Low Loading and High Utilization Ratio of Iridium Catalyst Coated Smoltek Carbon Nanofibers Used as Anode Material for PEM Water Electrolyzers

Proton exchange membrane water electrolyzers (PEMWE) are a core technology for the future green hydrogen production market. The installed power for PEMWE is estimated to be 40 GW by 2030 [1]. The oxygen evolution reaction (OER) catalyst on the anode side is dominated by Iridium (Ir)-based materials, one of the rarest noble metals in the crust of Earth. It is critical to lower the loading of Ir-based catalyst to ≈ 0.1 mg Ir/cm 2 without compromising the overall performance to enable the mass manufacturing targets. It is a big challenge due to the poor electrical contact between the resulting catalyst layers and the anode substrate [2-3]. To reach this goal, Smoltek invented an advanced porous transport electrode (PTE) concept using its proprietary carbon nanofiber (CNF) technology [4] and unique Ir coating technology. An anode porous transport layer (PTL) is first modified by vertically aligned CNFs to increase surface area, followed by coating a corrosion-resistant and conductive layer (e.g. Platinum) and a subsequent OER catalyst layer (Fig. 1a). Cathodic electrodeposition in a three-electrode static cell was performed for Ir-based catalyst deposition. We demonstrate that with this method, the morphology and deposition process of Ir are controllable at very low loading amounts (≥ 0.1 mg Ir/cm 2 ). An Ir coating layer can be formed on the highly structured CNF-based surface. The electrodeposited Ir has strong adhesion with the CNF PTEs, resulting in a high electrical conductivity [5]. This unique Ir-electrodeposited CNF PTEs structure maximizes the anode surface area and paves a new way to increase the utilization ratio of catalyst surface at a low loading amount, which makes it a competitive anode material in today’s PEMWE market. References Stiber et al. Adv. Energy Mater. , 2021, 11, 2100630. Möckl et al. J. Electrochem. Soc. , 2022, 169, 064505. Bernt et al. Chem. Ing. Tech. , 2020, 92, 31-39. https://www.smoltek.com/applications/electrolyzers/ Krivina et al. Adv.Mater. , 2022, 34, 2203033. Figure 1