The Role of Defects in Carbon Nanostructures Probed through Ion Implantation and Electrochemistry
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1142-JJ04-04
The Role of Defects in Carbon Nanostructures Probed through Ion Implantation and Electrochemistry. Mark Hoefer1, Jeff Nichols1, and Prabhakar Bandaru1 1 Materials Science and Engineering, U. of California, San Diego, La Jolla, Ca, 920930418, USA ABSTRACT As carbon nanotubes (CNTs) inevitably contain defects, an understanding of their effect on the electrochemical behavior is crucial. We consider, through Cyclic Voltammetry and Raman Spectroscopy the influence of both intrinsic and extrinsically introduced defects. Bamboo and hollow multi-walled carbon nanotube morphologies provided examples of the former while the controlled addition of Argon and Hydrogen ions was used for studying extrinsic defects. We show that the electrocatalytic response of the hollow type CNTs can be tailored significantly, while bamboo type CNTs have innately high reactive site densities and are less amenable to modification. Argon irradiation also differs greatly from that of Hydrogen irradiation. CNT irradiation with Argon appears to positively charge CNTs, while Hydrogen irradiation neutralizes defects further allowing for the tuning of CNT defect density. The work has implications in the design of nanotube and nanowire based chemical sensors.
INTRODUCTION The postulated fast electron transfer kinetics1, related to the large surface area/ volume ratios of carbon nanotubes (CNTs), could be useful for the development of increased sensitivity, CNT based, electrode materials, electrochemical sensors, supercapacitors etc.,2, 3. In this context, it has been pointed out that the electrocatalytic behavior along the length of the CNTs would be similar to the basal planes of graphite, while the ends correspond to the edge planes4, 5 and could be influenced by dangling bonds6, as in edge-plane graphite. The latter corresponds to a large defect density, which could be profitably used for the enhanced sensitivity. While the nature and extent of the defects in CNTs can also be altered through the addition of functional moieties7-9, in this study, we investigate the influence of external irradiation on nanotube behavior. We show that Ar and H ions can be used to systematically tune the electrochemistry of CNTs. We investigated the tunability characteristics in both multi-walled, hollow-core carbon nanotubes (HCNTs), and bamboo-type carbon nanotubes (BCNTs). Structural modification, through defects, influences the predicted performance of CNTs for high efficiency electrodes6, 10, 11. Such sensitivity was investigated through Cyclic Voltammetry (CV) and Raman Spectroscopy. Consequently, non-ideal electrode behavior, linked to irreversible electron transfer/adsorption processes12 were monitored.
EXPERIMENTAL DETAILS Both the hollow core (HCNTs) and bamboo (BCNT) carbon nanotube morphologies were grown via thermal chemical vapor deposition (CVD) on Si substrates, aided by 5 nm thick Fe catalyst13, 14 to form vertically aligned arrays. The BCNTs were synthesized at 850oC with a gas feedstock comprising 100mL/min of benzene, 500 sccm of Ar, an
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