3d-transition metal (Fe, Co, Ni, and Mn)-based MXene materials have been predicted to demonstrate exceptional electrochemical performance because of their good electrical conductivity and the presence of metallic atoms with multiple charge states. However, until now, there have been no reports on MXenes based on Fe, Co, Ni, and Mn, due to the lack of 3d-metal-layered precursors. Herein, we successfully synthesized the first 3d-transition metal-based MXenes, Mn₂CT_x by exfoliating a layered precursor derived from the anti-perovskite bulk Mn₃GaC. The as-prepared Mn₂CT_x MXene nanosheets were employed as anode materials in lithium-ion batteries, which exhibited stable storage capacity of 764.7 mAh·g⁻¹ at 0.5 C, placing its storage capacities at an upper-middle level compared with other reported MXene materials as well as other Mn-based anode materials. Overall, this study opens a new avenue for MXene research by synthesizing 3d-transition metal-based MXenes for electrochemical applications.

The emerging Au-assisted exfoliation technique enables the production of a wealth of large-area and high-quality ultrathin two dimensional (2D) crystals. Fast, damage-free, and reliable determination of the layer number of such 2D films can greatly promote layer-dependent physical studies and device applications. Here, an optical method has been developed for simple, high throughput, and accurate determination of the layer number for Au-assisted exfoliated MoS₂ and WS₂ films in a broad thickness range. The method is based on quantitative analysis of layer-dependent white light reflection spectra (WLRS), revealing that the intensity of exciton-induced reflection peaks can be used as a clear indicator for identifying the layer number. The simple yet robust method will facilitate fundamental studies on layer-dependent optical, electrical, and thermal properties and device applications of 2D materials. The technique can also be readily combined with photoluminescence (PL) and Raman spectroscopies to study other layer-dependent physical properties of 2D materials.