Patent ID: 8277998

Claim:
A method of operating an electrochemical fuel cell stack comprising a plurality of fuel cells, each of the fuel cells comprising an anode, an ion transfer membrane, and a cathode, the method comprising: delivering fluid fuel to one or more fluid flow channels in each anode of one or more fuel cells in the electrochemical fuel cell stack; delivering fluid oxidant to one or more fluid flow channels in each cathode of the one or more fuel cells; exhausting reaction by-products and unused oxidant from the one or more fluid flow channels in each cathode of the one or more fuel cells; and delivering a sufficient quantity of liquid water to the one or more fluid flow channels in each cathode of the one or more fuel cells such that a relative humidity of 100% is maintained throughout the one or more fluid flow channels in each cathode of the one or more fuel cells; wherein delivering the sufficient quantity of liquid water comprises: determining, for each of a plurality of currents, a maximum voltage for the one or more fuel cells as a function of liquid water flow rate, the each of a plurality of currents being within a range of operating conditions of the one or more fuel cells; determining a calibration function expressing a minimum liquid water flow rate as a function of current and/or air stoichiometry, the calibration function being determined by variation of water flow rate to the cathode operating at constant current and constant air stoichiometry to determine minimum and maximum water flow rates repeated for a plurality of stack currents or air stoichiometries; and delivering at least the minimum liquid water flow rate for a corresponding current drawn from the one or more fuel cells and/or for the air stoichiometry, the delivered minimum liquid water flow rate being determined by the calibration function.