CO2 Electroreduction with Enhanced Ethylene and Ethanol Selectivity by Nanostructuring Polycrystalline Copper. Issue 6 (23rd April 2016) - Kwon, Youngkook
Abstract: There are a number of recent reports on the use of oxidation/reduction cycling of Cu surfaces to improve their selectivity for ethylene formation in the aqueous CO2 reduction reaction. Here, the oxidation/reduction process is examined in detail. It is found that the faradaic efficiencies for both ethylene and ethanol are enhanced after oxidation/reduction cycling in the presence of halide anions. Specifically, cycling of the electrode in the presence of chloride, bromide, or fluoride anions allows for an ethylene faradaic efficiency of approximately 15.2 %, a factor of 1.5 higher than that for polycrystalline copper (at −1.0 V vs. RHE). The faradaic efficiency for ethanol is also enhanced from 2.65 to approximately 7.6 %. The effects of electrochemical oxidation/reduction with the chloride anion were investigated by using in situ Raman spectroscopy, and the changes in the surface morphology of copper were monitored by using SEM. Consistent with prior reports, it is observed that during the oxidation part of the cycle, anodic corrosion forms a Cu2 O layer, which consists of cubical crystals of about 150 nm. During the reduction sweep, it is converted to metallic copper, which forms irregular Cu nanoparticles of around 20 nm in diameter. The enhancement in ethylene formation is presumably attributed to the formation of grain boundaries, which may serve as active sites. Abstract : Enhancing selectivity : Cu2 O nanocubes can be created on the surface of polycrystalline copper through an anodic corrosion mechanism facilitated by the presence of halide anions. The Cu2 O nanocubes can be electrochemically reduced to Cu nanoparticles, which exhibit high ethylene selectivity. In situ Raman spectroscopy is used to study the corrosion and reduction process.