Optimization of Anode-Side Components in Proton-Exchange Membrane Water Electrolysis: A Structure-Function Relationship Analysis

Green hydrogen can be produced via water electrolysis when coupled to renewable energy sources. Among the available electrolysis technologies, proton-exchange membrane water electrolysis (PEMWE) is a promising technology because it can accommodate rapid load changes, it shows a high power density, and has a compact system design. These characteristics make PEMWE well-suited for a large-scale hydrogen production to the gigawatt scale. Nevertheless, PEMWE still faces several challenges that hinder its large-scale deployment. These include limited long-term durability, the need for optimization at critical component interfaces, and the reliance on scarce materials. Addressing these issues is essential to improve the cost competitiveness of PEMWE relative to conventional hydrogen production methods. This thesis explores these three challenges. First, advancing the long-term durability of PEMWE requires a deep understanding of degradation mechanisms. To elevate understanding, this thesis investigates degradation induced by four distinct accelerated stress test protocols using a combination of electrochemical diagnostics and quantitative ex situ characterization techniques. The study reveals multiple interconnected degradation pathways that are strongly influenced by the the operational mode. A key finding concerns the dissolution of the platinum coating from the anode porous transport layer (PTL), which alters the PTL | catalyst layer interface and results in platinum precipitation within the membrane. This migration process may intensify radical formation and chemical membrane degradation. While platinum coatings on Ti-based PTLs are often employed to prevent passivation and minimize contact resistance, their contribution in degradation has received only limited attention, highlighting the importance to probe PTL stability alongside that of the catalyst layers and membrane. Furthermore, changes in the oxidation state of the Ir-based anode catalyst are observed. Importantly, when cycling through redox transients, a higher degree of oxidation is achieved compared to a steady operation in an oxidative regime. Secondly, achieving cost-effective green hydrogen production requires the development of lower-cost components. The PTL plays a vital role in PEMWE facilitating water and gas transport and establishing electrical contact with the catalyst layer. To reduce PTL costs, a fabrication approach based on high-velocity oxy-fuel spraying is introduced. As analyzed and visualized by X-ray microscopy, the produced PTLs exhibit distinct surface morphologies with two sides of different roughness and porosity. The side with reduced porosity (21 %) is intended as a microporous layer, thereby improving the interface with the catalyst layer. This structure supports the use of thin catalyst layers and a porous transport electrode approach to further reduce costs. PEMWE single-cell testing demonstrates that the sprayed PTLs achieve performance comparable to commercially available PTL material and that performance improvements are possible with porous transport electrode approach at low loadings. Finally, the high price and scarcity of iridium necessitate substantial reductions in iridium loading. This thesis presents a scalable photodeposition-based synthesis method for a TiO2@IrOx core–shell catalyst design with reduced iridium contents of 40 wt% and 10 wt %. The synthesis yields titania support particles uniformly coated with a thin iridium oxide shell of only 2.1 ± 0.4 nm, exhibiting high ex situ activity. The reduced iridium content enables the preparation of sufficiently thick catalyst layers at decreased iridium loadings that maintain mechanical integrity during PEMWE operation. The novel TiO2@IrOx core–shell catalyst clearly outperforms the commercial reference in single-cell tests with an iridium loading below 0.3mgIr cm−2. Moreover, by increasing the annealing temperature during synthesis, the stability of the core-shell catalyst is improved, performing on par with commercial catalyst material.