Covalent Organic Frameworks for Piezocatalysis, Piezo-Photocatalysis and Piezoelectric Energy Harvesting

Low-grade mechanical energy widely exists in natural environments, such as ocean-wave fluctuation, industrial vibration and human-body motion, yet most of this energy remains underutilized. Piezocatalysis, piezo-photocatalysis and piezoelectric nanogenerators (PENGs) provide feasible routes to convert ambient mechanical-vibration energy into chemical energy and usable electricity. Distinct from conventional inorganic piezoelectric materials suffering from low specific surface area and limited structural tunability, covalent organic frameworks (COFs) possess tailorable skeletons, high porosity, excellent chemical–thermal stability and modular symmetry-engineering capability. Non-centrosymmetric COFs with intrinsic piezoelectric responses can be realized via rational monomer-level design. Nevertheless, research on piezoelectric-related COFs-based systems is still in its early exploratory stage, and comprehensive reviews covering piezocatalysis, piezo-photocatalysis and piezoelectric energy harvesting remain scarce. This review addresses both intrinsic piezoelectric COFs and COFs-containing hybrid composite systems. Notably, performance gains in composite systems cannot be simply attributed to the intrinsic piezoelectric response of the COFs component. We systematically discuss their fundamental mechanisms, unique flexible-pore electromechanical features, multi-scale modification strategies, diverse application scenarios, and unresolved challenges. We discuss the applicability and inherent limitations of core piezocatalytic interpretive frameworks for flexible porous COFs systems. Five mainstream strategies for boosting COF piezoresponse are summarized: building-block molecular design, defect engineering, morphology modulation, single-atom metal anchoring and heterostructure construction. Representative applications including water-energy conversion, CO2 reduction, organic-pollutant remediation, uranium (VI) reduction, antibacterial disinfection and mechanical-energy harvesting are presented. Key bottlenecks covering mechanistic ambiguity, characterization constraints, synthetic hurdles and long-term practical stability are highlighted, and targeted future research directions are proposed. This review offers instructive guidelines for developing high-performance symmetry-engineered COFs-based piezofunctional systems.