Thermal management in a fuel cell stack

A fuel cell stack (300) comprising multiple arrays of one or more fuel cells (302), each comprising an electrolyte layer, an anode layer and a cathode layer; gas separator plates (304, 306) between adjacent fuel cells; and oxidant gas distribution passages (308) and fuel gas distribution passages (312, 318) between adjacent fuel cells; and gas separators opening to the cathode layers and the anode layers, respectively, of the fuel cells. The fuel cell arrays comprise at least first stage fuel cell arrays having associated first fuel gas distribution passages (312) to receive fuel gas from one or more fuel gas supply manifolds (310) and second stage fuel cell arrays having associated second fuel gas distribution passages (318) which receive fuel exhaust from the fuel cells of the first stage fuel cell arrays. The second stage fuel cell arrays are interleaved in the stack between first stage fuel cell arrays to improve thermal gradients. Other interleaving arrangements are possible.