▎ 摘　　要

Carbon materials based on different hybridization of carbon atoms have drawn great attention because of their unique configurations and physical and chemical properties. Here, a previously unknown 2D carbon allotrope named L-2Gy, graphene-like carbon matryoshka graphynes (Gy) with two alkynyls (C C) inserted into the three-fold carbon atoms of graphene, has been constructed with considerable thermal, dynamical, and mechanical stability by using ab initio density functional theory. With the increasing number of alkynyls between the three-fold carbon atoms of graphene, the stability of Gy will seriously decrease. L-2Gy has a fascinating chemical bond environment consisting of sp- and sp(2)-hybridized carbon atoms, and delocalized pi electrons derived from the 27 three-center two-electron pi bonds. This particular electronic structure plays a vital role in chemically stabilizing L-2Gy. The electronic band structure reveals the semi-metallic features of L-2Gy mainly contributed by the p(x/z) orbitals of carbon atoms. Furthermore, compared with the acknowledged catalysts for the hydrogen evolution reaction (HER), L-2Gy, as a 2D carbon allotrope, shows excellent catalytic activity for the HER.