Two scientists from Japan have developed a new and straightforward approach to building nanoscale 3D materials using a technique called “diffusion-driven layer-by-layer assembly”. The process allows for the construction of graphene into porous 3D nanosheet structures, and could find uses in a range of applications in devices such as batteries and supercapacitors.

Although preparing graphene nanosheets into thin films has been shown to be relatively simple based on methods such as spin-coating, the construction of appropriate 3D macrostructures has proved much more difficult. The thinness of graphene means that when nanosheets of the material are stacked into larger architectures, there is a substantial reduction in its properties. Potential solutions have proved expensive and time consuming, and also difficult to scale. However, as reported in Nature Communications [Zou, L, Kim, F. Nat. Commun. (2014) DOI: 10.1038/ncomms6254], Jianli Zou and Franklin Kim from Kyoto University have taken a process from polymer chemistry to construct graphene oxide sheets into porous 3D structures while preventing stacking between the sheets.

To achieve this, they placed graphene oxide next to an oppositely charged polymer so that the two components were able to form a stable composite layer, a method called interfacial complexation. As Jianli Zou said “Interestingly, the polymer could continuously diffuse through the interface and induce additional reactions, which allowed the graphene-based composite to develop into thick multi-layered structures.” The resulting products exhibited a porous foam-like structure, thought to be ideal for maximizing the benefits of graphene.

The assembly process was found to be comparatively robust and able to be utilized in various configurations to develop free-standing architectures with specific shapes or patterned films on a substrate. The porosity is also tunable by simple changes to conditions, and the process can be scaled to help develop large-area films that could be used as electrodes and membranes for energy generation or storage.

As principal investigator Franklin Kim told Materials Today, “we have shown that it is possible to prepare various types of porous graphene-based structures, in particular as large-area films. We hope that this discovery will accelerate the practical application of graphene in actual industrial products.”

Although this novel assembly concept has only been applied to the preparation of graphene-based structures, the pair now hope to further explore the material properties of their product and assess how it could serve as a general method for the assembly of other types of nanomaterials.