Contrasts between Mild and Harsh Oxidation of Carbon Nanotubes in terms of their Properties and Electrochemical Performance

Fundamental studies and electrochemical applications of carbon nanotubes (CNTs) have impacted a wide range of disciplines. A key issue for CNT electrochemistry is to understand how the physical, chemical, and electronic properties of different CNT materials affect their electrochemical performance. We investigate the differences arising from CNTs undergoing mild (H₂O₂) or harsh (HNO₃) oxidation processes. Morphological assessment and chemical characterization of CNT materials revealed that HNO₃ treatment (CNT–HNO₃) was effective in removing a large part of the metallic impurities, whereas H₂O₂ treatment (CNT–H₂O₂) was more proficient in eliminating carbonaceous imperfections in the starting CNT material (CNT_prist). We investigated the electrocatalytic and electron-transfer properties of CNT_prist and oxidized CNTs on a variety of electrochemical probes, which are sensitive to carbon surfaces as well as its oxygen-containing groups and/or metallic impurities. Electrochemical results show that, for the studied molecules, CNT_prist and CNT–H₂O₂ exhibit mostly indistinguishable performances, whereas CNT–HNO₃ yields an improved performance.