Contact between interconnect and cell in solid oxide cell stacks
Improved contact between interconnect and oxygen electrode material in solid oxide cell (SOC) stacks is achieved through a contact point between the oxygen electrode or an oxygen-side contact layer of the SOC and a coated ferritic stainless steel interconnect in the SOC stack, where the coating on the metallic interconnect comprises Cu.
1. A contact point between a solid oxide cell and an interconnect of a solid oxide stack, said contact point comprising:
a ferritic stainless steel interconnect substrate covered by a chromium oxide layer and at least one metallic layer comprising Co or Ni, the at least one metallic layer being coated by a coating comprising Cu having a thickness of approximately 100-200 nm, and
an oxygen electrode or an oxygen-side contact layer of a solid oxide cell,
wherein the Cu in the coating functions as a sintering aid towards the oxygen electrode or oxygen-side contact layer materials, and a fraction of the Cu in the coating diffuses into the oxygen electrode or oxygen-side contact layer of the solid oxide cell, thereby increasing the adhesion strength and lowering the electrical resistance of the contact point between the coated interconnect substrate and the oxygen electrode or oxygen-side contact layer of the solid oxide cell, such that the voltage drop across the contact point is less than 25 mV, when measured in air at 750° C., under a dc current density of 1.27 A/cm 2 , under a compressive load of 3 MPa.
2. A contact point according to claim 1 , wherein the coating on the metallic interconnect comprises an oxide of Cu and Fe, an oxide of Cu and Ni, an oxide of Cu and Cu, or an oxide of Cu, Co and Ni, or an oxide of Cu, Co, Ni and Fe.
3. A contact point according to claim 1 , wherein the oxygen electrode or oxygen-side contact layer material comprises a perovskite, a double perovskite, or a Ruddlesden-Popper phase material.
4. A contact point according to claim 1 , wherein the adhesion strength of the contact point is of the same order of magnitude as the adhesion strength between the electrolyte and the barrier layer of the solid oxide cell.
5. A contact point according to claim 1 , wherein the operating temperature of the solid oxide cell stack is between 500° C. and 900° C.
6. A method for creating a contact point between a coating on an interconnect and an oxygen electrode or oxygen-side contact layer of a solid oxide cell (SOC), comprising the steps of:
providing a ferritic stainless steel interconnect substrate,
depositing at least one layer of Co or Ni on an oxygen side of the interconnect;
coating the layer of Co or Ni on the oxygen side of the interconnect with a coating comprising Cu having a thickness of approximately 100-200 nm,
providing a solid oxide cell, and
sintering the coated interconnect substrate and the solid oxide cell by heat treatment in air at a temperature exceeding 800° C.,
where the Cu in the coating functions as a sintering aid towards the oxygen electrode or oxygen-side contact layer materials, and a fraction of the Cu in the coating diffuses into the oxygen electrode or oxygen-side contact layer of the solid oxide cell, thereby increasing the adhesion strength and lowering the electrical resistance of the contact point between the coated interconnect substrate and the oxygen electrode or oxygen-side contact layer of the solid oxide cell, such that the voltage drop across the contact point is less than 25 mV, when measured in air at 750° C., under a dc current density of 1.27 A/cm 2 , under a compressive load of 3 MPa.