The role of chlorine in its ability to create defects on the surface of carbon nanomaterials (CNMs) was investigated using transmission electron microscopy (TEM), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). A variety of chlorinated alkanes, and aromatic hydrocarbons were used as sources of chlorine whereas for nitrogen-doped CNMs acetonitrile was used as a source of nitrogen. CNMs generated from trichloroethane (TCE) and 1,2-dichlorobenzene (DCB) contained more defects, as evidenced by high ID/IG values and the growth of secondary carbon nanotubes and carbon nanofibers on the surface of the main CNTs. CNMs generated from feeds containing large volumes of DCB were highly defected for nitrogen-doped chlorinated CNMs. XPS and TEM showed that the types of defects present in these materials ranged from boundary-like, vacancy-like, hoping and on-site defects. The defected carbon nanomaterials can be used as potential metal or metal chalcogenides nanoparticle supports in electrochemical conversions.