Investigation and Assessment of basic Flow Field Designs for the cathodic Gas Supply in low Temperature Fuel Cells

Abstract

One of the major challenges in the development of polymer electrolyte fuel cells (PEFCs) is to exploit the whole potential that inheres a given membrane electrode assembly. For this purpose, the fuel cell performance can be maximised by optimising the flow field design with regard to the intended operating point. As a prerequisite for such an optimisation, the electrochemical performance of PEFCs with various cathodic flow fields (Parallel flow, serpentine, spiral and interdigitated) has been investigated. In addition, the influence of the rib width was studied by utilising each structure with different rib widths, whereby the width and the height of the channels remain constant. The characterisation of the gas distributor structures was carried out by measuring overall polarization curves and local current density distributions by means of a segmented laboratory cell with an active area of 25 cm2. The optimum gas distributor structure strongly depends on the particular operating point. Consequently, each basic structure has to be adapted for the intended operating conditions. For example, a serpentine flow field generates the highest current densities for high air fluxes whereas an interdigitated structure is preferred for small flow rates. In the same way it can be shown that a spiral structure produces the most uniform current density distributions, whereas the current density distribution of a flow field with parallel channels is extremely inhomogeneous and becomes unsteady for higher water generation rates. The variation of the rib width has shown that all areas with a high catalytic activity are situated directly over the gas channels. In contrast, the covered areas represent only a small fraction of the global performance, whereby the general tendency is independent of the basic structure of the flow field.