Defect Engineering in Two-Dimensional Piezocatalysts: A Trifunctional Perspective on Mechanisms and Design.

Piezocatalysis, which harnesses ubiquitous mechanical energy to drive chemical transformations, offers a sustainable approach for energy production and environmental remediation. While two-dimensional (2D) materials serve as ideal platforms for piezocatalysis, their practical performance is often hindered by intrinsic limitations such as weak piezoelectricity and insufficient active sites. Defect engineering has emerged as the most effective strategy to overcome these challenges. However, a comprehensive understanding of defect functionality remains under development. In this review, a unifying trifunctional framework to deconstruct and rationalize the roles of defects is introduced. It is proposed that their contributions can be systematically classified into three roles: modulation of the piezoelectric response through symmetry breaking (Role 1), regulation of charge carrier dynamics via electronic structure engineering (Role 2), and creation and optimization of active sites to reduce reaction energy barriers (Role 3). This framework is applied to examine recent advances across diverse applications, from environmental remediation and energy conversion to biomedicine. Finally, key challenges and future directions are outlined, offering a conceptual blueprint to guide the rational design of next-generation 2D piezocatalysts.