In-situ Raman spectra were acquired by a self-design electrochemical cell. (3D-printed by Protolabs, UK) with a miniature leakless Ag/AgCl reference electrode (eDAQ), and platinum sheet counter electrode (Sigma-Aldrich, USA). The samples were spin coated at 1000 r.p.m. for 60 s on an ITO slide (Kintec Inc, Hong Kong). Spectra were acquired in the Raman Stokes region using 532 nm excitation wavelength, in the range 150-2200 cm -1 (Horiba Xplora Confocal Raman). A 10x Olympus objective was used to perform measurements with laser power set at < 0.963 mW to avoid sample degradation. For a good signal-to-noise ratio, each spectrum was taken over an integration time of 20-30 s and averaged over three measurements. The spectrometer was calibrated through a Si sample using the spectral line 520.7 cm -1 . Spectra were analyzed using OMNIC software. Electrochemical signals were applied through a Bio-Logic potentiostat. A constant voltage was held for at least 30 seconds before each Raman measurement.