% of the acrylamide addition amount by mass; Freeze-dry the gel until the mass is constant to obtain a dry gel; Under the protection of a mixed gas of N2 and CO2 with a ratio of 3 - 10:1, heat the dry gel to the first temperature of 300 - 400 °C at a rate of 0.5 - 1 °C / min and calcine for 1 - 2 h; After the calcination at the first temperature is completed, heat it to 600 - 700 °C in air and calcine for 2 - 4 h to obtain the product.

[0021] Second aspect, the present invention provides an electrolyte material for a solid oxide electrolytic cell, and the electrolyte material for the solid oxide electrolytic cell is prepared by the above preparation method.

[0022] The electrolyte material for the solid oxide electrolytic cell has a controllable specific surface area, fine particles, clear crystal phase boundaries, and relatively dispersed aggregates.

[0023] The above electrolyte material for the solid oxide electrolytic cell has higher conductivity at 700 - 750 °C.

[0024] The beneficial effects of the present invention include: By constructing a polymer network through monomer in-situ polymerization reaction to fix ions, during the gel drying and heat treatment processes, the uniform mixing of multiple components can be maintained, aggregation can be avoided, and the chemical composition of the synthesized product can be controlled, so that the prepared GDC powder has higher conductivity after pressing. Its conductivity can reach 0.0183 S / cm at 700 °C and 0.0353 S / cm at 750 °C.

[0025] Through the dynamic matching of temperature range - atmosphere type, the sequential separation of organic matter combustion and nitrate decomposition is realized, the heat - oxygen coupling condition required for the combustion chain reaction is cut off from the root, and the adverse behavior of gel deflagration is prevented, so that the prepared GDC powder has a more controllable specific surface area and powder morphology.

[0026] The preparation method of the GDC material provided by the present invention does not require metal alkoxides as raw materials, has less consumption of organic matter, simple process, low equipment requirements, easy process control, short synthesis cycle, and is suitable for large-scale industrial production. Description of the Drawings

[0027] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0028] Figure 1 It is the XRD pattern of the GDC materials synthesized in each example and comparative example provided by the present invention.

[0029] Figure 2 It is the scanning electron microscope morphology characterization of the GDC materials synthesized in each example and comparative example provided by the present invention, where Figure 2 A in is the morphology of the GDC material synthesized in Example 1, Figure 2 B in is the morphology of the GDC material synthesized in Example 2, Figure 2 C in is the morphology of the GDC material synthesized in Comparative Example 1,Figure 2 D is the morphology of the GDC material synthesized in Comparative Example 2, Figure 2 E is the morphology of the GDC material synthesized in Comparative Example 3, Figure 2 F is the morphology of the GDC material synthesized in Comparative Example 4. Detailed implementation manners

[0030] To make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions in the present invention will be clearly and completely described below with reference to the accompanying drawings in the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present invention without making creative efforts shall fall within the protection scope of the present invention.

[0031] Example 1 Weigh cerium nitrate hexahydrate and gadolinium nitrate hexahydrate according to the chemical stoichiometry of Gd 0.1 Ce 0.9 O 2-δ Add them into 100 ml of deionized water to prepare a nitrate solution with a concentration of 0.5 mol / L. Add 5 g of urea, and while stirring, add 9 g of AM and 1 g of MBAM. After stirring for 20 min, add 1 ml of 10% APS, and perform a water bath treatment. The water bath temperature is 80°C, and after a water bath time of 5 - 20 min, a translucent hydrogel is obtained. The obtained wet gel is placed in a freeze-drying oven until the mass is constant. The dry gel is heated in a mixed gas of N2 / CO2 = 5:1 at a heating rate of 1°C / Min to 300°C and calcined for 1 h, and then switched to air and calcined at 650°C for 3 h to obtain the GDC material.

[0032] Example 2 Weigh cerium nitrate hexahydrate and gadolinium nitrate hexahydrate according to the chemical stoichiometry of Gd 0.1 Ce 0.9 O 2-δ Add them into 100 ml of deionized water to prepare a nitrate solution with a concentration of 1 mol / L. Add 10 g of urea, and while stirring, add 9 g of AM and 1 g of MBAM. After stirring for 20 min, add 1 ml of 10% APS, and perform a water bath treatment. The water bath temperature is 80°C, and after a water bath time of 5 - 20 min, a translucent hydrogel is obtained. The obtained wet gel is placed in a freeze-drying oven until the mass is constant. The dry gel is heated in a mixed gas of N2 / CO2 = 5:1 at a heating rate of 1°C / Min to 300°C and calcined for 1 h, and then switched to air and calcined at 650°C for 3 h to obtain the GDC material.

[0033] The only difference between this example and Example 1 is that: the concentration of nitrate in the nitrate solution is 1 mol / L, and the amount of urea added is 10 g.

[0034] Comparative Example 1 According to Gd 0.1 Ce 0.9 O 2-δ Weigh cerium nitrate hexahydrate and gadolinium nitrate hexahydrate according to the stoichiometric ratio, add 100 ml of deionized water to prepare a 0.5 mol / L nitrate solution, add 5 g of urea, and add 9 g of AM and 1 g of MBAM while stirring. After stirring for 20 min, add 1 ml of 10% APS, and perform a water bath treatment. The water bath temperature is 80 °C, and after a water bath time of 5 - 20 min, a translucent hydrogel is obtained. The obtained wet gel is placed in a freeze-drying oven until the mass is constant. The dry gel is calcined in a mixed gas of N2 / CO2 = 5:1 at 650 °C in air for 3 h to obtain a GDC material.

[0035] The only difference between this comparative example and Example 1 is that it is sintered in one step to 650 °C.

[0036] Comparative Example 2 According to Gd 0.1 Ce 0.9 O 2-δ Weigh cerium nitrate hexahydrate and gadolinium nitrate hexahydrate according to the stoichiometric ratio, add 100 ml of deionized water to prepare a 0.5 mol / L nitrate solution, add 5 g of urea, and add 9 g of AM and 1 g of MBAM while stirring. After stirring for 20 min, add 1 ml of 10% APS, and perform a water bath treatment. The water bath temperature is 80 °C, and after a water bath time of 5 - 20 min, a translucent hydrogel is obtained. The obtained wet gel is placed in a freeze-drying oven until the mass is constant. The dry gel is rapidly heated to 300 °C in a mixed gas of N2 / CO2 = 5:1 and calcined for 1 h, and then switched to air and calcined at 650 °C for 3 h to obtain a GDC material.

[0037] The only difference between this comparative example and Example 1 is that it is rapidly heated to 300 °C.

[0038] Comparative Example 3 According to Gd 0.1 Ce 0.9 O 2-δ Weigh cerium nitrate hexahydrate and gadolinium nitrate hexahydrate according to the stoichiometric ratio, add 100 ml of deionized water to prepare a 0.5 mol / L nitrate solution, and add 9 g of AM and 1 g of MBAM while stirring. After stirring for 20 min, add 1 ml of 10% APS, and perform a water bath treatment. The water bath temperature is 80 °C, and after a water bath time of 5 - 20 min, a translucent hydrogel is obtained. The obtained wet gel is placed in a freeze-drying oven until the mass is constant. The dry gel is heated to 300 °C at a heating rate of 1 °C / Min in a mixed gas of N2 / CO2 = 5:1 and calcined for 1 h, and then switched to air and calcined at 650 °C for 3 h to obtain a GDC material.

[0039] The only difference between this comparative example and Example 1 is that no urea is added.

[0040] Comparative Example 4 Press Gd 0.1 Ce 0.9 O 2-δ Weigh cerium nitrate hexahydrate and gadolinium nitrate hexahydrate in a stoichiometric ratio, add 100 ml of deionized water to prepare a 0.5 mol / L nitrate solution, add 5 g of urea, and add 9 g of AM and 1 g of MBAM while stirring. After stirring for 20 minutes, add 1 ml of 10% APS and treat in a water bath at 80 ° C for 5 to 20 minutes to obtain a translucent hydrogel. The obtained wet gel is placed in a freeze drying oven until the mass is constant. The dry gel is heated to 300 ° C at a heating rate of 1 ° C / Min in a N2 mixed gas and calcined for 1 hour, then switched to air and calcined at 650 ° C for 3 hours to obtain GDC material.

[0041] The only difference between this comparative example and Example 1 is that pure nitrogen is used as the protective gas.

[0042] The properties of the GDC materials prepared in each embodiment and comparative example were characterized by the following method: 1. The crystal structure of the GDC materials prepared in each embodiment and comparative example was tested using a Rigaku D / max2200 x-ray diffractometer. The Cu target Ku radiation (wavelength λ=0.15418nm) was used, the step length was 0.02°, and the scanning range was 10-90°. The results are as follows: Figure 1 As shown. Figure 1 It can be seen that the XRD spectra of the powders prepared using the above method are free of impurities, which is in line with expectations.

[0043] 2. Use JSM-6700F scanning electron microscope of Japan Electronics to observe the prepared material powder sample. Fix the powder sample on the copper table with conductive glue, spray gold and put it into the sample area. The test results are as follows Figure 2 shown.

[0044] Figure 2 A and B show that the SEM images show that the microscopic appearance of Example 1 and Example 2 is fine particles, clear crystal phase boundaries, and relatively dispersed agglomerates. Figure 2 C and D show that Comparative Examples 1 and 2 have an amorphous agglomerate structure due to the violent combustion of organic matter and nitrate, and the interior is loose and porous, so they have a higher specific surface area. Figure 2 E and F alleviated the rapid decomposition of nitrate to a certain extent and diluted the oxygen concentration. The microstructure was clumping and no obvious grain boundaries were formed.

[0045] The GDC materials prepared in each example and comparative example were pressed into rectangular bars at a pressure of 10 MPa, with a thickness of 4 mm, a width of 4 mm, and a length of 35 mm, and then sintered at 1250 °C for 3 h. The relative density of the samples was above 95%. The conductivity was measured in air by the standard DC four-probe method. Silver wires were connected to the test samples with silver paste, and the conductivity of the powder was measured. The results are shown in Table 1.

[0046]

[0047] As can be seen from Table 1, the conductivities of the GDC materials prepared by the methods of Example 1 and Example 2 were 0.0183 S / cm and 0.0172 S / cm at 700 °C, and 0.0353 S / cm and 0.0338 S / cm at 750 °C respectively after pressing, which were significantly higher than those of Comparative Example 1 and Comparative Example 2. The conductivities of Comparative Example 3 and Comparative Example 4 were 0.0236 S / cm and 0.0288 S / cm at 750 °C, which were lower than those of Example 1 and Example 2.

[0048] 4. The specific surface areas of the GDC materials prepared in each example and comparative example were characterized by a Micromeritics ASAP 2460 physical adsorption analyzer using the low-temperature liquid nitrogen static adsorption method. The results are shown in Table 2.

[0049]

[0050] As can be seen from Table 2, due to the loose powder, the specific surface areas of Comparative Example 1 and Comparative Example 2 were relatively large, much larger than those of Example 1 and Example 2.

[0051] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present invention and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing examples, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing examples, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the present invention in each example.

Claims

1. A method for preparing an electrolyte material of a solid oxide electrolytic cell, characterized in that, It includes the following steps: (1) Mix nitrate raw materials, organic monomers, crosslinking agents and urea and dissolve them in water, add an initiator to initiate a crosslinking reaction to obtain a gel; (2) Freeze-dry the gel until the mass is constant to obtain a dry gel; (3) Under the protection of an inert gas, heat the dry gel to a first temperature of 300-400 °C at a rate of 0.5-1 °C / min and calcine it. After the calcination is completed, raise the temperature to a second temperature and calcine it in air to obtain the product; The nitrate raw materials are a mixture of at least two of cerium nitrate, gadolinium nitrate, samarium nitrate, lanthanum nitrate, yttrium nitrate, strontium nitrate, and calcium nitrate, and at least contain cerium nitrate; The inert gas in step (3) is a mixed gas of N2 and CO2, and the ratio of N2 to CO2 is 3-10:

1.

2. The preparation method according to claim 1, wherein The concentration of the nitrate dissolved in water is 0.5-1 mol / L.

3. The preparation method according to claim 2, characterized in that, In step (1), the organic monomer is acrylamide, the crosslinking agent is N,N'-methylenebisacrylamide, and the initiator is ammonium persulfate.

4. The preparation method according to claim 3, characterized in that, The addition amount of the organic monomer is 5-40% of the mass of water, the mass ratio of the organic monomer to the crosslinking agent is 3:1-10:1, the addition amount of the initiator is 1-2% of the mass of the organic monomer, and the addition amount of urea accounts for 2-5 wt% of the total system.

5. The preparation method according to claim 4, characterized in that, After adding the initiator in step (1), it also includes heating in a water bath at 60-80 °C for 2-30 min.

6. The preparation method according to claim 5, characterized in that, In step (3), the temperature of the first temperature is 300-400 °C, the calcination time is 1-2 h, and the heating rate is 0.5-1 °C / min; And / or, the temperature of the second temperature is 600-700 °C, and the calcination time is 2-4 h.

7. The preparation method according to any one of claims 1-6, characterized in that, It includes: Prepare an aqueous solution of cerium nitrate, gadolinium nitrate, acrylamide, N,N'-methylenebisacrylamide and urea according to the required stoichiometric ratio, where the total concentration of cerium nitrate and gadolinium nitrate is 0.5-1 mol / L, the addition amount of acrylamide is 5-40% of the mass of water, the mass ratio of acrylamide to N,N'-methylenebisacrylamide is 3:1-10:1, and the addition amount of urea accounts for 2-5 wt% of the total system; Add ammonium persulfate to the aqueous solution, place it in a water bath at 60-80 °C and heat for 2-30 min to obtain a gel, and the addition amount of ammonium persulfate is 1-2% of the addition amount of acrylamide; Freeze-dry the gel until the mass is constant to obtain a dry gel; Under the protection of a mixed gas of N2 and CO2 with a ratio of 3-10:1, heat the dry gel to a first temperature of 300-400 °C at a rate of 0.5-1 °C / min and calcine it for 1-2 h; After the calcination at the first temperature is completed, raise the temperature to 600-700 °C in air and calcine it for 2-4 h to obtain the product.

8. An electrolyte material for a solid oxide electrolysis cell, characterized in that, The electrolyte material of the solid oxide electrolytic cell is prepared by the preparation method described in any one of claims 1-7.

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