Fig. 1. (Color online) Schematic illustration of the OM-assisted synthesis process and the structural evolution of CZTS nanocrystals.

Fig. 2. (Color online) (a) XRD patterns of CZTS-0 and CZTS-3, the blue and red symbols represent kesterite and wurtzite; (b, c) TEM images of CZTS nanosheets (CZTS-0) and CZTS nanorods (CZTS-3); (d) Size distribution histogram of the diameter of CZTS nanosheets; Size distribution histogram of width (e) and length (f) of CZTS nanorods.

Fig. 3. (Color online) (a–f) TEM images and (g) XRD patterns of CZTS nanocrystals with different morphologies under the OM addition amounts of 0, 0.5, 1.0, 1.5, 2.0, and 3.0 mL; (h) Schematic representation of the proposed growth mechanism of OM-dependent CZTS nanocrystals.

Fig. 4. (Color online) (a) LSV polarization curves of bare GCE, and CZTS-n (n = 0, 1.0, 2.0 and 3.0) supported on GCE for the HER at the 5 mV/s scan rate; (b) Overpotentials at the current density of 10 mA/cm², (c) the corresponding to the Tafel plot, and (d) the Nyquist plot of CZTS-n (n = 0, 1.0, 2.0 and 3.0); (e) Double-layer capacitance (Cdl) measurements by CV at different scan rates of 20, 40, 60, 80 and 100 mV/s for CZTS-1.0; (f) Linear fitting of the capacitive currents versus CV scan rates. The curves were obtained from the CV.

Fig. 5. (Color online) (a) The correlation between structures and performance of CZTS nanocrystals for the HER; (b) Schematic illustration of the electrocatalytic HER process of CZTS-1.0.

Table 1. Fitting equivalent circuit parameters of EIS measurement.