Co-flow / counter-flow fuel cell or electrolysis cell

A cell stack comprising a plurality of cells according to any of the preceding claims, wherein the first part of each cell which has counter-flow is larger than the second part of each cell which has co-flow, said first part preferably being between 95% and 50% of each cell or preferably between 85% and 70% of each cell.

A cell stack comprising a plurality of cells according to any of the preceding claims, wherein the cells are Solid Oxide Fuel Cells or Solid Electrolysis Cells.

Method of operating at least one cell stack comprising a plurality of cells, where said cells are adapted to operate as fuel cells or electrolysis cells and are stacked on top of each other to form a plurality of cell layers in the at least one cell stack, each of said cells comprising an anode, an electrolyte and a cathode, where each cell is flat and has at least one edge, at least one anode gas inlet region, at least one anode gas outlet region, at least one cathode gas inlet region and at least one cathode gas outlet region, where each layer of cells is divided by an interconnect with gas channels on each side, viz. a first side facing the anode side of an adjacent cell and providing an anode gas flow, and a second side facing the cathode side of an adjacent cell and providing a cathode gas flow, said method comprising the steps of

• providing a counter-flow of the anode gas flow direction relative to the cathode gas flow direction across more than half the total cell area
• providing a co-flow of the anode gas flow direction relative to the cathode gas flow direction across less than half the total cell area.