Structural properties of inkjet-printed and ultrasound-spray-coated PEM fuel cell catalyst layers and their impact on fuel cell performance

Catalyst layers (CLs) are critical to the performance and durability of proton exchange membrane fuel cells (PEMFCs). As shown previously, inkjet printing (IJP) represents an attractive CL production technology ensuring efficient catalyst utilization. This study provides a comparative structural analysis of CLs fabricated via IJP and ultrasonic spray coating (USC), aiming to explain the performance differences observed in operating fuel cells utilizing these two types of CL. This allows further optimisation of the CL deposition by IJP. A combination of advanced experimental and modeling techniques was employed to accomplish this task, including in-plane electron conductivity measurements, optical profilometry, FIB-SEM tomography, and 3D structure-based transport simulations. IJP CLs were consistently thinner (4-10 μm vs. 6-18 μm), smoother (Ra ~0.38-0.44 μm vs. ~0.55-0.63 μm), and exhibited significantly fewer surface cracks (0.18-0.61 % vs. 1.34-4.05 %) compared to USC layers. Despite similar porosities at the microscale (40.0 % for IJP vs. 38.3 % for USC), IJP layers showed higher electrical conductivity (448 ± 135 S m-1 vs. 387 ± 96 S m-1) and more homogeneous Pt distribution. FIB-SEM reconstructions confirmed isotropic and statistically homogeneous structures of CLs produced by both methods, with negligible isolated porosity and comparable transport properties. However, macroscale features such as crack formation, layer thickness, and surface roughness strongly impacted overall performance and Pt utilization. These results highlight the critical role of deposition method in determining catalyst layer architecture and reveal inkjet printing as a highly promising approach for producing low-loading, high-performance CLs with potential for scalable, additive manufacturing.