Overall direct photocatalytic water-splitting on C2mm-graphyne: a novel two-dimensional carbon allotrope

A novel two-dimensional (2D) carbon allotrope, named C2mm-graphyne, is predicted with the aid of the first-principles calculations. Its lattice dynamic and thermodynamic stabilities have been confirmed by evaluating its phonon dispersion relation and the trajectory from the ab initio molecular dynamics (AIMD) simulation at 1000 K. The unique network consists of sp-sp² hybridized carbons. This 2D carbon allotrope possesses a direct quasi-particle (QP) band gap of 3.06 eV at the Γ point, which is close to the value of rutile. Significantly, some of its extended structures containing B and N dopants possess direct or quasi-direct QP band gaps in the range of 1.37-2.42 eV, which are falling into the visible light region. More exciting, their band arrangements just meet the requirements of photocatalytic water splitting. Furthermore, the HER and the OER are clearly discussed.