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1. WO2012018297 - PILE À COMBUSTIBLE

Note: Texte fondé sur des processus automatiques de reconnaissance optique de caractères. Seule la version PDF a une valeur juridique

[ EN ]

FUEL CELL

Technical Field of the Invention

The present invention relates to the field of fuel cells and the production thereof.

Background Art

A fuel cell is a device that converts chemical energy of a fuel and an oxidant (air or oxygen) into electricity. Fuel cell construction generally consists of a fuel electrode (anode) and an oxidant electrode (cathode) separated by an ion-conducting electrolyte membrane. Oxygen passes over one electrode, and hydrogen over the other, generating electricity, water and sometimes heat. At the anode, hydrogen and its electrons are separated so that the hydrogen ions (protons) pass through the electrolyte while the electrons are directed through an external electrical circuit as Direct Current (DC). This current can power useful devices. The hydrogen ions combine with the oxygen at the cathode and are recombined with the electrons to form water.

Conventional fuel cell technologies usually requires three functional components, a porous anode, a dense and gas-tight electrolyte and a porous cathode, which forms a Membrane Electrode Assembly (MEA). The

electrolyte should offer electronic insulation but be fully ionic permeable, e.g. for O2- or H+, to separate fuel and oxidant completely. Existing MEA

technologies all request detailed constructions with complete compatibility between the components both mechanically (e.g. in terms of thermal expansion etc.) and electrochemically. Especially the electrolyte ion transport capability, conductivity and density are key issues that put high demand on the fuel cell construction.

Therefore, several different types of fuel cells have been developed based on different types of electrolytes, such as PEMFC (polymer electrolyte membrane fuel cell), AFC (alkaline fuel cell), PAFC (phosphoric acid fuel cell), MCFC (molten carbonate fuel cell), and SOFC (solid oxide fuel cell). The electrolyte type and its electrical properties determines the type of fuel cell technology utilized as well as the final energy system that can be used. It also determines the energy conversion efficiency rate that can be realized at certain temperatures. As an example, a temperature of 1000 °C is typically needed for the most used SOFC electrolyte YSZ (yttrium stabilized zirconia) in order to obtain sufficient high ionic conductivity. This has historically seriously constrained the choice of construction materials which has resulted in high costs for a commercialization.

A type of fuel cell is disclosed in the article by Riess, I. Solid state ionics, 52 (1992) 127-134, in which the electrolyte is replaced by MIEC (mixed ion and electronic conductor). The device is based on an

anode/electrolyte/cathode configuration, in which MIEC is used to replace the conventional electrolyte and has the function of an electrolyte. Thus, a single phase based on bulk conducting mechanisms was used. However, such as device has some electronic short circuit problems, as seen the article

To summarize, there is a need in the art for fuel cells with improved properties.

Summary of the Invention

It is an object/aim of the present invention to provide an improvement of the fuel cells of the prior art.

As a first aspect of the invention, there is provided a fuel cell comprising a conducting body with a first and a second end surface for collecting currents, wherein said body comprises a composite material comprising:

- at least one semiconducting metal oxide of n and/or p type, and

- at least one ionic conducting material.

As a second aspect of the invention , there is provided a method for producing a composite material mixture for a fuel cell comprising the steps of a) providing at least one semiconducting metal oxide of n and/or p type and at least one ionic conducting material in a mixture;

b) heating said mixture to provide said composite material.

As a third aspect of the invention, there is provided a composite material obtainable according to the second aspect.

As a fourth aspect of the invention, there is provided a method for producing a fuel cell comprising the steps of

a) providing a composite powder comprising at least one semiconducting metal oxide of n and/or p type and at least one ionic conducting material; b) pressing said composite powder to form a tablet; and

c) pasting the end surfaces of the tablet with silver (Ag) and/or nickel (Ni)-foam to form current collecting end surfaces.

As a fifth aspect of the invention, there is provided the use of a composite material comprising at least one semiconducting metal oxide of n and/or p type and at least one ionic conducting material in a fuel cell.

As a sixth aspect of the invention, there is provided the use of a composite material comprising at least one semiconducting metal oxide of n and/or p type and at least one ionic conducting material together with a composite material comprising a BSCF and a SDC in a fuel cell.

Detailed description of the Invention

As a first aspect of the invention, there is provided a fuel cell comprising a conducting body with a first and a second end surface for collecting currents, wherein said body comprises at least one composite material comprising:

- at least one semiconducting metal oxide of n and/or p type, and

- at least one ionic conducting material.

A "fuel cell" refers to an electrochemical cell with the ability to convert chemical energy from a fuel into electric energy.

A "conducting body" refers to a body in which protons and/or electrons may pass. The conducting body has at least two end surfaces for collecting currents.

A "composite material" refers to a material made from two or more constituent materials with different physical or chemical properties which remain separate and distinct at the macroscopic or microscopic scale within the finished structure. Thus, the composite material comprises more than one phase, i.e. more than one region having the same composition and structure

throughout, and is separated from the rest of the material by a distinct interface. The phase may contain one or more components.

The conducting body may comprise more than one composite material, such as two composite materials (a duel component).

A "semiconducting metal oxide of n type" refers to a semiconducting metal oxide having an excess of negative (n-type) electron charge carriers.

A "semiconducting metal oxide of p type" refers to a semiconducting metal oxide having an excess of positive (p-type) charge carriers.

The first aspect of the invention is based on the insight that a fuel cell with a conducting body comprising a composite, which comprises at least one semiconducting metal oxide of n and/or p type and at least one ionic conducting material, has excellent properties. Without being bound to any theory, it is believed that the fuel interfaces between the phases of the composite material facilitates important key functions of the fuel cell, such as conductivity, charge and phase separation between electrons and ions.

Compared to conventional fuel cell, the fuel cell of the present invention has advantages, especially regarding chemical stability, mechanical property and compatibility. This means that the electrolyte problems with compatibility between the anode-electrolyte and electrolyte-cathode are in principal avoided. The fuel cell of the present invention has demonstrated

extraordinary performances between 200 and 1000 mWcm-2 under 300-3000 mAcm-2 in the region 400 to 600°C. Further, the fuel cell of the present disclosure provides may be produced at relatively low cost and has thus a great market potential.

In an embodiment of the first aspect of the invention, at least one semiconducting metal oxide comprises at least one transition metal.

As a further example, the metal oxide may be an oxide of any one of Li, Na, K, Cu, Ni, Zn, Mg, Ag, Fe, Sn, Al, Co, Mn, Mo, Cr, In, Ca, Ba, Sr, 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 system, e.g. Fe-oxide system, such as undoped BiFeO3, single doped BiFeO3 (e.g.

Bi0.9Ba0.1 FeO3, BiFe0.9Mn0.1O3, Bi0.9Ca0.1 FeO3, BiFe0.9Cr0.1O3 etc.) and double doped BiFeO3 (e.g. Bi0.9Ba0.1 Fe 0.9Mn 0.1O 3, Bi 0.9Ca 0.1Fe0.9Cr0.1O3), Zn-oxide system with both n- and p-type ZnO. As n-type dopants, Al, Ga, and In may be used as substitutional elements for Zn, and CI and I may be used as substitutional element for O. p-type ZnO include Li, Na, and K, Cu, Ag, and N, P, As.

In an embodiment of the first aspect, the least one semiconducting metal oxide comprises Li, Ni, Cu, Fe, Zn and/or Co.

As an example, the at least one semiconducting material may comprise LiNiCuZn oxide.

As an example, the at least one semiconducting metal oxide comprises LiNiO2, LiCoO2, LiCoFeOx and/or other oxides of LiNi and/or LiCoFe.

In an embodiment of the first aspect, the at least one semiconducting metal oxide comprises Li:Ni:Zn in molar ratios of about 1 :4:5 or 2:4:4.

These molar ratios have been found to give rise to fuel cells having excellent properties.

As a further example, the least one semiconducting metal oxide comprises molar ratios of Li : Ni of about 5:5, Li:Co of about 5:5 and/or

Li:Co:Fe of about 3:2:5.

In an embodiment of the first aspect, the ionic conducting material comprises ionic doped ceria.

As an example, the ionic doped ceria may be described by MxCe1-xO2, wherein M is a dopant. The dopant may be selected from Ca2+, Sr2+, Gd3+, Sm3+ and Y3+. Further, the molar ratio of M to Ce1-xO2 may be equal to or below 20%.

In an embodiment of the first aspect, the ionic conducting material may comprise Y2O3-doped BaCeO3 (BCY).

Furthermore, the ion doped ceria may for example be ion doped ceria, such as SDC: samarium doped ceria; GDC: gadolinium doped ceria; yttrium doped ceria; calcium doped ceria and Sm-Pr or Gd-Pr doped ceria.

As an example, the ionic doped ceria may comprise Gd3+ or Sm3+ doped ceria and/or their nanocomposites.

In the context of the present disclosure, Sm3+ doped ceria is referred to as SDC.

The SDC may be NSDC (Samarium doped ceria with Na2CO3).

As an example, the ionic doped ceha may comprise nanocomposites of

Ce0.8Sm0.2O2-δ.

As a further example, the ionic doped ceria may comprise Na2CO3- Ce0.8Sm0.2O2-δ.

In embodiments of the first aspect, the ionic conducting materials are proton or oxygen ion conducting materials, such as doped Ba(Ce,Zr)O3 ceramics mixed rare-earth oxides, praseodymium in a mixture with lanthanum and cerium (commonly known as "LCP"), Yttria-stabilized zirconia (YSZ), Scandia-stabilized zirconia (ScSZ), or LaGaMgO3.

In an embodiment of the first aspect ionic conducting material comprises praseodymium in a mixture with lanthanum and cerium (LCP).

LCP may for example be made from minerals monazite or bastnasite (or bastnaesite). A type of LCP is what remains of such mixtures, after neodymium and all the heavier, rarer lanthanides have been removed, e.g. by solvent extraction.

LCP could for example comprise one or several of La2O3, CeO2, Pr6O11, Nd2O3, Sm2O3, and Y2O3.

Further, if the ionic conducting material comprises LCP, it may also comprise at least one alkaline or alkaline earth carbonate.

As an example, the at least one alkaline or alkaline earth carbonate is MxCO3, wherein M is Li, Na, K, Ca, Sr or Ba and x is 1 or 2. Some of the CeO2 in the LCP and the MxCO3 may form, e.g. during heat treatment, a kind of ionic doped ceria such as MxCe1-xO2, which may further increase the performance of the fuel cell.

In an embodiment of the first aspect, the said body comprises a second composite material comprising barium copper sulphur fluoride (BCSF) and SDC.

BCSF may for example be bulk barium copper sulphur fluoride.

As an example, the BCSF may be Ba0.6Sr0.4Co0.85Fe0.15.

As a further example, SDC may be Ce0.8Sm0.2O2-δ.

In a further embodiment of the first aspect, the at least one

semiconducting metal oxide of n and/or p type and at least one ionic conducting material is one and the same material. As an example, such a material could be based on proveskite oxides such as Ba0.5Sr0.5-Co0.8Fe0.2O 32d(a BSCF), (Ba/Sr/Ca/La)0.6MxNb1-xO3-δ ( in which M is Mg, Ni, Mn, Cr, Fe, In, Sn), doped LaMO3 (M= Ni, Cu, Co, Mn), e.g. LaNi0.2Fe0.65Cu0.15O3 .

In an embodiment of the first aspect of the invention, the weight ratio of the at least one semiconducting metal oxide to the at least one ionic conducting material is between about 80:20 and 20:80, such as about 40:60.

In an embodiment, the weight ratio of the at least one semiconducting metal oxide to the at least one ionic conducting material is between about 1 :3 and 3:1 .

The inventor has found that a weight ratio of the at least one

semiconducting metal oxide to the at least one ionic conducting material that is in between the specified ranges, such as between about 80:20 and 20:80, such as between about 70:30 and 30:70, such as about between about 35:65 and 45:55, such as about 40:60, provides for a fuel cells with almost no electronic short circuit effects. This is further seen in Example 4 of the present disclosure.

In embodiments of the first aspect, the ionic conducting material comprises NSDC (Samarium doped ceria with Na2CO3).

In embodiments of the first aspect, the conducting body comprises a mixture of LiNiCuZn oxide and NSDC (Samarium doped ceria with Na2CO3). Such as fuel cell has shown to give a performance (mWcm-2) of 300-1000 at the temperature of 400-650°C.

In a further embodiment, the conducting body comprises LiNiCuZnSrO.

In an embodiment of the first aspect, the conducting body further comprises a redox catalyst.

The inventor has found that the incorporation of a redox catalyst in the conducting body further enhances the performance of the fuel cell, as seen in Example 3 of the present disclosure. As an Example, the redox catalyst may comprise Fe. For example, Fe (NO3)3 may be used, e.g. during preparation of the conducting body.

In an embodiment of the first aspect, the composite material is porous.

A certain porous structure throughout the composite material may be an advantage for practical device demands since any fuel cell devices in

practical uses need to ensure that a self temperature is maintained to keep the device operation at hundreds of degrees. To meet this request, extra fuel is usually required to heat the device externally. In conventional fuel cells, it may cause an inhomogeneous temperature distribution over the fuel cell device or stack, which may lead to thermal problems or failures. However, with a porous structure, heat may be supplied more homogenously throughout a fuel cell. The means for keeping the self device temperature and the electricity production can be well realized within one device.

As an example, the porosity of the composite material may be about 30-40 %.

In an embodiment of the first aspect, the first end surface for collecting current is arranged to be in contact with oxygen (O) and said second end surface for collecting current is arranged to be in contact with hydrogen (H2).

If the fuel cell of the present disclosure is situated in H2 and air, both H2 and O2 may be catalytic dissociated into H+ and O2- and generate electricity due to bi-catalyst functions of the component. H+ and O2- combine together on a particle surface and produce H2O. During this process, the H2 contacting side acts as an anode to release electrons by forming H+, and the air (O2) contacting side as a cathode to receive electrons and fuel cell reaction is completed as long as H+ and O2- are available. In the fuel cell of the present invention, the ionic transportation in the electrolyte in a conventional fuel cell may thus be replaced by surface ionization, movement and reaction in an "electrolyte-free" fuel cell reactor. Consequently, the fuel cell of the present disclosure does not require ion (H+ or O2-) transport through a conventional electrolyte.

In an embodiment of the first aspect, the first and/or second end surface for collecting current comprises silver (Ag) or nickel (Ni)-foam.

As an example, the first end surface may comprise silver and the other end surface may comprise Ni-foam. As another example, both end surface may comprise silver.

In embodiments of the first aspect, the conducting body comprises a composite material mixture according to the second aspect of the invention described below.

As a second aspect of the invention, there is provided a method for producing a composite material mixture for a fuel cell, comprising the steps a) providing at least one semiconducting metal oxide of n and/or p type and at least one ionic conducting material in a mixture;

b) heating said mixture to provide said composite material

The inventor has found that a composite material mixture produced according to the second aspect of the invention may work as an excellent conducting body for fuel cells. The composite material mixture produced according to the second aspect is thus suitable to use in fuel cells, i.e. it provides an intermediate material mixture in the production of a fuel cell.

In an embodiment of the second aspect, the step of heating is performed at a temperature between 600-800 °C, such as about 700 °C.

Such temperatures are advantageous as they facilitate formation of a composite mixture.

In embodiments of the second aspect, the at least one semiconducting metal oxide of n and/or p type and/or the at least one ionic conducting material is as described in the first aspect above.

As an example, the ionic conducting material may comprise

praseodymium in a mixture with lanthanum and cerium (LCP) and step a) further comprises addition of at least one alkaline or alkaline earth carbonate to the mixture.

During the heat treatment of step b), some of the CeO2 in the LCP and the MxCO3 may form, a kind of ionic doped ceria such as MxCe1-xO2, which may further increase the performance of the fuel cell.

As an example, the at least one alkaline or alkaline earth carbonate may be MxCO3, wherein M is Li, Na, K, Ca, Sr or Ba and x is 1 or 2.

In a further embodiment of the second aspect, step a) further comprises adding at least one redox catalyst to said mixture.

The redox catalyst may for example comprise Fe. As an example, Fe (NO3)3·6H2O, e.g. in a 5-10 wt% solution, may be added to the mixture of the at least one semiconducting metal oxide of n and p type and at least one ionic conducting material.

In an embodiment of the second aspect, step a) further comprises adding a composite comprising BCSF or SDC.

In an embodiment of the second aspect, the BCSF is

Ba0.6Sr0.4Co0.85Fe0.15

In an embodiment of the second aspect the SDC is Ce0.8Sm0.2O2-δ.

In an embodiment of the second aspect, the composite material is in powder form.

In an embodiment of the second aspect, the composite material is porous. As an example the pore size may be between x and y.

A powder is suitable for a following production of a fuel cell from the composite material.

As a third aspect of the invention, there is provided a composite material obtainable according to the second aspect.

As a fourth aspect of the invention, there is provided a method for producing a fuel cell comprising the steps of

a) providing a composite powder comprising at least one semiconducting metal oxide of n and/or p type and at least one ionic conducting material; b) pressing said composite powder to form a tablet; and

c) pasting the end surfaces of the tablet with silver (Ag) and/or nickel (Ni)-foam to form current collecting end surfaces.

In an embodiment of the fourth aspect, step b) comprises pressing said composite powder uniaxially with a load of about 100-300 MPa.

In an embodiment of the fourth aspect, the composite powder of step a) has been prepared according to the second aspect above.

In embodiments of the fourth aspect, the at least one semiconducting metal oxide of n and p type and/or the at least one ionic conducting material is as disclosed in relation to any embodiment of the first aspect above.

As a fifth aspect of the invention, there is provided the use of at least one composite material comprising at least one semiconducting metal oxide of n and/or p type and at least one ionic conducting material in a fuel cell.

As a sixth aspect of the invention, there is provided the use of at least one composite material comprising at least one semiconducting metal oxide of n

and/or p type and at least one ionic conducting material together with a composite material comprising a BSCF and a SDC in a fuel cell.

In an embodiment of the sixth aspect, the BSCF is Ba0.6Sr0.4Co0.85Fe0. 15. In an embodiment of the sixth aspect, the SDC is Ce0.8Sm0.2O2-δ.

Brief description of the drawings

Figure 1 shows a general outline of a fuel cell according to the present invention.

Figure 2 shows a I-V (current density-voltage) and I-P (power density) characteristics for the fuel cells as described in Examples 2a-2e below. The data from the experiments are represented by a-e in the Figure, in which a) and b) concern commercial GDC and SDC as ionic conducting materials, mixed metal oxides of the Ni-Cu-Zn-oxide as electronic one; c) LCP-LiNiCu-oxide; d) SDC-LiNaCO3 composite- LiNiCu-oxide; e) Na2CO3-SDC

nanocomposite- LiCuZnNi-oxide.

Figure 3 displays an improvement in the catalyst function due to addition of metal oxides. LiCuZnNi-Fe-oxide and a nanocomposite Na2CO3-SDC ion conductor was used. Fuel H2, oxidant: air, gas flow: 80 to 120 ml/min, gas pressure: 1 atm; Cell size: 13 mm in diameter with active area 0.7 cm2.

Figure 4 shows the I-V/I-P characteristics for a fuel cell produced according to Example 2g. The data sets of a), b) and c) are at 480, 520 and 560°C, respectively. Fuel H2, oxidant: air, gas flow: 150 to 200 ml/min, gas pressure: 1 atm; Cell size: 20 mm in diameter with active area 2.1 cm2.

Figure 5 shows I-V/I-P characteristics of the fuel cells produced according to Example 2h. The data sets of a), b) and c) are at 480, 500 and 520°C, respectively. Fuel H2, oxidant: air, gas flow: 80 to 120 ml/min, gas pressure: 1 atm; Cell size: 13 mm in diameter with active area 0.7 cm2

Figure 6 shows I-V/I-P characteristics of the fuel cell with the membrane prepared from a slurry casting process according to Example 2i. Fuel H2, oxidant: air, gas flow: 1000 -2000 ml/min, gas pressure: 1 atm. Cell size: 6x 6 cm2 in diameter with active area 25 cm2.

Figure 7 shows the XRD pattern for the synthesised LiNiZn-oxide and NSDC materials according to Example 3 of the present disclosure.

Figure 8 shows the result from SEM-analysis of the composite material as produced in Example 3 of the present disclosure.

Figure 9 shows I-V and I-P characteristics for material produced in

Example 3 of the present disclosure. For comparison, the performance of a conventional NSDC electrolyte-based three-component fuel cell is shown in the same figure.

Figure 10 displays the performance of the fuel cell from Example 3 operated at different temperatures; 400, 450, 500, and 550 °C, respectively.

Figure 1 1 shows further displays the performance of the fuel cell of Example 3 after addition of a redox catalyst Fe element.

Figure 12 shows OCV changes from Example 3.

Figure 13 shows impedance data from Example 3.

Figure 14 (missing) shows I-V and I-P characteristics from Example 4 using single-component at 550°C. (a) and (b) represent data for single component fuel cells of the present disclosure. (A) and (B) represent data for conventional MEA fuel cells.

Figure 15 (missing) shows I-V and I-P characteristics using dual component(s) at 550°C. (a) and (b) represent data fuel cells of the present disclosure. (A) and (B) represent data for conventional MEA fuel cells.

Figure 16 (missing) shows SEM (a) and TEM (b) pictures for the material used for the conducting body in Example 4.

Figure 17 (missing) shows the calculation in Example 4 on efficiency for the fuel cells of the present disclosure (denoted "Electrolyte free SOFC") as compared to the conventional MEA fuel cells (denoted SOFC).

Figure 18 shows Electrochemical impedance spectra results for the complex LiCoFe-SDC and LiNi-SDC mixture in various compositions at 550°C, respectively in H2 and air, where the EIS slightly shifting to higher values in Z-real axis correspond to the air; (a), (b), (c) and (d) contain ionic conducting phase, NKSDC from 0, 30, 60, 70 wt%, respectively.

Examples

The following non-limiting examples will further illustrate the present invention

Example 1 - General description of a fuel cell

A fuel cell according to an embodiment of the present invention is seen in Fig. 1 b and Fig. 1 c, as compared to a conventional fuel cell shown in Fig. 1 a. A fuel cell of the present invention comprises a conducting body comprising composite material comprising at least one semiconducting metal oxide of n and/or p type, and at least one ionic conducting material (Fig. 1 b). The conducting body comprises a first and a second end surface for collecting currents. One end surface is arranged to be in contact with oxygen (O) and a second end surface for collecting current is arranged to be in contact with hydrogen (H2).The conducting body of a fuel cell of the present disclosure may comprise second composite material, as shown in Fig. 1 c. Then, only the outermost end surfaces are arranged to be in contact with oxygen and H2, respectively, as seen in Fig. 1 c.

In the fuel cells of the present disclosure, most reactions and processes are thought to be completed on sites of the particles' surfaces through a direct combination between H+ and O2- ions.

Without being bound to any specific theory and without limiting the scope of protection, it is proposed that the reaction for the fuel cell processes are as described below:

at H2 side:

at air (O2) side:

overall reactions:


Example 2 - Experimental examples

Materials and preparations

Ionic conducting materials:

i) SDC (samarium doped ceria), GDC (Gadolinium doped ceria) and YSZ

(yttrium stabilized zirconia) oxygen ion conductors were from Seattle

Specialty Ceramics (Seattle, WA, USA).

ii) Nanostructure SDC-Na2CO3, i.e. nanocomposite electrolyte, was

synthesized by a co-precipitation process. In the synthesis of the ceria-carbonate composites, the following chemicals were used for 1 .0

M solutions: Ce(NO3)3·6H2O (Sigma-Aldrich) and Sm(NO3)3·6H2O (Sigma-Aldrich). The solution of Sm(NO3)3·6H2O was mixed with the solution of Ce (NO3)3·6H2O to desired molar ratios. To achieve a molar ratio of metal ion:carbonate ion 1 :2, a pertinent amount of Na2CO3 solution (1 .0 M) was added slowly (10 ml/min) to complete the ceria- carbonate composites wet chemical co-precipitation process. A mixture of SDC and carbonates was also used in the same process. After this process the mixture was filtered by suction filtration method. The precipitate was dried over night in the oven at 50°C. Finally, the dried solid was crushed in a mortar and sintered at 800°C for 2 h.

iii) LCP was purchased from Baotou rare-earth plant, Inner Mongolia, China. Table 1 below lists the contents of the LCP after heat-treatment at 800°C for 2 hours. By direct heat-treatment of the LCP at this temperature, the resulting materials formed rare-earth oxide

mixture/composite with major components of CeO2, La2O3, and several percent Pr6O11 (see Table 1 ). The LCP could further be modified by adding some other alkaline or alkaline earth carbonates, e.g. MxCO3 (M= Li, Na, K, Ca, Sr, Ba, x = 1 , 2). During the heat-treatment, a part of CeO2 in the LCP and MxCO3 may form a kind of ionic doped ceria, such as MxCe1 -xO2, which may further increase the performance of the fuel cell.

Electronic conducting materials:

The electronic conducting mixed metal oxide materials were prepared by standard solid state reaction methods. Stoichiometric amounts of Li2CO3, NiCO3. 2Ni (OH) 2 · 6H2O (Sigma Aldrich, USA) and Zn (NO3)2·6H2O (Sigma Aldrich, USA) and CuCO3 (99.99%, Aldrich) were mixed, grounded and sintered at 700-800 °C for 3 hours.

A BSCF (Ba0.2SrCo0.4Fe0.6Ox) was synthesized by a co-precipitation process. Following chemicals were used for 1 .0 M solutions: Ba (NO3)2 (Sigma- Aldrich), Sr(NO3)2, Co(NO3)3·6H2O (Sigma-Aldrich) and Fe(NO3)3· 9H2O. According to desired molar ratios, all these nitrates were mixed to prepare in 1 .0 M solution. Appropriate "metal ion: carbonate ion" molar ratios were used to make complete deposition of Ba, Sr, Co and Fe as carbonates and a pertinent amount of Na2CO3 solution (1 .0 M) was added slowly (10 ml/min) to complete the co-precipitation process. After this process the precipitate was filtered and dried over night in an oven at 50°C. Finally, the dried solid was sintered at 800°C for 2 h.

Preparation of fuel cells

The resulting above electronic conducting materials were further mixed with above ionic conductors in a weight ratio between 1 :3 and 3:1 .

The resulting powder was pressed uniaxially into pellets in one step with a 300MPa load to a tablet which formed the conducting body of the fuel cell. Both end surfaces of this body were pasted by silver as the current collectors. The size of the tablet was normally 13 mm or 20 mm in diameter and 0.60-1 .0 mm in thickness.

A conducting body with a large area, 6x6 cm2, was also constructed by hot-pressing technique with 600°C heating and 10-20 tons in pressure for shaping the materials. Silver coated metal nets were used on both sides on this conducting body as the current collectors.

Fuel Cell measurements

The cell performances were tested by a computerized instrument (L43, Tianjin, China) over the temperature 400-600 °C, where respective hydrogen and air were in the range of 80-120 ml min-1 at 1 atm pressure on each side for 13 mm cells with active area of 0.7 cm2, and 1 -2 litre min-1 for the 6x6 cm2 cells. The following experiments were performed:

Example 2a: 1 g commercial GDC was mixed with 1 g Li0.1Ni0.5Zn0.4-oxide. The mixture was pressed under 200 kg in a 13 mm die to form the pellet with 0.6-0.8 mm thickness. The fuel cell performance is shown in Figure 2, the data represented by a).

Example 2b: 1 g commercial SDC was mixed with 1 g Li0.1Ni0.5Zn0.4-oxide. The mixture was further heated at 700°C for 2 hours then pressed under 200 kg in a 13 mm die to form the pellet with 0.6-0.8 mm thickness. The fuel cell performance is shown in Figure 2, the data represented by b).

Example 2c: 10 g LCP was mixed with sodium carbonate in weight ratio from 20:1 to 4:1 followed by adding 0.5-1 .0 g of NiCO3 2Ni (OH) 2 · 6H2O , Zn (NO3)2·6H2O, CuCO3, 0.5-1 .0 g Fe(NO3)9H2O, and 0.5-1 .0 g LiNO3. The mixture was granted thoroughly. The mixture was heated at 720°C for 2 hours. The resulting material was then pressed under 200 kg in a 13 mm die to form the pellet with 0.6-0.8 mm thickness. The fuel cell performance is shown in Figure 2, the data represented by c).

Example 2d: 10 g SDC-NaCO3 nancomposites as ionic conductor mixed with Li0.1Cu0.4Zn0.5-oxide obtained by the synthesising procedure described above. The mixture was sintered at 700°C for 2 hours, then pressed under 200 kg in a 13 mm die to form the pellet with 0.6-0.8 mm thickness. The fuel cell performance is shown in Figure 2, the data represented by d).

Example 2e: 10 g mixed with 5 g Li0.2Ni0.3Cu0.2Zn0.3-oxide. The mixture was further heated at 700 °C for 2 hours then pressed under 200 kg in a 13 mm die to form the pellet with 0.6-0.8 mm thickness. The fuel cell

performance is shown in Figure 2, the data represented by e).

Example 2f: To further improve the catalyst function of the metal oxides catalyst, Fe was added: 1 .2 g Na2CO3-SDC -0.6 g LiNiCuZn-oxide was further mixed with 0.6 g Fe(NO3)9H2O and then granted completely. The mixture was heated at 720 °C for 2 hours. The resulting material was then pressed under 200 kg in a 13 mm die to form the pellet with 0.6-0.8 mm thickness. The fuel cell performance is shown Figure 3 and the effect of catalyst function by adding Fe elements is seen in the data represented by b) compared to the data represented by 3a), which originates from a fuel cell that does not comprise Fe.

Example 2g: A fuel cell with having a conducting body with two

components was constructed. One component was made by

Li0.2Ni0.3Cu0.2Zn0.3O x -SDC mixture and the other was a BSCF-SDC mixture. The powder mixtures were then pressed in two-layer configuration under 300 kg in a 20 mm die to form the pellet with 0.6-0.8 mm thickness. The fuel cell performance is shown in Figure 4. The data sets of a), b) and c) are at 480, 520 and 560°C, respectively.

Example 2h: The performance of fuel cell from Example 2f above was improved by carefully adjusting portions between the ionic and electronic conductivities. A 1 :1 .5 weight ratio between the Na2CO3-SDC and

LiNiCuZnFe-oxide was used. The fuel cell performances are shown in Figure 5. The data sets of a), b), c) and d) are at 480, 500, 520 and 540°C, respectively.

Example 2i: A fuel cell was made by using the composition in Example 2h which was further proceeded with a conventional slurry casting process to prepare a membrane, followed by a hot-pressing at 550°C and 20 ton pressure. The subjecting I-V/I-P characteristics of the fuel cell is shown in Figure 6.

Example 2j: Further examples of the performance of fuel cells according to the present invention are shown in Table 2 below.

Example 3. Performance of a fuel cell according to an embodiment of the present invention

Example 3 illustrates the performance of a fuel cell according to an embodiment of the present invention.

Materials

Two types of materials was used in the conducting body in the fuel cells of the present disclosure; a semiconductor and an ionic conductor. Different semiconducting (n and p types) metal oxides were investigated, mainly based on transition metals, e.g. Ni, Cu, Fe, Zn and Co etc. The semiconducting materials in this study were prepared by LiNiZn-mixed oxides synthesised by solid state reaction methods. Stoichiometric amounts of Li2CO3, NiCO3.2Ni (OH) 2·6H2O and Zn (NO3)2·6H2O were mixed, grounded and sintered at 800 °C for 2-4 hours. Some typical compositions with a molar ratio among metal elements are: Li:Ni:Zn = 1 :4:5 and 2:4:4.

The ionic conducting materials used consisted of Na2CO3-Ce0.8Sm0.2O2-δ (SDC) nanocomposites (NSDC), and were prepared through in one step using co-precipitation. Stoichiometric amounts of 80 mol% Ce(NO3)3·6H2O and 20 mol% Sm(NO3) 3·6H2O were mixed and dissolved in de-ionized water in 0.5 M and stirred at 80°C. Na2CO3 solution (0.5 M) was used as a precipitation agent and added to the above Sm-Ce-nitrate solution with a molar ratio, (Ce3++Sm3+): CO32- = 1 : 2 under vigorous stirring. The precipitate was washed three times in de-ionized water, then filtrated for drying in an oven at 120 °C for 8 - 10 h.

The dried material precursor powder was sintered in a furnace at 800 °C for 4 h. The resulting material was ground completely to obtain homogenous

NSDC nanocomposite powders.

The conducting body of the fuel cells of the present disclosure was prepared by using synthesized LiNiZn-semiconducting materials and an ionic conducting nanocomposite Na2CO3-SDC (NSDC) in a mixture with various weight ratios. A typical value for achieving good fuel cell performance was 40

(semiconductor) / 60 (ionic conductor) in weight ratio. In our experiments the mixtures were further heated at 700 °C for 1 hour.

Further improvement of the conducting body was achieved by adding 5-10 wt% Fe (NO3)3·6H2O in a solution to be mixed with the above LiNiZn-oxide and NSDC materials in a 40:60 ratio followed by sintering to prepare a homogenous mixture. Following drying and sintering at 700°C for 1 hour, composite materials was obtained for use as the conducting body in the fuel cells of the present disclosure.

The crystal structure of the prepared LiNiZn oxides was identified by X-ray diffraction (XRD) with Rigaku-D/Max-3A diffractometer using Cu Kα radiation (λ = 1 .5406 A). The LiNiCuZn oxides morphology was studied with a Zeiss Ultra 55 field emission scanning electron microscopy (FESEM).

Fuel cell fabrication and electrochemical measurements

Fuel cells were fabricated by pressing the above prepared mixture powders uniaxially with a 100-300 MPa load to form tablets as a single-component NEFC, on which both end surfaces were pasted by silver to collect current. The tablet diameter was normally 1 .3 cm and its thickness 0.06 - 0.10 cm.

For comparison, conventional three-component fuel cells were

constructed using a symmetrical configuration, i.e. using the same material of the mixture of the LiNiZn-oxide and NSDC for both anode and cathode, and NSDC as the electrolyte, layer by layer fitted into the die and pressed as 1 .3 cm diameter tablet cells and keep the same thickness of 0.06 - 0.10 cm to make an effective comparison possible.

The fuel cells were measured using a computerized instrument (L43 Inc, Tianjin, China) over the temperature range of 400 - 550 °C. Hydrogen and air were supplied in the range of 80 - 1 10 ml min"1 under 1 atm on each side for the cells.

AC Impedance spectra and conductivity measurements were performed using a VERASTA2273 (Princeton Applied Research, USA) analyzer from 0.01 mHz to 1 M Hz with the amplitude of 10 mV at various temperatures both in air and H2 for 1 .3 cm pellet.

Results

It was seen that the material used for the conducting body according to this embodiment of the present invention had a mixture of individual metal oxides of NiOx and ZnO (Fig. 8). Li was possibly further doped into Ni- or Zn-oxides. A ceria phase diffraction pattern was also clearly identified for NSDC in the component, which indicates that the material displayed all independent phases in a composite nature.

Moreover, it was observed that such a composite material consists of a homogenous distribution of all material particles from SEM analysis, as shown in Figure 8. The particle size in the composite was in the range from tens of nm up to a couple of hundreds of nm.

It was further seen that a fuel cell produced as described above reached OCVs above 1 .0 V, the same as for a conventional electrolyte-based three-component fuel cell (see Fig. 9 and 10). Both types of fuel cells displayed comparable performances, and power outputs between 400-600 mW/cm2 were obtained. In some cases the fuel cell according to this embodiment of the invention showed even better performance than that of the conventional, electrolyte-based device.

Further, the performance of the fuel cell was improved after addition of a redox catalyst comprising Fe, as seen in Fig. 1 1 . The improvement led to power that reached more than 800 mW/cm2 at 550°C.

The experiments also showed that there is a range of appropriate compositions within which the electron and ion conducting materials, (usually 30:60 wt% ionic conducting material) can avoid an electronic short circuit effect, as well as reaching the same OCV level as that from the conventional three-component devices.

These results showed that a fuel cell according to an embodiment of the invention had the characteristics of a conventional fuel cell, indicating a conversion of H2 and O2 to H2O and electricity through an electrochemical route.

Suggested reactions for the fuel cell of this embodiment of the invention may be described as follows:

at H2 side:


at air (O2) side:

overall reactions:


Combing eq. 3a and 3b:


A conventional three-component fuel cell has the following reactions: at anode:

at cathode:

overall reaction:

Eq. 3a and 3b are necessary to indicate the difference from the electrolyte based fuel cell device. The device overall reactions of a fuel cell according to an embodiment of the present invention are thought to be completed through two steps as long as H+ and O2- appear in close proximity anywhere in the component. The final overall reaction is thought be the same as conventional fuel cells, implying that a fuel cell of the present disclosure realizes the same fuel cell functions.

A fast reversible response for the single-component device by exchanging H2 and air supplies was also seen. After exchanging, i.e. when hydrogen supply was replaced by air and air by hydrogen, an immediate OCV change was observed. However, after some time, an opposite OCV with the same value as that obtained in the previous supply configuration was achieved, see Figure 12. This indicates fast catalytic and device reaction processes and that both sides of the fuel cell may function as anode for H2 oxidation and cathode for oxygen reduction, thus completing the redox reactions and generating electricity as a fuel cell, once an external circuit is connected.

The impedance data showed fast diffusion processes for both proton and oxygen ions, with the proton one being even faster than that of the oxygen ions (Fig. 13). It can be seen from Fig. 13 that the EIS (electrochemical impedance spectrum) with a "semicircle" is followed by a "tail" both in H2 and air. Based on the small intercept at the Re Z axis of the semicircle portion in H2 and air, it can be concluded that both the functional anode reaction and cathode reactions include fast kinetic processes . This implied that LiNiCuZn based oxide-SDC materials have high catalytic activity both for H2 and O2.

Example 4 - Performance of a fuel cell according to an embodiment of the present invention - comparison with a conventional fuel cell

Experimental

The electronic conducting materials for the fuel cell were prepared from LiNiO2 (LiNi), LiCoO2 (LiCo), LiCoFeOx (LiCoFe) -oxides by solid state reaction methods. These were prepared from Li2CO3, Ni(NO3)3·6H2O, Co (NO3)3·6H2O, and Fe (NO3)3·6H2O (All these chemicals were bought from Sigma-Aldrich, USA.), which were mixed in stoichiometric amounts, grounded and sintered at 800 °C for 2-4 hours. Some typical compositions with a molar ratio among metal elements were: Li:Ni = 5:5, Li:Co =5:5 and Li:Co:Fe = 3:2:5.

The ionic conducting materials of Na2CO3-Ce0.8Sm0 2O2-δ (SDC) nanocomposites (NSDC), were prepared through a direct preparation in one-step using the co-precipitation. The stoichiometric amounts of 80 mol% Ce(NO3)3·6H2O and 20 mol% Sm(NO3) 3 .6H2O were mixed and dissolved in a deionic water in 0.5 M with a stirring at 80°C. Na2CO3 solution (0.5 M) was used as a precipitation agent and added into the above Sm-Ce-nitrate solution with a molar ratio, (Ce3++Sm3+): CO32- = 1 :2.0 under vigorous stirring, The precipitate was washed three times in deionized water, then filtrated for drying in own at 120 °C over night.

The dried material precursor powder was sintered in a furnace at 800 °C for 4 h. The resulting material was ground completely to obtain homogenous NSDC nanocomposite powders for studies.

A Ba0.6Sr0.4Co0.85Fe0.15 (BSCF) - Ce0.8Sm0.2O2-δ (SDC) composite (for a second component of the conducting body of the fuel cell) was prepared by wet rout chemical one-step method. A stoichiometric amount of BaCO3, Sr(NO3)2, Co(NO3)2. 6H2O, and Fe(NO3)2·9H2O (all chemicals from Sigma Aldrich, USA), were used as starting material and dissolved into 200 ml deionized water. 10% oxalic acid was then added followed by stirring for 10 minutes. A mixture of Ce (NO3)3·6H2O and Sm (NO3)3·6H2O in Ce:Sm = 80:20 molar ratio was added into the solution of BSCF and stirred at 80 °C continuously until drying. The dried powders were calcined at 800 °C for 4 h in air. The amount of the formed SDC in the composites was adjusted at 40 w% of the final BSCF-SDC products.

Fuel cell fabrications and measurements

The synthesized electronic and ionic conducting materials, e.g. LiNiO2 (LiNi), LiCoO2 (LiCo), LiCoFeOx (LiCoFe) -oxides and Na2CO3-SDC (NaSDC) nanocomposite which was reported as good ion conductors (Rizwan, 2010, Int Hydr Ener) were mixed. The mixtures for LiNiO2 (LiNi), LiCoO2 (LiCo), LiCoFeOx (LiCoFe) and NaSDC were used in various weight ratios. Typical, at 40 (electronic material) : 60 (ionic material) weight ratio in the mixture was used for achieving good fuel cell performances. The mixtures were further heated at 700 °C for 1 hour.

The fuel cells were fabricated by pressing the above prepared mixture powders uniaxially with a 100-300 MPa load to form tablets as a single-component fuel cell, on which both end surfaces were pasted by silver, or one end using the Ni-foam and another pasted by the silver to collect current. The tablet diameter was normally 1 .3 cm and its thickness 0.06 - 0.10 cm.

For the fuel cells having a conducting body with two components, the LiCo or LiCoFe-oxide and NSDC mixture in 40:60 weight ratio and the prepared BSCF-SDC composite were pressed layer by layer at 100-300 MPa into pellets as a dual-component configuration. Silver pastes were used on both sides as current collectors.

For comparison, conventional electrolyte based fuel cells were

fabricated. For these, the same single component was used as both anode

and cathode, and NSDC as the electrolyte, layer by layer fitted into the die and pressed as 1 .3 cm diameter tablet cells for comparison with a fuel cell of the present disclosure. Further, the LiCo or LiCoFe-oxide was used as the anode, BSCF-SDC composite as the cathode and NSDC as the electrolyte, layer by layer shaped into 1 .3 cm diameter tablet cells, for comparison with the fuel cells having a conducting body with two components.

All fuel cells of Example 4 were measured using a computerized instrument (L43 Inc, Tianjin, China) over the temperature range of 400 - 550 °C. Hydrogen and air were supplied in the range of 80 - 1 10 ml min-1 under 1 atm on each side for the cells.

AC Impedance spectra and conductivity measurements were performed using a VERASTA2273 (Princeton Applied Research, USA) analyzer from 0.01 mHz to 1 M Hz with the amplitude of 10 mV at various temperatures both in air and H2 for 1 .3 cm pellet. The conductivity was calculated using resistance noted from impedance spectra.

Results

Figure 14 shows the I-V and I-P characteristics of fuel cells according to an embodiment of the present disclosure using a single component of a homogenous layer with mixture of various electronic conductors, LiNiO2 (LiNi), LiCoO2 (LiCo), LiCoFeOx (LiCoFe) and ion conducting materials, e.g. Na2CO3-SDC (NSDC) nanocomposite materials (ref. Rizwan, Int Hydr Ener 2010). Figure 15 shows the fuel cell performances using the dual-component, LiCo (NSDC) or LiCoFe (NSDC)-BSCF (SDC), in a fuel according to an embodiment of the present disclosure. The performances for conventional electrolyte based three component fuel cells are also inserted in Fig 14 and 15 for comparison. It can be seen from Fig. 15 and 16 that fuel cells of the present disclosure reach above 1 .0 V, the same as for a conventional three-component fuel cell. The results also indicate a fuel cell reaction for the fuel cells of the present disclosure, i.e. converting H2 and O2 to H2O and electricity through an electrochemical route. Both conventional electrolyte based fuel cells and the fuel cells of the present disclosure show comparable

performances, e.g. cell voltages and power outputs in the same level, delivering a max. power density between 500-700 mWcm-2 at 550 °C. In some cases, the fuel cells of the present disclosure using one component with showed even better performances than that of the electrolyte based three-component fuel cells.

It is believed that the fuel cell of the present disclosure may function as follows (without being bound to any theory): When the two sides of the FC are situated in H2 and air, respectively, both H2 and O2 can be catalytically dissociated into H+ and O2- due to the bi-catalysis functions of the new material. H+ and O2- combine together on the particle surfaces somewhere in the material and produce H2O and electricity in the same time. During this process, the H2 contacting side acts as a anode function to release electrons by forming H+, and the air (O2) contacting side as a cathode function to receive electrons. The fuel cell reactions are completed immediately as long as H+ and O2- appear in close proximity anywhere, more preferentially at particles' surfaces, in the material.

Example 4 demonstrates that the fuel cells of the present disclosure can directly convert H2 and O2 (via H+ and O2-) to generate the electricity without the electrolyte process. Fig. 16 shows SEM and TEM pictures for the single component material. It can be seen from Fig. 16 that basic block particles formed by SDC particles are covered by nano-particles which are electronic conducting material analyzed by EDX. These nano-particles are highly distributed among the SDC particles as the catalysts. It implies that a conversion of the H2 and O2 (via H+ and O2-) may be realized in a highly efficient way. All reactions and processes may be completed on the surfaces of the particles in the material through direct combination between H+ and O2- ions. Fig. 16 further shows that the material used for the conducting body in this embodiment of the present disclosure is porous.

Further calculations on potential efficiency were carried out for comparing the electrolyte based fuel cells and the fuel cells of the present disclosure.

The calculations were completed on the device efficiency by comparisons with conventional YSZ SOFCs in removal of the electrolyte. Fig. 17 shows the calculated results. The calculations are based on the following considerations and conditions: i) Anode and cathode activations and concentrations are assumed the same for conventional SOFC and EFFC, just removal of the contribution of the electrolyte to the voltage/efficiency loss; ii) The same current efficiency (or fuel and oxidant utilization) and theoretical efficiency (or delta G/delta H) for conventional SOFC and EFFC. The overall efficiency equals to voltage efficiency/current efficiency/theoretical efficiency.

The calculations showed that there were potential advantages by removing the electrolyte and related two interfaces (anode/electrolyte and electrolyte/cathode) of a conventional fuel cell.

Under the assumptions above (the overall efficiency equals to the voltage efficiency), up to 18% higher overall efficiency could be gained compared to that of conventional fuel cells (as shown in Fig. 17) by just removing the electrolyte layer in the electrolyte based fuel cells.

This demonstrates that the fuel cells of the present disclosure may realize the energy conversion more efficiently without limits from the electrolyte and the two interfaces of a conventional fuel cell.

Figure 18 shows Electrochemical impedance spectra results for the complex LiCoFe-SDC and LiNi-SDC mixture in various compositions at 550°C, respectively in H2 and air, where the EIS slightly shifting to higher values in Z-real axis correspond to the air; (a), (b), (c) and (d) contain ionic conducting phase, NKSDC from 0, 30, 60, 70 wt%, respectively. This thus demonstrates that a fuel cell in which the weight ratio of the at least one semiconducting metal oxide to the at least one ionic conducting material is between about 80:20 and 20:80, preferably about 40:60, have excellent fuel cell properties.

Example 4 shows that, in addition to the advantages concerning cost, simplicity and stability, the fuel cells of the present disclosure are also able to improve energy conversion efficiency compared to conventional electrolyte based three-component fuel cells.