###### Abstract
Bimetallic nanomaterials have been also shown to be effective in the reduction of CO\({}_{2}\), including AuCu, PdPt, and CuI [57; 58; 59], while non-metallic catalysts including MoS\({}_{2}\), C-nanofibers, C\({}_{3}\)N\({}_{4}\), N-doped nanodiamond, and B-doped diamonds [60] have been also used as catalysts for CO\({}_{2}\) reduction. The most common reactions in the CO\({}_{2}\) reduction are shown below [60; 61; 62]:  
\[\text{CO}_{2}+2\text{H}^{+}+2\text{e}^{-}\rightarrow\text{CO}+\text{H}_{2} \text{O}\,\text{E}^{0}=-0.53\text{ V} \tag{1}\]  
\[\text{CO}_{2}+2\text{H}^{+}+2\text{e}^{-}\rightarrow\text{HCOOH}\,\text{E}^{0 }=-0.61\text{ V} \tag{2}\]  
\[\text{CO}_{2}+4\text{H}^{+}+4\text{e}^{-}\rightarrow\text{HCOOH}+\text{H}_{2} \text{O}\,\text{E}^{0}=-0.48\text{ V} \tag{3}\]  
\[\text{CO}_{2}+6\text{H}^{+}+6\text{e}^{-}\rightarrow\text{CH}_{3}\text{OH}+ \text{H}_{2}\text{O}\,\text{E}^{0}=-0.38\text{ V} \tag{4}\]  
\[\text{CO}_{2}+8\text{H}^{+}\,8\text{e}^{-}\rightarrow\text{CH}_{4}+2\text{H}_{ 2}\text{O}\,\text{E}^{0}=-0.24\text{ V} \tag{5}\]  
\[2\text{CO}_{2}+12\text{H}^{+}+12\text{e}^{-}\rightarrow\text{C}_{2}\text{H}_{ 4}+4\text{H}_{2}\text{O}\,\text{E}^{0}=-0.34\text{ V} \tag{6}\]  
These reactions are typically performed in a series of steps, with single electron transfers occurring. Typically, the reaction starts with the binding of the CO\({}_{2}\) molecule and the formation of radical species, which control the reaction pathway. For example, via the formation of the HCOO\({}^{*}\) radical, which forces the reaction to produce formate/formic acid. However, the formation of COOH\({}^{*}\) radical species typically forces the reaction to go through the pathway for the formation of CO as the final product [63]. The formation of methanol requires the formation of the CO\({}^{*}\) radical species followed by the formation of the CHO\({}^{*}\) and the HCHO\({}^{*}\) radicals. Subsequently, further hydrogenation can occur to form methanol (CH\({}_{3}\)OH) [64]. Ethanol synthesis from CO\({}_{2}\) requires the hydrogenation of CO\({}_{2}\) to CH\({}_{3}\)\({}^{*}\) radicals (which may come from methanol degradation) followed by the coupling of a CO\({}_{2}\)\({}^{*}\) with the CH\({}_{3}\)\({}^{*}\), hence forming the CH\({}_{3}\)COO\({}^{*}\) intermediate, which loses water and forms CH\({}_{3}\)CH\({}_{2}\)OH [65]. The formation of CH\({}_{4}\) typically occurs through the formation of the CO\({}^{*}\) radical, which is hydrogenated to form the HCO\({}^{*}\) radical species followed by subsequent hydrogen addition reactions to give CH\({}_{4}\)[66]. The formation of C\({}_{2}\)H\({}_{4}\) usually originates from the formation of the \({}^{*}\)CO-CHO radical via coupling non-adsorbed CO with \({}^{*}\)CHO. The coupling reaction is followed by subsequent hydrogenation reactions [67]. These different reaction pathways have been shown to depend on the type of TMS used in the electrocatalytic reduction of CO\({}_{2}\). This review will focus on the types of sulfide nanomaterials that have been investigated primarily in the CO\({}_{2}\) reduction reactions. There are many reviews on the applications of nanomaterials in electrocatalytic systems. However, most of the work that has been performed in the field does not focus on the specific application of TMS and their composite nanomaterials in the CO\({}_{2}\)RR. The present review focuses on the application of TMS and their composite nanomaterials in the CO\({}_{2}\)RR. The theory behind the catalytic activity of TMS is out of the scope of this review.