Heteroatom-doped electrochemically exfoliated graphene thin films: A Raman spectroscopy and density functional theory study

Abstract

This work presents a combined experimental and theoretical investigation of freestanding, heteroatom-doped electrochemically exfoliated graphene (EEG) thin films. The films were synthesized via a two-step process involving graphite intercalation and exfoliation in a sulphuric-phosphoric acid mixture, enabling in-situ doping with nitrogen (N), phosphorus (P), and sulphur (S). The exfoliated product was vacuum-filtered to produce porous films. Raman spectroscopy revealed Fermi level shifts of ~0.5 eV and heterogeneous defect distributions. Electrical conductivity was significantly enhanced (~10,000 S·m −1 ), attributed to effective heteroatom incorporation. X-ray photoelectron spectroscopy confirmed successful doping, while force-distance curve measurements showed reduced adhesion forces, indicating improved interfacial properties. Complementary density functional theory (DFT) calculations provided atomic-level insights into mono- and multi-element doping effects. N and O dopants caused localized charge redistribution with minimal lattice distortion, while P and S introduced more pronounced structural perturbations and delocalized electronic states. Co-doped models with O, N, P, and S exhibited larger Fermi level shifts (up to ~1 eV) and increased carrier densities (~1.25 × 10 14 e/cm 2 ). Bader charge analysis established a strong correlation between dopant identity, charge localization, and doping efficiency. Electrochemical investigations indicated that Fermi level shifts enhance interfacial charge transfer by lowering the potential barrier between the electrode and electrolyte. The EEG film displayed a prolonged discharge time, and a specific capacitance of 150.5 F g −1 at 1.0 A g −1 . These results provide a comprehensive approach for engineering doped EEG thin films with tailored electronic properties for supercapacitor applications. • Electrochemically exfoliated graphene (EEG) films exhibit tunable Fermi level shifts (0.4–0.5 eV) due to heteroatom doping. • Raman mapping and peak shift analysis reveal spatially heterogeneous doping and defect distributions. • DFT models show that multi-doped graphene (O, N, P, S) achieves Fermi level shifts up to 1.3 eV and high carrier density. • XPS confirms incorporation of N, P, and S dopants, enhancing electrical conductivity up to ~10,000 S m −1 . • Fermi level shifts in EEG promoted enhanced interfacial charge transfer, leading to a high specific capacitance of 150.5 F g −1 at 1 A/g.

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