In this study, the process of catalyst ink drops drying in room air is investigated experimentally, which is key to the fabrication of, hence the microstructure formation in, the catalyst layers of polymer electrolyte membrane fuel cells (PEMFCs). The real-time drying process is observed through an optical microscopy and the dried deposition is investigated with a scanning electron microscopy (SEM) and the optical microscopy. This study provides insight into the fundamental understanding of complex drying dynamics during catalyst ink drying, and laid theoretical foundation for further studies...