Do We Really Need an Ionomer? Direct Nano-Printing of Iridium-Layers for PEM-Water Electrolysis

Proton Exchange Membrane Water Electrolysis (PEMWE) is a key technology for efficient hydrogen production; however, its reliance on iridium and PFSA-based polymers in the catalyst layer (CL) drives up costs and raises sustainability concerns [1] . Iridium remains the only stable catalyst for the oxygen evolution reaction (OER) in acidic conditions, and PFSA additives enhance proton conductivity and layer adhesion. While traditional methods with ~2 mg/cm² loadings forming thick catalyst layers that relied on ionomer as catalyst binder, the shift toward ultra-thin (~0.1 mg/cm²) sub-micron layers raises the question of whether ionomers will be necessary for the next-gen layers. Recently in ECS Prime’24 and in our white paper [1] , we demonstrated ionomer-free catalyst layers (ifCLs) with 0.4 mgIr/cm² coated on 25 cm² titanium porous transfer layers (PTL) yielding a -4 mV decay on a standard PTL and a +27 mV improvement on microporous layered version (MPL-PTL) after 500 hours of stability testing hold at 2 A/cm² and 60 °C. In short, the achievement of this performance metric is attributed to the high porosity and surface area of Ir, made possible by the spark ablation-based synthesis of 2–5 nm nanoparticles and their deposition into a micro-patterned layer [1] . Herein, for the first time, we will display the performance of our 0.1 mgIr/cm² ifCLs applied on Aquivion® membranes and PTLs, to realize CCM and CCS approaches, respectively. We will show our findings on the influence of CL loading and thickness on the surface conductivity across different substrates, and present electrochemical performance data from a 4 cm² Fraunhofer-ISE test cell, including polarization curves and impedance spectroscopy in an industrial-scale PEMWE setup operating at 80°C and 2 bar. Additionally, we will discuss the importance of pre-treatment and conditioning protocols chosen for ultra-low loadings and show that optimized nanoporous ifCLs fabricated via spark ablation reach 3 A/cm² below 1.8 V/cell - that is within the targets of the DOE 2026 [2] . We anticipate that our results will engage a broad audience across electrolysis fields as it circumvents the PFSA additives and facilitates precious metal recycling. [1] (a) Irtem et. al., Advanced Nano-Porous Thin Films: Automating Water Electrolysis with Spark Ablation Printing, 2024 ECS Meet. Abstr. MA2024-02 2855, (b) VSParticle B.V. (2025) White Paper, Advancements in scaling PEM water electrolysis with reduced iridium usage, Netherlands [2] Hydrogen Shot: Water Electrolysis Technology Assessment, Energy Earthshots U.S. Department of Energy, 2013 This project has received funding from the European Union’s Horizon Europe research and innovation programme under the Grant Agreement No 101091777. © 2023 CLEANHYPRO Figure 1