Fig. 1

Schematic microstructural diagram of the CCL[8]"

Fig. 2

SEM images recorded in back-scattered mode of (a) a pristine MEA and of (b)—(d) the MEA, aged under repeated 136 SU/SD cycles, taken at different locations i.e. from the cathode outlet to the cathode inlet. The upper electrodes are the cathodes[11]"

Fig. 3

Schematic diagram of a XMT scanning device[15]"

Fig. 4

The procedures of FIB-SEM 3D reconstruction. (a) Stack of images produced with FIB-SEM, (b) imaging 3D reconstruction, and (c) quantitative 3D reconstruction and modeling[20]"

Fig. 5

Three-dimensional pore structure of the pristine cathode catalyst layer (a) and after start/stop cycling (b). The colored phase represents the pore structure[22]"

Fig. 6

Electron tomography imaging of Nafion® layer deposited on carbon black in conventional catalyst layers (The blue and light blue regions correspond to Nafion®)[30]"

Fig. 7

Cross-sectional STEM images and EDS mapping of cathode electrocatalyst layers with varying Nafion® ratio[23]"

Fig. 8

Cross section of the electrode of a Nafion®-based MEA: (a) 3D topography image; (b) Current mapping at bias voltage U=2 V; (c) Adhesion mapping; (d) Adhesion image of a cross section of the catalyst layer of a Nafion®-based MEA, overlaid with a diagram where white dots indicate the average ionomer content of an area of 1 μm2 with 1 μm step width[31]"

Fig. 9

STEM images and Pt distributions at both interior and exterior surfaces of the carbon-supported Pt catalysts[34]"

Fig. 10

3D reconstructed images and 2D TEM projections of the two kinds of Pt/Cs, (a) TEC10V50E and (b) TEC10E50E. The gray and black particles in 3D images of part (b) correspond to Pt particles inside and at the surface of carbon substrate. Parts (c) and (d) are the digitally sliced images of TEC10V50E and TEC10E50E. The small pores can be visible inside the carbon as indicated by white arrows in part (d)[37]"

Fig. 11

Representative IL-SEM images of the cathodic catalytic layer highlighting different types of catalyst changes from BOL (fresh) to after each AST session until EOL (14,000 cycles overall). The red circles mark general growth of particles, the yellow dashed square shows particles that migrate and coalesce, and the blue dashed circle represents particles that first grow and then shrink. The markers are not comprehensive and only illustrate the main degradation effects during the AST cycling procedure. Scale bar = 50 nm[40]"

Fig. 12

Pt catalyst nanoparticle size mapping of 1 cm × 1 cm area (a) near air outlet of the non-aged MEA (b) in the middle of the flow field of the non-aged MEA, (c) near air inlet of the non-aged MEA, (d) near gas outlet of the post-AST MEA, (e) in the middle of the flow field of the post-AST MEA, and (f) near gas inlet of the post-AST MEA. Insets show the corresponding flow field geometry for each measured 1 cm × 1 cm location[41]"