*2.7. X-ray Diffraction and Scanning Electron Microscopy*

X-ray Diffraction (XRD) measurements were obtained with a D8 Advance diffractometer (Bruker) equipped with the LynxEye linear detector, using Cu Ka radiation (k = 1.5418 Å) and operating at 40 kV/40 mA. The diffraction patterns were collected from 15 to 80 <sup>o</sup> with a step size of 0.02<sup>o</sup> and a counting time of 0.6 s. The sample surface was imaged on an EVO HD electron microscope (Zeiss) at 10 kV after being fixed onto stubs using a carbon film.

#### **3. Results and Discussion**

#### *3.1. Characterization of the Materials by X-Ray Diffraction and Scanning Electron Microscopy*

The materials utilized for the construction of the photoelectrochemical platform were evaluated by X-ray diffraction (XRD). In Figure 1A (red line), the characteristic peaks of the BiVO4/FTO can be observed. The 2θ values of BiVO4 at 18.7, 28.7, 30.4, 34.5, 35.2, 39.7, 42.2, 46.7, 50.3, 53.3, and 58.4 correspond to the (110)(011), (−130)(−121)(121), (040), (200), (002), (211), (051), (240), (202), (−161)(161), and (−321)(321) planes of the monoclinic BiVO4 scheelite (JCPDS 014-0688) [16]. A small amount of the BiVO4 tetragonal phase (JCPDS 014-0133) was also detected, and its most intense peak (200) can be seen at 24.4◦. Furthermore, additional diffraction peaks appear after the Bi2S3 electrodeposition, as can be seen in Figure 1A (black diffractogram). In this figure, the XRD spectrum of the BiVO4/Bi2S3/FTO photoelectrochemical platform shows the characteristic diffraction peaks of the BiVO4/FTO platform. In addition, one can see a peak at 27.2◦ from the (012) plane of the Bi rhombohedral phase and the (220) and (130) peaks (at 22.3 and 24.8, respectively) of the orthorhombic Bi2S3 phase (JCPDS 017-0320), clearly demonstrating that the modification process was effective and that all samples display a high crystallinity. In addition, to show the morphology of the Bi2S3/BiVO4/FTO platform, a scanning electron microscopy (SEM) image was obtained. Figure 1B shows smaller particles covering an agglomerated material. These smaller particles resulted from the electrodeposition of Bi2S3 on the BiVO4/FTO platform surface after the preparation procedure of the Bi2S3/BiVO4/FTO electrochemical platform, which was described in the experimental section.

**Figure 1.** (**A**) X-Ray diffraction patterns of BiVO4/FTO and BiVO4/Bi2S3/FTO. (**B**) SEM image of BiVO4/Bi2S3/FTO. Scale bar = 1 μm.
