Comparative Investigation on Waste Heat Driven Air Supply Systems for PEM Fuel Cells

Abstract

The air supply system plays a key role for Proton Exchange Membrane (PEM) fuel cells. The performance of PEM fuel cells can be significantly improved by increasing the air supply pressure and air stoichiometric ratio. However, the increased electrical power consumption of the conventional motor driven air compressor operated at higher pressure would reduce the overall efficiency of the PEM fuel cell system. This paper proposes three novel air supply systems in which the compressor is driven by the waste heat recovered by the Organic Rankine Cycle (ORC) from the stack cooling water and the exhaust gas. The influences of air supply pressure and air stoichiometric ratio on the PEM fuel cell performance and exhaust gas are investigated through the fuel cell stack model. The performance analysis of the air supply system is carried out using a thermodynamic simulation model. And the proposed three air systems are compared to an air system driven by the exhaust gas and the assisted motor. Results show that both the air pressure and air stoichiometric ratio are improved significantly. The gross output electric power and the net efficiency of the PEM fuel cells are also improved greatly because of higher operating pressure and the elimination of the compressor power consumption. Among the 3 proposed air systems, the air system which has a self-circulation to maintain the stack temperature has the best performance and is most stable in operation.