Abstract

Inspired by the superior properties of Janus MA2Z4, the electronic properties, quantum capacitance, and photocatalytic activity of Janus MSiGeN4 (M=Cr, Hf, Mo, Nb, Ta, Ti, V, W, and Zr) monolayers are explored. The results indicate that TiSiGeN4, ZrSiGeN4, and HfSiGeN4 are semiconductors with the bandgap larger than 2 eV. NbSiGeN4 is a spin-polarization semiconductor with magnetic moment of 0.61 μB. VSiGeN4 exhibits the character of half-metal and its spin-up channel hosts a Dirac cone around Fermi level, which is derived from V-d states. The analysis of Bader charge shows that built-in electric field in these systems appears and promotes the charge redistribution across the Janus atomic layer. All systems except NbSiGeN4 and TaSiGeN4 are cathode materials because of |Qp|/|Qn| larger than 1 in aqueous system. Broad voltage keeps the electrode type of all systems unchangeable. MSiGeN4 (M=Hf, Nb, Zr, V, Ti) can perform photocatalytic water splitting, while all MSiGeN4 can reduce N2 to NH3, but are not good CO2 photocatalysts. The Bader charge, work function, and optical properties are further explored.

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