Patent ID: 7465504

Claim:
A direct oxidation fuel cell system, the system comprising: at least one membrane electrode assembly (MEA) comprising an anode, cathode and a proton-conductive electrolyte membrane, which is sandwiched between an anode current collector plate and a cathode collector plate; a fuel cartridge containing high concentration fuel of at least 10 M, in fluid communication with the anode of the at least one MEA; an oxidant source in fluid communication with the cathode of the at least one MEA; and a controller for controlling an oxidant stoichiometric ratio to about 5 or less, in order to maximize liquid water contained in the cathode exhaust, wherein: the controller controls the oxidant stoichiometric ratio according to equation (i): ζ c = 0.42 ⁢ ( γ + 2 ) 3 ⁢ η fuel ⁢ p p sat ( i ) wherein ξ c is the oxidant stoichiometry, γ is the ratio of water to fuel in the fuel supply, p sat is the water vapor saturation pressure corresponding to the cell temperature, p is the cathode operating pressure, and η fuel is the fuel efficiency.