Nitrogen doping has been proven to be a facile modification strategy to improve the electrochemical performance of 2D MXenes, a group of promising candidates for energy storage applications. However, the underlying mechanisms, especially the positions of nitrogen dopants, and its effect on the electrical properties of MXenes, are still largely unexplored. Herein, a comprehensive study is carried out to disclose the nitrogen doping mechanism in Ti 3 C 2 MXene, by employing theoretical simulation and experimental characterization. Three possible sites are found in Ti 3 C 2 T x (T = F, OH, and O) to accommodate the nitrogen dopants: lattice substitution (for carbon), function substitution (for-OH), and surface absorption (on-O). Moreover, electrochemical test results confirm that all the three kinds of nitrogen dopants are favorable for improving the specific capacitance of the Ti 3 C 2 electrode, and the underlying factors are successfully distinguished. By revealing the nitrogen doping mechanisms in Ti 3 C 2 MXene, this work provides theoretical guidelines for modulating the electrochemical properties of MXene materials for energy storage applications.

for electron and charge transfer. Therefore, the OV-T n QDs@ PCN/S cathode delivers a superb long-term cycling stability (88% capacity retention over 1000 cycles at 2C) under a S-mass loading of 2.2 mg cm −1 and an E/S ratio of 10 µL mg −1 . In addition, the cathode exhibits good Li + storage at high S-mass loading (4.8 mg cm −1 ) and lean electrolyte (E/S ratio: 4.5 µL mg −1 ), demonstrating its great potential for practical implementation. Our strategy may be extended to other MXenes (e.g., Ti 3 CNT x , Nb 2 CT x , and V 2 CT x ) and pave the way to realize the facile synthesis of QDs with rich OVs for advanced Li-S batteries.

We have developed a facile route to the synthesis of CNTs@MXene hybrids with impressive electrochemical performance.

MAX phases (Ti3SiC2, Ti3AlC2, V2AlC, Ti4AlN3, etc.) are layered ternary carbides/nitrides, which are generally processed and researched as structure ceramics. Selectively removing A layer from MAX phases, MXenes (Ti3C2, V2C, Mo2C, etc.) with two-dimensional (2D) structure can be prepared. The MXenes are electrically conductive and hydrophilic, which are promising as functional materials in many areas. This article reviews the milestones and the latest progress in the research of MAX phases and MXenes, from the perspective of ceramic science. Especially, this article focuses on the conversion from MAX phases to MXenes. First, we summarize the microstructure, preparation, properties, and applications of MAX phases. Among the various properties, the crack healing properties of MAX phase are highlighted. Thereafter, the critical issues on MXene research, including the preparation process, microstructure, MXene composites, and application of MXenes, are reviewed. Among the various applications, this review focuses on two selected applications: energy storage and electromagnetic interference shielding. Moreover, new research directions and future trends on MAX phases and MXenes are also discussed.

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