Thermodynamic principles governing MXene formation by molten salt etching

Controlled reactions between MAX phases and molten salts allow selective A-element substitution or full A-element removal, providing a versatile route to both new MAX phases and two-dimensional (2D) MXenes. Despite its success, the broader applicability of this strategy remains limited, and the predictive power of theoretical approaches has not been systematically established. We recently introduced a thermodynamic methodology based on process-specific phase diagrams to describe reactions of MAX phases in molten salts, demonstrated for a narrowly defined set of representative systems. Here, we generalize this framework by adopting a more inclusive description of competing reaction outcomes and assess its applicability across a broad chemical space comprising 14 MAX phases and 7 molten salts. The predictions are benchmarked against reported experimental data and complemented by new experiments on previously unexplored MAX–salt combinations, encompassing both MXene synthesis and reaction outcomes beyond A-element substitution and MXene formation. While idealized stoichiometric models capture many trends, we identify experimentally relevant cases where non-ideal features – particularly non-stoichiometric A-element substitution and reduced termination occupancy – are required for quantitative agreement. More broadly, analysis of thermodynamic trends across all MAX–salt combinations yields clear criteria under which MXene formation is highly likely. The resulting framework provides a validated basis for computational screening and is expected to guide molten-salt-driven exfoliation strategies toward new two-dimensional materials beyond the MXene family.