Investigation of optimized spraying process for directly coated electrode in polymer electrolyte membrane fuel cell

Membrane electrode assembly (MEA) is a core component in polymer electrolyte membrane fuel cells (PEMFCs). A well-constructed catalyst layer is essential for achieving high-performance and reliable fuel cells. Among MEA fabrication processes, direct spray coating has advantages regarding cost-efficiency, processability, and controllability compared to direct sputtering and decal transfer method. In the spray process, the morphology of the catalyst layer depends on conditions in which ink droplets are sprayed and evaporated. Although quantitatively optimizing the spray process is crucial, there is still a lack of well-defined research for optimized spray process. Herein, we propose k-value that can indicate uniform coverage, expressed as a ratio of the area where ink droplets spread compared to the sprayed area. The k-1.0 MEA is fabricated under k-value conditions of one by adjusting nozzle moving speed, which is expected to have the most uniform coverage. Compared to k-0.3 MEA and k-3.0 MEA, the power density improves by 22.3% and 11.1%, respectively. This is attributed to the reduced ion transport resistance of the catalyst layer being reduced by 23.7% and 8.5% and the increased electrochemical active surface area by 16.1% and 9.4%, respectively. Furthermore, the morphology of catalyst layers and substrate temperature effect are investigated.