We employ a widefield hyperspectral imaging method on an optical microscope to ensure our spectroelectrochemistry data stems from only ML-MoS2 material. Fig. shows the experimental setup. A MoS2-coated ITO sample serves as the working electrode in an optically transparent three-electrode electrochemical cell (see Methods for detailed metal-organic chemical vapor deposition (MOCVD) MoS2 growth and subsequent wet transfer procedure). In a typical experiment, we immerse the ML-MoS2 sample in dry, N2-saturated electrolyte consisting of 0.25 M tetrabutylammonium hexafluorophosphate ([Bu4N][PF6]) and acquire hyperspectral image stacks at constant 𝐸 by illuminating a microscopic 0.01 cm 2 sample region with monochromatic light over the range of 400-700 nm in 2 nm increments (Fig. ). A 60× objective collects the transmitted light from the sample and projects it onto a sensitive sCMOS camera. Fig. shows a representative bright field transmission image of the sample. The uniform image contrast across a large 1 mm 2 area indicates the sample is predominantly ML-MoS2, as confirmed by Raman microspectroscopy measurements (Fig. ). However, microscopic defects such as tears, voids, wrinkles, and multilayer folds exist within the sample (see black arrows in Fig. and Fig. ). Those defect features ordinarily contribute to and complicate the interpretation of ensemble-level electrochemical and optical data.