A Segmented Along the Channel Test Cell for Locally Resolved Analysis at High Current Densities in PEM Water Electrolysis

For the scale-up of proton exchange membrane (PEM) water electrolysis, understanding the cell behavior on industrial scale is a
prerequisite. A proper distribution of current and temperature in the cell can improve performance and decrease overall degradation
effects. Due to water consumption as well as the concomitant gas evolution and accumulation, gradients and inhomogeneities along
the reaction coordinate are expected. These effects increase along the water supply channels of a flow field and are expected to lead
to spatial gradients in cell performance and temperature. In this study we present a new test cell that is segmented along the flow
field channels and is designed for the operation at high current densities. We show polarization curve measurements at 10 bar
differential pressure up to 10 A∙cm$^{−2}$ at ∼2.7 V without observing any mass transport limitations and conduct current density,
temperature and impedance distribution measurements. At harsh conditions (low water flow rates of 2 ml∙min^{−1}$ ∙cm^{−2}$ and high
current densities up to 6 A∙cm^{−2}$ ) we see significant temperature and current density increase of ∼13 K and 0.7 A∙cm^{−2}$ which can
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be explained by decreasing membrane resistance determined via EIS of >10 mΩ⋅cm 2 along the channel. The validity of the
impedance measurements is proofed by comparison of the impedance at 100 mHz with the direct current resistance of the cell
extracted by the local slope of the polarization curve.