Process for forming a metal supported solid oxide fuel cell
A process for forming a metal supported solid oxide fuel cell is provided. The process can include the steps of: a) applying a green anode layer including nickel oxide and a rare earth-doped ceria to a metal substrate; b) prefiring the anode layer under non-reducing conditions to form a composite; c) firing the composite in a reducing atmosphere to form a sintered cermet; d) providing an electrolyte; and e) providing a cathode; wherein the reducing atmosphere comprises an oxygen source, a metal supported solid oxide fuel cell formed during this process, fuel cell stacks and the use of these fuel cells.
1. A process for forming a metal supported solid oxide fuel cell, the process comprising the steps of:
a) applying a green anode layer including nickel oxide and a rare earth-doped ceria to a metal substrate;
b) thereafter, prefiring the green anode layer under non-reducing conditions to form a composite and a passivation layer interposed between the composite and the metal substrate;
c) thereafter, firing the composite in a reducing atmosphere to form a sintered cermet, form nickel metal, maintain the rare earth-doped ceria in a partially-reduced state, and retain the passivation layer, wherein the reducing atmosphere comprises a reducing agent and an oxygen source, and wherein an oxygen partial pressure in the reducing atmosphere is in the range 10 −14 to 10 −22 bar;
d) thereafter, providing an electrolyte; and
e) thereafter, providing a cathode.
2. The process according to claim 1 , wherein the reducing agent is a gaseous reducing agent, and wherein the oxygen source is a gaseous oxygen source, and further wherein the reducing atmosphere of firing step c) comprises an inert gas.
3. The process according to claim 2 , wherein the reducing agent is selected from hydrogen, carbon monoxide and combinations thereof.
4. The process according to claim 2 , wherein the gaseous oxygen source is selected from carbon dioxide, water vapour and combinations thereof.
5. The process according to claim 2 , wherein the reducing atmosphere of firing step c) comprises in the range 0.01 to 50 volume % of the oxygen source and/or 0.5 to 50 volume % reducing agent.
6. The process according to claim 1 , wherein in firing step c) the nickel oxide is reduced to nickel metal prior to sintering.
7. The process according to claim 1 , wherein in firing step c) the nickel oxide is at least partially sintered prior to reduction to nickel metal.
8. The process according to claim 1 , wherein at least one of the prefiring of the green anode layer and the firing of the composite occurs at a temperature in the range 950° C. to 1100° C.
9. The process according to claim 1 , comprising bracing the metal substrate during at least one of a heating step selected from: prefiring the green anode layer, firing the composite, or combinations thereof.
10. The process according to claim 1 , wherein the nickel oxide and rare earth-doped ceria are powdered, the powders being of particle size distribution d 90 in the range 0.1 to 4 μm.
11. The process according to claim 1 , wherein the nickel oxide and rare earth-doped ceria are applied as an ink.
12. The process according to claim 11 , wherein the application of the green anode layer includes an initial application of the ink to the metal substrate, and drying the ink to provide a printed layer of thickness in the range 5 to 40 μm.
13. The process according to claim 1 , further comprising a step of compressing the green anode layer at pressures in the range 100 to 300 MPa.
14. The process according to claim 1 , further comprising the step of reoxidising the sintered nickel prior to the provision of the electrolyte.
15. A metal supported solid oxide fuel cell formed by the process according to claim 1 .
16. A fuel cell stack comprising two or more fuel cells according to claim 15 .
17. The process according to claim 1 , wherein the rare earth-doped ceria has the formula Ce 1−x RE x O 2−x/2 , wherein RE is a rare earth and 0.3≥x≥0.5.