Composition for use as an electrolyte in a protonic ceramic fuel cell and a fuel cell thereof

Abstract

The present invention relates to a solid oxide fuel cell especially protonic ceramic fuel cell which can operate at intermediate temperature and fuel cell thereof. The composition comprising a formula BaCe.sub.0.7Zr.sub.0.25-xY.sub.xZn.sub.0.05O.sub.3-δ or BaCe.sub.0.7Zr.sub.0.1Y.sub.0.2-xPr.sub.xO.sub.3-δ, wherein x=0.05, 0.1, 0.15, 0.2 or 0.25 to vary Zr and Y percentage at the B-site, and Ba=100%, Ce=70%; and Zn=5%.

Claims

1. A composition for an electrolyte, the composition comprising: BaCe.sub.0.7Zr.sub.0.25-xY.sub.xZn.sub.0.05O.sub.3-δ; wherein x=0.15, 0.2 or 0.25, δ=0.1, 0.125, 0.15 or 0.175, respectively, to vary Zr and Y percentage at B-site; Ba=100% at A-site; Ce=70%; and Zn=5% at the B-site.

2. The composition for the electrolyte as in claim 1, wherein bulk and total conductivity of the composition reaches 9.23×10.sup.−3 and 1.55×10.sup.−02 Scm.sup.−1 for BCZYZn05 at 600° C. in wet condition.

3. The composition for the electrolyte as in claim 1, wherein activation energies of the composition for bulk and total conductivity in wet conditions below 650° C. are 0.58 and 0.60 eV respectively.

4. A composition for an electrolyte in a protonic ceramic fuel cell, the composition comprising: BaCe.sub.0.7Zr.sub.0.1Y.sub.0.2-xPr.sub.xO.sub.3-δ; wherein x=0.15 or 0.2 and δ=0.1 to vary Y and Pr percentage at B-site; Ba=100% at A-site; Ce=70%; and Zr=10% at the B-site.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Reference will be made to embodiments of the invention, examples of which may be illustrated in accompanying figures. These figures are intended to be illustrative, not limiting. Although the invention is generally described in the context of these embodiments, it should be understood that it is not intended to limit the scope of the invention to these particular embodiments.

(2) FIG. 1 is a graph showing I-V and power-density of a fuel cell using the claimed composition in accordance with an embodiment of the present invention.

(3) FIG. 2 shows a schematic 3D diagram of the fuel cell arrangement for a performance test in accordance with an embodiment of the present invention.

(4) FIG. 3 shows an exploded view of the fuel cell in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

(5) The present invention is directed towards a solid oxide fuel cell especially protonic ceramic fuel cell which can operate at intermediate temperature.

(6) FIG. 1 shows the current-voltage and power-density curves of the fuel cell using humidified H.sub.2 (3% H.sub.2O) as the fuel and ambient air as the oxidant for the cathode at 500˜700° C. in accordance with an embodiment of the present invention.

(7) In an embodiment, the present invention discloses a composition for use as an electrolyte in a protonic ceramic fuel cell. The composition comprising a formula BaCe.sub.0.7Zr.sub.0.25-xY.sub.xZn.sub.0.05O.sub.3-δ or BaCe.sub.0.7Zr.sub.0.1Y.sub.0.2-xPr.sub.xO.sub.3-δ In an exemplary embodiment, the value of x can be selected from 0.1, 0.15, 0.2 or 0.25 for BaCe.sub.0.7Zr.sub.0.25-xY.sub.xZn.sub.0.05O.sub.3-δ to vary Zr and Y percentage at the B-site. The value of δ is 0.1, 0.125, 0.15 or 0.175 for x=0.1, 0.15, 0.2 or 0.25, respectively. Further, in an exemplary embodiment, the percentage value of Ba at the A-site is 100% and Ce, and Zn at the B-site is 70% and 5%. Advantageously, the composition shows high power density at an intermediate temperature range during the operation of a fuel cell. For BaCe.sub.0.7Zr.sub.0.1Y.sub.0.2-xPr.sub.xO.sub.3-δ the value of x can be selected from 0.05, 0.15, or 0.2 to vary Y and Pr percentage at the B-site where Ba, Ce, and Zr are 100%, 70%, and 10%, respectively. The value of δ is 0.1 on the composition to calculate the total oxygen occupancy.

(8) The method of making the abovementioned composition will now be explained. In an exemplary embodiment, the composition of BaCe.sub.0.7Zr.sub.0.1Y.sub.0.15Zn.sub.0.05O.sub.3-δ is prepared by using solid-state reaction method from BaCO.sub.3 (99% purity, Merck, Germany), CeO.sub.2 (99% purity, Aldrich, China), ZrO.sub.2 (99% purity, Sigma-Aldrich, UK), Y.sub.2O.sub.3 (99.9% purity, Aldrich, China) and ZnO (99% purity, Merck, Germany). Firstly, stoichiometric amounts of aforesaid selected materials are ball-milled in ethanol using zirconia balls for more than 24 h using. Thereafter, the ball-milled materials are dried in the oven and then calcined at about 650° C. for about 10 hours, cooled down to room temperature (“RT”), and subsequently grounded and palletized using 15 mm diameter die under pressure 20 MPa for about 1 min. The palletized BaCe.sub.0.7Zr.sub.0.1Y.sub.0.15Zn.sub.0.05O.sub.3-δ sample is then sintered at 1000° C. for about 10 hours and cooled down to RT. The pellet is again grounded, re-palletized and sintered again at 1200° C. for about 10 hours.

(9) The final sintering of BaCe.sub.0.7Zr.sub.0.1Y.sub.0.15Zn.sub.0.05O.sub.3-δ is at 1400° C. for about 10 hours for cell performance and other characterization.

(10) In an embodiment, Solid-state reaction (SSR) method is used for the preparation of three different compositions of BaCe.sub.0.7Zr.sub.0.1Y.sub.0.2-xPr.sub.xO.sub.3-δ (x=0.05, 0.1 and 0.2) (BCZYP). Firstly, a stoichiometric amount of BaCO.sub.3 (99% purity, Merck, Germany), CeO.sub.2 (99% purity, Aldrich, China), ZrO.sub.2 (99% purity, Sigma-Aldrich, UK), Y.sub.2O.sub.3 (99.9% purity, Aldrich, China) and Pr.sub.6O.sub.11 (99% purity, Sigma-Aldrich, UK) are mixed by ball milling with ethyl alcohol and zirconia balls for 24 h. thereafter, the finely ground dried powders are calcined at 650° C. for 12 hours in zirconium crucible with a heating rate of 5° C. min.sup.−1. The hydraulic press is utilized to make 32 mm diameter pellets under the pressure of 269 MPa for 1 min.

(11) The palletized BaCe.sub.0.7Zr.sub.0.1Y.sub.0.2-xPr.sub.xO.sub.3-δ sample is then sintered at 900° C. for about 12 hours and cooled down to RT. The pellet is again grounded, re-palletized and sintered again at 1200° C. for about 12 hours.

(12) The final sintering of BaCe.sub.0.7Zr.sub.0.1Y.sub.0.2-xPr.sub.xO.sub.3-δ is at 1550° C. for about 12 hours for cell performance and other characterization. All heat treatments are carried out in the air with heating and cooling rate of about 5°/min.

(13) In an exemplary embodiment, materials are characterized by using X-ray powder diffraction (XRPD), neutron powder diffraction (NPD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), particle size analysis, impedance spectroscopy, and single-cell measurements.

(14) Tests conducted by the inventors revealed that Rietveld analysis of XRD and Neutron data reveal a pure orthorhombic structure with PBNM space group for all compounds and the relative densities were more than 95%.

(15) Further, in BaCe.sub.0.7Zr.sub.0.1Y.sub.0.15Zn.sub.0.05O.sub.3-δ, Y doped by Zr with adding Zn exhibit positive performance in terms of conductivity enhancement. For instance, Bulk and total conductivity of the claimed composition reaches 9.23×10.sup.−3 and 1.55×10.sup.−02 Scm.sup.−1 at 600° C. in wet condition. Furthermore, activation energies for bulk and total conductivity in wet conditions below 650° C. are 0.58 and 0.60 eV, respectively. The total conductivity of the BaCe.sub.0.7Zr.sub.0.1Y.sub.0.2-xPr.sub.xO.sub.3-δ significantly change for Pr concentration and measuring temperature. At low temperatures, higher % of Pr show higher conductivity, but at a high temperature lower % of Pr show higher conductivity. The total conductivity values were 8.94×10.sup.−3 Scm.sup.−1, 9.07×10.sup.−3 Scm.sup.−1 and 1.14×10.sup.2 Scm.sup.−1 measured at 600° C. for x=0.05, 0.15 and 0.20 respectively under wet H.sub.2 condition. The measured activation energies were 0.57 eV, 0.49 eV and 0.32 eV under wet H.sub.2 condition for x=0.05, 0.15 and 0.20 respectively.

(16) In another exemplary embodiment, the inventors have prepared a single NiO—BaCe.sub.0.7Zr.sub.0.1Y.sub.0.15Zn.sub.0.05O.sub.3-δ (BCZYZn15|BCZYZn15|Ba.sub.0.5Sr.sub.0.5Co.sub.0.8Fe.sub.0.2O.sub.3 BCZYZn15 cell and advantageously observed that peak power densities of 161, 278, 445, 670 and 872 mWcm.sup.2 at 500, 550, 600, 650 and 700° C., respectively, which is the highest performance until now. Further, the open-circuit voltage (OCV) values of the cell were 0.998, 1.034, 1.037, 1.027, and 1.0 V at 500, 550, 600, 650, and 700° C., respectively, which is also advantageous.

(17) FIG. 2 shows a schematic 3D diagram of the fuel cell arrangement for a performance test in accordance with an embodiment of the present invention.

(18) FIG. 3 shows an exploded view of the fuel cell in accordance with an embodiment of the present invention. In an embodiment, anode supported planar individual cells are prepared using the composition as described hereinabove. As shown in the cell stack 300, the interconnect 310 is a connective layer that physically and electrically connects the anode of one fuel cell to the cathode of the adjacent fuel cell in the SOFC stack. In operation, the cells are arranged in a stack and put in the manifold 320. The gas (water Out channel) 320 and airflow channels (air O.sub.2 Out 330 and air O.sub.2 In 331) provide equal and sufficient gas distribution. Interconnects are used to make the stack in series to get the expected output. In operation, at anode 340 oxidation reaction happens (electrons are released). At Cathode 350 reduction reaction occurs (electrons are acquired). In the fuel cell, hydrogen is oxidized at the anode 340, and oxygen reduction occurs at the cathode. An electrolyte 360 is provided which conducts ions from one electrode to the other.

(19) While the present invention has been described with respect to certain embodiments, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the scope of the invention as defined in the following claims