Layered transition metal dichalcogenides (TMDCs) have become promising candidates for photoelectrochemical (PEC) studies from the 80’s. Both n- and p-type MoSe2, and WSe2 materials were studied in photoelectrocatalytic reactions using model redox couples and hydrogen evolution reaction. (1-2) Exfoliation of the bulk, layered crystals to single- and few-layered two-dimensional (2D) nanosheets leads to new physical phenomena, different from their bulk counterparts. (3) The electrochemical properties of 2D nanoflakes −which define the performance of these materials in energy-related applications− depends on their structural properties. These structural features include the number of layers, the basal/edge planes, and the defect density. (4-5) Therefore, to employ 2D nanosheets for energy conversion and storage we need to understand their fundamental PEC properties, using an approach with spatial resolution. In our study, TMDCs samples, MoSe2, WSe2, and MoWSe2 nanosheets were mechanically exfoliated to get bulk, few-layered, and monolayer specimens. The number of layers, and defect density in the separated nanosheets were characterised by Raman spectroscopy and atomic force microscopy. Our recently developed custom-designed microdroplet cell-based photoelectrochemical approach was applied to identify the structural parts and to measure the PEC activity of the flakes (10-50 μm droplets in diameter). PEC measurements, including photovoltammetry, photocurrent transient analysis, and quantum efficiency were carried out to reveal the role of structural properties on the light harvesting, charge transport, and recombination properties of TMDCs. We have determined the band diagrams of these materials using bandgap values from PEC studies and work functions achieved from ambient pressure photoemission spectroscopy (APS) and surface photovoltage spectroscopy (SPS) measurements. Our photoelectrochemical microscopy technique also allowed to probe the PEC reactivity of novel member of 2D family, such as MoWSe2 mixed transition metal dichalcogenide. Finally, I demonstrate the use of model reversible redox species (K4[Fe(CN)6], (NH4)2[IrCl6]) to mimic photoelectrocatalytic processes. (1) F. R. F. Fan, H. S. White, B. L. Wheeler, A. J. Bard; J. Am. Chem. Soc. 1980, 102, 5142-5148 (2) W. Kautek, H. Gerischer; Ber. Bunsenges. Phys. Chem. 1980, 84, 645-653 (3) K. S. Novoselov, D. Jiang, F. Schedin, T. J. Booth, V. V. Khotkevich, S. V. Morozov, A. K. Geim; PNAS, 2005, 102, 10451-10453 (4) P. S. Toth, A. T. Valota, M. Velický, I. A. Kinloch, K. S. Novoselov, E. W. Hill, R. A. W. Dryfe; Chem. Sci., 2014, 5, 582-589 (5) M. Velický, M. A. Bissett, C. R. Woods, P. S. Toth, T. Georgiou, I. A. Kinloch, K. S. Novoselov, R. A. W. Dryfe; Nano Lett., 2016, 16, 2023-2032