fig4

Figure 4. (A) Investigation of the sodium-storage mechanism: Ex situ XRD of NFP/C-HT_0.02 during discharge; (B) evolution of the unit cell volume and in situ impedance Rct of NFP/C-HT_0.02 during discharge; in situ EIS spectra of NFP/C-HT_0.02 during discharge (C) and charge (D); (E) Fe 2p spectra of NFP/C-HT_0.02 after charging; SEM images of NFP/C-HT_0.02 after charging (F) and after long-term cycling (G); (H) elemental mapping of the metallic sodium surface on the counter electrode after charging of NFP/C-HT_0.02.