Fuel cell stack

1. Solid oxide fuel cell stack obtainable by a process comprising the steps of:

(a) forming a first fuel cell stack assembly by alternating at least one interconnector plate with at least one fuel cell unit, in which each fuel cell unit comprises an anode, a cathode and an electrolyte arranged between the anode and cathode, and providing a glass sealant in between the interconnector plate and each fuel cell unit in which the glass sealant has the composition:

50-70 wt % SiO 2 , 0-20 wt % Al 2 O 3 , 10-50 wt % CaO, 0-10 wt % MgO, 0-6 wt % (Na 2 O+K 2 O), 0-10 wt % B 2 O 3 , and 0-5 wt % of functional elements selected from TiO 2 , ZrO 2 , F, P 2 O 5 , MoO 3 , Fe 2 O 3 , MnO 2 , La.Sr—Mn—O perovskite (LSM) and combinations thereof;

(b) converting said first fuel cell stack assembly into a second assembly having a glass sealant of thickness 5-100 μm by heating said first assembly to a temperature of 500° C. or higher and subjecting the cell stack to a load pressure of 2 to 20 kg/cm 2 ,

(c) converting said second assembly into a final fuel cell stack assembly by cooling the second assembly of step (b) to a temperature below that of step (b).

2. Solid oxide fuel cell stack according to claim 1 , wherein the content of B 2 O 3 is 3-6 wt %.

3. Solid oxide fuel cell stack according to claim 2 , wherein the glass sealant is a glass with composition: 52-62 wt % SiO 2 , 12-16 wt % Al 2 O 3 , 16-25 wt % CaO, 0-5 wt % MgO, 0-2 wt % (Na 2 O+K 2 O), 0-10 wt % B 2 O 3 , 0-1.5 wt % TiO 2 , 0.05-0.8 wt % Fe 2 O 3 , 0-1.0 wt % F (fluoride).

4. Solid oxide fuel cell according to claim 1 , wherein in step (b) the temperature is 800° C. or higher and the load pressure is 2 to 10 kg/cm 2 .

5. Solid oxide fuel cell stack according to claim 1 , wherein the content of SiO 2 , Al 2 O 3 , CaO and MgO represents 85-95 wt % of the glass sealant composition, the content of Na 2 O+K 2 O and B 2 O 3 represents 3-8 wt % of the glass sealant composition and functional elements selected from TiO 2 , F, ZrO 2 , P 2 O 5 , MoO 3 , Fe 2 O 3 , MnO 2 and La.Sr—Mn—O perovskite (LSM) and combinations thereof represent 0-5 wt %.

6. Solid oxide fuel cell stack according to claim 1 , wherein the glass sealant is a glass with composition: 52-62 wt % SiO 2 , 10-15 wt % Al 2 O 3 , 18-25 wt % CaO, 0.5-4 wt % MgO, 0.25-2 wt % Na 2 O, 3.5-5.5 wt % B 2 O 3 .

7. Solid oxide fuel cell stack according to claim 1 , wherein the glass sealant in step (a) is provided as a sheet of glass fibres.

8. Solid oxide fuel cell stack according to claim 1 , wherein the sheet of glass fibres contains fibres in an amount of 70-100 g/m 2 towards the cell and 30-60 g/m 2 towards the interconnect plate.

9. Solid oxide fuel cell stack according to claim 1 , wherein the glass sealant in step (a) is loaded with filler material in the form of MgO, steel-powder, quartz, leucite and combinations thereof.

10. Solid oxide fuel cell stack wherein the glass sealant is a paste formed by mixing a glass powder having the composition of claim 1 with a binder and an organic solvent.

11. Solid oxide fuel cell stack according to claim 10 , wherein the glass powder is mixed with a filler material in the form of MgO, steel-powder, quartz, leucite and combinations thereof.

12. Use of glass with composition 52-56 wt % SiO 2 , 12-16 wt % Al 2 O 3 , 16-25 wt % CaO, 0-6 wt % MgO, 0-6 wt % Na 2 O+K 2 O, 0-10 wt % B 2 O 3 , preferably 3-6 wt % B 2 O 3 , 0-1.5 wt % TiO 2 , 0-1 wt % F as a glass sealant in solid oxide fuel cell stacks.

13. Use according to claim 12 , wherein the glass is provided as a sheet of glass fibres.

14. Use according to claim 13 , wherein the sheet of glass fibres contains fibres in an amount of 70-100 g/m 2 towards the cell and 30-60 g/m 2 towards the interconnect plate.

15. Use of E-glass with composition 52-62 wt % SiO 2 , 10-15 wt % Al 2 O 3 , 18-25 wt % CaO, 0.5-4 wt % MgO, 0.25-2 wt % Na 2 O, 3.5-5.5 wt % B 2 O 3 as a glass sealant in solid oxide fuel cell stacks.