Fuel cell stack with multiple groups of cells and flow passes

A method of flowing an anode reactant and a cathode reactant through a fuel cell stack having a plurality of fuel cells, the method comprising:

• dividing said stack into a plurality of first groups for said anode reactant and a plurality of second groups for said cathode reactant, each of said first groups and each of said second groups respectively connected together electrically in series;
• selecting a number of said first groups and a number of fuel cells in each of said first groups to maintain a substantially constant anode reactant stoichiometry for each of said first groups, wherein a number of said fuel cells in each of said first groups is decreasing from upstream to downstream;
• selecting a number of said second groups and a number of fuel cells in each of said second groups to maintain a substantially constant cathode reactant stoichiometry for each of said second groups, wherein a number of said fuel cells in each of said second groups is decreasing from upstream to downstream, at least one of said number of said first groups and said number of said second groups, and said number of fuel cells in each of said first groups and said number of fuel cells in each of said second groups being different;
• and
• distributing said anode reactant in series to each of said first groups and in parallel within each of said first groups and distributing said cathode reactant in series to each of said second groups and in parallel within each of said second groups.