Theoretical Study on Chloride-Mediated Electro-Oxidation of Ethylene through Reactive Oxygen Species on the FeFeN ₆ Dual-Atomic-Site in Graphene under Low Applied Potential and with a Wide U-pH Range

Acetaldehyde (AA) and ethylene oxide (EO) are important fine chemicals and extensively used essential materials for further producing high-value chemical products. The emerging electrochemical oxidation process of ethylene can utilize the reactive oxygen species (*O) derived from water electrolysis generated on anodic catalyst under mild conditions via suitable applied potential to directly oxidize ethylene and can also conquer the excessive oxidation of ethylene or harmful waste emissions during traditional industrial processes. However, there are still issues with high applied potential to generate and narrow U-pH range to stabilize active oxygen intermediates and even high-energy barriers for the following electro-oxidation of ethylene. Inspired by the fact that the chlorine evolution reaction generally makes Cl to preferentially adsorb on the catalyst surface over the initial intermediate of oxygen evolution reaction, it may regulate the reactivity of reactive oxygen species and widen the conditions of ethylene oxidation utilizing the interplaying on dual-atomic-site catalysts between chlorine evolution reaction and oxygen evolution reaction. Hereby, the feasibility of Cl-mediated electro-oxidation of ethylene to AA and EO using the *Cl*O intermediate on dual-atomic site catalysts (DASCs) of MM′N6@graphenes is identified achievable at lower applied potential through controlling the reactive activity of *O through first-principles calculations. Electrochemical process calculations and Pourbaix diagram analysis indicate that the optimal *Cl*O intermediate of Fe(*Cl)Fe (*O)N 6 @graphene is stabilized in a wide U-pH range, among six investigated (FeFe-, CoCo-, NiNi-, FeCo-, FeNi-, and CoNi-) catalysts, and possesses the corresponding lowest applied potential of 0.66 V under pH = 9.57 for its generation and also obviously lower value (0.83 V under the same pH condition) compared to FeFe(*O)N 6 @graphene. More significantly, the kinetic energy barriers of ethylene-oxidation to AA and EO are 0.73 and 1.04 eV through the Fe(*Cl)Fe(*O)N 6 @graphene intermediate compared to 1.20 and 1.61 eV through FeFe(*O)N 6 @graphene. Electronic structure analysis clearly indicates that the chemisorption of Cl on the adjacent metal can effectively enhances the activity of *O intermediate toward ethylene, decrease the bonding strength of Fe−O and boost the transfer of O atom to ethylene. In particular, this study effectively illustrated the tremendous strategy to regulate the activation of one metal through the Cl-bonding on the other metal in anodic dual-atomic site catalysts, which opens up a new dimension and also calls for further experimental exploration.