2.3.3. Influence of H2

H2 was introduced to some experiments (e.g., experiment H1), to promote the WO*x* and H2S reaction. In these samples, the majority of the product is IF-WS2 of less than 100 nm in size (Figure 12a,b), with very few 2H-WS2 (Figure 12c). Rod shaped WS2 were also observed occasionally, as shown in Figure 12d. Indeed, the formation of IF-WS2 nanotubes was previously reported in the presence of H2 in the reaction gases [27,39,40]. The XRD profile looks identical to those without H2. Overall, the results show a positive effect when H2 was added to the reaction gas.

Similarly, many previous studies have indicated that, during the conversion from WO3 to WS2, the WO3 was first reduced to tungsten suboxide such as W20O58, W18O49 *etc.* From a localized view, the S replaced the O as soon as the reduction of tungsten oxide initiated. From an overall point of view, the reduction and sulfurization processes must have taken place in parallel [26,31–33]. Thus, the addition of H2 into the reaction gases would accelerate the reduction of tungsten oxides and speed up the subsequent sulphidization, thereby leading to prompt formation of the WS2 layers on the oxide surface. Since the early formation of an inert WS2 layer would prohibit the diffusion and agglomeration of neighbouring nanoparticles, H2 introduction helped prevent particles from agglomeration, hence effectively reducing the chance for the formation of 2H-WS2.

**Figure 12.** SEM images of samples involving H2 in reaction, showing particles less than 100 nm (**a**–**c**), and the presence of nanotubes (**d**).
