Integrated unit-cell-thin MXene and Schottky electric field into piezo-photocatalyst for enhanced photocarrier separation and hydrogen evolution

• Flaky Ti 3 C 2 T x (FTC) combines with piezoelectric ZnO to form Schottky junctions. • Schottky interface facilitates separation of carrier by piezo-promoted charges. • Piezoelectric charges in FTC-ZnO directly participate in hydrogen evolution. • Piezoelectric polarization can reduce the refraction loss of incident laser. Piezocatalysis and photocatalysis have been integrated on zinc oxide (ZnO) to pioneer a new field of piezo-photocatalysis for developing alternative clean energy resources. However, the large potential barrier of pristine ZnO prevents the transportation of photogenerated carriers, thus restricting overall photoelectric performance. Herein, we report the piezoelectric–promoted separation of photocarriers in a two-dimensional interfacial Schottky heterojunction, which were assembled by depositing ultrathin and flaky Ti 3 C 2 T x (FTC) on ZnO films. Experimental results and density functional theory calculations show that this hybrid piezo-photocatalyst can facilitate the separation of photogenerated electron–holes under the piezo-polarization charges induced by piezoelectricity. Moreover, the piezoelectric charges can participate in the surface redox reactions of the piezo-photocatalytic process. Further, the refraction loss of incident illumination caused by the interface between metal and semiconductor can be reduced owing to the piezoelectric polarized orientation of the built-in electric field. Consequently, FTC-ZnO integrated by unit-cell-thin MXene and Schottky electric field, can be optimized considerably in terms of photocatalytic hydrogen evolution under illumination and ultrasonic irradiation. The findings of this study can help expand the horizon on ZnO films as piezo-semiconductors for piezo-photocatalytic hydrogen evolution, and provide a reference for introducing a series of metallic MXenes into the construction of innovative piezo-photocatalysts.