Suchergebnisse

Zr2Al3C4 coatings are potential candidates to prevent claddings of traditional Zr-based alloys from severe oxidation in water steam at high temperature. However, the diffusion of aluminum between coating and substrates at high temperature results in a coating composition deviating from the compositional domain for formation of the Zr2Al3C4 phase. Thus, synthesis of Zr2Al3C4 coatings on zirconium-alloy substrates is challenging. Here, we report that the Zr2Al3C4 phase can be obtained on zirconium alloy (ZIRLO) substrates where an Al-C/Si interlayer deposited by magnetron sputtering is introduced. The Al-C/Si interlayer prevented elemental diffusion of aluminum between the Zr-Al-C coating and the substrates during a post-annealing process at 800 degrees C for 3 h. The Al/Zr ratio of the Zr-Al-C coating after annealing was 0.96 and 0.59 in the cases of with and without Al-C/Si interlayer, respectively. Hence, the Al-C/Si interlayer acts as diffusion barrier and greatly decreases the deviation from the standard stoichiometric ratio of the Zr2Al3C4 phase, which facilitates the formation of the Zr2Al3C4 phase in the final coating. ; Funding Agencies|National Natural Science Foundation of China [91226202, 91426304, 51873146]; Major Project of the Ministry of Science and Technology of China [2015 ZX06004-001]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009 00971]

The class of two-dimensional metal carbides and nitrides known as MXenes offer a distinct manner of property tailoring for a wide range of applications. The ability to tune the surface chemistry for expanding the property space of MXenes is thus an important topic, although experimental exploration of surface terminals remains a challenge. Here, we synthesized Ti3C2 MXene with unitary, binary, and ternary halogen terminals, e.g., -Cl, -Br, -I, -BrI, and -ClBrI, to investigate the effect of surface chemistry on the properties of MXenes. The electrochemical activity of Br and I elements results in the extraordinary electrochemical performance of the MXenes as cathodes for aqueous zinc ion batteries. The -Br- and -I-containing MXenes, e.g., Ti3C2Br2 and Ti3C2I2, exhibit distinct discharge platforms with considerable capacities of 97.6 and 135 mA.g(-1). Ti3C2 (BrI) and Ti3C2 (ClBrI) exhibit dual discharge platforms with capacities of 117.2 and 106.7 mAh.g(-1). In contrast, the previously discovered MXenes Ti3C2Cl2 and Ti3C2 (OF) exhibit no discharge platforms and only similar to 50% of capacities and energy densities of Ti3C2Br2. These results emphasize the effectiveness of the Lewis-acidic-melt etching route for tuning the surface chemistry of MXenes and also show promise for expanding the MXene family toward various applications. ; Funding Agencies|National Natural Science Foundation of ChinaNational Natural Science Foundation of China (NSFC) [51902320, 21805295, U2004212]; International Partnership Program of Chinese Academy of Sciences [174433KYSB20190019]; Leading Innovative and Entrepreneur Team Introduction Program of Zhejiang [2019R01003]; Ningbo Top-Talent Team Program; GRF [N_CityU11305218]; Science Technology and Innovation Committee of Shenzhen Municipality [JCYJ20170818103435068]; Knut and Alice Wallenberg FoundationKnut & Alice Wallenberg Foundation [KAW 2015.0043]; Swedish Foundation for Strategic Research (SSF)Swedish Foundation for Strategic Research [EM16-0004, RIF 14-0074]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009 00971]

New MAX phases Ti2(AlxCu1−x)N and Nb2CuC were synthesized by A-site replacement by reacting Ti2AlN and Nb2AlC, respectively, with CuCl2 or CuI molten salt. X-ray diffraction, scanning electron microscopy, and atomically resolved scanning transmission electron microscopy showed complete A-site replacement in Nb2AlC, which lead to the formation of Nb2CuC. However, the replacement of Al in Ti2AlN phase was only close to complete at Ti2(Al0.1Cu0.9)N. Density-functional theory calculations corroborated the structural stability of Nb2CuC and Ti2CuN phases. Moreover, the calculated cleavage energy in these Cu-containing MAX phases are weaker than in their Al-containing counterparts. The preparation of MAX phases Nb2CuC and Ti2(Al0.1Cu0.9)N were realized by A-site replacement in Ti2AlN and Nb2AlN, respectively. ; Funding agencies: National Natural Science Foundation of ChinaNational Natural Science Foundation of China (NSFC) [21671195, 51902319, 91426304]; Chinese Academy of SciencesChinese Academy of Sciences [2019VEB0008, 174433KYSB20190019]; Swedish Government Strategic Research