New Structural Insights into Densely Assembled Reduced Graphene Oxide Membranes

Abstract

Densely assembled graphene‐based membranes have attracted substantial interest for their widespread applications, such as compact capacitive energy storage, ion/molecular separation, gas barrier films, and flexible electronics. However, the multiscale structure of densely packed graphene membranes remains ambiguously understood. This article combines X‐ray and light scattering techniques as well as dynamic electrosorption analysis to uncover the stacking structure of the densely stacked reduced graphene oxide (rGO) membranes. The membranes are produced by reducing graphene oxide (GO) membranes with hydrazine, during which the colloidal interactions between GO sheets are modulated by the electrolyte solution. In contrast to the common notion that direct reduction of densely assembled GO sheets in parallel tends to result in significant “graphitization”, this article unexpectedly discovers that the resultant densely packed rGO membrane can still retain the interconnected network nanochannels and show good capacitive performances. This inspires the development of a hierarchical structural model to describe the densely packed rGO membranes. This article further shows that the nanochannel network can be fine‐tuned at the sub‐nanometer level by tailoring the salt concentration and the reduction temperature to render exceptional volumetric capacitance and good rate performance for rGO membranes even with increased packing density.

Subnanometric Stacking of Two-Dimensional Nanomaterials: Insights from the Nanotexture Evolution of Dense Reduced Graphene Oxide Membranes

“…To evaluate the occupation number of large voids to the total pores of the membranes, we estimated the ratio between the slit number of large voids and the total slit number of the rGO membranes ( n voids / n total ) and found that it is <1.1% (Figure S7c) (see Methods for more details). Such a small percentage suggests that the contribution of the large voids to the total pore structures can be nearly neglected in the HI-reduced GO membranes compared to that in N 2 H 4 -reduced rGO membranes we recently reported, where a much higher content of such voids with a wider range of size distributions (30 ∼ 200 nm) exists . Unlike N 2 H 4 -rGO, the reaction in HI-rGO membranes neither leads to the loss of carbon atoms nor introduces the gaseous phase to the membrane, and it is thus expected to eventually contribute to the compact stacking of rGO nanosheets …”

“…42 A weak hump is observed in the low-q region (0.002 Å −1 to 0.1 Å −1 ) of the SAXS scattering curve (Figure 2b), indicating the existence of a group of large slit-like pores (i.e., voids) with a characteristic dimension (d void = 2π/q max ) at tens of nanometers. According to the structural model of rGO membranes established previously, 27 these slit-like voids are likely attributed to the gaps between the lamellae (an intermediate structure composed of stacked nanosheets). Specifically, the d void first increases from 32 nm (rGO-20-1h) to 73 nm (rGO-20-28h) and then decreases to 13 nm (rGO-20-99h) (Figure S7a,b).…”

Practical Graphene Technologies for Electrochemical Energy Storage

“…Besides, the hierarchical structure of the graphene films can be fine‐tuned by using salt concentration to modulate their colloidal interactions to offer an exceptional volumetric capacitance in aqueous electrolytes. [ 116 ] Further, as mentioned above, we reported the first case of a dense yet porous carbon assembled with graphenes by simple evaporation, which has a density close to artificial graphite and pore structure similar to activated carbons, showing ultra‐high specific volumetric capacity in aqueous SCs. [ 11 ] Nevertheless, the relatively small pores are not suitable for the fast diffusion of ionic liquid electrolytes which can withstand the high voltage.…”

Covalent organic framework assisted interlocked graphene oxide based thin-film composite membrane for effective water remediation

“…[13][14][15][16][17][18] GO nanosheets are layered structures that operate as nanochannels for selective separation of water organic molecules. 15,[19][20][21][22][23][24][25][26] Due to tortuous pathways, GO membranes often show low permeation flux. [27][28][29] One suitable approach to enhance the flux is to widen the interlayer distance by adding intermittent materials, such as zeolite imidazole frameworks, 30 metalorganic frameworks, 31,32 TiO 2 , 33,34 carbon nanotubes, 35 and other functional materials.…”