School of Chemistry, University of Bristol, Cantocks Close, Bristol BS8 1TS, UK.
Chemphyschem. 2012 Aug 27;13(12):2956-63. doi: 10.1002/cphc.201200407. Epub 2012 Aug 2.
The properties of graphene oxide (GO) and DNA-stabilised reduced graphene-oxide (rGO) sheets as electron-transfer mediators in partially blocked electrodes are evaluated employing electrochemical impedance spectroscopy. Evidences obtained from UV/Vis, Raman and FTIR spectroscopies, as well as atomic force microscopy, confirm that the reduction of exfoliated GO single sheets by hydrazine yields partially reduced graphene oxide featuring a high defect density. Two-dimensional assemblies of GO and rGO were formed through electrostatic adsorption at Au electrodes, sequentially modified with 11-mercaptoundecanoic acid (MUA) and poly-diallyldimethylammonium chloride (PDADMAC). The MUA:PDADMAC generates a strong blocking layer to the electron-transfer reaction involving the ferri/ferrocyanide redox couple. This blocking behaviour is not significantly affected upon adsorption of GO. However, adsorption of a sub-monolayer of rGO decreases the charge-transfer resistance by more than two orders of magnitude. Analysis of cyclic voltammograms and impedance spectra suggests that electron transfer in rGO assemblies is mediated by occupied states located just below the redox Fermi energy of the probe. These findings are discussed in the context of on-going controversies regarding the electrochemical reactivity of sp(2)-carbon basal planes.
采用电化学阻抗谱研究了氧化石墨烯（GO）和 DNA 稳定的还原氧化石墨烯（rGO）片作为部分阻塞电极中电子转移介质的性质。从紫外/可见、拉曼和傅里叶变换红外光谱以及原子力显微镜获得的证据证实，通过水合肼还原剥离的 GO 单分子片得到了具有高缺陷密度的部分还原氧化石墨烯。通过在 Au 电极上依次进行静电吸附，形成了 GO 和 rGO 的二维组装体，并用 11-巯基十一酸（MUA）和聚二烯丙基二甲基氯化铵（PDADMAC）进行修饰。MUA:PDADMAC 生成了一个强阻塞层，阻止了涉及铁/亚铁氰化物氧化还原对的电子转移反应。这种阻塞行为在吸附 GO 时没有明显影响。然而，rGO 的亚单层吸附使电荷转移电阻降低了两个数量级以上。循环伏安法和阻抗谱的分析表明，在 rGO 组装体中电子转移是由位于探针的氧化还原费米能级以下的占据态介导的。这些发现将在关于 sp(2)-碳基面的电化学反应性的持续争议的背景下进行讨论。
