Soec stack with fuel flow from periphery towards center

Method of performing solid oxide electrolysis in a solid oxide electrolysis cell stack comprising a plurality of stacked cell units, each cell unit comprises a cell layer comprising an active cell area, and an interconnect layer comprising an interconnect, one interconnect layer separates one cell layer from the adjacent cell layer in the cell stack, each interconnect layer has a fuel side with at least one fuel inlet and a fuel inlet active cell area, and at least one fuel outlet and a fuel outlet active cell area and an oxy side;

• wherein the fuel inlet active cell area is at least 50% larger than the fuel outlet active cell area, said method comprising the steps of
• providing a fuel fluid comprising H2O or CO2 or a mixture of H2O or CO2 to said at least one fuel inlet and fuel inlet active cell area
• providing flow of said fuel fluid from said at least one fuel inlet and fuel inlet active cell area towards said at least one fuel outlet and fuel outlet active cell area
• applying an electrolysis current through the solid oxide electrolysis stack to electrolytically reduce at least a fraction of the fuel fluid, transfer oxygen ions across an electrolyte of the solid oxide electrolysis cell, produce molecular oxygen on the oxy side of said solid oxide electrolysis cell,
• whereby the density of said fuel fluid decreases as it flows from said at least one fuel inlet and fuel inlet active cell area towards said at least one fuel outlet and fuel outlet active cell area
• exiting the now density reduced fuel fluid through said at least one fuel outlet.