Advances in Porous Graphene and Scalable Wet-Spinning Fiber Assembly

Abstract

CONSPECTUS: Two-dimensional (2D) materials with astonishing properties and thickness dimensions are attractive for nanodevices and optoelectronics devices. Among them, 2D graphene-an atomically thin single layer with a strong covalently bonded sp2hybridized hexagonal carbon network-has fascinating physicochemical properties. 2D graphene is at the tip of the iceberg of 2D materials. However, graphene is prone to selfrestacking and agglomeration, deteriorating its properties. The introduction of porous structures to graphene sheets ameliorates their properties, e.g., increasing the surface area, providing ion transport channels, and enhancing the stability; thus, the performance of graphene-based materials is improved. Owing to their exciting properties, 2D holey graphene (HG) with nanoholes in its 2D basal plane and three-dimensional (3D) porous graphene with structural pores and interconnected architectures structural derivatives of graphene are promising for addressing the aforementioned challenges synergistically. Perforation in 2D graphene with tunable pore size, pore density, and uniformity is crucial for improving the performance of dense graphene. The unique pore structure and large exposed edges indicate the improved properties of porous graphene. Furthermore, macroscopically assembled one-dimensional (1D) fibrous electrodes of holey and porous graphene building blocks are promising, as they are lightweight, have high flexibility, and have strong wearability for future next-generation electronics. In this Account, we systematically highlight our efforts related to the conventional synthesis methodologies to recent emerging methods of "holey" or "porous" graphene/graphene oxide. First, we focus on the synthesis strategies and advances of 2D HG inplane holes suitable for fast ion transport. Recent emerging synthesis methodologies are discussed for preparing 2D HG, which uses an environmentally benign approach with low toxicity compared to conventional etching methods, which frequently involve the use of hazardous or toxic oxidizing reagents, thereby causing severe environmental pollution. Second, compared with graphene, the 3D porous graphene comprises self-assembled graphene sheets (holey) containing structural macropores with a larger accessible surface area, high pore volume, and better flexibility, stability, and mechanical properties preferred for energy conversion and storage applications. Here, the recent progress and emerging synthesis approaches for 3D porous graphene-based nanomaterials are comprehensively discussed. Furthermore, the advantages of 2D HG and 3D porous graphene are discussed for water transport and electrochemical storage. Third, recent advances in the use of straightforward, large-scale wet-spinning processes to fabricate macroscopically assembled 1D fibrous electrodes with excellent mechanical flexibility and deformability using holey or porous graphene-based fibers (GFs) are described. Different approaches are discussed for preparing holey or porous GFs, such as wetspinning assembly of holey graphene oxide (HGO), coagulant-assisted porous structures, and the post-activation process. Thus, the wet-spun holey or porous GFs are promising for miniaturized-based next-generation wearable electronic devices. Finally, we focus on the current status, fundamental understanding, future directions, and challenges of wet-spinning assemblies of holey/porous graphene-based nanomaterials for the next generation of wearable electronics.