Comment on "synthesis and in situ sulfidation of molybdenum carbide MXene using fluorine-free etchant for...

A recent paper published in this journal, titled Synthesis and in situ sulfidation of molybdenum carbide MXene using fluorine-free etchant for electrocatalytic hydrogen evolution reactions, reports the successful preparation of MoS₂/Mo₂CT_x. The process utilizes Mo₃AlC₂ as the precursor, synthesizes Mo₂C MXene via a fluorine-free etching method employing NaOH and Na₂S, combined with microwave hydrothermal technology, and then performs in situ sulfidation using thioacetamide (TAA). Traditionally, Mo₂C MXene can only be synthesized using Mo₂Ga₂C as the precursor. The commented paper reports, for the first time, the preparation of Mo₂C MXene with Mo₃AlC₂ as the precursor. If this finding holds, it will significantly reduce the production cost. Thus, this paper further clarifies the core scientific issues of molybdenum carbide MXenes. Theoretically, the etching of Mo₃AlC₂ to remove the Al layer should yield Mo₃C₂ MXene instead of Mo₂C MXene. If the product is confirmed to be Mo₃C₂ MXene or Mo₂C MXene, the two corresponding possible reaction equations are proposed, respectively. As a stable new phase, Mo₃C₂ MXene differs essentially from Mo₂C MXene in crystal structure and theoretically exhibits higher structural stability. By clarifying the corresponding relationship between phase structures, and supplementing the transformation mechanism and characterization methods, this paper ensures the rigor of molybdenum carbide MXene materials and the scientific validity of their performance optimization.