Fluid-induced piezoelectric field enhancing photocatalytic hydrogen evolution reaction on g-C₃N₄/LiNbO₃/PVDF membrane

Piezoelectric materials have been widely used in photocatalytic systems as it forms a built-in electric field to facilitate the migration of photo-induced charge-carriers. Herein, we report a three-dimensional (3D) porous g-C₃N₄/LiNbO₃/PVDF membrane with an enhanced fluid-induced piezoelectric field for photocatalytic hydrogen evolution reaction (HER). The freezing phase inversion strategy is critical to the formation of piezoelectric sensitive β phase PVDF. The unique 3D porous membrane structure and the fluid-induced piezoelectric potential synergistically contribute to the HER efficiency under white light illumination. The as-prepared g-C₃N₄/LiNbO₃/PVDF piezoelectric photocatalytic membrane (19.6875 cm² in size) exhibited HER rate of 136.02 µmol h⁻¹, which was even higher than that of the g-C₃N₄/LiNbO₃ powder sample (111.8 µmol h⁻¹) with the identical mass of catalyst particles. In-situ diffuse reflection infrared Fourier transform spectroscopy (DRIFTS) demonstrates a better water affinity of the porous g-C₃N₄/LiNbO₃/PVDF piezoelectric membrane prepared by the freezing phase inversion than other PVDF membranes prepared by traditional phase inversion and vacuum drying methods. Piezoelectric force microscopy (PFM), in-situ piezoelectric and piezoelectric current measurements further visualized the fluid-induced piezoelectric field on 3D g-C₃N₄/LiNbO₃/PVDF membrane, by which boosting the HER efficiency.