Highly compressible 3-D hierarchical porous carbon nanotube/metal organic framework/polyaniline hybrid sponges supercapacitors

Jing Gong,Zhichao Xu,Liang Zhang,Zhuo Tang,Jing Zhong

doi:10.1063/1.5109042

Abstract

Optimization of the transport behaviors of ions and electrons is the key for the property improvement of supercapacitor, which are essentially controlled by the design of hierarchical porous structure and electrical conductive backbone, from nanoscale to microscale, respectively. However, such design requirements are very difficult to be satisfied simultaneously, because the generation of porosity would result to the detrimental effects on the electrical conductivity of electrode. In this study, we propose to prepare a hierarchical porous supercapacitor electrode, with a novel 3-D highly porous (with pore size in the range of 50-100 nm) carbon nanotube sponges (CNTS) as a conductive substrate for the successively deposition of metal organic frameworks (MOF) and polyaniline. The porous structure of the sponge is beneficial for precursor penetration and uniform deposition of MOF and polyaniline (PANI) on to the nanotubes. The highly porous CNTS not only provides conductive highway for electrons, but also channels for ions quick diffusion. The coated MOF offers extra ion storage reservoir, while PANI further wire the insulating MOF together. In addition, the composite structure does not require any conductive additives or mechanical binders and delivers excellent capacitance coupled with flexible, compressive, and have relatively high specific capacitance.

Highlights

Since the carbon nanotube sponges (CNTS) was treated by acid before the coating of metal organic frameworks (MOF), the hydrophilic groups could act as nucleates for the growth of MOFs uniformly on each carbon nanotube (CNT)
TEM characterization (Figure 2d) again, confirms that MOF are firmly coated on the surface of CNTs, with average size of ∼200 nm
Consists of sub-micro sized pores formed by CNTs and nanoscale pores in MOFs, provides hierarchical pores for the effective transport of ions, greatly benefitting the supercapacitor performance

Summary

INTRODUCTION

Electrochemical capacitors, known as supercapacitors, represent a unique class of energy storage devices that bridge the gap between batteries and dielectric capacitors. With the outstanding comprehensive performance in terms of high power density, long cycle lifetime and safety, supercapacitors have been proved their important role in complementing or even replacing batteries in the energy storage field. The former store energy by physical adsorption of ions and electrons at the interface between the electrodes and electrolyte, and typically, activated carbon with high surface area is employed as electrode materials. The latter, on the other hand, store energy by redox reaction, and can significantly increase the energy storage capability at the price of decreasing power density and cycle life. Electrode structural design is the key step for the performance optimization for both of those two types of supercapacitors. With the outstanding comprehensive performance in terms of high power density, long cycle lifetime and safety, supercapacitors have been proved their important role in complementing or even replacing batteries in the energy storage field.2–5 The former store energy by physical adsorption of ions and electrons at the interface between the electrodes and electrolyte, and typically, activated carbon with high surface area is employed as electrode materials.. Advanced nano carbon materials, especially carbon nanotubes and graphene, have attracted great interest as supercapacitor electrodes, mainly because they have combined high conductivity, relatively high surface area and super mechanical property.. Advanced nano carbon materials, especially carbon nanotubes and graphene, have attracted great interest as supercapacitor electrodes, mainly because they have combined high conductivity, relatively high surface area and super mechanical property.2–4,10,11 These materials have little or no internal pores and even worse, they can agglomerate, which results to very limited accessible surface are to ions.

EXPERIMENT

RESULTS AND DISCUSSION

CONCLUSIONS