Fig. 1. SEM images of (a) raw-Ta₃N₅ electrode, (b) TaCl₅–Ta₃N₅ electrode, and (c) necked-Ta₃N₅ electrode. (d) HRTEM image of necked-Ta₃N₅ electrode. (e) XPS spectra of O 1s and Ta 4f for raw-Ta₃N₅ (orange), heated-Ta₃N₅ (blue), TaCl₅–Ta₃N₅ (pink) and necked-Ta₃N₅ (black) electrodes.