Imaging optimization of FIB cross sections for reliable porosity analysis of PEMFC cathode catalyst layers

Abstract

Abstract Focused ion beam–scanning electron microscopy (FIB–SEM) was used to investigate the effects of acceleration voltage, beam current, and cryogenic conditions on the cross-sectional preparation of proton exchange membrane fuel cell (PEMFC) cathode catalyst layers. Milling at 30 kV and 0.26 nA effectively minimized curtaining artifacts and produced an apparent cross-sectional pore morphology similar to that obtained by cryogenic milling, indicating that optimized room-temperature milling can provide cross sections suitable for consistent two-dimensional (2D) pore-area analysis under the conditions examined. Representative FIB–SEM cross-sectional images of PEMFC cathode catalyst layers prepared under different FIB milling conditions: (a–c) 5 kV at room temperature, (d–f) 30 kV at room temperature, and (g–i) 30 kV under cryogenic conditions (− 150 °C). The indicated voltage and current values represent the FIB acceleration voltage and ion beam current used for milling, respectively. The red dashed box in (f) highlights the optimized room-temperature milling condition (30 kV, 0.26 nA) used for comparison with the corresponding cryogenic condition in (i).