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 .

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

Two-dimensional (2D) transition metal carbides/nitrides Mn+1Xn labeled as MXenes are attracting increasing interest due to promising applications as Li-ion battery anodes and hybrid electro-chemical capacitors. To realize MXenes devices in future flexible practical applications, it is necessary to have a full understanding of the mechanical properties of MXenes under deformation. In this study, we extensively investigated the stress-strain curves and the deformation mechanisms in response to tensile stress by first principles calculations using 2D Tin+1Cn (n = 1, 2 and/or 3) as examples. Our results show that 2D Ti2C can sustain large strains of 9.5%, 18% and 17% under tensions of biaxial and uniaxial along x and y, respectively, which respectively increase to 20%, 28% and 26.5% for 2D Ti2CO2 due to surface functionalizing oxygen, which is much better than graphene (15% biaxial). The failure of 2D Tin+1Cn MXene is due to the significant collapse of the surface atomic layer; however, surface functionalization could slow down this collapse, resulting in the improvement of mechanical flexibility. We have also discussed the critical strains and Young's modulus of 2D Tin+1Cn and Tin+1CnO2. Our results provide an insight into the microscopic deformation mechanism of MXenes and hence benefit their applications in flexible electronic devices.