*4.3.1. Electrochemical reduction of CO2*

The kinetics of the electrochemical reduction is sluggish due to the reorganization of the linear CO2 molecule into more active bent form, which creates overpotential to the first electron transfer after the adsorption of the molecule onto the working electrode. This step is mostly identified as the rate-determining step initiating at −1.9 V, and it forms CO<sup>2</sup> •− anion radical that is further protonated into HCOO• or HOOC• and reduced into HCOO<sup>−</sup> (formate) or CO, respectively. The majority of electrochemical reductions of CO2 produce HCOOH or CO as primary products. Very few electrocatalysts (e.g., Cu) ensure the further reduction of CO into hydrocarbons, but without an elucidated mechanism till now. Various electrolytic materials have been investigated in the CO2 reduction processes including metals (Sn, Pd, Cu, Pt, etc.), layered transition metal dichalcogenides (e.g., WS2 , MoSe2 , and MoS2 ), and heteroatomfunctionalized carbonaceous catalysts such as N-doped carbon nanofibers and graphene quantum dots [19].
