To address aggravating environmental and energy problems, active, efficient, low-cost, and robust electrocatalysts (ECs) are actively pursued as substitutes for the current noble metal ECs. Therefore, in this study, we report the preparation of graphene flakes (GF) doped with S and N using 2-5-dimercapto-1,3,4-thiadiazole (S₃N₂) as precursor followed by the immobilization of cobalt spinel oxide (Co₃O₄) or manganese spinel oxide (Mn₃O₄) nanoparticles through a one-step co-precipitation procedure (Co/S₃N₂–GF and Mn/S₃N₂–GF). Characterization by different physicochemical techniques (Fourier Transform Infrared (FTIR), Raman spectroscopy, Transmission Electron Microscopy (TEM) and X-ray Diffraction (XRD)) of both composites shows the preservation of the metal oxide spinel structure and further confirms the successful preparation of the envisaged electrocatalysts. Co/S₃N₂–GF composite exhibits the best ORR performance with an onset potential of 0.91 V vs. RHE, a diffusion-limiting current density of −4.50 mA cm⁻² and selectivity for the direct four-electron pathway, matching the results obtained for commercial Pt/C. Moreover, both Co/S₃N₂–GF and Mn/S₃N₂–GF showed excellent tolerance to methanol poisoning and good stability.

ZnO and TiO₂ nanoparticles were prepared through a plant-extract mediated hydrothermal synthesis. X-ray diffraction (XRD) study confirmed the crystalline nature and the phase characteristic of the obtained nanoparticles. X-ray diffraction profile analysis models such as Williamson–Hall analysis, size-strain plot and Rietveld analysis were further used in evaluating the microstructural parameters of the obtained materials. The calculated particle size for all the models was in great agreement, with values in the range of 55.46–87.6 nm recorded for ZnO, while for TiO₂, the crystallite size was in the range of 33.82–41.9 nm. The calculated crystal microstrain varied based on the model, while the stress in the ZnO and TiO₂ nanoparticles was evaluated at 3.8 and 13.7 MPa, respectively. Furthermore, TiO₂ nanoparticles had a higher energy density of 8.96 × 10^–8 KJ m⁻³ compared to 7.12 × 10^–8 KJ m⁻³ obtained for ZnO.