Controlling the microstructure of the catalyst layer in polymer electrolyte membrane fuel cells (PEMFCs) is crucial for enhancing performance. This study focuses on understanding the impact of solvent composition on the catalyst ink structure and morphology. By investigating inks composed of Pt/C, ionomer, and a solvent mixture of 1-propanol (NPA) and water, we examine three different ink compositions and evaluate their stability, rheological properties, and crack characteristics on the catalyst layer. The inks with higher water content exhibit gel-like behavior due to ionomer network structures, while the inks with higher NPA content show liquid-like behavior with well-dispersed catalyst particles. Remarkably, the NPA-rich ink with strong liquid properties effectively suppressed crack formation in the catalyst layer. These findings provide valuable insights into the relationship between solvent composition, ink structure, and crack formation, enabling the optimization of ink design to enhance PEMFC performance.