Effect of Back Pressure and Flow Geometry on PEM Fuel Cell Performance - An Experimental Study

The purpose of this study is to examine the performance of a PEM fuel cell at different back pressures and channel geometries. Experiments are conducted in BHEL (R&D), Hyderabad with a single cell to study the effect of back pressure created in the hydrogen flow channel on fuel cell performance. The outlet tube from the hydrogen flow channel is immersed in water to a specified depth in a graduated cylindrical container. The back pressure created in the channel depends on the depth to which the outlet tube is immersed in water in the cylinder. The hydrogen bubbles through water to the exit. The excess pressure induced on the fluid helps in forcing the gas through the GDL to the catalyst surface. The voltage and power are measured as functions of current density at different back pressures in the hydrogen flow channel and with different flow fields. The rate of power generation depends on the rate of diffusion of hydrogen through the gas diffusion layer (GDL). After diffusing through GDL hydrogen splits into hydrogen ion and electron on the surface of the catalyst layer. Hence an increase in voltage or power is obtained at a specified current density. Experiments are conducted with three different flow field plates, viz., for 4-Serpentine flow, interdigitated flow and dual inlet single outlet flow. Experimental data have been obtained at three different back pressures with each flow field plate. The three different back pressures are created by immersing the tube in the cylinder at three different depths. An increase in power production is obtained clearly with an increase in back pressure. Further the augmentation in voltage is the highest in the case of serpentine flow.