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ACS Appl Mater Interfaces. 2018 Aug 29;10(34):28572-28581. doi: 10.1021/acsami.8b08428. Epub 2018 Aug 20.

On the Role of Sulfur for the Selective Electrochemical Reduction of CO2 to Formate on CuS x Catalysts.

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Department of Chemistry, Faculty of Science , National University of Singapore , 3 Science Drive 3 , 117543 Singapore.
Solar Energy Research Institute of Singapore , National University of Singapore , 7 Engineering Drive 1 , 117574 Singapore.
Institute of Materials Research and Engineering , Agency for Science, Technology and Research (A*STAR) , 2 Fusionopolis Way , Innovis, 138634 Singapore.
National Nanotechnology Center (NANOTEC) , National Science and Technology Development Agency (NSTDA) , Pathum Thani , 12120 Thailand.


The efficient electroreduction of CO2 has received significant attention as it is one of the crucial means to develop a closed-loop anthropogenic carbon cycle. Here, we describe the mechanistic workings of an electrochemically deposited CuS x catalyst that can reduce CO2 to formate with a Faradaic efficiency (FEHCOO-) of 75% and geometricĀ current density ( jHCOO-) of -9.0 mA/cm2 at -0.9 V versus the reversible hydrogen electrode. At this potential, the formation of other CO2 reduction products such as hydrocarbons and CO was notably suppressed (total FE < 4%). The formate intermediate (HCOO*) was identified by operando Raman spectroscopy with isotopic labeling. A combination of electrochemical and materials characterization techniques revealed that the high selectivity toward formate production can be attributed to the effect of S dopants on the Cu catalyst, rather than surface morphology. Density functional theory calculations showed that the presence of sulfur weakens the HCOO* and *COOH adsorption energies, such that the formation of *COOH toward CO is suppressed, while the formation of HCOO* toward formate is favored.


Raman spectroscopy; carbon dioxide reduction; copper sulfide; density functional theory; electrochemistry; formate


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