An Optimized Humidity And Temperature Control System For Fuel Cells

Hydrogen Fuel Cells require humidity to function efficiently and cost effectively. There is an optimum range of humidity for any given load condition and cell design. Hydrogen Fuel Cells inherently produce water, thus creating some of the necessary humidity for the cell to function. However, this self humidification through the back diffusion from the cathode side provides a limited range of operation for the fuel cells. Without external control of the humidity, fuel cells do not operate at optimum condition. They generally have a warm up time lasting many minutes, in which they operate at limited output power. During operation, flooding could occur when there is an excessive amount of moisture built up in the fuel cell when the cell temperature is relatively low and inlet reactant gases are externally humidified. The humid air could condense to water inside the cell. The water then limits the flow of air through the reactant flow conduits and isolates the catalyst surface from the reactant gases and the electrolyte. Air carries oxygen to the active sights in the Membrane Electrode Assembly (MEA). Oxygen flow should be adjusted at the exact stoichiometric ratio otherwise the fuel cell will starve for its reactant fuel, thus the output power efficiency is reduced to unsatisfactory levels. As the temperature of the fuel cell rises to 50 oC or higher, another phenomenon occurs that limits a hydrogen fuel cell’s output power. The internal heat generated by the fuel cell electrochemical reaction is enough to evaporate any water or moisture built up. This dries the conductive membranes, which in turn reduces their ionic conductivity thus curtailing the output power. This condition does not allow fuel cells to reach maximum allowable operating temperatures. This paper presents an optimized humidity control system, which monitors vital data from humidity sensors and makes necessary adjustments to the external humidification apparatus at all given load conditions. This method ensures maximum power efficiency at all load and operating conditions.