DOI: 10.1002/slct.201601169 Full Papers z Energy Technology & Environmental Science High-Selectivity Electrochemical Conversion of CO to 2 Ethanol using a Copper Nanoparticle/N-Doped Graphene Electrode Yang Song,[a] Rui Peng,[a] Dale K. Hensley,[a] Peter V. Bonnesen,[a] Liangbo Liang,[a] Zili Wu,[a,b] Harry M. Meyer, III,[c] Miaofang Chi,[a] Cheng Ma,[a] Bobby G. Sumpter,[a,d] and Adam J. Rondinone*[a] Though carbon dioxide is a waste product of combustion, it ature and pressure. Lacking noble metals or other rare or ex- canalsobeapotentialfeedstockfortheproductionoffineand pensivematerials,thecatalystiscomprisedofCunanoparticles commodityorganicchemicalsprovidedthatanefficientmeans on a highly textured, N-doped carbon nanospike film. Electro- to convert it to useful organic synthons can be developed. chemical analysis and density functional theory (DFT) calcu- Herein we report a common element, nanostructured catalyst lations suggest a preliminary mechanism in which active sites for the direct electrochemical conversion of CO to ethanol on the Cu nanoparticles and the carbon nanospikes work in 2 with high Faradaic efficiency (63% at 1.2V vs RHE) and high tandem to control the electrochemical reduction of carbon selectivity(84%)thatoperatesinwaterandatambienttemper- monoxidedimertoalcohol.
Full Papers spikesorCNS.TheCNSstructureisdisorderedduetothehigh nitrogen content which prevents well-ordered stacking. In the current report, a carbon nanospike (CNS) electrode with elec- tronucleatedCunanoparticles(Cu/CNS)isshowntohavemuch higher selectivity for CO electroreduction than H evolution, 2 2 withasubsequenthighFaradaicefficiencytoproduceethanol.
Full Papers Figure2.HR-TEMofelectrodepositedcoppernanoparticlesoncarbonnano- spikeelectrode.ElectrodepositedparticlesareimbeddedinN-dopedcarbon nanospikesprovidingintimatecontactbetweencoppersurfaceandreactive sitesinthecarbon.
Full Papers uct was in contact with the copper electrode.[8a,22] In contrast, the binding between OCCO and CNS is weaker, though strong with this experiment we have not been able to detect any C2 enoughtopreventeasydesorptionoftheC2intermediate.The product except ethanol using the Cu/CNS (ethylene was de- calculationsofferimportantinsightsintotheobservedselective tected in the control sample Cu/glassy carbon), indicating that reduction,andweexpectthattheoxygenatomononeendof the dominant reaction mechanism precludes competitive re- the C2 intermediates is covalently bound on reactive copper duction to ethylene or ethane. Kondo, et al. reported that the surfaceforcompletereductionto-CH,whiletheoxygenatom 3 electronic structure near the Fermi level of graphene is modi- on the other end of the C2 intermediates is adsorbed on less fied in N-doped graphene, where localized p electronic states reactive CNS and thus protected from complete reduction are reported to form at the neighboring carbon atoms, and (henceforming-CHOH),therebyprovidingapathwaytowards 2 propagate anisotropicallyaroundthedefectduetothepertur- selectivereductiontoethanol.Thepossibilitythatasynergistic bation of the p-conjugated system. Due to electron-with- effect between Cu and CNS is responsible for the selectivity is drawing effects in the graphene p-conjugated system, the car- surprisinggiventhelargesizeoftheCunanoparticles,however bon atoms adjacent to nitrogen are positively polarized. This there is no doubt that the Cu is necessary for this reaction as polarization may provide an active site adjacent to the copper bare CNS do not produce the same products. Likewise, Cu fortheC2intermediatestoadsorb,whichmayinhibitcomplete nanoparticles nucleated onglassycarbon (orany othercopper electroreduction. Other doped or defected graphenes are reported to date) do not produce the same products without well known to be catalytically active for reactions such as de- CNS.WhiletheCuparticlesarerelativelylarge,theyareonthe hydrogenation. scaleoftheCNSwhicharearound50nminlengthandtendto First-principles density functional theory (DFT) calculations beimbeddedwithinthespikes.Amoredetailedunderstanding werecarriedouttoinvestigatewhetherthenitrogendopantor of the reaction pathway of such selective reduction of CO to 2 strongly curledmorphologyintheCNScanhelptoadsorbthe ethanolwarrantsfurtherstudy.