Influence of the bolt torque on PEFC performance with different gasket materials

Abstract

In this work, different gasket materials (NBR, expanded PTFE and PTFE) with different thicknesses were investigated by evaluating the electrochemical performance as function of a torque moment applies to fasten the cell. Because the materials composing the gasket are subjected to a different deformation, depending on their mechanical properties, a different compression was obtained on the GDL as a function of the clamping force. These effects influence the cell performance, above all the diffusive region of the polarisation curves, where the problems related to the mass transport are more important. These problems are minimised when the cell is fed with gas pressurized at 3 bar abs, in fact at higher pressure the gas concentration is higher and the diffusion is favoured despite the lowering of GDL porosity due to the compression. When the gas pressure is 1 bar abs, the cell performance is more evidently affected by the GDL compression and contact resistance increase. In any case, an optimal clamping force was found to be as a function of the mechanical properties of materials composing the gasket. The NBR and Expanded PTFE reached the best performance with a torque moment of 11Nm while the PTFE reached similar performance at 9Nm. It was found that thinner PTFE is more stable than others during the time, with an average power density of 250 mWcm −2 and the lowest standard deviation. The expected over-compression of the GDL is prevented by distortion of the clamping plates. This distortion results in unexpectedly good cell performance.