Article about 2D Heterostructures/superlattices Published on Energy & Environmental Science

Recently, Junwu Zhu and Pan Xiong from School of Chemical Engineering, Nanjing University of Science and Technology published a review article titled "Two-dimensional organic-inorganic superlattice-like heterostructures for energy storage applications" in the international top journal Energy & Environmental Science (IF: 30.2). Prof. Junwu Zhu (Nanjing University of Science and Technology) and Prof. Takayoshi Sasaki (National Institute for Materials Science, Japan) are the corresponding authors and Prof. Pan Xiong is the first author.

Recently, in parallel with the great efforts on isolation of two-dimensional nanosheets, much attention has been paid to integrate them into a new type of artificial architecture, known as 2D heterostructures or superlattices. 2D heterostructures/superlattices, assembled by vertical stacking of 2D materials on top of each other, are a new class of artificial 2D materials of significant scientific and technological importance. These 2D heterostructures/superlattices greatly enrich the composition of 2D materials and provide new ideas for the artificial design of new two-dimensional multifunctional materials. Compared to inorganic 2D materials, the molecular design of organic molecules/polymers is much more feasible, resulting in an almost unlimited number of potentially available organic materials with designed functional groups. Therefore, introduction of the chemical tunability of 2D organic molecules/polymers within 2D heterostructures/superlattices provides unlimited possibilities for the design of 2D organic–inorganic superlattices with predictable functionalities.

In the structure of 2D organic-inorganic superlattices, organic and inorganic phases are hybridized at sub-nanometre to nanometer scales, providing a method to design new nanoarchitectures as well as the ability to improve the properties of both components. Hence, 2D organic-inorganic superlattices are highly promising for improved performance in energy storage systems, especially the combination of electroactive inorganic nanosheets with conductive organic polymers.The intercalation of organic polymers remarkably increases the interlayer spacing of the layered inorganic host, resulting in enhanced charge transport. Besides, the conductive polymers provide additional charge storage sites for improved capacities. More importantly, the intimate interaction between inorganic materials and organic polymers strengthens the layered structure, and thus a stable cycling performance is supposed to be achieved. However, the primary challenge of two-dimensional organic-inorganic hybrid superlattice structures is to achieve a simple and effective preparation method.

Difffferent methods for fabrication of 2D organic-inorganic superlattices (a) Direct intercalation of polymer layers. (b) Intercalation of monomers and interlayer polymerization. (c) Layer-by-layer assembly. (d) Delamination and reassembly.

In the minireview,the authors firstly summarized the four kinds of main synthetic strategies for the fabrication of 2D organic-inorganic superlattices.Then, they discussed the improved electrochemical performance and storage mechanism of these 2D superlattices in some energy storage systems such as supercapacitors, Li/Na/K ion batteries, and multivalent-ion batteries. Finally, they provided an outlook on challenges and perspectives associated with 2D organic–inorganic superlattices for further research. This minireview summarizes their recent progress in 2D superlattice materials and current research progress in 2D organic-inorganic hybrid superlattice structures, and may open up a new idea for the artificial design of 2D heterostructures or superlattice structures at the atomic/molecular level.

In recent years, Junwu Zhu and Pan Xiong have focused on the scalable synthesis of artificial 2D heterostructures/superlattices, structure regulation and the synergistic effect at the 2D heterointerfaces towards electrochemical energy storage and catalytic applications. This work was supported by the National Natural Science Foundation of China (51772152 and 51902161) and the Fundamental Research Funds for the Central Universitie (30919011269).