## 3 Synthesis of Transition-Metal-Sulfide-Based Nanomaterials
### MoS\({}_{2}\)  
As mentioned earlier, MoS\({}_{2}\) is a well-known catalyst in different fields including electrocatalysis. [PERSON] et al. reported that the edge sites of MoS\({}_{2}\) have the catalytic capability for CO\({}_{2}\) reduction to form CO [145]. The authors demonstrated that the bridging S atom at the edges of MoS\({}_{2}\) could selectively bind the intermediate COOH\({}^{*}\) over the CO product, which gave rise to the transition-metal scaling relationship of intermediates in CO\({}_{2}\) reduction processes and therefore remarkably enhanced CO\({}_{2}\) reduction activities on transition-metal catalysts. [PERSON] et al. investigated the conversion of CO\({}_{2}\) to 1-propanol at MoS\({}_{2}\) electrodes [146]. The results showed that at a potential of \(-\)0.59 V (compared to a standard hydrogen electrode (SHE)) for large MoS\({}_{2}\) crystals, an efficiency of approximately 3.5% was observed, and with thin films it showed approximately 1%. However, the bulk crystals showed degradation by loss of S as H\({}_{2}\)S but the formation of H\({}_{2}\)S was not observed in the thin film studies. [PERSON] et al. investigated the electroreduction of CO\({}_{2}\) to CO using MoS\({}_{2}\) and N-doped C dots [147]. In that work, the MoS\({}_{2}\)-N-doped carbon dot hybrid was prepared using a solvothermal process, with the formation of the C dots on the MoS\({}_{2}\) nanosheet surfaces in dimethyl formamide (DMF). The composite catalysts showed a faradaic efficiency of 90% with an overpotential of 0.130 V. The authors also performed density functional theory (DFT) calculations which indicated that N-doping of the MoS\({}_{2}\) could decrease the energy barrier of the \({}^{*}\)COOH intermediate and generate more electrons on the Mo edge of the MoS\({}_{2}\) and thus enhance the catalytic activity. [PERSON] et al. investigated the effects of decorating E-MoS\({}_{2}\) nanosheets with fluxosilane (FAS) for the reduction of CO\({}_{2}\) to CO [148]. The authors exfoliated MoS\({}_{2}\) sheets from the bulk using ball milling and subsequently decorated the surface with FAS. The FAS-modified MoS\({}_{2}\) sheets showed the ability to be tuned for syngas production from CO\({}_{2}\) and H\({}_{2}\)O mixtures. Additionally, the FAS-modified MoS\({}_{2}\) sheets showed a faradaic efficiency for CO production of 81% at a current density of 61 mA and an over-potential of \(-1.1\) V. DFT calculations indicated that the FAS modified the electrochemistry of the edge Mo sites which facilitated the desorption of the CO and thus enhanced reaction over non-modified MoS\({}_{2}\) sheets. [PERSON] et al. investigated the layering of TiO\({}_{2}\) over MoS\({}_{2}\) nanosheet arrays for the electrocatalytic reduction of CO\({}_{2}\) to ethanol [149]. The TiO\({}_{2}\)-MoS\({}_{2}\) composites were formed through atomic layer deposition. The composite material showed a 50% faradaic efficiency at \(-0.6\) V. The authors also performed DFT computation studies of the electrocatalysis, which indicated the formation of a Mo-Ti active site at the interface between the TiO\({}_{2}\) and MoS\({}_{2}\). [PERSON] et al. investigated the electrocatalytic reduction of CO\({}_{2}\) to CO using TiO\({}_{2}\)-modified MoS\({}_{2}\)[150]. The optimized composite in KHCO\({}_{3}\) solution showed an onset over-potential of 100 mV and a maximum faradaic efficiency of 82% at -0.7 V with a current density of 68 mA/cm\({}^{2}\). The authors also performed DFT calculations which indicated that the Ti-S bonds formed between the TiO\({}_{2}\) and MoS\({}_{2}\) composite changed the electric properties of the MoS\({}_{2}\) and adsorption on the Mo sites. [PERSON] et al. investigated MoS\({}_{2}\) rods supported on TiO\({}_{2}\) NPs for the electrocatalytic and photo-enhanced electrocatalytic reduction of CO\({}_{2}\) to methanol [151]. The electrocatalytic reduction showed a faradaic efficiency of 42% percent; however, the addition of light showed a faradaic efficiency of 112%.