Fig. 3: Characterization of the Pt-Fe-N-C electrocatalyst after durability measurements.
a, HAADF-STEM image of the Pt-Fe-N-C catalyst after 100,000 cycles, in which the blue and red dashed circles denote the Fe and Pt single atoms, respectively. b, EELS analysis to probe the well-preserved Pt–N and Fe–N configurations. c,d, The HAADF-STEM image (c) and corresponding line profile (along the green line in c) for the HAADF intensity analysis (d) illustrate the PtFe@Pt core–shell structure. e–g, HAADF-STEM images of the larger Pt-Fe-N-C catalyst nanoparticles after 100,000 cycles (e,f) and EDX line profile (g) along the purple arrow in f show the mass content differential between Fe and Pt and further reveal the formation of a pit in the centre.
