2D Piezoelectric Covalent Organic Frameworks: Construction, Characterization, and Potential Applications.

2D piezoelectric covalent organic frameworks (2D p-COFs) represent a transformative class of materials merging structural precision, symmetry breaking, dynamic covalent chemistry, and electromechanical functionality. Unlike inorganic piezoelectrics (e.g., ZnO, perovskites) or conventional polymers, 2D p-COFs leverage their atomically ordered, noncentrosymmetric architectures to achieve efficient mechanical-to-electrical energy conversion while offering tunable structure, permanent porosity, and stability. Given the successful examples set by fluoropolymer-based energy harvesters, grafting fluorine-substituted alkyl chains onto COFs can facilitate dipole alignment and generate net spontaneous polarization, thereby inducing piezoelectricity. Recent advances in synthesis-fluorinated side-chain functionalization and hybrid system designs-have enabled large piezoelectric coefficients and high open-circuit voltages in nanogenerators. This review delves into the core principles of piezoelectricity, construction methodologies, the characterization of distinctive properties, and the burgeoning applications of 2D p-COFs in energy harvesting, catalysis, and sensing, while also facing challenges associated with scalability and stability.