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

Abstract

In this work, ≈25 µm thin titanium microporous layers (MPLs) with ≈2 µm small pores and low surface roughness were coated and sintered on top of ≈260 µm thick commercial titanium-powder-sinter sheets with ≈16 µm pores, maintaining a porosity of ≈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 mΩ 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 ≈1 µm thin anodes with an iridium loading of ≈0.2 mgIr cm-2, the use of an MPL leads to a ≈24 mV improvement in HFR-free cell voltage at 6 A cm-2. As no such benefit is observed for ≈9 µm thick anodes with ≈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 membrane