Abstract
AbstractIn 2017, a new family of in‐plane, chemically‐ordered quaternary MAX phases, coined i‐MAX, has been reported since 2017. The first i‐MAX phase, (Mo2/3Sc1/3)2AlC, garnered significant research attention due to the presence of chemically ordered Sc within the Mo‐dominated M layer, and the facilitated removal of both Al and Sc upon etching, resulting in 2D i‐MXene, Mo1.33C, with ordered divacancies. The i‐MXene renders an exceptionally low resistivity of 33.2 µΩ m−1 and a high volumetric capacitance of ≈1150 F cm−3. This discovery has been followed by the synthesis of, to date, 32 i‐MAX phases and 5 i‐MXenes, where the latter have shown potential for applications including, but not limited to, energy storage and catalysis. Herein, fundamental investigations of i‐MAX phases and i‐MXenes, along with their applicability in supercapacitive and catalytic applications, are reviewed. Moreover, recent results on ion intercalation and post‐etching treatment of Mo1.33C are presented. The charge storage performance can also be tuned by forming MXene hydrogel and through inert atmosphere annealing, where the latter renders a superior volumetric capacitance of ≈1635 F cm−3. This report demonstrates the potential of the i‐MXene family for catalytic and energy storage applications, and highlights novel research directions for further development and successful employment in practical applications.
Highlights
Introduction been observed inMAX phases; out-of-plane chemical order and in-plane chemical order (i-MAX), both with M ele-The multitude of compositions and structures of 2D layered ment ordering.[13] o-MAX phases have a sandwich-like stacking materials render promise for next-generation energy storage,[1] with the two M-elements separated in distinct layers, for thermoelectric,[2] catalytic,[3] and memory devices.[4]
We have carried out detailed studies to explore their potential for electrochemical energy storage applications, and we summarize the progress on utilization of different i-MXenes in supercapacitor electrodes and present some of our most recent results in this area
The in-plane chemical order and selective removal of both M2- and A-elements from (M12/3M21/3)2AC i-MAX phases result in i-MXenes with ordered divacancies, rendering promise for a range of applications, including energy storage and catalysis
Summary
The first indication of an i-MAX phase was observed during the structural characterization of a sample containing the Mo2ScAlC2 o-MAX phase.[18]. Ahmed El Ghazaly received his MSc (2017) in Nanotechnology from the American University in Cairo, Egypt He worked as a visiting researcher at the Department of Materials Science and Engineering at Georgia Institute of Technology, USA. Johanna Rosen is the head of the Materials Design Group in the Department of Physics, Chemistry, and Biology (IFM) at Linköping University She received her Ph.D. from RWTH-Aachen University in Germany, and after being a post-doc and visiting scientist at LBNL at Berkeley (USA) and Sydney University (Australia), she returned to Sweden to establish her research platform. One should note that the structure of a traditional MAX phase, viewed along [1120], looks identical to the structure of i-MAX along the [100] direction This is in contrast to the HRSTEM image viewed along [110] axis, showing a clear contrast between Sc and Cr/ Mn atoms, and confirming the presence of chemical order in the M-layer. Slight alternations in chemical composition of the parent i-MAX phase may significantly influence the existence and quality of resulting i-MXene
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