SE535245C2 - Fuel cells without octrolytes - Google Patents

Abstract

The invention relates to a completely new type of fuel cell (FC), without a single anode, electrolyte or cathode construction, but made of a single component with both ionic and electronic conductivity. Two-component versions are also possible. With this configuration without electrolyte, the conventional three-component FC technology is not needed. Instead, the one- or two-component design is constructed using materials of suitable porosity, which makes this FC technology completely different from conventional FC technology, which requires a dense electrolyte and porous electrodes (anode and cathode). The new one- or two-component FC has demonstrated excellent and stable function that gives 200 to 900 mWcmJ between 400 and 600 ° C. This new technology has also demonstrated good results with large areas such as 6x6 cmz, then with a contribution of 10-20 watts. The new F C technology described here will have major advantages in terms of overhead production, costs, performance and competitiveness and has the potential to revolutionize future FC technology, development and markets.

Description

535 245 zirconia) to achieve sufficiently high ionic conductivity. This has historically severely limited the choice of construction materials, resulting in excessively high costs for commercialization.

As a consequence, great efforts have been made to develop new, alternative electrolyte materials for SOFCs with the aim of lowering the operating temperature, reducing costs and making the choice of materials easier, etc. Examples of materials are fluorite-structured ion-doped cerium oxides, proveskite-type O2 conducting oxides and proton conducting ceramics, as well as other complex materials such as LagMoO, BaN2-based oxides, apatite-type oxides and annatz. SOFC electrolytes can be developed by designing structures based on various new materials.

The new invention described here represents a breakthrough and a completely new fuel cell technology that does not require an MEA design/technology. It is electrolyte-free and instead uses only one or two components. The materials in the FC are either based on cerium composites consisting of nanocomposites of metal oxides or industrial products with mixed earth oxides.

Figure 1 shows a conventional FC constructed from three components. la) The invention - an FC technology without electrolyte, lb) Without anode and cathode with only a single component.

When the FC without electrolyte is placed in H2 and air, both H2 and O2 can be catalytically separated as H* and O2' and generate electricity through a dual catalytic function of the component. H* and O2' become one on the particle surface and produce H2O. During this process, the H2' contact side acts as an anode which releases electrons by creating H* and the air (O2) contact side acts as a cathode which accepts electrons, which means that the FC reaction is immediately completed as long as I-Y and O2' are in suitable or close contact. In this invention, the ion transport that occurs within the electrolyte in a conventional FC is replaced by surface ionization, movement and reaction in an FC reactor without electrolyte. All reactions and processes are completed on the particle surface by a direct 535 245 combination of H* and O2' ions. The reaction process for the patent-pending FC is described below. on the H2 side: H2 -+ 2H+ +2e' (1) at the air side (o2); 1/20, + 2 e' _» 02' (2) general reactions: H2 + 1/202 -> 2H+ + 02' (3-a) 2 H* + 02' -» H20 (s-b) This should be compared with FC reactions/processes, e.g. in the case of an I-f -conducting electrolyte. at the anode: H2 -> ZH* +2e' (4) at the cathode: 1/202 + 2 l-Ü + 2e' -v H20 (5) general reactions: H2+I/202 -> H20. (6) And in the case of the O2' -conducting electrolyte: at the anode; H2+o2' -+ H20 - ze' (7) at the cathode; 1/2o2 + 2 e' _» 02' (s) general reactions: H2+1/202 -+ H20. (9) The significant difference between other FCs and this invention is that this FC does not involve ion (l-Ü or 02-) transport through the electrolyte. The FC reaction instead occurs directly with the H* and 02' ions on the surface of the particles. In this way, the invented FC is a reactor and not like a conventional fuel cell device.

There has been one invention, a single-body SOFC with patent number US 5298235, 1994, Worrell et al. However, that FC device was still based on an electrolyte and electrode ternary function.

Another US patent, 20090258276, 2009, describes a fuel cell constructed from materials with P-N functions. For this there was no need to construct an electrolyte but it was irradiated with light later.

Summary of the Invention This invention relates to a revolutionary new fuel cell technology - the FC without electrolyte and technology. The FC was designed based on one or two components which have a mixed electronic and ionic conduction, where mixed earth metals (oxides) both natural and synthesized as ionic conducting materials are mixed with metal oxides as electronically conducting materials. In all existing fuel cell technologies and devices there are three basic fuel cell components: anode, electrolyte and cathode. These form a so-called MEA (membrane and electrolyte assembly). The electrolyte should offer electronic insulation but be fully permeable to ions, e.g. 02' or PF' -conduction to completely separate the propellant and the oxidant. Existing SOFC technologies require all designs with complete detailed compatibility between the components both mechanically and electrochemically. They should also offer good chemical stability. In particular, the ion-transporting capacity or conductivity of the electrolyte has limited the operating functions. For example, in the case of SOFCs, currently "yttrium stabilized zirconia" (Y SZ) achieves a desired conductivity of 0.1 S/cm at 1000°C, resulting in operation at high temperatures. In this invention, the FC without electrolyte has no separate anode, electrolyte and cathode.

Instead, only one or two components are used. The FC consists of at least two functions for electronic and ionic, e.g. l-fl/O2 conduction capability and catalyst for both H2 and O2.

The FC is constructed of either one or two components of a homogeneous material or two components of different materials and an interface between the two components.

No electrolyte. The components have mixed ionic and electronic conductive (MIEC) materials made from pure MIE conductors or a mixture/composite of electronic and ionic conductors/materials. The components are made with the appropriate structure and necessary porosity which is necessary for all fuel cell technologies. Normal ceramic sintering or ceramic film forming technologies have been used.

According to this invention, the ion-conducting materials are proton- or oxygen-ion-conducting materials usually i) doped Ba(Ce,Zr)O3 ceramics; ii) ion-doped cerium (SDC: samarium-doped cerium; GDC: gadolinium-doped cerium; yttrium-doped cerium; calcium-doped cerium; Sm-Pr- or Gd-Pr-doped cerium; iii) mixed earth metals (oxides), e.g. DCP (patented in Sweden..xxx); iv) YSZ, ScSZ; v) LaGaMgO3 etc.; vi) 535 245 cerium-based including LCP composites as patented previously, PCT and Swedish patent number 0101424-0.

According to another preferred embodiment of the invention, the electronically conductive phase materials are based on metal oxides, in particular, M (M= Li, Na, K, Cu, Ni, Zn, Mg, Ag, Fe, Sn, Al, Co, Mn, Mo, Cr, In, Ca, Ba, Sr) oxides and their complex oxides with two or more of these oxides in a mixture or composite.

These metal oxides can be defined in different metal oxide systems, e.g. Fe oxide systems, such as undoped BiFeO3, singly doped BiFeO3 (e.g. Bi0_9Ba0_1FeO3, ßiFeogMnoJOg, ßiogCaoiFeOg, ßiFeogCruiOg etc.) and doubly doped BiFeO3 (e.g. Bi0.9Ba0.1Fe0.9Mn0.1O3, Bi0.9Ca0.1Fe0.9CrO.103) Zn oxide systems with both an n- and p-type of ZnO. Al, Ga, and in such substitutional ingredients as Zn and Cl and in such substitutional ingredients as O can be used as n-type dopants; p-type Zn0 with Li, Na, and K, Cu, Ag, and N, P, As.

According to another more detailed concrete form of the invention, certain materials naturally contain both ionic and electronic conductivity based on the tested oxides of Ba0.5Sr0.5-Co0.8Fe0.2032d(BSCF), (Ba/Sr/Ca/lßW6MxNbl-xO3-å (M: Mg, Ni, Mn, Cr, Fe, In, Sn); doped LaMO3 (M= Ni, Cu, Co, Mn), e.g. LaNi0_,Fe,,,,Cu.,_,,0, etc.

Compared to other FC technologies, the electrolyte-free fuel cell technology constructed with one or two components has advantages especially in terms of chemical stability, mechanical properties and compatibility (the electrolyte compatibility problems between the anode and the electrolyte as well as the electrolyte and the cathode are thus avoided). The new electrolyte-free single-component FC has demonstrated extraordinary FC performance, between zoo and iooo mwcm* under soo-sooo mAcm-Z within the rempemmformåaa (400 m1 600°C).

The electrolyte-free fuel cell technology can offer an extremely low-cost FC technology with a large market potential. There is a great potential for further development with a person skilled in the art. The key lies in optimizing materials, mixtures, synthesis and manufacturing technologies by using ceramic membrane technologies. 535 245 Brief description of the drawing and figures Some typical FC performances with a single or two-component design are shown in the figures and are also listed in Table 2 below.

Figure 1. A conventional fast-cell FC (left) with three components (including cathode, electrolyte and anode). On the right, FCs without electrolytes.

Figure 2 illustrates typical characteristics; I-V (current density-volt) and I-P (power density) for a single-component FC device with different material compositions: a) and b). b) refers to commercial GDC and SDC as ion-conducting materials, mixed metal oxides, of Ni-Cu-Zn oxide as the electronic one; c) LCP-LiNiCu oxide; d) SDC-LiNaCO3 composite-LiNiCu oxide; e) Na2CO3-SDC nanocomposite-LiCuZnNi oxide.

Fuel: H2, Oxidant: air. Gas flow: 80 to 120 ml/min, gas pressure: I atm; Cell size: 13 mm in diameter with an active area of 0.7 cm2.

Figure 3 shows increased performance by improving the catalytic function of the metal oxide in the LiCuZnNi-Fe oxide and the Na2CO3-SDC ion conductor of the nanocomposite.

Fuel: H; Oxidant: air. Gas flow: 80 to 120 ml/min, gas pressure: 1 atm; Cell size: 13 mm in diameter with an active area of 0.7 cm2.

Figure 4 shows the I-V/I-P characteristics of a two-component FC without electrolyte. a, b and c are at 480, 520 and 560°C, respectively.

Fuel: H; Oxidant: air. Gas flow: 150 to 200 ml/min, gas pressure: 1 atm; Cell size: 20 mm in diameter with an active area of 2.1 cm2.

Figure 5 shows the I-V/I-P characteristic of the best FC by improving both the ionic and electronic conduction properties. a, b and c are at 480, 500 and 520°C, respectively.

Fuel: H; Oxidant: air. Gas flow: 80 to l20 ml/min, gas pressure: l atm; Cell size: 13 mm in diameter with an active area of 0.7 cm2. 535 245 Figure 6 shows the l-V/l-P characteristics of F Cn with membranes manufactured by slurry casting process and hot-pressing at 550°C.

Fuel: H2_ Oxidant: air. Gas flow: 1000 to 2000 ml/min, gas pressure: 1 atm; Cell size: 6 x 6 cm2 diameter with an active area of 25 cm2.

Detailed description of the intended embodiment Materials and preparations The ion conducting materials: i) iii) SDC (cerium doped with samarium), GDC (cerium doped with gadolinium) and YSZ (yttrium stabilized zirconia) oxygen ion conductors were purchased from (Seattle Specialty Ceramics, Seattle, WA, USA).

Nanostructured SDC-NagCQ-n i.e. nanocomposite electrolytes were synthesized in a co-filling process. In synthesizing the erium carbonate composites, the following chemicals were used in 1.0 M solutions, Ce (NO;)3'6H2O (Sigma-Aldrich) and Sm (NO3);'6H2O (Sigma-Aldrich). According to the desired molar ratios, the solution of Sm (NO;)3'6H2O was mixed with a solution of Ce (NO3);'6H2O. Regarding the "metal ion":Carbonate ion 1:2 in molar ratio, a substantial amount of Na2CO3 solution (1.0 M) was added slowly (10 ml/min) to completely fabricate the cerium carbonate composites by a wet chemical precipitation process. In the same process, a mixture of SDC and carbonates was prepared. After this process, the mixture was filtered by the "suction filtration method". The precipitate was dried overnight in an oven at 50°C. Finally, the dried solid was crushed in a mortar and sintered at 800°C for one hour.

The LCP was purchased from Baotou rare-earth plant, Inner Mongolia, China, a world-renowned rare-earth producer. Table 1 lists the content of the LCP after heat treatment at 800°C for 2 hours. By directly heat treating the LCP at this temperature, the resulting materials created rare-earth oxides in a 535,245 mixture/composite with the main components consisting of CeO2, LaO2 and several percent Pr2O3, see Table 1. These LCPs were used as electrolytes for SOFCs. The LCPs can be further modified by adding other alkaline or alkaline-earth carbonates, e.g., MXCO2 (M = Li, Na, K, Ca, Sr, Ba, x = 1, 2). During the heat treatment, parts of CeO2 and MXCO2 can form some form of ion-doped cerium, MxCenxO2, the resulting materials even became better SOFC electrolytes.

Table I Composition of an industrial LCP product after 2 hours of heat treatment at 800°C LCP TREO LagOg CeOg PrOOn NdgOg Sm-2O3 Y2O3 Re2(C03) 3 43.25 36.55 57.69 5.59 0.18 < 0.01 < 0.04 Electronically conductive materials: The electronically conductive metal oxide mixtures were prepared by conventional solid state reaction methods. Stoichiometric amounts of Li2CO3, NiCO; . 2Ni (OH) 2- 61-120 (Sigma Aldrich, USA) and Zn (l\I03)2-6H2O (Sigma Aldrich, USA) and CuCOg (99.99%, Aldrich) were mixed, ground and sintered at 700-800 °C for 3 hours.

BSCFn (Ba0.2SrCo0.4Fe0.60x) was synthesized in a coprecipitation process. The following chemicals were used for 1.0 M solutions, Ba (N 03); (Sigma-Aldrich), Sr(NO3)2, Co(N03)s'6H2O (Sigma-Aldrich) and Fe(NO;);' 9H2O. To achieve the desired molar ratios, all these nitrates were mixed to prepare in 1.0 M solution. "Metal ions and carbonate ions in the appropriate molar ratio to make a complete precipitation of Ba, Sr, Co and Fe as carbonates, a considerable amount of Na2CO3 solution (1.0 M) was added slowly (10 ml/min) to complete the coprecipitation process. After this, the precipitate was filtered and dried overnight in an oven at 50°C. Finally, the dried solid was sintered at 800°C for 12 hours.

Preparation of the FC component without electrolyte and FC structures 535 245 The resulting above-described electronically conductive materials were mixed with above-described ionic conductors in the weight ratio of 1:3 and 3:1.

The resulting powder was uniaxially pressed into pellets in one step with a 300MPa pressure to form a tablet of the one-component, both surfaces of which were coated with silver as a current collector. Its size was usually 13 mm or 20 mm in diameter and 0.60-1.0 mm thick. The larger, 6x6 cm2 one-component FCs were constructed by hot pressing technique with 600°C heat and 10-20 tons pressure to shape the materials. Silver-coated metal mesh was used on both sides as current collectors.

Fuel cell measurements Cell performance was tested by computerized instruments (L43, Tianjin, China) at temperatures of 400-600°C where the hydrogen and air were at 80-110 ml min* at 1 atm pressure on both sides for the 13 mm cells and 1-2 liters min-1 for the 6x6 cm2 cells.

Example 1: 1 g of commercial GDC was mixed with 1 g of Li0.1Ni0.5Zn0.4 oxide.

The mixture was pressed at 200 kgs pressure in a 13 mms mold to create pellets with 0.6-0.8 mm thickness. The FC performance is shown in Figure 2a.

Example 2: 1 g of commercial SDC was mixed with 1 g of Li0.1Ni0.5Zn0.4 oxide. The mixture was further heated at 700°C for 2 hours and pressed with 200 kgs pressure in a 13 mm mold to create pellets with 0.6-0.8 mm thickness, see Figure 2b.

Example 3: 10 g of LCP was mixed with sodium carbonate in a weight ratio of 20:1 to 4:1 followed by adding 0.5-1.0 g of NiCO3 . 2Ni (OH)2- 6H2O , Zn (NO;)2-6H2O, CuCO3 0.5-1.0 g of Fe(NO3)9H2O, and 0.5-1.0 g of LiNO3 mixed thoroughly. The mixture was heated at 720°C for 2 hours. The resulting material was then pressed with 200 kgs pressure in a 13 mms mold to create pellets with 0.6-0.8 mm thickness, Figure 2c. 535 245 10 Example 4: 10 g of SDC-NaCO3 nanocomposites as ion conductors were mixed with Li0.1Cu0.4Zn0.5 oxide produced in the above synthesis. The mixture was sintered at 700°C for 2 hours and then pressed with 200 kgs pressure in a 13 mms mold to create pellets with 0.6-0.8 mm thickness, Figure 2d.

Example 5: 10 g was mixed with 5 g of Li0.2Ni0.3Cu0.2Zn0.3 oxide. The mixture was further heated at 700C for 2 hours and then pressed with 200 kgs pressure in a 13 mms mold to create pellets with 0.6-0.8 mm thickness, Figure 2e.

Example 6: For improved catalytic function of the metal oxide catalyst, Fe was added. 1.2g Na2CO3-SDC -0.6g LiNiCuZn oxide was further mixed with 0.6g Fe(NO3)9H2O and mixed thoroughly. The mixture was heated at 720°C for 2 hours. The resulting material was then pressed with 200 kgs pressure in a 13 mms mold to create pellets with 0.6-0.8 mm thickness. The FC performance is shown in Figure 2, effect of catalyst function by adding Fe elements 3b) compared to non-Fc, 3a).

Example 7: To construct two-component FCn without electrolyte. One component was made using a Li0.2Ni0.3Cu0.2Zn0.30x -SDC blend and another using a BSCF-SDC blend. The powder blends were pressed in a two-layer configuration with 300 kgs of pressure in a 20 mm mold to create pellets with 0.6-0.8 mm thickness. The FC performance is shown in Figure 4.

Example 8: The best single-component FC performance of this invention was improved by carefully matching the parts between the ionic and electronic conduction modes using the samples from Example 6. The weight ratio of 1:1.5 between the Na2CO3-SDC and the LtNiCulnFe oxide was used. The FC performance shown in Figure 5. a, b, c and d are at 480, 500, 520 and 540°C respectively. 535 245 ll Example 9: The single-component was made by using the best composition of Example 8 which was further processed by slurry casting process to produce membranes and followed by hot pressing at 550°C and 20 tons pressure. The final I-V/I-P characteristics of the FC are shown in Figure 6.

More examples are listed in Table 2, with indications of their corresponding ITSOFC performance.

Those skilled in the art will appreciate that the above examples are for illustrative purposes only and are not intended to be limiting of the present invention. 535 245 Table 2. More examples of one-component materials Ionic conductive Electronic conductive material FC Temperature performance material (mwcmq) (°C) i) LiNi0.6Cu0.40x 200-600 450 - 600 LCP oxides ii) LiCu0.4Zn0.60x 200-500 450-600 iii) LaM03 (M=Ni, Cu, Co, Mn) 150-400 400-650 The weight ratios between the electronic 300-1000 conductor and the LCP are 1:1 400-650 Ionic doped 200-700 500-700 M,.Ce1-,.O2 iv) LiNi0.6Cu0.40x Dopant M < 20 mol%* and v) BSCF 120-540 500-700 = ef, SF, Gas* smsi v" ** BCY vi) LiNi0.6Cu0.40x 220-880 450 - 700 240-800 450-700 Note to table 2: * mol% means molar ratio, wt% is weight ratio References cited US patent 5298235, Worrell et al, 1994 Electrochemical devices based on single-component solid oxide fuel bodies 535 245 US patent, 20090258276, Kenneth Ejike Okoye Emenike Chinedozi Ejiogu Sachio Matsui, 2009 Fuel cell unit, fuel cell unit array, fuel cell module and fuel cell system Other publications 1.

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Claims (10)

1. A fuel cell comprising a porous body having a first side arranged to be incontact with H2 and a second side arranged to be in contact with air (02), andmeans for collecting current at said first and second side, wherein the bodycomprises one or two components for catalyzing dissociation of H2 and 02and comprising at least one ionic conducting material and at least one electron conducting material.

2. A fuel cell according to claim 1, wherein the component or components area composite of at least one ionic conducting material and at least one electron conducting material.

3. A fuel cell according to claim 1 or 2, wherein the component or componentsare a mixture of at least one ionic conducting material and at least one electron conducting material.

4. A fuel cell according to any previous claim, wherein at least one ionic conducting material is a proton or oxygen ion conducting material.

5. A fuel cell according to claim 4, wherein the at least one ionic conductingmaterial is selected from - doped Ba(Ce,Zr)O3 ceramics, - ion doped ceria, such as SDC (samarium doped ceria) GDC,(gadolinium doped ceria) yttrium doped ceria, calcium doped ceria, Sm-Pr orGd-Pr doped ceria, - mixed rare-earth oxides, such as LCP, -YSZ (yttrium stabilized zirconia), ScSZ (Scandia stabilized zirconia), - LaGaMgOg,

6. 26. A fuel cell according to any previous claim, wherein at least one electron conducting material is a metal oxide, such as oxides of Li, Na, K, Cu, Ni, Zn, Mg, Ag, Fe, Sn, Al, Co, Mn, Mo, Cr, ln, Ca, Ba, Sr and their complex oxides.

7. A fuel cell according to claim 6, wherein the at least one electron conducting material further comprises Fe.

8. A fuel cell according to any previous claim, wherein the weight ratiobetween the at least one electron conducting material and the at least oneionic conducting material is between 1:3 and 3:1.

9. A fuel cell according to any one of claims 1, wherein the at least one ionicconducting material and the at least one electron conducting material is the one and the same material.

10. A fuel cell according to claim 9, wherein the material is -proveskite oxides of Ba05Sr0_5-Co0_8Fe0_2O32d (BSCF),(Ba/Sr/Ca/La)O.6MxNb1-xO3-ö in which M is selected from Mg, Ni, Mn, Cr,Fe, ln and Sn, or -doped LaMO3 in which M =(Ni, Cu, Co, Mn), such as LaNiozFeoßscUotsøs -