Figure 2.

In operando Raman spectroscopic evolution of NiO₂H_x thin film model electrode operated in a 2 m KOH aqueous electrolyte. The corresponding CV profile (10 mV s⁻¹) is shown on the right panel. The potential of each spectrum is indicated by the color bar located between the spectra and the CV curve. The color bar is separated to 20 grids. Each grid represents a potential interval of 0.05 V, over which, the spectrum was acquired during the in operando measurements. The red shifts and blue shifts of A_1g mode and E_g mode are marked on the spectra. A schematic sketch of breaking/formation of O‐H bond is also shown to illustrate the redox behavior on the basis of quantitative analyses.