Free layer-dependent piezoelectricity of oxygen-doped MoS2 for the enhanced piezocatalytic hydrogen evolution from pure water

The piezoelectricity of MoS2 only exists in monolayer and odd-number layers, owing to the inversion symmetry of the even number layers, which limits the efficient utilization and mass synthesis of MoS2. Herein, the structure of MoS2 is adjusted by oxygen doping, which could break the layer-dependent piezoelectricity and induce out-ofplane polarization. This endows O-doped MoS2 the free layer-dependent and enhanced piezoelectricity. Benefiting from the optimized piezoelectricity, higher concentration of carriers, higher Hall mobility and lower resistivity, the O-doped MoS2 exhibits an improved activity of piezocatalytic H2 production from pure water, and the corresponding H2 evolution rate reaches up 47.75 mu mol center dot h- 1 center dot g- 1. Under the same conditions, the hydrogen production rate of MoS2 is only 20.19 mu mol center dot h- 1 center dot g- 1. This work not only provides a new strategy for modulating piezoelectricity of transition mental dichalcogenides, whose bulk materials are non-piezoelectric, but also breaks new ground for developing high-efficiency piezocatalysts.