Investigation of the Photo-Responsive Electrochemical Activity of van der Waals Heterostructures by Multiple Scanning Probe Microscopies

Excessive use of fossil energy by human activities leads to global warming and climate change. To address this issue, it is necessary to develop new renewable energy materials using earth-abundant and low-cost resources. Here, we focus on two-dimensional(2D) materials, which are single atoms or molecules thick and have an ideal planar structure. 2D materials such as graphene and molybdenum disulfide (MoS₂) are widely used in hydrogen reduction reactions and water splitting. MoS₂ is considered an ideal photocatalyst material due to its suitable band structure in the visible light region. Furthermore, Van der Waals (VdW) heterostructures are fabricated by dry transfer method from chemical vapor deposition grown MoS₂ flakes, and their structures are analyzed using Raman spectroscopy, photoluminescence (PL), and scanning transmission electron microscopy (STEM). To understand the photocatalytic reaction mechanism of VdW heterostructures, we have developed active site mapping techniques including combined atomic force microscopy-scanning electrochemical microscopy (AFM-SECM) and scanning electrochemical cell microscopy (SECCM). These techniques investigate the light-responsive electrochemical current on single-crystal VdW heterostructure samples, which can further establish the mechanism of photocatalytic carbon dioxide/hydrogen reduction reaction catalysis corresponding to their electronic structures.