South Windsor, CT--In order to achieve adequate efficiencies, the oxygen in PEM fuel cells is typically fed under pressure. Creating that pressure takes a compressor, and compressors consume energy, reducing efficiency of the overall fuel cell.
Engineers at Int'l Fuel Cells (IFC) in South Windsor, CT, believe they have developed a way to eliminate the compressor while maintaining efficiency. "We can run ours at ambient or nearly ambient pressure," says Alfred Meyer, the company's director of engineering.
The secret lies in a patented method of "passive water management" that lets IFC create optimum conditions for the electrodes and achieve a level of performance at ambient pressure equivalent to what others achieve with pressurized systems, says Meyer.
PEM fuel cells require that the hydrogen electrode (anode) have a source of water to keep it wet and enhance its performance. Water is also created at the air electrode (cathode) as a product of the reaction. Because they are low-temperature devices, PEM cells produce their water in the liquid phase, and this water tends to film on the cathode, slowing diffusion of oxygen through the film.
The fuel-cell plates typically have a gas housing on either side of the electrode with ribs formed on it and slots in between through which gases pass into the cell. IFC makes these plates of porous graphite, which acts as a sponge to absorb water off the electrode. With the water out of the way, the air gains optimum access to the electrode and no compressor is needed to help improve diffusion.
The company has built cells running at 0.8 psi gauge using a blower instead of compressor. Meyer claims that for a 50 kW power plant delivered to Ford they achieved a total efficiency of 50%. When the power was reduced to 20% of maximum--approximately cruise output for the car--efficiency rose to 60%.