Topochemical Engineering of Two-Dimensional MXenes and Beyond.

Two-dimensional (2D) materials have gained tremendous attention for their structural diversity and versatile functionality. However, conventional synthesis and post-synthetic modification often provide limited control over where and how structural or chemical changes occur, restricting the precise tailoring of composition, atomic configuration, and electronic structure. Topochemical engineering offers a distinct approach by directing chemical reactions at predefined sites while preserving key structural features of parent materials, thereby enabling precise and selective modulation at the atomic and molecular levels through four core strategies: conversion, termination, substitution, and transformation. Herein, we present a systematic and critical review of the latest advances in the topochemical engineering of MXenes and other representative 2D materials (TE-2DMs). We establish the conceptual framework and classification criteria for these strategies and discuss their implementation and underlying structural regulation mechanisms. Special emphasis is placed on the structure-performance correlations of TE-2DMs in electrochemical energy storage and conversion. We further summarize general design principles and practical guidelines for selecting and implementing appropriate topochemical strategies. Finally, we identify key challenges and emerging opportunities in this rapidly evolving field, with the aim of guiding the rational design of high-performance 2D functional materials for next-generation electrochemical energy technologies.