Scalable salt-templated synthesis of two-dimensional transition metal oxides.

Xu Xiao,Shizhe Lin,Zhimi Hu,Jun Zhou,Liying Jiao,Jiang Tang,Tianqi Li,Qi Zhang,Yury Gogotsi,Ying Zhou,Jiyu Sun,Bo Yang,Huaibing Song,Xiaojun Zhan

doi:10.1038/ncomms11296

Abstract

Two-dimensional atomic crystals, such as two-dimensional oxides, have attracted much attention in energy storage because nearly all of the atoms can be exposed to the electrolyte and involved in redox reactions. However, current strategies are largely limited to intrinsically layered compounds. Here we report a general strategy that uses the surfaces of water-soluble salt crystals as growth templates and is applicable to not only layered compounds but also various transition metal oxides, such as hexagonal-MoO3, MoO2, MnO and hexagonal-WO3. The planar growth is hypothesized to occur via a match between the crystal lattices of the salt and the growing oxide. Restacked two-dimensional hexagonal-MoO3 exhibits high pseudocapacitive performances (for example, 300 F cm−3 in an Al2(SO4)3 electrolyte). The synthesis of various two-dimensional transition metal oxides and the demonstration of high capacitance are expected to enable fundamental studies of dimensionality effects on their properties and facilitate their use in energy storage and other applications.

Highlights

Two-dimensional atomic crystals, such as two-dimensional oxides, have attracted much attention in energy storage because most of the atoms can be exposed to the electrolyte and involved in redox reactions
Pseudocapacitors are of great interest for energy storage owing to their fast charging/discharging, high power density and excellent cycling stability, which are beneficial to many potential applications ranging from ubiquitous portable electronics to grid energy storage[1,2,3,4,5,6,7]
On the basis of the SEM and optical images (Supplementary Fig. 4), all of the samples possess 2D morphology with the size of some flakes exceeding 400 mm[2], which is much larger than that of liquid-exfoliated or chemically synthesized samples in which sizes are typically limited to a few micrometres[27]

Summary

Introduction

Two-dimensional atomic crystals, such as two-dimensional oxides, have attracted much attention in energy storage because most of the atoms can be exposed to the electrolyte and involved in redox reactions. The synthesis of two-dimensional (2D) nanosheets followed by restacking of these nanosheets to form electrodes has attracted much attention[8,9,10,11] Because of their nanometre/sub-nanometre thickness, most of the metal atoms can be exposed to the electrolyte and potentially involved in redox reactions, resulting in pseudocapacitances that approach the theoretical values[9]. Nanosheets are highly preferable because ion diffusion within the oxide lattice is minimized, enabling the simultaneous achievement of a large volumetric capacitance (high energy density) at a high rate (high power density). This behaviour is typically very challenging to achieve for both bulk and one-dimensional materials. Materials bonded by van der Waals or other weak forces in one direction can be cleaved by the intercalants

Methods

Results

Conclusion