Interfacial and bulk properties between the catalyst layer and the porous transport layer (PTL) restrict the iridium loading reduction for proton exchange membrane water electrolyzers (PEMWEs), by limiting their mass and charge transport. Using titanium fiber PTLs of varying thickness and porosity, the bulk and interface transport properties are investigated, correlating them to PEMWEs cell performance at ultra-low Ir loadings of ≈0.05 mg_Ir cm⁻². Electrochemical experiments, tomography, and modeling are combined to study the bulk and interfacial impacts of PTLs on PEMWE performance. It is found that the PEMWE performance is largely dependent on the PTL properties at ultra-low Ir loadings; bulk structural properties are critical to determine the mass transport and Ohmic resistance of PEMWEs while the surface properties of PTLs are critical to govern the catalyst layer utilization and electrode kinetics. The PTL-induced variation in kinetic and mass transport overpotential are on the order of ≈40 and 60 mV (at 80 A mg_Ir⁻¹), respectively, while a nonnegligible 35 mV (at 3 A cm⁻²) difference in Ohmic overpotential. Thus at least 150 mV improvement in PEMWE performance can be achieved through PTL structural optimization without membrane thickness reduction or advent of new electrocatalysts.

中文翻译：

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深入了解超低铱负载下影响质子交换膜水电解槽性能的界面和体传输现象

催化剂层和多孔传输层 (PTL) 之间的界面和体积特性通过限制质子交换膜水电解槽 (PEMWE) 的质量和电荷传输来限制铱负载的减少。使用不同厚度和孔隙率的钛纤维 PTL，研究了体积和界面传输特性，将它们与 PEMWEs 电池在 ≈0.05 mg _Ir cm ^-2的超低 Ir 负载下的性能相关联. 结合电化学实验、断层扫描和建模来研究 PTL 对 PEMWE 性能的体积和界面影响。发现 PEMWE 性能在很大程度上取决于超低 Ir 负载下的 PTL 特性；整体结构特性对于确定 PEMWE 的传质和欧姆电阻至关重要，而 PTL 的表面特性对于控制催化剂层利用率和电极动力学至关重要。PTL 引起的动力学和传质过电位的变化分别约为 ≈40 和 60 mV（在 80 A mg _Ir ^-1），而不可忽略的 35 mV（在 3 A cm ^-2) 欧姆过电位的差异。因此，通过 PTL 结构优化可以实现至少 150 mV 的 PEMWE 性能改进，而无需减少膜厚度或出现新的电催化剂。