Nanoscale Mapping of Hydrogen Evolution Activity in MoS₂-MoSe₂ Lateral Heterostructures via SECCM

We investigated the hydrogen evolution reaction (HER) in CVD MoSe₂-MoS₂ lateral heterostructures using scanning electrochemical cell microscopy (SECCM), overcoming initial surface wetting challenges through the addition of polyvinylpyrrolidone (PVP) to a 100 mM HClO₄ electrolyte. SECCM mapping at 250 nm resolution revealed a 3-fold higher HER activity in MoS₂ domains compared to MoSe₂. The junction at the heterointerface facilitated efficient charge transfer, enhancing catalytic performance. Complementary Kelvin probe force microscopy (KPFM) identified a 50-100 mV surface potential gradient and a ~20 mV interfacial potential well, indicative of band bending and charge trapping. The type-II band alignment, defects and alloyed regions (e.g., MoSexS2-x) modulated the work function to align the Fermi level closer to the H+/H2 redox potential. Despite SECCM’s resolution limits (~250 nm) averaging signals across nanoscale interfaces, this study underscores the critical role of interfacial engineering and electronic structure optimization in advancing 2D heterostructures for energy conversion technologies.