Nanoscale Mapping of Hydrogen Evolution Activity in MoS2–MoSe2 Lateral Heterostructures Nanosheets via Scanning Electrochemical Cell Microscopy

Scanning electrochemical cell microscopy (SECCM) is a spatially resolved electrochemical technique capable of providing information on structure–activity relationships with nanoscale resolution. The spatial resolution of SECCM is governed by both the pipette aperture size and the extent of the wetted area. Even when nanoscale apertures are employed, droplet spreading can enlarge the effective interrogation region several-fold, limiting the ability to resolve sharp heterointerfaces. Here, we report nanoscale mapping of hydrogen evolution reaction (HER) activity in CVD-grown MoSe2–MoS2 lateral heterostructures using SECCM. MoSe2 and MoS2 exhibit distinct wettability behaviors, and controlled meniscus wetting was achieved through the addition of polyvinylpyrrolidone (PVP) to a 100 mM HClO4 electrolyte, enabling spatially resolved measurements with a lateral resolution of approximately 250 nm. The resulting activity maps reveal pronounced spatial heterogeneity between MoS2 and MoSe2 domains, as well as localized variations at their lateral interfaces. Complementary Kelvin probe force microscopy (KPFM) measurements identify surface potential gradients on the order of 100–300 mV and an interfacial potential modulation of approximately 200 mV, consistent with interfacial band alignment effects and charge redistribution across the heterojunction. This work highlights the capability of SECCM to resolve electrochemical heterogeneity in lateral heterostructures composed of materials with distinct wettability characteristics and provides a nanoscale framework for investigating structure–activity relationships in two-dimensional catalytic systems.