Dopant-dependent structure–property relationships in functionalized graphene and MWCNTs for sustainable energy applications

Abstract This study investigates the functionalization of carbon-based materials with halogen atoms (fluorine, bromine) and an alkali metal (lithium), subsequently examining the comparative impact of these modifications on their structural, optical, and electrical characteristics. Graphene oxide was modified with fluorine using hydrofluoric acid to produce fluorinated graphene (FG) and with bromide in the form of tetrabutylammonium bromide (TBAB) to produce G-TBAB. Separately, multi-walled carbon nanotubes (MWCNTs) were functionalized with lithium fluoride to form Li-MWCNTs. The materials were characterized via FTIR, XRD, SEM, TEM, AFM, and XPS. Optical properties were evaluated using UV–Vis and photoluminescence spectroscopy, and electrical behavior was assessed through electrochemical impedance spectroscopy (EIS). The findings demonstrate that among the three materials, FG exhibits the lowest charge transfer resistance (R CT = 2.54 Ω.cm −2 ) and film resistance (R f = 1.19 Ω.cm −2 ) in EIS measurements, suggesting more efficient charge transport under the tested conditions. G-TBAB and Li-MWCNTs show distinct EIS parameters, including higher capacitance values R CT 12.91 Ω.cm −2 and 17.73 Ω.cm −2 , which may be relevant for applications where charge accumulation is prioritized. These results indicate that hetero-functionalization of carbon allotropes provides a tunable platform, with each modification (F, Br, or Li) imparting distinct electrical and optical behavior.