Hydrogenation-Induced Phase Transition in Atomic-Layered α‑MoCl₃ Driven by Laser Illumination in a Moist Atmosphere

Hydrogenation plays a critical role in tuning the material structural phase that fundamentally determines their electronic, optical, magnetic, and catalytic properties. However, prevailing hydrogenating techniques rely on noble-metal catalysis, high-temperature/pressure conditions, and high-energy proton implantation. Here, we report an optically controlled hydrogenation strategy of atomic-layered material α-MoCl₃ via laser illumination treatment in a moist atmosphere environment. With the assistant of laser, hydrogens are generated from the reaction between water molecules and highly electronegative element chlorine, intercalate into α-MoCl₃, and ultimately produce a more conductive phase with a maximum hydrogen-doping density of 0.04 wt %. Without laser, hydrogens are reversibly released and the structure restores to pristine α-MoCl₃. Density-functional theory studies reveal the facile mechanism of α-MoCl₃ hydrogenation including the dependence on the laser wavelength and power, the concomitant electronic phase transition, and improved material stability. Our results provide a plausible way for hydrogenating low-dimensional materials through precise control of laser treatment, which can find its multifunctional applications in hygrometer, photodetector, and photocontrollable smart devices.