Orientation Engineering of MXene Flakes

MXene, a family of 2D transition-metal carbides, nitrides, or carbonitrides, uniquely integrates metallic conductivity, surface tunability, and compositional versatility, enabling their widespread applications across energy, electronics, sensors, and environmental systems. Beyond conventional optimization (e.g., composition, termination, defects), a new research frontier has recently emerged that focuses on engineering the orientation of MXene flakes, i.e., the deliberate control of flake alignment within MXene-based structures such as fibers, films, membranes, and gels. Engineered orientation transforms inherently disordered MXene assemblies into highly anisotropic structures with directionally optimized electron, ion, and stress transport pathways. Compared with their randomly stacked counterparts, these oriented MXene structures exhibit remarkably enhanced electrical, ionic, and mechanical properties, unlocking new routes to tailor the macroscopic performance of MXene-based devices. This review aims to provide a comprehensive and systematic summary of the orientation engineering of MXene flakes, covering the fundamental properties governed by MXene flake orientation, characterization techniques for revealing MXene orientation information, fabrication methodologies for achieving engineered MXene orientation, representative advances of oriented MXene structures in diverse functional systems, and forward-looking design opportunities for MXene orientation engineering. This article offers both a concise knowledge framework and forward-looking insights for inspiring the rational design of next-generation MXene-based materials and devices.