NiO- and MnO-nanoparticle-modified pyrogallol-formaldehyde-derived carbon matrix

Abstract

A pyrogallol-formaldehyde-derived carbon matrix (CM) and its nanocomposites modified with nickel oxide (NiO) and manganese oxide (MnO) nanoparticles were synthesized via a sol–gel method. X-ray diffraction revealed the amorphous nature of the carbon matrix, the presence of metallic Ni and the preserved structural stability of MnO. SEM images revealed a highly porous morphology favorable for nanoparticle incorporation, with homogeneous Ni dispersion and MnO nanoparticles showing some clustering. EDX and XPS analyses verified the successful integration of metal oxides and the presence of residual chlorine exclusively in the CM/MnO nanocomposite. Raman spectroscopy showed a progressive increase in structural disorder from CM (I_D/I_G = 0.76) to the CM/MnO nanocomposite (I_D/I_G = 1.53), consistent with an enhanced defect density and charge carrier sites. Electrical measurements demonstrated semiconducting behavior with improved conductance upon the incorporation of metal oxides. The CM/MnO nanocomposite exhibited the highest conductance and the lowest activation energy (80 meV), attributed to the Mn²⁺/Mn³⁺ redox activity and chlorine-induced defect formation. Impedance and dielectric studies revealed Maxwell–Wagner-type interfacial polarization with non-Debye relaxation behavior, governed by distinct conduction mechanisms: correlated barrier hopping (CBH) in the CM/NiO nanocomposite and small polaron hopping (SPH) in the CM/MnO nanocomposite. These results highlight the important role of transition metal oxides in electrical conduction and provide valuable insights for designing efficient carbon-based nanocomposites for advanced electronic applications.