Patent ID: 7862948

Claim:
A method of operating a fuel cell system, said method comprising: configuring said system to comprise: a first fuel cell stack and a second fuel cell stack, each comprising a plurality of individual fuel cells within, each of said individual fuel cells comprising an anode, a cathode and a membrane disposed between said anode and cathode; a cathode flowpath configured to couple said cathodes of said individual fuel cells within each of said first and second stacks to an oxygen source; an anode flowpath configured to couple said anodes of said individual fuel cells within each of said first and second stacks to a fuel source, said anode flowpath configured to be connected between said first and second stacks such that fuel present within said anode flowpath cycles back and forth between said first and second stacks; at least one bleed valve fluidly coupled to said anode flowpath; and at least one sensor configured to measure a voltage; introducing fuel into said anode flowpath such that said fuel flows through said stacks in a first direction; introducing oxygen into said cathode flowpath; repeatedly reversing said flow of fuel through said anode flowpath such that said fuel flows through stacks in a second direction from the second fuel cell stack to the first fuel cell stack; sensing a voltage difference between the fuel cell stacks associated with operation of said system; correlating said sensed voltage difference with a fuel concentration in said anode flowpath; and upon attainment of a threshold value of said voltage difference based on said correlating, manipulating said at least one bleed valve to allow at least a portion of said fluid present in said anode flowpath to escape.