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Yes—in one direct nanoscale study, pristine carbon nanotube (CNT) forests transferred electrons rapidly at both their closed ends and sidewalls, challenging the idea that intact sidewalls are universally electrochemically inert. The result does not show that every CNT surface is active under every condition: tube type, defects, impurities, processing, redox chemistry, and measurement geometry all affect what an experiment can establish.
What did the 2012 study find?
In “Electrochemistry at carbon nanotube forests: sidewalls and closed ends allow fast electron transfer,” Thomas S. Miller, Neil Ebejer, Aleix G. Güell, Julie V. Macpherson, and Patrick R. Unwin reported fast electron transfer at both closed ends and sidewalls of pristine CNT forests. Their central claim was that these sites could be active without activating or processing the nanotubes. The paper appeared in Chemical Communications, volume 48, pages 7435–7437; it was first published on 14 May 2012. Read the Royal Society of Chemistry article record and abstract.
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The finding directly challenges a broad rule that electron transfer on CNT electrodes must occur mainly at open ends or defects. It is evidence that intact sidewalls can support electron transfer in the tested system—not proof that defects and ends are never important, or that all CNTs behave alike.
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The team used a nanopipet electrochemical cell to probe specific locations on dense forests of pristine, closed-end CNTs grown by chemical vapour deposition. In the reported setup, electrolyte containing redox species filled a double-barrelled nanopipette, and current flowed between the two barrels. This nanoscale arrangement let the researchers investigate selected nanotube sites without cutting or processing the CNTs first. Chemistry World’s contemporary account describes the cell and experiment.
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That distinction matters: processing can create defects or change surface chemistry, making it harder to tell whether measured activity belongs to an original sidewall or to a newly altered site. A localized measurement also addresses a different question from an ensemble electrode result, where many surface sites and material features contribute together.
Why did the result challenge earlier interpretations?
Earlier work often explained CNT electrochemical activity through edge-plane-like defects, open ends, or impurities rather than intact sidewalls. A 2005 article by Banks, Davies, Wildgoose, and Compton argued that much of graphitic-carbon catalytic activity and electron transfer occurs at surface defect sites, especially edge-plane-like defects, and questioned claims that CNT-modified electrodes have special catalytic properties. See the 2005 article record.
But the literature was not uniform. A 2009 review by Dumitrescu, Unwin, and Macpherson described the debate as unresolved: much of the literature presumed sidewall inertness, while studies of well-characterized single-walled nanotubes indicated sidewall activity. The review identified CNT type, impurities, electrode-fabrication processing, and experimental arrangement as factors that can help explain differing results. See the 2009 review. A separate 2009 critical minireview by Martin Pumera also cautioned that apparent CNT electrochemical or electrocatalytic activity may arise from defects or impurities. See Pumera’s review.
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What determines whether sidewalls, ends, or defects appear active?
There is no single site attribution that can safely be generalized across all CNT experiments. The interpretation depends on the material tested and on how the electrochemical measurement is performed.
- Site and structure: A result at an intact sidewall, a closed cap, an open end, or a defect answers a different question. Defects may provide reactive sites even if sidewalls can also transfer electrons.
- Tube type and sample quality: Single-walled and multi-walled CNTs are not interchangeable. Purity and residual impurities can complicate attribution of activity to the nanotube surface itself.
- Processing: Cutting, oxidation, or other treatment can alter the surface and introduce or change active sites. Measurements on unprocessed material help isolate the behavior of that material, but do not automatically predict the behavior of processed electrodes.
- Redox probe and reaction: Electron-transfer behavior can depend on the probe chemistry. A finding for one probe should not be extended to all electrochemical reactions.
- Measurement geometry: A site-specific nanopipet experiment and an ensemble electrode measurement sample different features and can support different levels of inference.
A later review continues to describe competing edge/defect and sidewall interpretations and notes that oxidation and oxygen-containing groups can create or alter active sites. It does not, on the evidence available here, settle the broader debate. See the later review.
What is the main caveat about the 2012 result?
In the contemporary coverage, CNT electroanalytical expert Gareth Keeley called the study “a very interesting and exciting paper,” but argued that its challenge to the importance of open ends would be unlikely to gain wide acceptance until demonstrated with inner-sphere redox probes. That is a concern about how broadly to interpret the result, not evidence that the nanopipet measurements were invalid. The contemporary report includes Keeley’s comment.
The accessible abstract establishes the authors’ finding of fast electron transfer at sidewalls and closed ends in their pristine CNT forest system. The sources cited here do not establish whether later work resolved Keeley’s specific probe concern or determine the current field-wide consensus. The careful conclusion is therefore narrower than either “sidewalls are inert” or “all CNT sidewalls are active”: the universal inert-sidewall rule is not supported by this experiment, but activity remains context-dependent.
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