## 7 Conclusions/Future Perspectives  
The TMS are very capable of reducing CO\({}_{2}\) to form value-added products such as CO, HCOO\({}^{-}\)/HCOOH, CH\({}_{3}\)OH, CH\({}_{3}\)CH\({}_{2}\)OH, CH\({}_{4}\), and C\({}_{2}\)H\({}_{4}\). There are a few studies that showed even larger molecule formation. However, the TMS-composite materials showed much more promise in the development of value-added products from CO\({}_{2}\). For example, the doping of individual TMS with various materials showed much higher faradaic efficiencies than the pristine materials, such as was observed with MoS\({}_{2}\), CdS, In\({}_{2}\)S\({}_{4}\), Ag\({}_{2}\)S, SnS, CuS, and among the other sulfides presented in the review. The doping of materials changes the ability to attract CO\({}_{2}\) and the binding strength of the reduction products to the surface and allows for higher efficiencies.  
The Future of the electrocatalytic reduction of CO\({}_{2}\) will be dependent on the development of nanomaterials that are not only TMS but composites of two or more systems. In addition, very favorable results have been observed especially in the substitution of Ni into Fe\({}_{y}\)S\({}_{x}\) and Fe into the Ni\({}_{y}\)S\({}_{x}\). The substitution appears to create a redox couple within the material and the CO\({}_{2}\)RR appears to be enhanced. The addition of carbon and N-doped carbon appears to have a large effect on the catalytic activity of the material. The synergistic effect of catalytic supports as well as the development of hybrid materials will be a major push forward in the use of TMS in CO\({}_{2}\)RR. In addition, the movement of the reactions away from acidic pHs will increase the use of sulfides in electrocatalysis while the movement away from acidic pHs will improve the stability of the TMS in the reaction media. Furthermore, a movement away from aqueous media will also increase the stability of TMS and thus the longevity of both the reaction and the TMS' materials. By controlling the structure of the catalytic material and the support, very controlled catalytic reactions can be achieved. Through the development of new composite materials, catalytic reactivities will be increased, which was observed in the HDS reaction catalysis. The synthesis of Co/Ni on MoS\({}_{2}\) and WS\({}_{2}\) catalysts resulted in synergistic activities and higher reaction rates for the catalysts. As more composite materials are used, the field and application of TMS in the CO\({}_{2}\)RR will grow, while the application of TMS in electrocatalysis is in its infancy as can be observed by the lower number of papers reported on using TMS in CO\({}_{2}\)RR compared to other types of materials.  
The most effective catalysts will be those which can do both the CO\({}_{2}\)RR but also perform the HER reaction simultaneously. As it was discussed in this review, the hydrogenation of the reduced CO\({}_{2}\) species is a key parameter in controlling the reaction pathways, and ultimately the final reaction products.  
Conceptualization, J.P.; writing--original draft preparation, J.P.; writing--review and editing, J.P. and M.A.; funding acquisition, J.P. and M.A.; All authors have read and agreed to the published version of the manuscript.  
[PERSON] acknowledges and is grateful for the support provided by a funding from the UTRGV Chemistry Departmental Welch Foundation Grant (Grant No. BX-0048), and [PERSON] acknowledges funding from NSF PREM (DMR-2122178) Partnership for Fostering Innovation by Bridging Excellence in Research and Student Success.  
Not applicable.  
The authors declare no conflict of interest.