Capillary shrinkage of graphene oxide hydrogels
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Published online 5 December 2019 | https://doi.org/10.1007/s40843-019-1227-7
Capillary shrinkage of graphene oxide hydrogels 1,4†
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Changsheng Qi , Chong Luo , Ying Tao , Wei Lv , Chen Zhang , Yaqian Deng , Huan Li , 1,4 3 1,4* Junwei Han , Guowei Ling and Quan-Hong Yang ABSTRACT Conventional carbon materials cannot combine high density and high porosity, which are required in many applications, typically for energy storage under a limited space. A novel highly dense yet porous carbon has previously been produced from a three-dimensional (3D) reduced graphene oxide (r-GO) hydrogel by evaporation-induced drying. Here the mechanism of such a network shrinkage in r-GO hydrogel is specifically illustrated by the use of water and 1,4dioxane, which have a sole difference in surface tension. As a result, the surface tension of the evaporating solvent determines the capillary forces in the nanochannels, which causes shrinkage of the r-GO network. More promisingly, the selection of a solvent with a known surface tension can precisely tune the microstructure associated with the density and porosity of the resulting porous carbon, rendering the porous carbon materials great potential in practical devices with high volumetric performance. Keywords: graphene oxides, porous carbons, hydrogels, capillary force, network shrinkage
INTRODUCTION Graphene, a single layer of carbon atoms arranged in a honeycomb network, has unique and versatile properties and can be considered as the building block of carbon materials [1]. For example, zero-dimensional (0D) fullerene can be regarded as a sphere of monolayer graphene and a one-dimensional (1D) carbon nanotube can be considered as a rolled graphene sheet [2]. As for conventional three-dimensional (3D) carbon materials, there are two factors involved in their structures, the stacking
and packing of the sheets. As illustrated in Fig. 1, face-toface parallel stacking produces a high density but nonporous carbon, like graphite, while edge-to-edge random packing results in porous carbon structures with high porosity but low density [3]. Graphite materials with stacked graphene sheets have a high density but show an electrochemical activity only for lithium and potassium ions [4,5]. Although carbon materials with random packing have an interconnected pore network and sufficient channels for ion transport, their low packing density and poor volumetric performance restrict their practical use in energy storage devices [6]. It is therefore hard for conventional carbon materials to achieve both high density and high porosity through the traditional assembly of carbon layers. With the rapid development of portable electronics and electric vehicles, exploring materials with high volumetric performance is essential for energy storage [7,8]. Highly porous yet dense materials would deliver a high volumetric performance which is important for energy storage. However, using conventional strategies [9–11], it is hard to obtain materials with both high density and large surface ar
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