In situ cyclic voltammetry-surface-enhanced Raman spectroscopy: studies on the doping–undoping of polypyrrole film

The redox behavior of polypyrrole (PPy) film in 0.2 M aqueous KNO3 solution was investigated by cyclic voltammetry (CV) in situ surface-enhanced Raman spectroscopy (SERS). The results show that the Raman intensity of CC backbone stretching decreases and increases regularly with the anodic and cathodic scans, respectively, owing to the change of surface roughness and the possibility of state transition. The peak position of CH in-plane deformation remains unchanged both in anodic and cathodic scans. Furthermore, the peak positions of NH in-plane deformation and ring deformation shift to lower and higher wavenumbers with anodic and cathodic scans, respectively. Also the Raman peak of the NO3− dopant ions appears significant when PPy is in a more oxidized state.