Investigating the effect of porous transport layer defects on structural and transport properties in proton-exchange-membrane water electrolyzers

• Pore-network model quantifies how PTL defects alter structure and transport. • Thickness variation and positive protrusions at the CL drive PTL water permeability near zero. • Cracks, pinholes and negative protrusions cause minor roughness change and enhance water permeability. • Porosity gradients create trade-offs: gases favor high-porosity paths, water uses denser regions. • Orienting the PTL with the defected side toward the flow field mitigates transport losses. Cost reduction of clean hydrogen is of utmost priority to leverage widespread adoption of hydrogen technologies, and porous transport layers (PTL) are known to be a significant cost driver for proton-exchange-membrane (PEM) water electrolyzers. This study reveals how the key morphological defects in the PTL that arise during manufacturing process can critically impact the performance of PEM water electrolyzers. A sintered titanium powder PTL was chosen as the baseline configuration for this model, due to its widespread use in commercial PEM water electrolyzers. Stochastic modelling is used to examine defects including thickness variations, positive protrusions, pinholes, porosity variations, cracks, and negative protrusions. Pore network modelling is used to characterize the impact of each defect on the transport properties, including single-phase and two-phase permeability as well as oxygen saturation profiles. Simulation results reveal that thickness variations and positive protrusions are defects that severely affect electrolysis, stemming from poor contact with the catalyst layer. They also significantly reduce single-phase permeability by increasing tortuosity. Furthermore, thickness variations and positive protrusions reduce water’s effective permeability by causing flooding of oxygen gas, preventing reactant water from reaching reaction sites. In contrast, cracks, negative protrusions, and pinholes are defects with minor impact on electrolysis. In fact, they enhance the single-phase and two-phase permeability of liquid water in the through-plane direction. Finally, we suggest an effective remediation strategy for certain defects, which is to simply reorient the defect PTL during cell assembly to mitigate the negative impacts. Implementing these strategies will contribute in reduction of capital costs for PEM water electrolyzers.