Ethylene Electrooxidation to 2-Chloroethanol in Acidic Seawater with Natural Chloride Participation

Ethylene oxidation to oxygenates via electrocatalysisis practicallypromising because of less energy input and CO2 output comparedwith traditional thermal catalysis. However, current ethylene electrooxidationreaction (EOR) is limited to alkaline and neutral electrolytes toproduce acetaldehyde and ethylene glycol, significantly limiting cellenergy efficiency. Here, we report for the first time an EOR to 2-chloroethanolproduct in a strongly acidic environment with natural seawater asan electrolyte. We demonstrate a 2-chloroethanol Faradaic efficiency(FE) of & SIM;70% with a low electrical energy consumption of & SIM;1.52x 10(-3) kWh g(-1) over a commercialPd catalyst. We establish a mechanism to evidence that 2-chloroethanolis produced at low potentials via direct interaction of adsorbed chlorideanions (*Cl) with ethylene reactant because of the high coverage of*Cl during reaction. Importantly, this differs from the accepted multiplestep mechanism of subsequent chlorine oxidation and ethylene chlorinationreactions at high potentials. With highly active Cl- participation, the production rate for 2-chloroethanol in acidicseawater is a high 26.3 g m(-2) h(-1) at 1.6 V operation. Significantly, we show that this is 223 timesgreater than that for ethylene glycol generation in acidic freshwater.We demonstrate chloride-participated EOR in a proton exchange membraneelectrolyzer that exhibits a 68% FE for 2-chloroethanol at 2.2 V operationin acidic seawater. This new understanding can be used for designingselective anode oxidation reactions in seawater under mild conditions.