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TY  - THES
AU  - Borowec, Julian Manuel
TI  - Mechanics and electrics of electrolyzer materials - a micro- and nanoscale analysis
PB  - RWTH Aachen University
VL  - Dissertation
CY  - Aachen
M1  - RWTH-2025-06489
SP  - 1 Online-Ressource
PY  - 2025
N1  - Veröffentlicht auf dem Publikationsserver der RWTH Aachen University
N1  - Dissertation, RWTH Aachen University, 2025
AB  - Understanding Proton Exchange Membrane Electrolyzer Cell (PEMEC) aging is essential for durability enhancement and thus competitive electrochemical hydrogen production. Therefore, the catalyst layers of a long-term operated (>5000 h) web-woven fiber reinforced Membrane Electrode Assembly (MEA) were investigated using nanomechanical and nanoelectrical Atomic Force Microscopy (AFM) techniques, nanoindentation, and Microscopic Four-Point Probe (μ4PP) and Macroscopic Four-Point Probe (Ma4PP) analysis. Reinforcement fibers locally increase the stiffness and hardness and proved to be suitable for long-term operation. Nanoindentation reveals an increased Reduced Modulus and hardness with operation, accompanied by a stiffening of the near-surface catalyst shown by AFM. This effect is promoted by a loss of low-stiffness ionomer, confirmed by the increase of electrically conductive anode surface area. The most significant anode aging effects were observed only at a small surface fraction — at certain Porous Transport Layer (PTL) related domains. Compared to the anode, only minor aging was observed at the cathode. Micrometer-sized ionomer plateaus exhibit a stable nature upon operation, as their stiffness and frequency on the surface remained constant. The catalyst slightly stiffened at positions within and outside of Carbon Fiber (CF) PTL imprints, indicating no influence of the local PTL compression on the aging. While most PEMEC utilize a cathodic PTL with microscale CFs, Carbon Nanofiber (CNF) networks are a potential next-generation PTL material, especially for the Anion Exchange Membrane Electrolyzer Cell (AEMEC). To tailor the overall macroscopic electrical properties of Polyacrylonitrile (PAN)-based CNF networks, microelectrical and nanoelectrical properties of CNFs, carbonized at temperatures from 600 °C to 1000 °C, are studied by conductive AFM. At the microscale, the CNF networks show good electrical interconnections enabling a homogeneously distributed current flow. Strikingly, nanoscale current maps of individual CNFs reveal a large high-resistive surface fraction, representing a clear limitation. High-resistive surface domains are either attributed to disordered high-resistive carbon structures at the surface or the absence of electron percolation paths in the bulk volume. With increased carbonization temperature, the conductive surface domains grow in size resulting in a higher conductivity. This thesis enhances the understanding of PEMEC catalyst layer aging related to reinforcement fibers and PTLs, revealing aging phenomena especially at anode-PTL related interfaces. Moreover, next generation CNF PTLs were electrically analyzed. Therefore, this work also contributes to existing micro-structural models of CNFs by extending them with electrical properties, especially electron percolation paths.
LB  - PUB:(DE-HGF)11
DO  - DOI:10.18154/RWTH-2025-06489
UR  - https://publications.rwth-aachen.de/record/1015631
ER  -