Sources of Current Density Distribution in the Land-Channel Direction of a PEMFC

Abstract

A proton exchange membrane fuel cell (PEMFC) was segmented to measure local current density, electrochemical surface area, and high frequency resistance (HFR) distribution in the land-channel direction at resolution of 350 μm. An in-house catalyst coated membrane of 3 mm × 3 mm active area was prepared to represent a small area in a larger scale cell with 1 mm land and channel widths. This design was employed to measure current density and HFR distribution at 60°C with several different operating conditions. Local electrical resistance was also measured separately so that local protonic resistances can be discerned from local HFR. To analyze the effect of the land-channel geometry a method was developed to quantify the sources of current distribution, such as distributions of oxygen concentration at the electrode, oxygen transport resistance, cathode catalyst layer resistance, and membrane water content. Current density distribution is strongly correlated with the distribution of membrane water content and electrode resistance in dry condition, and oxygen concentration distribution in wet condition, while in moderate condition both oxygen concentration and water content in membrane are critical to the local current density distribution. The results imply the limitation of uniform condition assumption used in a differential cell study.