Bromine-Enhanced Generation and Epoxidation of Ethylene in Tandem CO₂ Electrolysis Towards Ethylene Oxide

The indirect electro-epoxidation of ethylene (C₂ H₄ ), produced from CO₂ electroreduction (CO₂ R), holds immense promise for CO₂ upcycling to valuable ethylene oxide (EO). However, this process currently has a mediocre Faradaic efficiency (FE) due to sluggish formation and rapid dissociation of active species, as well as reductive deactivation of Cu-based electrocatalysts during the conversion of C₂ H₄ to EO and CO₂ to C₂ H₄ , respectively. Herein, we report a bromine-induced dual-enhancement strategy designed to concurrently promote both C₂ H₄ -to-EO and CO₂ -to-C₂ H₄ conversions, thereby improving EO generation, using single-atom Pt on N-doped CNTs (Pt₁ /NCNT) and Br^- -bearing porous Cu₂ O as anode and cathode electrocatalysts, respectively. Physicochemical characterizations including synchrotron X-ray absorption, operando infrared spectroscopy, and quasi in situ Raman spectroscopy/electron paramagnetic resonance with theoretical calculations reveal that the favorable Br₂ /HBrO generation over Pt₁ /NCNT with optimal intermediate binding facilitates C₂ H₄ -to-EO conversion with a high FE of 92.2 %, and concomitantly, the Br^- with strong nucleophilicity protects active Cu⁺ species in Cu₂ O effectively for improved CO₂ -to-C₂ H₄ conversion with a FE of 66.9 % at 800 mA cm^-2 , superior to those in the traditional chloride-mediated case. Consequently, a single-pass FE as high as 41.1 % for CO₂ -to-EO conversion can be achieved in a tandem system.