Ultrathin Microporous Transport Layers: Implications for Low Catalyst Loadings, Thin Membranes, and High Current Density Operation for Proton Exchange Membrane Electrolysis

Abstract Porous transport layers (PTL) and their surface properties have the potential to improve the performance of proton exchange membrane water electrolyzers (PEMWE), which is imperative to reduce feedstock costs and lead to their widespread implementation. This work introduces a novel generation of titanium microporous layers (MPLs) with ultra‐low thicknesses of ≈20 µm which reduces raw material costs. They also feature advanced interfacial properties tailored to maximize catalyst utilization at low Ir‐loadings. The bulk morphology and surface properties of the hierarchically structured PTLs are assessed by X‐ray tomographic microscopy. The low surface roughness of the MPL allows the use of thinner membranes since it minimizes possible deformations in the membrane. Cells containing the MPLs outperformed those containing state‐of‐the‐art commercially available PTL materials by up to 100 mV at 7 A cm −2 in combination with low‐loaded catalyst‐coated membranes of 0.4 mg Ir cm −2 . Hydrogen crossover is also reduced, especially at low current densities, leading to a larger turndown ratio which can enable more cost‐effective operating strategies. Finally, these rationally designed MPLs also lead to high catalyst utilization by overcoming the naturally occurring high in‐plane resistance of low‐loaded catalyst layers.