Identifying suitable photocatalysts for photocatalytic water splitting to produce hydrogen fuel via sunlight is an arduous task by the traditional try-and-error method.Thanks to the progress of density functional theory one can nowadays accelerate the process of finding candidate photocatalysts. In this work, by ab initio calculations we investigated on 48 two-dimensional (2D) transition metal carbides also referred to as MXenes to understand their photocatalytic property. Our results highlight 2D Zr 2 CO 2 and Hf 2 CO 2 as the candidate single photocatalysts for possible high efficient photocatalytic water splitting. The significantly property of 2D Zr 2 CO 2 and Hf 2 CO 2 is that they exhibit unexpectedly high and directionally anisotropic carrier mobility, which may effectively facilitate the migration and separation of photogenerated electron-hole pairs. Meanwhile, these two MXenes also exhibit very good optical absorption performance in the wavelength ranging approximately from 300 to 500 nm.The stability of 2D Zr 2 CO 2 and Hf 2 CO 2 in liquid water is expected to be good based on ab initio molecular dynamics simulations. Finally, the absorption and decomposition of water molecule on the 2D Zr 2 CO 2 surface and the subsequently followed formation process of hydrogen were studied, which contributes to the unraveling of the micro-mechanism of photocatalytic hydrogen production on MXene.Our findings will open a new way to facilitate the discovery and application of MXenes for photocatalytic water splitting. Fig. 3. The electronic band edge positions with respect to the water reduction and oxidation potential levels.Fig. 4. Imaginary part of the dielectric function of 2D Zr 2 CO 2 and Hf 2 CO 2 .

This review highlights recent advances of MXenes and their composites in the environment-related applications including catalysis, water purification and sensors.

Graphene-like two-dimensional materials have garnered tremendous interest as emerging device materials for nanoelectronics due to their remarkable properties. However, their applications in spintronics have been limited by the lack of intrinsic magnetism. Here, using hybrid density functional theory, we predict ferromagnetic behavior in a graphene-like two-dimensional Cr2C crystal that belongs to the MXenes family. The ferromagnetism, arising from the itinerant Cr d electrons, introduces intrinsic half-metallicity in Cr2C MXene, with the half-metallic gap as large as 2.85 eV. We also demonstrate a ferromagnetic-antiferromagnetic transition accompanied by a metal to insulator transition in Cr2C, caused by surface functionalization with F, OH, H, or Cl groups. Moreover, the energy gap of the antiferromagnetic insulating state is controllable by changing the type of functional groups. We further point out that the localization of Cr d electrons induced by the surface functionalization is responsible for the ferromagnetic-antiferromagnetic and metal to insulator transitions. Our results highlight a new promising material with tunable magnetic and electronic properties toward nanoscale spintronics and electronics applications.

A new family of transition metal borides MBenes are reported with remarkable applications in Li ion batteries and electrocatalysis.

Phase change materials based on chalcogenide alloys play an important role in optical and electrical memory devices. Both applications rely on the reversible phase transition of these alloys between amorphous and metastable cubic states. However, their atomic arrangements are not yet clear, which results in the unknown phase change mechanism of the utilization. Here using ab initio calculations we have determined the atomic arrangements. The results show that the metastable structure consists of special repeated units possessing rocksalt symmetry, whereas the so-called vacancy positions are highly ordered and layered and just result from the cubic symmetry. Finally, the fast and reversible phase change comes from the intrinsic similarity in the structures of the amorphous and metastable states.