A Dual-Piezoelectric Metal-Organic Cage/COF Z-Scheme Heterojunction for Solar-Mechanical Water Splitting

Developing efficient solar-mechanical energy conversion systems is crucial for sustainable H₂/H₂O₂ production. We report an unprecedented piezoelectric metal-organic cage (MOC-FA3), integrated with piezoelectric β-ketoenamine COF (S-COF) into a Z-scheme heterojunction via supramolecular interactions. The non-centrosymmetric piezoelectricity of MOC-FA3 is confirmed by multimodal characterization (KPFM, piezoelectric coefficient measurement, and in situ spectroscopy) and piezocatalytic H₂/H₂O₂ production (334.3/203.6 µmol g^-1 h^-1). Under ultrasound (60 W, 40 kHz) and AM 1.5G, the heterojunction achieves exceptional synergistic pure water splitting at 1297.6 H₂ and 1304.2 H₂O₂ µmol g^-1 h^-1, among the highest for COF-based piezo-photocatalysts, with 1.95-fold and 2.06-fold enhancements over S-COF. This stems from Z-scheme charge transfer coupled with piezoelectric-field-enhanced separation. Experimental results and DFT calculations identify Pd sites (H₂ evolution) and C²-C³ sites (2e^- water oxidation → H₂O₂), with in situ EPR confirming •OH intermediates. This work introduces MOCs as a new piezoelectric material class, demonstrating synergistic Z-scheme/piezoelectric coupling for mechano-photonic energy conversion.