MXenes are a large family of two-dimensional (2D) transition-metal carbides, nitrides, and carbonitrides. The MXene family has expanded since their original discovery in 2011, and has grown larger with the discovery of ordered double transition-metal (DTM) MXenes. These DTM MXenes differ from their counterpart mono-transition-metal (mono-M) MXenes, where two transition metals can occupy the metal sites. Ordered DTM MXenes are comprised of transition metals in either an in-plane or out-of-plane ordered structure. Additionally, some DTM MXenes are in the form of random solid solutions, which are defined by two randomly distributed transition metals throughout the 2D structure. Their different structures and array of transition-metal pairs provide the ability to tune DTM MXenes for specific optical, magnetic, electrochemical, thermoelectric, catalytic, or mechanical behavior. This degree of control over their composition and structure is unique in the field of 2D materials and offers a new avenue for application-driven design of functional nanomaterials. In this article, we review the synthesis, structure, and properties of DTM MXenes and provide an outlook for future research in this field.

MXene是一大类二维（2D）过渡金属碳化物，氮化物和碳氮化物。自从2011年首次发现MXene系列以来，它的规模不断扩大，并且随着订购的双过渡金属（DTM）MXenes的发现，其规模也不断扩大。这些DTM MXene与对应的单过渡金属（mono-M）MXene不同，后者的两种过渡金属可以占据金属位置。有序DTM MXene由面内或面外有序结构的过渡金属组成。此外，某些DTM MXene呈无规固溶体形式，由整个2D结构中的两种随机分布的过渡金属定义。它们的不同结构和过渡金属对阵列可为特定的光学，磁性，电化学，热电，催化或机械行为。这种对它们的成分和结构的控制程度在2D材料领域是独一无二的，并为功能纳米材料的应用驱动设计提供了新途径。在本文中，我们回顾了DTM MXene的合成，结构和性质，并为该领域的未来研究提供了前景。