Figure 2. (a) XRD pattern of the ZSONT/CC and carbon cloth. XPS spectra of ZSONT/CC (b) C 1s, (c) O 1s, (d) S 2p, and (e) Zn 2p. (f) TEM image of ZSONT. (g) HAADF-STEM image and the corresponding EDS maps of ZSONT.
The phase of the final product ZSONT/CC and the naked carbon cloth was determined by X-ray diffraction (XRD) (Fig. 2a ). The peaks located at 25.1° and 43° were the typical peaks of carbon cloth.[36] Several sharp peaks appeared at 28.2°, 47.2°, and 56.1°, being characteristic of the ZnS diffraction.[37] Another three small peaks at 32.5°, 69.2°, and 76.6° can be assigned to ZnO, suggesting the co-existence of ZnS and ZnO in the 3D current collector [38]. X-ray photoelectron spectroscopy (XPS) was exploited to disclose the chemical composition and the chemical bonding property of the ZOSNT/CC, From the XPS survey scan (Fig. S1 ), peaks of Zn, O, C, and S were identified. A fine scan of these compositional elements can be found inFigure 2b-e . The carbon 1s located at 284.1, 285.2, and 288 eV could correspond to the C-C/C=C, C-OH, and COOH (Fig. 2b ). As shown in the O 1s spectrum (Fig. 2c ), The peak located at 530.8 eV can be assigned to O-Zn, being consistent with XRD results. The other two peaks were associated with C-OH and COOH, likely introduced in the process of acid-treatment of carbon cloth. Figure 2d depicted the S 2p peaks centered at 161.0 and 162.1 eV, which can be ascribed to S 2p3/2 and S 2p1/2 of ZnS.[39.40] Figure 2e showed the Zn 2p, for which two peaks at 1020.9 and 1043.9 eV can be attributed to the Zn 2p3/2 and Zn 2p1/2 of ZnS and/or ZnO (the chemical shifts of Zn-O and Zn-S are too small to be distinguished). The tubular structure of ZSONT was recorded by transmission electron microscopy (TEM) (Fig. 2f ).Figure 2g showed the HAADF image of individual nanotubes and EDS mapping of Zn, S, and O. Taken from such a sample, only Zn, S, and O were found in the EDS spectra, and they were uniformly distributed in the entire nanotube. Quantitative composition results of a typical ZSONT sample were shown in Figure S2 , in which one can find that the Zn (38.84 at. %) and the S (33.50 at. %) are the major components, and the amount of O is low (7.76 at. %). This result suggested that most of O in the original structure of ZnO was replaced by S (The copper signal came from the TEM grid).