Determination of oxygen mass transport resistance in proton exchange membrane fuel cells with an open flow field architecture

Abstract

In this work, we demonstrate the applicability and validity of our novel method in determining the oxygen mass transport resistance of proton exchange membrane fuel cells (PEMFCs) using a commercially relevant open flow field design. The method is based on the measurements of the limiting current when a cathode is fed by highly diluted O2 mixtures. Mass transport resistance originating from Knudsen diffusion and dissolution through liquid and ionomer films in a cathode catalyst layer (RK+film) can be separated from molecular diffusion in the gas phase (Rm, N2) by varying the diluent molecular weight. The performance and mass transport properties of the single cell open field (SCOF) design were evaluated and compared with a serpentine land/channel architecture under subsaturated and oversaturated conditions. Analysis of the SCOF under subsaturated conditions showed that RK+film and Rm, N2 were 74.85 and 35.65 s m−1, respectively. These values were found to be lower than those for the serpentine cell and explained the superior performance of the SCOF. The SCOF demonstrated better performance under oversaturated conditions as well due to the low Rm, N2, which compensated for the high RK+film. The results indicated that the open flow field architecture ensured good transport in the gas phase, uniform humidification of the catalyst layer and efficient oxygen diffusion through the ionomer.