NOVELTY - Coolant is directed towards cathode inlet through distribution channel arranged between coolant inlet and outlet, to cool process oxidant stream adjacent to the cathode inlet. A pressure controller supplies coolant along fluid field, to maintain positive pressure difference between oxidant and coolant streams within coolant flow field, so that pressure of coolant is lower than pressure of oxidant.    USE - For fuel cell power plant used in generating electrical power from reducing and oxidizing fluids for on-board space vehicles, transportation vehicles.    ADVANTAGE - Enhances relative humidity of process oxidant without need for direct addition of water and other coolants. Restricts leakage of liquid coolant from sealed coolant plates into oxidant path, thereby facilitates condensation and recovery of water leaving the fuel cells. The coolant is distributed along the entire length of cathode inlet, thereby lowers temperature of oxidant and hence evaporation of water from electrolyte is minimized. By maintaining positive pressure difference between oxidant and coolant paths, the water generated at the cathode is pumped out away from the electrode, effectively. Simplifies dehumidification by eliminating need for pumps, valves and related piping.    DETAILED DESCRIPTION - A fuel cell unit (12) includes an electrolyte (48) between anode catalyst (50) and cathode catalyst (52). A cathode flow field (26) adjacent to the catalyst (52), extends between cathode inlet and outlet for directing process oxidant towards the cathode catalyst. The coolant flow field includes porous coolant plate so that coolant is in fluid communication with reducing fluid or process oxidant distribution channel arranged between coolant inlet and outlet. An INDEPENDENT CLAIM is also included for method of increasing relative humidity of process oxidant within cathode flow field of fuel cell.    DESCRIPTION OF DRAWING(S) - The figure shows the schematic cross-sectional view of fuel cell of humidification system.    Fuel cell unit (12)    Cathode flow field (26)    Electrolyte (48)    Anode catalyst (50)    Catalyst (52)