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Abstract

The invention relates to a method for ascertaining the overvoltage of a working electrode in a fuel cell, in which the potential of a reference electrode compared to the grounded counter electrode is measured. For the measurement, a fuel cell comprising a polymer electrolyte membrane is used, in which the counter electrode comprises a lateral edge having at least one convexly curved region, and the electrolyte membrane surface, adjoining the counter electrode, comprises an electrode-free region in which the reference electrode is disposed on the electrolyte membrane surface. In contrast, the working electrode is continuous, which is to say has a large surface. The minimum distance L_gap between the reference electrode and the edge of the counter electrode L_gap=3×L_l,r with (a) and (b), where m=ionic conductivity of the electrolyte membrane (Ω⁻¹ cm-¹), b_ox=Tafel slope of the half cell for the electrochemical reaction of the working electrode l_m=membrane layer thickness (cm) and j_ox⁰=exchange current density of the catalyst of the working electrode per unit of electrode surface in (A cm⁻²). This arrangement can advantageously be used to ensure that the potential measured at the hydrogen-fed reference electrode corresponds to the overvoltage of the working electrode with sufficient accuracy. The method can be applied to polymer electrolyte membrane fuel cells (PEMFC), to direct methanol fuel cells (DMFC) or to high-temperature fuel cells (SOFC).

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