Gas-phase mass-transfer resistance at PEMFC electrodes. Part 2 - Effects of the flow geometry and the related pressure field

It has been demonstrated that it is possible to have a better understanding of the mass-transfer phenomena occurring at PEMFC electrodes by distinguishing the various diffusive regimes taking place inside the porous layer close to the electrodes themselves. In each regime the interactions between diffusive and forced flows have been expressed in terms of Peclet numbers and the overall diffusive resistances have been expressed in terms of Sherwood numbers. Now the comparison of traditional and non-traditional geometrical arrangements can be more fully discussed and the geometrical optimisation of the cell can be more clearly determined by explicitly considering the role of the geometrical arrangement of the cell channels and the related pressure field. Both interdigitated and serpentine cells can be operated in such a way that high Sherwood numbers and, then, a high limit current are attained. Both types of cells are penalised by higher head losses than traditional cells, but these appear to be much greater in the serpentine arrangement. The ultimate goal of reaching high, almost uniform Sherwood numbers and low head losses is still problematic. A partially interdigitated configuration might be a step in the right direction.