Reactivity in Molten Salts of MAX, MXenes and Related Materials: from Mechanisms to New Materials

David Portehault^a, Emile Defoy^a, Sushil S. Pathak^a, Nora Benbakoura^b, Valentin Fogiel^b, Stéphane Célérier^b, Aurélien Habrioux^b, Solenn Reguer^c, Dominique thiaudière^c

^aSorbonne Université, CNRS, Laboratoire de Chimie de la Matière Condensée de Paris (LCMCP), Paris

^bUniversité de Poitiers, CNRS, Institut de Chimie des Milieux et Matériaux de Poitiers (IC2MP), Poitiers, France

^cSynchrotron SOLEIL, Gif-sur-Yvette, France

Proceedings of MATSUS Fall 2025 Conference (MATSUSFall25)

E.24 Frontiers in MXene Research: From Fundamentals to Applications - #MXFrontiers

València, Spain, 2025 October 20th - 24th

Organizers: Sara GOBERNA FERRON and Ana Primo

Invited Speaker, David Portehault, presentation 270
Publication date: 17th July 2025

Inorganic molten salts are non-volatile liquids stable at high temperatures, often up to 1000 °C. Performing chemical reactions in inorganic molten salts is a way to trigger reactivity in liquids at temperatures that usually pertain to solid-state reactions. This enables syntheses of unprecedented materials, including new compounds like oxychalcogenides[1] and oxyhalides,^[2] but also original nano-objects, from III-V quantum dots[3] to bidimensional carbides[4] and strongly covalent materials,[5] like borides[6,7] or silicides.[8–10] Such opportunities have been demonstrated for MXenes in the last years. Indeed, the adequate choice of molten salts enables selective etching and replacement of A elements (A=Al, Si, Ga) in MAX phases, thus delivering carbide and nitride MXenes[4,11–13] with new terminations and properties. The involved reactions remain however poorly understood, which hinders their precise control. Especially reaction kinetics, and the applicability range for surface modification and the recovery of new compounds are still to be discovered.

In this talk, we will discuss the reactivity of layered materials into molten salts, first by studying in situ their synthesis, the etching and replacement mechanisms, second by considering post-modifications of MXenes directly in molten salts. We will introduce the sample environment we have developed to enable synchrotron-based in situ X-ray diffraction and X-ray absorption spectroscopy experiments in molten salts. We will then discuss how galvanic etching, replacement and delamination reactions occur in MAX phases depending on the composition of the MAX phase and of the molten salts.[14] We will then introduce the synthesis and reactivity of layered metal borides (so-called ‘MAB’ phases[15,16]) phases in molten salts. Finally, we will discuss how to trigger modifications of the composition of MXenes through molten salt-mediated reactions for the design of electrocatalysts for water splitting.

References:

[1] Zhou, X.; Kolluru, V. S. C.; Xu, W.; Wang, L.; Chang, T.; Chen, Y.-S.; Yu, L.; Wen, J.; Chan, M. K. Y.; Chung, D. Y.; Kanatzidis, M. G. Discovery of Chalcogenides Structures and Compositions Using Mixed Fluxes. Nature 2022, 612 (7938), 72–77.

[2] Kumar, R.; Song, Y.; Ghoridi, A.; Boullay, P.; Rousse, G.; Gervais, C.; Coelho Diogo, C.; Kabbour, H.; Sassoye, C.; Beaunier, P.; Castaing, V.; Viana, B.; Luisa Ruiz Gonzalez, M.; Calbet, J. G.; Laberty-Robert, C.; Portehault, D. Molten Salts-Driven Discovery of a Polar Mixed-Anion 3D Framework at the Nanoscale: Zn4Si2O7Cl2, Charge Transport and Photoelectrocatalytic Water Splitting. Angew. Chem. Int. Ed. 2023, 62, e202303487.

[3] Ondry, J. C.; Zhou, Z.; Lin, K.; Gupta, A.; Chang, J. H.; Wu, H.; Jeong, A.; Hammel, B. F.; Wang, D.; Fry, H. C.; Yazdi, S.; Dukovic, G.; Schaller, R. D.; Rabani, E.; Talapin, D. V. Reductive Pathways in Molten Inorganic Salts Enable Colloidal Synthesis of III-V Semiconductor Nanocrystals. Science 2024, 386 (6720), 401–407.

[4] Li, M.; Lu, J.; Luo, K.; Li, Y.; Chang, K.; Chen, K.; Zhou, J.; Rosen, J.; Hultman, L.; Eklund, P.; Persson, P. O. Å.; Du, S.; Chai, Z.; Huang, Z.; Huang, Q. Element Replacement Approach by Reaction with Lewis Acidic Molten Salts to Synthesize Nanolaminated MAX Phases and MXenes. J. Am. Chem. Soc. 2019, 141 (11), 4730–4737.

[5] Portehault, D.; Gómez-Recio, I.; Baron, M. A.; Musumeci, V.; Aymonier, C.; Rouchon, V.; Godec, Y. L. Geoinspired Syntheses of Materials and Nanomaterials. Chem. Soc. Rev. 2022, 51 (11), 4828–4866.

[6] Gouget, G.; Bregiroux, D.; Grosjean, R.; Montero, D.; Maier, S.; Gascoin, F.; Sanchez, C.; Portehault, D. Liquid-Phase Synthesis, Sintering, and Transport Properties of Nanoparticle-Based Boron-Rich Composites. Chem. Mater. 2021, 33 (6), 2099–2109.

[7] Igoa Saldaña, F.; Gaudisson, T.; Le Floch, S.; Baptiste, B.; Delbes, L.; Malarewicz, V.; Beyssac, O.; Béneut, K.; Coelho Diogo, C.; Gervais, C.; Rousse, G.; Rasim, K.; Grin, Y.; Maître, A.; Le Godec, Y.; Portehault, D. Transforming Nanocrystals into Superhard Boron Carbide Nanostructures. ACS Nano 2024, 18 (44), 30473–30483.

[8] Song, Y.; Gómez-Recio, I.; Ghoridi, A.; Igoa Saldaña, F.; Janisch, D.; Sassoye, C.; Dupuis, V.; Hrabovsky, D.; Ruiz-González, M. L.; González-Calbet, J. M.; Casale, S.; Zitolo, A.; Lassalle-Kaiser, B.; Laberty-Robert, C.; Portehault, D. Heterostructured Cobalt Silicide Nanocrystals: Synthesis in Molten Salts, Ferromagnetism, and Electrocatalysis. J. Am. Chem. Soc. 2023, 145 (35), 19207–19217.

[9] Janisch, D.; Igoa Saldaña, F.; De Rolland Dalon, E.; V. M. Inocêncio, C.; Song, Y.; Autran, P.-O.; Miche, A.; Casale, S.; Portehault, D. Covalent Transition Metal Borosilicides: Reaction Pathways in Molten Salts for Water Oxidation Electrocatalysis. J. Am. Chem. Soc. 2024, 146 (31), 21824–21836.

[10] Song, Y.; Ghoridi, A.; Igoa Saldaña, F.; Gómez-Recio, I.; Janisch, D.; de Rolland Dalon, E.; Thiaudière, D.; Ruiz-González, M. L.; González-Calbet, J. M.; Lassalle-Kaiser, B.; Zitolo, A.; Laberty-Robert, C.; Portehault, D. In and Out: Shuttling Atoms in Covalent Nanocrystals, from Synthesis in Molten Salts to Water-Splitting Electrocatalysis. J. Am. Chem. Soc. 2025.

[11] Urbankowski, P.; Anasori, B.; Makaryan, T.; Er, D.; Kota, S.; Walsh, P. L.; Zhao, M.; Shenoy, V. B.; Barsoum, M. W.; Gogotsi, Y. Synthesis of Two-Dimensional Titanium Nitride Ti4N3 (MXene). Nanoscale 2016, 8 (22), 11385–11391.

[12] Kamysbayev, V.; Filatov, A. S.; Hu, H.; Rui, X.; Lagunas, F.; Wang, D.; Klie, R. F.; Talapin, D. V. Covalent Surface Modifications and Superconductivity of Two-Dimensional Metal Carbide MXenes. Science 2020, 369 (6506), 979–983.

[13] Zhang, T.; Shevchuk, K.; Wang, R. J.; Kim, H.; Hourani, J.; Gogotsi, Y. Delamination of Chlorine-Terminated MXene Produced Using Molten Salt Etching. Chem. Mater. 2024, 36 (4), 1998–2006.

[14] Defoy, E.; Baron, M.; Séné, A.; Ghoridi, A.; Thiaudière, D.; Célérier, S.; Chartier, P.; Brette, F.; Mauchamp, V.; Portehault, D. Galvanic Replacement and Etching of MAX-Related Phases in Molten Salts toward MXenes: An In Situ Study. Chem. Mater. 2023, 35 (19), 8112–8121.

[15] Zhou, J.; Palisaitis, J.; Halim, J.; Dahlqvist, M.; Tao, Q.; Persson, I.; Hultman, L.; Persson, P. O. Å.; Rosen, J. Boridene: Two-Dimensional Mo4/3B2-x with Ordered Metal Vacancies Obtained by Chemical Exfoliation. Science 2021, 373 (6556), 801–805.

[16] Igoa Saldaña, F.; Defoy, E.; Janisch, D.; Rousse, G.; Autran, P.-O.; Ghoridi, A.; Séné, A.; Baron, M.; Suescun, L.; Le Godec, Y.; Portehault, D. Revealing the Elusive Structure and Reactivity of Iron Boride α-FeB. Inorg. Chem. 2023, 62 (5), 2073–2082.

Acknowledgements:

This work has received funding from the European Research Council (ERC) Consolidator Grant GENESIS under the European Union's Horizon 2020 research and innovation programme (grant agreement n° 864850), and from the National Agency for Research (ANR), under the project PIXIES (grant agreement ANR-22-CE08-0014).

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