High‐Entropy Carbonitride MAX Phases and Their Derivative MXenes

Abstract

Although high‐entropy layered transition metal carbonitride MAX phases and their derivative MXenes have been proposed to exhibit unique physicochemical features for widespread applications, it is still challenging to synthesize them owing to the easy formation of separated phases during the traditional synthetic process. Here, a new high‐entropy carbonitride MAX phase (HE CN‐MAX, (Ti1/3V1/6Zr1/6Nb1/6Ta1/6)2AlCxN1–x) is synthesized on the basis of metallurgically treating medium‐entropy MAX (ME‐MAX) (Zr1/3Nb1/3Ta1/3)2AlC and other MAX phases (Ti4AlN3 and V2AlC). During the metallurgical process, the unique usage of a medium‐entropy MAX phase effectively solves the phase separation issue for the formation of a high‐entropy MAX phase owing to their low entropy difference. After selective extraction of an A species, a high‐entropy carbonitride MXene (HE CN‐MXene) with high mechanical strains and five types of metal‐nitrogen bonds is achieved, which shows good adsorption and catalytic activities for lithium polysulfides. As a result, a lithium–sulfur battery with HE CN‐MXene delivers a high‐rate capability (702 mAh g−1 at 4 C) and good cycling stability.

Two-Dimensional High-Entropy Metal Phosphorus Trichalcogenides for Enhanced Hydrogen Evolution Reaction

“…As a class of materials system, high-entropy alloys (HEAs) have attracted wide interest in the past few years due to their mechanical properties and potential applications. − In contrast to the traditional multicomponent alloys with one or two principal elements, HEAs are a kind of alloying strategy that involves the combination of five or more elements in a relatively high concentration (5–35 at. %). , Because of the abundant elemental composition, HEAs can provide an extensive combinatorial space for designing high-performance catalysts. − Moreover, the continuously tunable adsorption energies of HEAs also optimize the kinetic barrier for the adsorption/desorption of reaction intermediates and thus increase the catalytic performance. , However, the HEAs prepared by traditional methods are bulk materials rather than nanostructures. , The limited exposure of active sites makes it difficult to further improve the catalytic performance . Although the preparation of uniform nanostructured HEAs with specific equipment and high temperature with fast heating/cooling rate has been proposed, − achieving a large electrochemical active area and full utilization of active sites in HEAs is still challenging. , …”

2D non-carbide MXenes: an emerging material class for energy storage and conversion

“…For the rst time, a new high entropy carbonitride MXene (HE CN-MXene) was reported by Du et al, which was synthesized from HE MAX phase (Ti 1/3 V 1/6 Zr 1/6 Nb 1/6 Ta 1/6 ) 2 AlC x N 1Àx by in situ HF etching using LiF-HCl. 54 The HE MAX phase was formed through the metallurgical treatment of MAX phases such as Ti 4 AlN 3 and V 2 AlC with a medium entropy MAX phase (Zr 1/3 Nb 1/ through the LiF-HCl route had a compact structure with intercalations of Li + and H 2 O compared to the carbonitride MXene obtained via the HF route. The study also provided the insight that at a higher molar ratio of LiF to the MAX precursor, the Ti 3 CN MXene structures can be delaminated without the need for sonication.…”

“…In addition, the strong bonds between M and N enable enhanced structural stability, making them more attractive than their carbide counterparts. 48,54 Noncarbide MXenes have shown great promise in energy storage and conversion, electrocatalysis, EMI shielding, environmental remediation, electronics, and biomedical applications. The subsections below summarize their advanced applications in these elds.…”

“…For the first time, a new high entropy carbonitride MXene (HE CN-MXene) was reported by Du et al , which was synthesized from HE MAX phase (Ti 1/3 V 1/6 Zr 1/6 Nb 1/6 Ta 1/6 ) 2 AlC x N 1− x by in situ HF etching using LiF–HCl. 54 The HE MAX phase was formed through the metallurgical treatment of MAX phases such as Ti 4 AlN 3 and V 2 AlC with a medium entropy MAX phase (Zr 1/3 Nb 1/3 Ta 1/3 ) 2 AlC. It was proposed that this medium entropy MAX phase solves the issue of phase separation in HE MAX phases during synthesis, owing to their low entropy difference.…”

“…56 The mechanical strain and the presence of five types of metal–N bonds in HE CN-MXene enable them to exhibit a high rate capability of 702 mA h g −1 at 4C and long cycling stability when used as an electrode in lithium–sulfur batteries. 54 Lin et al investigated the feasibility of titanium nitride MXenes as host materials for lithium–sulfur batteries by using first-principles calculations through the framework of density functional theory (DFT). 29 The results showed that these nitride MXenes exhibit reasonable adsorption energies towards Li 2 S x species with minimal structural deformation.…”