Revisiting oxygen reduction reaction on oxidized and unzipped carbon nanotubes

Carbon-based electrocatalysts without metal or with trace metals are potentially effective in delivering robust and efficient oxygen reduction if the active sites are covalently located on a conductive support. In this report, we demonstrate that active sites on carbon nanotubes are created upon oxidation for efficient oxygen reduction to peroxide, whereas the saturation of oxygen groups at graphitic basal planes leads to the loss of electron conduction thereby deteriorates the electrocatalytic activity. Importantly, oxygen groups at different locations (basal/edge sites) and with different structures (C=O, C–OH, COOH, epoxide, etc.) have a significant impact on the oxygen reduction activity. In particular, epoxide bound oxidized carbon shows superior activity among other oxidized carbon nanotubes.