Laser-induced degradation of carbon nanotubes during in situ-Raman spectroscopy at high electrochemical potentials

• Results of in situ -Raman measurements are considerably affected by the procedure. • In-depth evaluation is achieved by cluster analysis of post mortem -Raman mappings. • Carbon corrosion at high potentials is amplified by simultaneous laser excitation. • Laser-induced degradation also depends on the excitation energy of the laser. In situ -Raman spectro-electrochemistry is frequently used for the investigation of carbon electrode materials, contributing to our fundamental understanding of reaction pathways, surface intermediates or degradation processes. A challenge when using the in situ -Raman technique is to ensure that the measurement results are not influenced by the irradiation with the high-energy laser beam. Therefore, reference experiments with laser irradiation only are commonly carried out to verify that repetitive Raman probing does not affect the electrochemical and structural properties of the investigated electrode material. However, the impact of simultaneous exposure to electrochemical stress and laser excitation is barely considered. In this work, we elucidate these combined effects for in situ -Raman investigation of carbon nanotubes during polarization to high potentials. The results demonstrate that the structural degradation, which is indicated by an increasing D:G-ratio, is significantly intensified by the Raman measurement with a 532 nm laser when the electrode is polarized to potentials higher than 1.3 V vs. Ag|AgCl|KCl sat. in strongly acidic environment at the same time. In-depth analysis by subsequent Raman mapping experiments further reveals that the structural degradation caused by high potentials is much more pronounced for the location of Raman investigation of the initial experiment. In addition, the impact of the excitation energy of the laser is examined, and it is indicated that the structural degradation is not amplified when a 785 nm laser excitation is used. These findings highlight the importance of carefully considering concomitant effects when using in situ -techniques.