Fig. 3

Raman spectra of Pt/C and bulk Pt at various conditions. The Raman spectra for: a Pt/C and b bulk Pt in water-based alkaline environments. c Pt/C in deuterium water-based alkaline environments. The marked overpotential is in comparison to the onset potential of HER (e.g., −0.1 V is 0.1 V more negative to onset potential). The Raman signals on the surface of the catalyst are identified as: G-band of carbon: ~1580 cm⁻¹; H₂O: ~1600 cm⁻¹; H₃O⁺: ~1750 cm⁻¹; D₃O⁺: ~2720 cm⁻¹; HD₂O/H₂DO⁺: ~2850 cm⁻¹; D₂O: ~2380 cm⁻¹, ~2500 cm^−143,44,45