Electrocatalytic Activity and Electroanalytical Performance of Nanodiamond-Derived Carbon Nano-Onions

Carbon nano-onions (CNOs) are an emerging, novel class of carbon nanomaterials. A CNO is a 0-D carbon analogue of a 1-D carbon nanotube (CNT) and a 2-D graphene. It is composed of sp²-bonded, concentric carbon shells surrounding a hollow core. The curved morphology of a CNO loosens the conjugation along the graphene sheet and results in the change in electronic structure. The unique structure as well as surface chemical functional groups of CNOs will significantly influence physicochemical, electronic, and electrochemical properties.

In this talk, the physicochemical and electrochemical properties of CNOs will be presented. First, morphology and microstructure of CNOs were characterized by scanning and transmission electron microscopies (SEM, TEM), X-ray diffraction (XRD), and Raman spectroscopy. Chemical composition and chemical functional groups were probed by X-ray photoelectron spectroscopy (XPS). Raman spectra of CNOs showed a large value of I_D/I_G ratio, indicating that carbon concentric shells of CNOs include defects, i.e., exposed edge planes. Second, heteroatomic doping of CNOs and its electrocatalytic activity toward oxygen reduction reaction will be presented, in comparison with other carbon nanomaterials. Last, redox activities and electron transfer kinetics of CNOs were studied. CNOs showed remarkable electrochemical activities for the detection of biologically important molecules (such as high sensitivity, high selectivity and fast ET kinetics). Electrochemical measurements were carried out with standard redox couples such as Ru(NH₃)₆^3+/2+, Fe^2+/3+, IrCl₆^2-/3- and Fe(CN)₆^3-/4- as well as redox-active biomolecules such as dopamine, epinephrine, and norepinephrine.  The results showed a stable and fast electrochemical response of CNOs for all of the redox analytes and often surpassed the performance of other carbon electrodes like carbon nanotubes, graphite nanoflakes, and glassy carbon.