Germanium and phosphorus co-doped carbon nanotubes (Ge–P-CNTs) were prepared by a simple and scalable approach. The morphology and structure of the Ge–P-CNTs was characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The ORR electrocatalytic performances were evaluated by exchange current density, reaction pathway selectivity, on-set potential, kinetic current density and H2O2 yields from rotating ring-disk electrode (RRDE) measurements, indicating that the co-doped GeP2C2, GeP3C and GeP4 + PC3 microstructures in Ge–P-CNTs are crucial to improving the ORR catalytic performance. In fact, the electrochemical performance enhancement results from the synergistic effects by the appropriate proportion of Ge and P atoms. The ORR catalytic synergistic effect has also been verified by calculating the work function based on density functional theory (DFT). Because of these outstanding features, it is expected that the Ge–P-CNTs materials will be a very suitable catalyst for fuel cells and metal–air batteries.

•Spectrum analysis on the reduction degree of GO reduced by different methods.•Determine the optimized reduction conditions of GO and polymer/r-GO composites.•The two-step reduction is more effective than one-step reduction.In this paper, the reduction degree of graphene oxide (GO) reduced using chemical reduction and thermal reduction methods was characterized by spectrum analysis. The optimized conditions of reducing GO were determined that the hydrazine hydrate is the best reducing agent and the appropriate thermal reduction temperature is at 240 °C. The obtained GO solution was mixed with polystyrene (PS) solution to prepare PS/r-GO composites by using two-step reduction technique under the optimized conditions. The structure and micro-morphology of GO, r-GO and PS/r-GO composites were characterized by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM) respectively. It is also observed that the two-step reduction pathway is more effective than one-step reduction for improving the reduction degree of GO. Accordingly, the electric conductivity of PS/r-GO composites prepared by two-step reduction technique is as high as 21.45 S m−1, which is much higher than that of composites fabricated by one-step reduction method. The spectrum techniques will highlight new opportunities for investigating the reduction degree of GO in polymer composites.