Rapid and scalable combustion synthesis of (Mo2/3Y1/3)2AlC i-MAX as the precursor for vacancy-ordered MXene

Abstract

For MXenes to be viable in commercial and industrial applications, their production must rely on processes that are energy-efficient, environmentally sustainable, and scalable. A critical factor influencing this viability is the synthesis route of the parent MAX phase. In this study, we report a novel and rapid approach for synthesizing a chemically ordered MAX phase (i-MAX), specifically the in-plane ordered (Mo_2/3Y_1/3)₂AlC, using self-propagating high-temperature synthesis (SHS) completed in one minute. The target MAX phase yield was estimated using Rietveld refinement to be 73.6% with the main impurity phases identified as Mo₃Al₂C and YF₃. Thermodynamic calculations combined with experimental characterizations indicate that the use of an aluminum–yttrium master alloy played a pivotal role in achieving high synthesis yield by facilitating a sequence of intermediate phase transformations that enhance reaction kinetics and i-MAX formation. This method involves the utilization of Poly(tetrafluoroethylene)—(C₂F₄)_n as a promoter, which enables the formation of volatile fluorides or fluorine-containing intermediates, making the reaction self-sustaining. Etching and delamination of the SHS-produced i-MAX phase yielded a vacancy-ordered MXene with the formula Mo_4/3CT_x, with a yield value twice that obtained using the conventional MAX-phase parent material preparation route. This work demonstrates the method’s effectiveness in achieving rapid, straightforward, and energy-efficient synthesis of a diverse range of MAX and i-MAX phases, thereby paving the way for scalable and efficient MXene production.