Opportunities of in situ diagnostics and current distribution in proton exchange membrane water Electrolyzers with segmented bipolar plates

The widespread implementation of renewable energy for the decarbonization of our society is a pressing challenge that requires the use of large-scale electrolyzers to produce green hydrogen. Proton exchange membrane water electrolysis (PEMWE) is ideal for this purpose given its small footprint and flexibility to operate dynamically. However, little is known about the degradation of PEMWEs, and advanced techniques are required for monitoring the health states of stacks. Here, we have successfully integrated a powerful tool for in situ diagnostics in a 25 cm 2 active area PEMWE. A segmented bipolar plate (SBPP) allows local measurements of current and temperature. A series of experiments showing the benefits of the SBPP are described in this work. First, clamping pressure due to uneven torque forces can be determined with the SBPP during cell assembly. When varying the temperature to 80 °C, the current distribution in the cell area is homogeneous over the cell area. Conversely, the tool reveals local current differences reaching 80 % when limiting the water flow in the catalyst-coated membrane (CCM). Furthermore, mass transport phenomena due to flow field design are nonuniform over the cell area and can be monitored at current densities approaching 5.5 A cm −2 . Finally, SBPP is used to investigate local degradation due to contaminants, showing different deactivation zones of the electrode due to poisoning, which is confirmed by energy dispersive X-ray spectroscopy (EDS). The SBPP is versatile and robust, and it opens the possibility for studying in situ a wide range of cell phenomena from mass transport to degradation, thus demonstrating its superior value for diagnostics in PEMWE systems in many different research fields. A segmented bipolar plate is successfully implemented in a proton exchange membrane water electrolyzer to monitor current distribution and study degradation effects. The tool offers new perspectives for in situ diagnostics of laboratory-scale electrolyzers. • In-situ diagnostic tool for PEM electrolyzers • Segmented bipolar plate for monitoring the state of health of PEM electrolyzers • Versatility of the segmented bipolar plate for studying gas removal/water supply, inadequate flow field designs in the bipolar plate and mass transport losses at high current densities • Advantage of the segmented bipolar plate for studying local degradation effects • Segmented bipolar plate combines in-situ diagnosis and on-line regulation