Towards Mass Production: Quantifying Equipment‐Induced Wet‐Film Thickness Deviations During High‐Speed Roll‐to‐Roll Slot‐Die Coating of Fuel Cell Catalyst Layers

ABSTRACT Scalable manufacturing of proton exchange membrane fuel cell (PEMFC) catalyst layers (CLs) requires stable and uniform wet‐film formation during high‐speed roll‐to‐roll (R2R) slot‐die coating. However, finite equipment precision inevitably introduces process fluctuations that can induce wet‐film thickness deviations during the coating stage. In this study, an equipment–process–product framework is established to quantify equipment‐induced wet‐film thickness deviations during CL coating. For cathode‐side coating, transverse‐direction (TD) wet‐film deviation is analyzed by coupling an analytical internal flow field model with finite‐element die‐deformation analysis, where pressure‐induced die‐lip deformation is introduced as a static equipment disturbance that modifies the transverse outlet‐flow distribution. For anode‐side coating, machine‐direction (MD) wet‐film deviation is examined using a two‐phase VOF external flow field model, where roller radial runout is introduced as a dynamic equipment disturbance that generates periodic coating‐gap fluctuation and drives the transient coating‐bead response. The effects of coating speed, die width, shim thickness, fluctuation amplitude, and fluctuation period are then evaluated. The results show that increasing coating speed raises the internal cavity pressure and induces convex die‐lip deformation, leading to center‐thick wet‐film distribution in TD. In MD, excessive gap fluctuation causes upstream ink accumulation at small gaps and meniscus instability with gas invasion at large gaps. The influence of fluctuation period depends on whether the coating process remains within the stable operating window, while higher coating speed reduces tolerance to gap fluctuation. This work quantitatively links practical equipment fluctuations to coating‐stage wet‐film thickness deviation and provides guidance for precision control in scalable PEMFC CL manufacturing.