Dual Modification of Metal-Organic Frameworks for Exceptional High Piezo-Photocatalytic Hydrogen Production

Metal-organic frameworks (MOFs) face significant challenges in photocatalysis due to severe carrier recombination. Here, a novel approach is presented that incorporates ─NH₂ groups and Cu ions onto MOFs with a MIL-125 skeleton, forming NH₂-MIL-125 and Cu-NH₂-MIL-125. This modification effectively enhances the polarity of MOFs, evidenced by significantly increased d₃₃ values (from 1.69 to 26.21 pm/V) and notable higher dipole moments (from 6.60 to 25.99 D). Notably, it's the first demonstration of boosting MOFs piezoelectricity via a dual modulation strategy. Moreover, the polarity can be further amplified by ultrasonic vibration based on the positive piezoelectric effect, which is justified by in situ Raman spectra, COMSOL simulations, and DFT calculations, by taking into account the applied pressure. The positive impact of introduced piezoelectric effect in facilitating charge separation and transfer of Cu-NH₂-MIL-125, proved by enhanced current response. Consequently, through coupling piezocatalysis and photocatalysis, the H₂ production rate of Cu-NH₂-MIL-125 can be significantly enhanced to ≈2884.2 µmol·g^-1·h^-1, 2.76 and 9.92 times higher than that of NH₂-MIL-125 and MIL-125, respectively, ranking first in all reported MOF-based piezo-photocatalysts. This research demonstrates the prospective opportunity for alleviating the severe carriers recombination problem for MOFs through the implantation of piezoelectric field driving force.