This doctoral thesis presents a comprehensive investigation into the electrochemical performance and degradation mechanisms of next-generation electrolysis systems, with a particular emphasis on anion exchange membrane electrolysers (AEMELs) and reversible solid oxide cells (rSOCs). Addressing both low- and high-temperature platforms, the work integrates multiscale methodologies encompassing material characterisation, electrochemical diagnostics, multiphysics modelling, and stack-level validation.
The first part of the study focuses on stainless steel porous transport layers (PTLs) as cost-effective and durable replacements for nickel-based substrates in AEMELs. Through pretreatment activation via potential cycling, a surface-enriched CrFeNi oxide layer is formed, reducing the polarisation resistance by approximately 68%. The findings are corroborated using SEM, EDX, XPS, XRD, and Raman spectroscopy.
Subsequently, a 3D Euler-Euler-Butler-Volmer model is developed to simulate the electrochemical behaviour of a fibre-based AEMEL membrane electrode assembly (MEA). Sensitivity analyses indicate that KOH concentration and membrane thickness are the most influential parameters affecting the area-specific resistance (ASR). The model is validated against experimental j-V curves and EIS-derived data using three-electrode and twin-reference configurations.
The third component of the thesis involves long-term degradation studies of MEAs with Sustainion® membranes and non-PGM catalyst layers. Distribution of relaxation times (DRT) analysis, supported by SEM, XPS, and electrochemical impedance spectroscopy, identifies evolving interfacial and transport-related losses over 1000 hours. Degradation is shown to be dominated by membrane degradation and charge transfer limitations.
Finally, the thesis advances stack-level validation by testing a 1 kWe AEMEL stack and a five-unit rSOC short stack. The AEMEL stack demonstrates voltage stability and cell-to-cell uniformity, while DRT analysis highlights the disappearance of transport-limited peaks at high current densities. The rSOC stack, operated under cyclic SOFC-SOEC conditions for more than 3000 hours, exhibits less than 2 %/kh degradation, with performance losses primarily attributed to charge transfer resistance in the fuel electrode.
Collectively, this work provides a unified perspective on the design, diagnostics, and durability of electrolysis systems, thereby contributing to the realisation of cost-effective, efficient, and scalable hydrogen technologies for the global energy transition.
