NOVELTY - A fuel cell assembly comprises fuel cell having anode to accept hydrogen-bearing compound, cathode to accept oxygen-bearing compound, and flowpath; and cooling system (700) in thermal communication with the fuel cell to regulate temperature. The cooling system comprises coolant reservoir (720), flow regulating device to permit selective relief of pressure buildup in the cooling system, and hydrogen removal unit (710) fluidly coupled to the coolant reservoir.    USE - For vehicle.    ADVANTAGE - The assembly ensures thorough removal of unreacted hydrogen from the cooling system of an operating fuel cell; and relieves pressure buildup in the cooling system so that oxygen-bearing fluid can be delivered to catalytic reaction site regardless of power setting in the fuel cell.    DETAILED DESCRIPTION - The fuel cell assembly comprises fuel cell having anode to accept a hydrogen-bearing compound, cathode to accept an oxygen-bearing compound, and flowpath corresponding to each of the anode and cathode and in respective fluid communication with them; and cooling system in thermal communication with the fuel cell to regulate temperature. The cooling system comprises coolant reservoir to contain a quantity of coolant; flow regulating device to permit selective relief of pressure buildup in the cooling system such that the oxygen-bearing compound can flow from the cathode flowpath to the cooling system over a substantial majority of pressures generated during operation of the fuel cell; and hydrogen removal unit fluidly coupled to the coolant reservoir such that upon receipt of unreacted hydrogen extant in the coolant and upon further receipt of a portion of the oxygen-bearing compound from the cathode flowpath, a reaction in the unit converts a portion of hydrogen into water. INDEPENDENT CLAIMS are included for:    (1) a vehicle comprising the fuel cell assembly;    (2) a device for reducing hydrogen presence in the fuel cell cooling system; and    (3) a method of removing hydrogen from coolant that is used to regulate the temperature of an operating fuel cell.    DESCRIPTION OF DRAWING(S) - The figure is a schematic view showing operation of hydrogen removal unit and coolant tank assembly.    Cooling system (700)    Hydrogen removal unit (710)    Coolant reservoir (720)    Valve (730A)    Conduit (750)