The Versatile Electronic, Magnetic and Photo-electro Catalytic Activity of a New 2D MA2Z4 Family.

The recent successful growth of MoSi2N4 and WSi2N4 monolayer led to the discovery of a new class of two-dimensional (2D) MA2Z4 materials with no known 3D layered allotropes, which renders great possibilities to integrate diverse properties by proper design of sandwiched "MZ2" building blocks and "A-Z" passivation layers. In this work, we theoretically probe the dynamic stability, electronic properties, and surface reactivity of the new MA2Z4 family, in which M is Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, A refers to Si or Ge, and Z is N, P or As. Among the proposed 54 possible combinations, about 42 compositions are dynamically stable, which vary from non-magnetic, anti-ferromagnetic, to ferromagnetic semiconductors, metals and half-metal. In particular, the VB (V, Nb, Ta) MA2Z4 possesses robust intrinsic ferromagnetism that is essential for spintronics applications. In regards to surface activity, most of MA2Z4, particularly for N or P terminated IVB and VB MA2Z4, have high catalytic potential for hydrogen evolution, and the ∆GH of non-magnetic MA2Z4 is highly correlated to the highest occupied p electronic states of surface Z atom. Moreover, the photocatalytic activity is also evaluated, MoSi2N4 and WSi2N4 within 4% tensile strain are capable of photocatalytic overall water splitting. Our findings indicate the new 2D MA2Z4 family has fascinating properties and possesses strong potential for applications but not limited to electronics, spintronics and catalysts, which will stimulate the interests of experimental synthesis.