Fig. 4: In situ Raman spectroscopy and kinetic analysis of ORR on carbon soot.

a Schematic illustration of the shell-isolated nanoparticles (Ag@SiO₂) on the surface of carbon-based catalysts with different sizes and the mechanism of the ORR process revealed by the SHINERS method, where the black, white, and red spheres represent carbon, hydrogen, and oxygen atoms, respectively. b TEM image of Ag@SiO₂. c Electromagnetic field distribution of Ag@SiO₂ on the glassy carbon substrate, where E and E₀ denote the localized electric field and the incident electric field. In situ surface-enhanced Raman spectra of the ORR system at the surface of CS-low (d), CS-middle (e), and CS-top (f) in a 0.1 M KOH solution saturated with O₂. g In situ surface-enhanced Raman spectra of CS-top catalyst in O₂-saturated 0.1 M KOH and 0.1 M KOD at 0.16 V vs. RHE. h LSV curves of CS-low, CS-middle and CS-top under gas diffusion electrode setup in 0.1 M KOH and 0.1 M KOD with iR-compensation. i Colored contour map of Raman intensity at ~1060 cm⁻¹ as a function of Tafel slope of CS-low, CS-middle and CS-top and potential in O₂-saturated 0.1 M KOH. Source data for (d–i) are provided as a Source Data file.