Anisotropic Strain‐Induced Piezoelectric Polarization in 3R‐MoS ₂ for Enhanced Piezo‐Photocatalytic Oxidation of Formaldehyde

ABSTRACT The efficient removal of formaldehyde (HCHO), a pervasive and hazardous atmospheric pollutant, remains challenging due to inherent limitations in conventional photocatalysis, particularly rapid charge recombination and insufficient reactive oxygen species (ROS) generation. Although the non‐centrosymmetric structure of sliding ferroelectric 3R‐MoS 2 enables piezoelectric polarization to overcome these constraints, the atomistic origin of how this anisotropic strain‐induced polarization modulates surface reaction kinetics is not well understood. Herein, we develop a first‐principles piezoelectric polarization model and integrate it with experimental validation to unravel the atomic‐scale piezo‐photocatalytic mechanism of 3R‐MoS 2 for HCHO degradation. Our results demonstrate that anisotropic compressive strain along the armchair direction induces strong piezoelectric polarization via asymmetric Mo─S displacements, while zigzag‐oriented strain produces negligible response. Experimental characterization confirms the successful synthesis of the non‐centrosymmetric 3R‐MoS 2 and its pronounced anisotropy. The tailored polarization establishes an internal electric field that simultaneously optimizes band structure and aligns with critical redox potentials for efficient charge separation. Remarkably, −6% armchair polarization reduces the energy barrier of the rate‐determining step by 92% through interfacial charge redistribution and d‐band center upshift. Experimental validation confirms a twofold catalytic enhancement in 3R‐MoS 2 over the 2H‐phase. This work elucidates strain‐directed piezo‐photocatalytic HCHO oxidation and paves the way for noble‐metal‐free environmental remediation.