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Transition metal dichalcogenides (TMDs) have garnered attention as potential catalysts for water splitting owing to their unique structures, diverse electronic properties, and composition from earth‐abundant elements. While certain TMD catalysts, notably MoS2, have shown promising activity for hydrogen evolution reactions (HER), achieving performance comparable to traditional platinum catalysts remains a challenge. While significant effort has been invested into understanding the effect of TMD's structural properties, such as defectiveness and crystalline phases, recent work has emphasized the role of extrinsic factors on HER. This review summarizes the current understanding of the impact of commonly overlooked electrocatalytic effects that exhibit an enhanced importance in TMD‐based HER. By combining recent advances in theoretical modeling and experimental work, we review the dominating effects of extrinsic factors including electronic resistance, interfacial barriers, surface roughness, oxidation, and valence impurities. Our work aims to provide insights into optimizing TMDs as highly efficient catalysts for HER, facilitating future advancements in hydrogen generation technology. [ABSTRACT FROM AUTHOR]

[Display omitted] • Morphology-dependent carrier transport on the HER properties of 2D-TMDs. • Uncompensated resistance controls the apparent Tafel slope of 2D-TMDs. • In-plane conduction as the origin of the low HER activity in 2D-TMDs. • HER correction scheme was applied to previously reported 2D-TMD results. 2D transition metal dichalcogenides (2D-TMDs) are considered promising materials for electrochemical catalysis and energy storage. However, large differences in electrochemical performance have been reported for 2D-TMD electrodes with different morphology, such as thickness, edge density, and porosity. We here demonstrate that limitations in the homogeneous charge transfer of 2D-TMDs are responsible for the significant observed variations in hydrogen evolution reactions (HER). Statistical electrochemical characterization was conducted on microscopic MoS 2 and WS 2 devices with compositional uniformity and controllable morphology by localized HER measurements. Detailed analysis establishes the dominating effect of the uncompensated resistance on overpotential and Tafel slope, which are commonly utilized as HER figures of merit. A correction scheme is presented that reveals the intrinsic electrocatalytic properties of 2D materials electrodes, independent of morphology. This approach was applied to previously reported polarization data and revealed differences between extracted and intrinsic Tafel slopes of up to 400% leading to potentially erroneous assignments of the HER mechanism. Finally, the correlation of two-terminal carrier transport measurements and electrochemical characterization demonstrates the in-plane conduction as the origin of the low electrochemical activity in 2D-TMDs. Our results highlight the impact of morphology-dependent carrier transport on the electrochemical properties of 2D materials. [ABSTRACT FROM AUTHOR]