Carbon nanotube-polypyrrole core-shell sponge and its application as highly compressible supercapacitor electrode

A carbon nanotube （CNT） sponge contains a three-dimensional conductive nano- tube network, and can be used as a porous electrode for various energy devices. We present here a rational strategy to fabricate a unique CNT@polypyrrole （PPy） core-shell sponge, and demonstrate its application as a highly compressible supercapacitor electrode with high performance. A PPy layer with optimal thickness was coated uniformly on individual CNTs and inter-CNT contact points by electrochemical deposition and crosslinking of pyrrole monomers, resulting in a core-shell configuration. The PPy coating significantly improves specific capacitance of the CNT sponge to above 300 F/g, and simultaneously reinforces the porous structure to achieve better strength and fully elastic structural recovery after compression. The CNT@PPy sponge can sustain 1,000 compression cycles at a strain of 50% while maintaining a stable capacitance （〉 90% of initial value）. Our CNT@PPy core-shell sponges with a highly porous network structure may serve as compressible, robust electrodes for supercapacitors and many other energy devices.

Direct fabrication of carbon nanotube-graphene hybrid films by a blown bubble method

Hybridization of carbon nanotubes （CNT） with graphene provides a promising means of integrating the attributes of both materials, thereby enabling widespread application. Here, we present a method to directly assemble hybrid CNT- graphene films by a blown bubble method combined with selective substrate annealing. We use polymethylmethacrylate （PMMA） as the polymeric matrix to blow bubbles containing self-assembled multi-walled CNT arrays, and then transform the bubble film into a CNT-graphene hybrid film by thermal annealing on a Cu substrate; PMMA serves as the carbon source for growing single to few-layer graphene among the CNT network until a continuously hybridized structure is formed. Compared to the bare （non-hybridized） CNT networks, the hybrid films exhibit improved electrical conductivity and structural integrity. Our method also enables the fabrication of a multi-walled CNT-Si solar cell, which has high power conversion efficiency, through the assembly of hybrid CNT-graphene structures.

Mechanical force-induced assembly of one-dimensional nanomaterials

There have been intensive and continuous research efforts in large-scale controlled assembly of one-dimensional(1D)nanomaterials,since this is the most effective and promising route toward advanced functional systems including integrated nano-circuits and flexible electronic devices.To date,numerous assembly approaches have been reported,showing considerable progresses in developing a variety of 1D nanomaterial assemblies and integrated systems with outstanding performance.However,obstacles and challenges remain ahead.Here,in this review,we summarize most widely studied assembly approaches such as Langmuir-Blodgett technique,substrate release/stretching,substrate rubbing and blown bubble films,depending on three types of external forces:compressive,tensile and shear forces.We highlight the important roles of these mechanical forces in aligning 1D nanomaterials such as semiconducting nanowires and carbon nanotubes,and discuss each approach on their effectiveness in achieving high-degree alignment,distinct characteristics and major limitations.Finally,we point out possible research directions in this field including rational control on the orientation,density and registration,toward scale-up and cost-effective manufacturing,as well as novel assembled systems based on 1D heterojunctions and hybrid structures.