To ensure our optical data stems from ML-MoS2 only, we spatially select regions of interest (ROIs) within each image that represent pristine ML-MoS2 and ITO (see Fig. ), and calculate A() = log10(I0()/I()), where I0() and I() are the monochromatic light intensities transmitted through the ITO substrate and ML-MoS2, respectively. In this way, we acquire spatially resolved in situ absorbance (𝐴) data as a function of applied potential (𝐸 (V) vs Ag wire quasi-reference electrode). Crucially, this procedure removes the contributions from macroscopic defects in the sample. The uncertainty in A is < 0.003 for measurements (see Fig. in Absorbance Error Analysis section in ESI).