Tailoring Structure, Composition, and Energy Storage Properties of MXenes from Selective Etching of In‐Plane, Chemically Ordered MAX Phases

• Published in: Small (Weinheim an der Bergstrasse, Germany) Vol. 14; no. 17; pp. e1703676 - n/a
• Main Authors: Persson, Ingemar, el Ghazaly, Ahmed, Tao, Quanzheng, Halim, Joseph, Kota, Sankalp, Darakchieva, Vanya, Palisaitis, Justinas, Barsoum, Michel W., Rosen, Johanna, Persson, Per O. Å.
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 01.04.2018
• Subjects: 2D materials; Atomic structure; Capacitance; Energy storage; Etching; in‐plane order; MXene; MXenes; Nanotechnology; Phases; Stoichiometry; Sulfuric acid; Supercapacitors; vacancies; vacancies; capacitance; in-plane order; 2D materials; MXene
• ISSN: 1613-6810; 1613-6829; 1613-6829
• DOI: 10.1002/smll.201703676

The exploration of 2D solids is one of our time's generators of materials discoveries. A recent addition to the 2D world is MXenes that possses a rich chemistry due to the large parent family of MAX phases. Recently, a new type of atomic laminated phases (coined i‐MAX) is reported, in which two different transition metal atoms are ordered in the basal planes. Herein, these i‐MAX phases are used in a new route for tailoriong the MXene structure and composition. By employing different etching protocols to the parent i‐MAX phase (Mo2/3Y1/3)2AlC, the resulting MXene can be either: i) (Mo2/3Y1/3)2C with in‐plane elemental order through selective removal of Al atoms or ii) Mo1.33C with ordered vacancies through selective removal of both Al and Y atoms. When (Mo2/3Y1/3)2C (ideal stoichiometry) is used as an electrode in a supercapacitor—with KOH electrolyte—a volumetric capacitance exceeding 1500 F cm−3 is obtained, which is 40% higher than that of its Mo1.33C counterpart. With H2SO4, the trend is reversed, with the latter exhibiting the higher capacitance (≈1200 F cm−3). This additional ability for structural tailoring will indubitably prove to be a powerful tool in property‐tailoring of 2D materials, as exemplified here for supercapacitors. Using atomically resolved electron microscopy, it is shown that the chemically ordered atomic laminate (Mo2/3Y1/3)2AlC can be used to derive either i) an in‐plane vacancy ordered Mo1.33C MXene or ii) (Mo2/3Y1/3)2C MXene with in‐plane elemental order. These materials have different electrochemical properties, with in one case a capacitance value exceeding 1500 F cm−3.