The HER performance of 2D materials is underestimated without morphology correction

Abstract

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 MoS2 and WS2 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.