In this work, we introduce the application of gas diffusion electrodes (GDE) for benchmarking the electrocatalytic performance of high surface area fuel cell catalysts. It is demonstrated that GDEs offer several inherent advantages over the state-of-the-art technique, i.e. thin film rotating disk electrode (TF-RDE) measurements for fast fuel cell catalyst evaluation. The most critical advantage is reactant mass transport. While in RDE measurements the reactant mass transport is severely limited by the gas solubility of the reactant in the electrolyte, GDEs enable reactant transport rates similar to technical fuel cell devices. Hence, in contrast to TF-RDE measurements, performance data obtained from GDE measurements can be directly compared to membrane electrode assembly (MEA) tests. Therefore, the application of GDEs for the testing of fuel cell catalysts closes the gap between catalyst research in academia and real applications.

Due to the slow kinetics of the oxygen evolution reaction (OER), high precious metal loadings are currently required at the anode of proton exchange membrane (PEM) electrolyzers. In this work, we present a novel, scalable and efficient method for the fabrication of high surface area iridium-based electrocatalysts. Using alternating sputtering of iridium and cobalt, followed by selective leaching, we produce a self-supported and highly active OER electrocatalysts for acidic environments. Nanostructured IrO_x-networks present a bulk-like behaviour, with a site-specific activity similar to that of extended polycrystalline IrO_x surfaces. Moreover, in terms of mass activity, the IrO_x-networks are among the most active Ir-based catalysts reported, presenting a mass activity enhancement by a factor of eight over commercial Ir-black nanoparticles. These novel self-supported Ir-based networks are very stable, which, combined with their enhanced mass activity, makes them promising anode catalysts for PEM electrolyzers.

The development of catalysts for the oxygen reduction reaction in low-temperature fuel cells depends on efficient and accurate electrochemical characterization methods. Currently, two primary techniques exist: rotating disk electrode (RDE) measurements in half-cells with liquid electrolyte and single cell tests with membrane electrode assemblies (MEAs). While the RDE technique allows for rapid catalyst benchmarking, it is limited to electrode potentials far from operating fuel cells. On the other hand, MEAs can provide direct performance data at realistic conditions but require specialized equipment and large quantities of catalyst, making them less ideal for early-stage development. Using sputtered platinum thin-film electrodes, we show that gas diffusion electrode (GDE) half-cells can be used as an intermediate platform for rapid benchmarking at fuel-cell relevant current densities (~1 A cm⁻²). Furthermore, we demonstrate how different parameters (loading, electrolyte concentration, humidification, and Nafion membrane) influence the performance of unsupported platinum catalysts. The specific activity could be measured independent of the applied loading at potentials down to 0.80 V_RHE reaching a value of 0.72 mA cm⁻² at 0.9 V_RHE in the GDE. By comparison with RDE measurements and Pt/C measurements, we establish the importance of catalyst characterization under realistic reaction conditions.