Preparation and Performance Evaluation of Microporous Transport Layers for Proton Exchange Membrane (PEM) Water Electrolyzer Anodes

In this work, approximate to 25 mu m thin titanium microporous layers (MPLs) with approximate to 2 mu m small pores and low surface roughness were coated and sintered on top of approximate to 260 mu m thick commercial titanium-powder-sinter sheets with approximate to 16 mu m pores, maintaining a porosity of approximate to 40% in both layers. Serving as porous transport layers (PTLs) on the anode side in proton exchange membrane water electrolyzers (PEMWEs), these pore-graded, two-layer sheets ("PTL/MPL") are compared to single-layer PTLs in single-cell PEMWEs. The PTL/MPL samples prepared here give a 3-6 m Omega cm2 lower high-frequency resistance (HFR) compared to the as-received single-layer PTL, which is attributed to a partial reduction of the TiO2 surface passivation layer during the MPL sintering process. For approximate to 1 mu m thin anodes with an iridium loading of approximate to 0.2 mgIr cm-2, the use of an MPL leads to a approximate to 24 mV improvement in HFR-free cell voltage at 6 A cm-2. As no such benefit is observed for approximate to 9 mu m thick anodes with approximate to 2.0 mgIr cm-2, mass transport resistances within the PTL/MPL play a minor role. Possible reasons for the higher catalyst utilization in ultra-thin electrodes when using an MPL are discussed. Furthermore, an MPL provides superior mechanical membrane support, which is particularly relevant for thin membranes.