Direct Electrooxidation of Ethylene to Ethylene Glycol over 90% Faradaic Efficiency Enabled by Cl<sup>–</sup> Modification of the Pd Surface
An-Zhen Li, Xiongbo Wang, Shuwei Li, Bo‐Jun Yuan, Xi Wang, Ruo-Pu Li, Liang Zhang, Bi‐Jie Li, Haohong Duan
Abstract
Direct electrochemical ethylene-to-ethylene glycol (C 2 H 4 -to-EG) conversion can potentially reduce the consumption of fossil fuels and the emission of carbon dioxide (CO 2 ) compared with the traditional thermo-catalytic approach. Palladium (Pd) prepared by electrodeposition is represented as a promising electrocatalyst; however, it exhibits low Ethylene glycol (EG) current density (<4 mA cm –2 ), Faradaic efficiency (<60%), and productivity (<10 μmol h –1 ), hindering practical applications. Herein, we report a nanodendrite palladium catalyst supported on a large-area gas diffusion electrode. This catalyst gives high EG current density (12 mA cm –2 ) and productivity (227 μmol h –1 ) but low Faradaic efficiency (65%). With further Cl – ions modification, Faradaic efficiency increased to a record-high value of 92%, and EG current density (18 mA cm –2 ) and productivity (∼340 μmol h –1 ) were also promoted. Experimental data suggest that the strong electron-withdrawing feature of Cl – reduces the oxidation ability of in situ generated Pd–OH species, inhibiting EG overoxidation to glycol aldehyde. Meanwhile, Cl – alters EG adsorption configuration─from parallel and dual-site coordination to vertical and single-site coordination─over the Pd surface, thus preventing C–C bond cleavage of EG to CO 2 . In addition, Cl – adsorption facilitates the generation of Pd–OH active species to improve catalytic activity. This work demonstrates the great potential of surface ion modification for improving activity and selectivity in direct electrochemical C 2 H 4 -to-EG conversion, which may have implications for diverse value-added chemicals electrosynthesis.