## 3 Synthesis of Transition-Metal-Sulfide-Based Nanomaterials
### Bi\({}_{x}\)S\({}_{y}\)- and Bi-Based  
[PERSON] et al. investigated the reduction of CO\({}_{2}\) over Bi\({}_{2}\)S\({}_{3}\) nanosheets of carbon paper [188]. The authors synthesized nanosheets with an average size of 10 nm for the reduction of CO\({}_{2}\) in aqueous solutions. The results indicated that the nanosheets had a better performance than the bulk material, as well as showed high selectivity towards the formation of formate and high stability over 5 h of electrolysis. [PERSON] et al. investigated a layered Bi\({}_{2}\)O\({}_{3}\)/Bi\({}_{2}\)S\({}_{3}\) with a thickness of approximately 10 nm for the reduction of CO\({}_{2}\) to form formate [189]. The composite material had a faradaic efficiency of 85.5% for formate production with a current density of 14.1 mA/cm\({}^{2}\) at a voltage of \(-\)1.0 V. In that work, the experiments were performed using FTIR and showed that the rate-determining step in the formation of formate from CO\({}_{2}\) was the formation of the HCOO' intermediate. [PERSON] et al. studied the sulfurization of bismuth oxide (Bi\({}_{2}\)O\({}_{3}\)) to generate a Bi\({}_{2}\)S\({}_{3}\)-Bi\({}_{2}\)O\({}_{3}\) hybrid material for the generation of formic acid from CO\({}_{2}\)[190]. The hybrid material was synthesized using a partial precipitation method to generate interfaces between the Bi\({}_{2}\)S\({}_{3}\) and Bi\({}_{2}\)O\({}_{3}\) nanomaterials. The results showed that the production of formic acid was preferential over the formation of CO. The nanomaterial showed a faradaic efficiency of greater than 90% with an over-potential of 0.7 V with a current density of 6.14 mA/cm\({}^{2}\). Furthermore, the catalyst showed excellent stability/durability over 24 h of reaction. The BiS\({}_{x}\) nanomaterials and BiS\({}_{x}\)/Bi\({}_{2}\)O\({}_{3}\) composite have been shown to be effective at multiple CO\({}_{2}\) reduction reactions. \begin{table}
\begin{tabular}{c c c} \hline
**CO\({}_{2}\)RR Product** & **Material** & **Reference** \\ \hline CHCOO\({}^{-}\) & CuS\({}_{X}\) & [168] \\  & CuS & [169] \\ CHOOH & CuS & [170] \\ CHOOH & Cu\({}_{2}\)S/CuS & [171] \\  & CuS\({}_{-}\)C\({}_{3}\)N\({}_{4}\) & [172] \\  & Cu2S & [173] \\  & CuS\({}_{X}\) & [174] \\ CH\({}_{4}\) & CuS-annosheet & [175] \\ CO, CH\({}_{4}\), C\({}_{2}\)H\({}_{4}\), CHOO\({}^{-}\) & CuS & [176] \\ CO & NiS & [177] \\ CH\({}_{3}\)OH & Fe\({}_{2}\)/NiS & [178] \\ CH\({}_{4}\) & NiS/FeS\({}_{2}\) & [179] \\ CO & NiS-C & [180] \\ CH\({}_{3}\)OH, CH\({}_{3}\)CHOOH, CH\({}_{3}\)COCOOH & Fe\({}_{3}\)S\({}_{4}\) & [182] \\ CHOO\({}^{-}\) & FeS\({}_{2}\) & [183] \\ CO & Fe\({}_{3}\)S\({}_{4}\) & [184] \\ CO & Fe\({}_{4.5}\)Ni\({}_{4.5}\)S\({}_{4}\) & [185] \\ CHCOO\({}^{-}\) & Co\({}_{3}\)S\({}_{4}\)–Co\({}_{3}\)O\({}_{4}\) & [187] \\ \hline \end{tabular}
\end{table} 
Table 2: Summary of products in the CO\({}_{2}\)RR using the various TMS from the first-row transition element nanomaterials and respective associated nanocomposites. However, the most common reaction observed was the formation of formate/formic acid. The composite/hybrid oxide/sulfide nanomaterials also appear to favor the formation of formate/formic acid. [PERSON] et al. investigated the use of Bi\({}_{2}\)S\({}_{3}\) as an electrochemical reduction catalyst for the formation of formate from CO\({}_{2}\)[191]. The authors synthesized Bi\({}_{2}\)S\({}_{3}\) nanorods which achieved a faradic efficiency of greater than 90% for the formation of formate. The authors used a potential range of \(-\)0.9 to \(-\)1.2 V while the catalyst showed prolonged stability for 12-20 h with a current density of 40 mA/cm\({}^{2}\). [PERSON] et al. used a Bi\({}_{2}\)S\({}_{3}\)/ZifF-8 (a zeolite) for the electrocatalytic reduction of CO\({}_{2}\) to form formate [192]. The results showed a faradaic efficiency of 74.2% at an over-potential of \(-\)0.7 V (compared to the reversible hydrogen electrode (RHE)) and current density of 16.1 mA/cm\({}^{2}\).