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

ABSTRACT Developing efficient solar‐mechanical energy conversion systems is crucial for sustainable H ₂ /H ₂ O ₂ 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 H ₂ /H ₂ O ₂ 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 H ₂ and 1304.2 H ₂ O ₂ 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 (H ₂ evolution) and C ² ‐C ³ sites (2e ⁻ water oxidation → H ₂ O ₂ ), 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.