Patent ID: 7976991

Claim:
A method of operating a fuel cell to obtain a desired relative humidity profile in the fuel cell, the fuel cell having anode and cathode reactant flow paths separated by a proton exchange membrane and a coolant flow path, the cathode reactant and coolant flow paths being in a substantially predominate co-flow arrangement relative to each other, the method comprising: (a) monitoring operating characteristics of the fuel cell; (b) ascertaining a relative humidity profile of the fuel cell at any point as a function of and at any stage of reaction progress; (c) adjusting at least one operating parameter of the fuel cell based on said ascertained profile to obtain a desired relative humidity profile in the fuel cell; (d) determining a high frequency resistance of the fuel cell as a function of a relative humidity of the cathode effluent exiting the fuel cell while said high frequency resistance is decreasing; and (e) applying said high frequency resistance to determine an approximate relative humidity of a cathode reactant flowing into the fuel cell, said high frequency resistance of said fuel cell applied to predict fuel cell operating conditions wherein a peak current density is achieved by the fuel cell.