Stacking Mode-Driven Enhancement of Optoelectronic and Electrocatalytic Properties in Bilayer 2H MoS₂

The stacking orientation of bilayer two-dimensional (2D) materials introduces an additional degree of freedom that can profoundly influence their electronic, optoelectronic, and electrochemical properties. While stacking-engineered phenomena such as ferroelectricity, superconductivity, and second harmonic generation have been widely studied in bilayer molybdenum disulfide (MoS₂), their impact on functional device performance, particularly photoresponse and electrocatalysis, remains largely unexplored. Here, we investigate how the stacking configuration governs the optoelectronic and electrocatalytic behavior of bilayer MoS₂, focusing on the two stable stacking orders: 2H and 3R synthesized via chemical vapor deposition (CVD). Photodetection measurements reveal that 2H stacked bilayer MoS₂ exhibits a remarkable two-orders-of-magnitude enhancement in photoresponsivity over its 3R counterpart, attributed to stronger interlayer coupling and more efficient charge transfer. Additionally, 2H MoS₂ demonstrates enhanced field-effect transistor (FET) characteristics and achieves twice the hydrogen evolution reaction (HER) activity compared to 3R MoS₂. We employ scanning electrochemical cell microscopy (SECCM) to achieve spatially resolved mapping of electrocatalytic reactivity, offering the first direct nanoscale visualization of stacking-dependent HER activity. These findings underscore the crucial role of stacking orientation of atomic layers in tuning both optoelectronic and electrocatalytic properties, paving the way for stacking-engineered 2D materials in next-generation photodetectors and electrocatalytic devices.