Molten Salt Derived Mo2CT MXene with Excellent Catalytic Performance for Hydrogen Evolution Reaction

MXenes are two-dimensional metal carbides , nitrides , and carbonitrides that are typically achieved by selectively etching the Asite elements from their corresponding MAX phase precursors. Thanks to the merits including high mechanical stability, excellent conductivity, and a high specific surface area , MXenes have attracted widespread attention in the field of energy storage and conversion. By far, most studies are focus on the synthesis and applications of Ti- or V-based MXenes. Mo-based MXenes, while less investigated due to the difficulty of synthesis, have shown significant potential in various fields, including electrochemical biomolecular sensing, electrocatalysis , and energy storage. The conventional method of preparing Mo-based MXenes involves etching precursors with hazardous HFcontaining solutions, which is not only time-consuming but also poses safety risks. In this study, we present a Lewis molten salt synthesis approach to prepare Mo 2 CT x MXene by etching Mo 2 Ga 2 C precursor that eliminates the need for hazardous HF and significantly reduces the synthesis time. The impact of etching temperature and time on the phase and microstructure of Mo 2 CT x MXene were carefully investigated, and our findings indicate that the Mo 2 Ga 2 C precursor can be almost fully etched at 600 °C for just 30 min using the molten salt method, which is a challenging feat to achieve using HF etching. Furthermore, it is found that Mo 2 CT x MXene can be obtained in a wide temperature range from 600 to 800 °C with excellent structural stability. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) confirmed the selective etching of Ga atoms from Mo 2 Ga 2 C and the successful preparation of Mo 2 CT x MXene, and X-ray photoelectron spectroscopy (XPS) suggests the preservation of Mo-C bonds in the Mo 2 CT x layered structure. The hydrogen evolution reaction (HER) performance of Mo 2 CT x MXene prepared by the molten salt method was investigated in alkaline electrolytes . The molten salt derived Mo 2 CT x MXene displayed exceptional catalytic performance for the HER, maintaining long-term stability in alkaline conditions, and exhibiting a low overpotential of only 114 mV and a Tafel slope of 124 mV∙dec −1 at 10 mA∙cm −2 . The much larger double layer capacitance of molten salt derived Mo 2 CT x MXene as compare to the Mo 2 Ga 2 C precursor suggests that accordion-like structure can greatly increase the electrochemical active sites and thus plays a key role in boosting the catalytic performance. This study demonstrates the first synthesis of Mo 2 CT x MXene by a molten salt method, and shows the high catalytic activity of Mo 2 CT x MXene for hydrogen production in alkaline solutions.