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The continuous roll‐to‐roll slot die coating technique has shown great potential for fuel cell electrode fabrication. It is essential to determine the particulate coating window to obtain a defect‐free film of uniform thickness and uniform particle dispersion. For this dual‐purpose, an additional upper operating limit has been proposed via a “flow field analysis scheme” that combines analysis and simulation. In this analysis, the fundamentals of flow pattern transition (Poiseuille–Couette–bubbly flow) behind coating limits are clarified. The Couette flow is advantageous for uniform shear rate and dispersion. Furthermore, phase‐field simulations systematically investigate the effect of fluid and geometrical parameters and quantitatively present the flow limit with explicit expression. Results reveal that the slope of the upper limit is inversely correlated with shear‐thinning index n while proportional to the coating gap H. Combining the bubble entrainment boundary, lower n and H are favorable for a larger particulate coating window.

The flow distribution is of significance to the fuel cell performance and durability, which has been studied from a theoretical and practical level in this work. The transverse‐flow‐control‐based mechanism behind flow distribution processes is revealed. The core lies in the reasonable generation and distribution of transverse flow, which are the prerequisite and co‐requisite for flow homogeneity. For the dual purpose, a novel design of combined‐mesh‐type distribution zone is proposed incorporating central horizontal meshes and lateral vertical meshes. The design philosophy and methodology are clarified. Under these guidelines, the novel distributor design is applied to different flow field plate geometries including the shorter distribution zone, higher expansion ratio, and scaled‐up fuel cell. Through organized and detailed simulations, two key geometrical parameters (porosities of central and lateral meshes) are quantified and the superior effect on flow distribution is validated.

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