Effects of assembly torque on a proton exchange membrane fuel cell with stamped metallic bipolar plates

In this work, a proton exchange membrane fuel cell with stamped 304 stainless steel bipolar plates is successfully assembled. The total weight of the bipolar plates, membrane electrode assembly and gaskets in the fuel cell is reduced by 37% when replacing milled graphite plates by the stamped 304 stainless steel plates. Moreover, the gas leaking rates and electrochemical characteristics of the fuel cell at different assembly torques are studied. It is found that increasing the torque increases the sealing performance. However, an excess torque (>6 N-m) decreases the power due to a decrease in the porosity and hydrophobicity of the gas diffusion layer, and a deformation of the flow channels in the metallic plate. The pressure loss rate declines by 56% as the torque increases from 2 N-m to 7 N-m. The best performance is obtained at 6 N-m. The cell performance increases by about 21% as the torque increases from 2 N-m to 6 N-m. However, the performance decreases by about 11% as the torque further increases from 6 N-m to 7 N-m. The suspected reason for the above phenomenon is verified via the electrochemical impedance spectroscopies and the microscopic images of the gas diffusion layer.