Patent ID: 7785746

Claim:
A fuel cell system comprising: a fuel cell comprising an anode, a cathode, and an ion exchange membrane between the anode and the cathode; a fuel delivery conduit comprising: a fluid flow field plate forming part of the anode, having a fluid flow channel extending through the fluid flow plate; a fuel delivery inlet coupled to one end of the fluid flow channel; a fuel delivery outlet coupled another end of the fluid flow channel; and a fluid flow regulator for controllably varying a quantity of fuel delivered to a mixing point adjacent to the fuel delivery inlet; a recirculation conduit for the anode, the recirculation conduit extending between the fuel delivery outlet and the fuel delivery inlet via the mixing point, wherein the mixing point is external to the fuel cell and comprises either (i) a reaction chamber for reacting fuel, or (ii) a pre-mixing chamber, the mixing point for mixing fuel from the fluid flow regulator with oxidant species from the recirculation conduit; and detection means for detecting a level of oxidant species present in at least part of the fuel delivery conduit, wherein the detection means comprises means for testing an open circuit voltage across the anode and cathode of the fuel cell.