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A measurement system for the mapping of current distribution in a free-breathing polymer electrolyte membrane fuel cell (PEMFC) is introduced. In the measurement system, the ridges of the flow-field are made of gold-plated stainless steel and the rest of the measurement plate is made of a non-conducting material. The gas diffusion layer is not segmented and the error resulting from this is analyzed computationally. The effect of the cell temperature on the current distribution is studied with the measurement system. It appears that the measurement system is useful for PEMFC characterization and even large spatial variations of current density can be measured with it. According to the results, the optimum operating temperature for the studied cell is around 60 8C without external humidification. In addition, it is concluded that the molecular diffusion is dominating mass transport mechanism at low temperatures but the current density profile is more homogeneous at elevated temperatures. #

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