Monolayer MoSe₂/MoS₂ Periodic Lateral Heterostructures with Built-In Electric Field Modulation for Hydrogen Evolution

The rational design of efficient, low-cost nonprecious metal catalysts is crucial for sustainable hydrogen production. Owing to their layered structures and tunable electronic properties, two-dimensional transition metal dichalcogenides are promising catalysts for the hydrogen evolution reaction, yet their low basal-plane activity and weak hydrogen adsorption limit their catalytic performance. Here, we fabricate MoSe₂/MoS₂ periodic lateral heterostructures via laser direct writing combined with selective selenization. Kelvin probe force microscopy reveals an interfacial transition region with a gradual variation in the potential, which generates a built-in electric field. Density functional theory calculations indicate that interfacial electronic reconstruction, together with this internal field, shifts the d-band center upward and increases the density of states near the Fermi level. Such modulation redistributes charge at active sites and drives the hydrogen adsorption free energy toward the thermoneutral value, thereby balancing the adsorption and desorption processes of the key H* intermediates. Benefiting from this, the heterostructures exhibit excellent HER activity, achieving an overpotential of 45 mV at 10 mA cm^-2 and a Tafel slope of 37.9 mV dec^-1. Therefore, interfacial potential modulation combined with energy band engineering provides an effective route to design high-performance 2D heterostructure catalysts, underscoring their promise as alternatives to precious-metal electrocatalysts.