Research progress on penta-graphene and its related materials: Properties and applications

The most direct and efficient strategy in designing and synthesizing new materials is to change the structural building units, which could lead to a new paradigm shift. Penta-graphene (PG) is such an example where the structural unit is pentagon rather than hexagon as in graphene. Since we proposed the unique structure of penta-graphene, a two-dimensional (2D) carbon allotrope entirely composed of carbon pentacyclic rings [Proc. Natl. Acad. Sci. U. S. A. 112, 2372 (2015)], tremendous efforts have been made to explore the novel properties of PG and its derivatives such as penta-nanotubes, penta-nanoribbons, multilayer PG, functionalized PG, and polycrystalline PG. These materials exhibit novel physical and chemical properties, including nano-auxeticity, intrinsic piezoelectricity, ferroelectricity, spontaneous polarization, and catalysis, showing great potential for the applications in battery anode, spin-splitting/filtering, gas separation, bio-detection, and heterojunctions. More importantly, PG has inspired a lot of efforts in the design and synthesis of other pentagon-based 2D materials with exceptional properties and promising applications (http://www.pubsd.com/). In this paper, we provide a comprehensive review on the progress made in this new field by focusing on the structure-property relationship. We discuss the main achievements that have provided an in-depth understanding of the novel properties and applications of pentagon-based materials, ranging from PG to PG derived materials, and PG’s cousins (penta-silicene and penta-germanene). This review can not only help to better understand the property evolution of the elemental penta-sheets in the same group, but also provides a bird's eye view on how the structural unit changes the functionalities of materials.