## 3 Synthesis of Transition-Metal-Sulfide-Based Nanomaterials
### In Sulfides  
[PERSON] et al. designed ultrathin ZnIn\({}_{2}\)S\({}_{4}\) nanomaterials grown on N-doped carbon cloth for the electrocatalytic reduction of CO\({}_{2}\) and the formation of ethanol [208]. The catalyst showed a 42% faradaic efficiency towards the formation of ethanol at a potential of \(-\)0.7 V in a CO\({}_{2}\)-saturated solution of 0.5 M KHCO\({}_{3}\). The authors also performed DFT calculations which showed that the N-doped carbon cloth promoted the CO-CO coupling process leading to the formation of ethanol. [PERSON] et al. investigated the stabilization of indium sulfide with Zn for the electrocatalytic reduction of CO\({}_{2}\) to from formate [209]. The ZnIn\({}_{2}\)S\({}_{4}\) nanomaterial could produce formate with a 99% faradaic efficiency. The catalyst operated at a current density of 300 mA/cm\({}^{2}\) for over 60 h without decay. In addition, the authors performed computational studies which showed that the Zn increased the covalency of the In-S bonds, which formed a catalytic site to activate both H\({}_{2}\)O and CO\({}_{2}\) and gave the HCOO\({}^{+}\) intermediate, and thus formate was the product of the reaction.  
There are only a few studies reported on the use of InS as an electrocataly in CO\({}_{2}\)RR, which have shown a variety of products such as formate/formic acid and ethanol. Zn doping appears to push the reaction towards formate, as well as a being a high-stability catalytic material. In fact, supporting the ZnIn\({}_{2}\)S\({}_{4}\) on carbon can push the reaction towards ethanol production, which may indicate that there is a contribution in the reaction from the carbon support.  
The sulfides of the later transition elements as well as the metal (non-transition) elements associated with rows 2 and 3 of the periodic table show a promise for application in the CO\({}_{2}\)RR. As can be seen in Table 3, the majority of the common products observed in the CO\({}_{2}\)RR are the sulfides and their composites, which include CO, CH\({}_{4}\), CHCOO/CHCO\({}^{-}\), C\({}_{2}\)H\({}_{4}\), and CH\({}_{3}\)CH\({}_{2}\)OH. The results showed the catalytic capability and the ability to specifically react with the C/O to break C-O bonds and form C-H bond to give specific products.  
\begin{table}
\begin{tabular}{c c c} \hline
**CO\({}_{2}\)RR Product** & **Material** & **Reference** \\ \hline CHOO\({}^{-}\)/CHOOH & Bi\({}_{2}\)S\({}_{3}\) & [188] \\  & Bi\({}_{2}\)O\({}_{3}\)/Bi\({}_{2}\)S\({}_{3}\) & [189] \\  & Bi\({}_{2}\)S\({}_{3}\)–Bi\({}_{2}\)O\({}_{3}\) & [190] \\  & Bi\({}_{2}\)S\({}_{3}\)–minords & [191] \\  & Bi\({}_{2}\)S\({}_{3}\)–ZiIF-8 & [192] \\  & Bi/Bi\({}_{2}\)S\({}_{3}\) & [193] \\ CO & CdS & [194] \\  & CdS-Ag & [195] \\ CHOO\({}^{-}\) & SnS\({}_{\rm x}\) & [196] \\  & SnS\({}_{\rm z}\) & [197] \\  & SnS & [198] \\  & InO–SnS\({}_{\rm z}\) & [199] \\  & Cu–SnS & [200] \\ CO, CH\({}_{4}\) & AgS\({}^{+}\) & [201] \\  & Ag\({}_{2}\)S/Ag & [202] \\  & Ag\({}_{2}\)S\({}^{+}\)Au & [203] \\  & Ag/AgS\({}_{2}\) & [205] \\  & Ag\({}_{2}\)S\({}^{+}\)C/dS & [206] \\ CH\({}_{3}\)CH\({}_{2}\)OH & ZnIn\({}_{2}\)S\({}_{4}\)–C\({}_{3}\)N\({}_{4}\) & [208] \\ CHOO\({}^{-}\) & ZnIn\({}_{2}\)S\({}_{4}\) & [209] \\ \hline \end{tabular}
\end{table}
Table 3: Summary of products in the CO\({}_{2}\)RR using various sulfides from the later transition/metal elements nanomaterials and their associated composite nanomaterials.