Microporous transport layers facilitating low iridium loadings in polymer electrolyte water electrolysis†

Minimizing the power-specific iridium loading in polymer electrolyte water electrolysis (PEWE) is essential for the commercialization and upscaling of this technology. However, decreasing the iridium loading can severely affect performance and stability. Microporous layers (MPL) can overcome some of these issues by maximizing catalyst utilization and increasing cell efficiency. In this study, we combined advanced synchrotron and lab-based X-ray imaging techniques and electrochemical characterization to improve the PEWE cell performance at low Ir loadings using novel MPLs. For the first time, the 3D nanostructure of the catalyst layer was characterized under dry and wet conditions using ptychographic X-ray laminography. We prepared catalyst layers (CL) at three iridium loadings between 2.5 and 0.1 mg_Ircm⁻² in two different configurations: depositing either on the membrane or on the Ti-substrate (MPL). The MPL structure and catalyst distribution at its surface were analyzed using X-ray tomographic microscopy. Moreover, we investigated the effect of introducing a thin protective Pt coating on the MPL. The electrochemical performance was characterized for all cell combinations, and an in-depth kinetic analysis revealed information on CL utilization. The MPLs exhibit significant benefits for reducing iridium loadings, allowing performance to be sustained with only modest voltage losses. The challenges in fabricating anodic CLs with reduced catalyst loadings and the advantages of using an MPL in both configurations are discussed. The findings of this study contribute to accomplishing the required targets in terms of power-specific iridium loadings for future PEWE systems.