Tingxi Li

Ultralow percolation threshold and enhanced electromagnetic interference shielding in poly(L-lactide)/multi-walled carbon nanotube nanocomposites with electrically conductive segregated networks

Electrically conductive segregated networks were built in poly(L-lactide)/multi-walled carbon nanotube (PLLA/MWCNT) nanocomposites without sacrificing their mechanical properties via simply choosing two different PLLA polymers with different viscosities and crystallinities. First, the MWCNTs were dispersed in PLLA with low viscosity and crystallinity (L-PLLA) to obtain the L-PLANT phase. Second, the PLLA particles with high viscosity and crystallinity (H-PLLA) were well coated with the L-PLANT phase at 140 °C which was below the melting temperature of H-PLLA. Finally, the coated H-PLLA particles were compressed above the melting temperature of H-PLLA to form the PLLA/MWCNT nanocomposites with segregated structures. The morphological observation showed the successful location of MWCNTs in the continuous L-PLLA phase, resulting in an ultralow percolation threshold of 0.019 vol% MWCNTs. The electrical conductivity and the electromagnetic interference (EMI) shielding effectiveness (SE) of the composites with the segregated structure are 25 S m−1 and ∼30 dB, showing three orders and 36% higher than that of the samples with a random distribution of MWCNTs with 0.8 vol% of MWCNT loading, respectively. High-performance electromagnetic interference (EMI) shielding was also observed mainly dependent on the highly efficient absorption shielding, which can be achieved by the densely continuous MWCNT networks and the abundant interfaces induced by the segregated structures. Furthermore, the composites with segregated structures not only showed higher Youngs modulus and tensile strength than the corresponding conventional composites, but also maintained high elongation at break because of the continuous and dense MWCNT networks induced by the segregated structures and the high interfacial interaction between H-PLLA and L-PLLA.

A graphene quantum dot decorated SrRuO3 mesoporous film as an efficient counter electrode for high-performance dye-sensitized solar cells

Hydrothermally synthesized electrically conductive perovskite strontium ruthenate (SrRuO3) nanoparticles were added into a binder solution and then cast onto fluorine doped tin oxide (FTO) glass to form a mesoporous SrRuO3 counter electrode (CE) for dye-sensitized solar cells (DSSCs). The high porosity and large specific surface area of the SrRuO3 CE allows easier and faster diffusion of electrolyte into the pores and involves more triiodide (I3−) in the redox reaction, thereby resulting in a higher power conversion efficiency (PCE, 7.16%) than that of our published research on sputtered SrRuO3 film CEs (6.48%). Furthermore, graphene quantum dots (GQDs) endowed with excellent intrinsic catalytic activity and high conductivity were decorated onto the SrRuO3 CE by a dipping technique to form a SRO–GQD hybrid. The synergistic effect of SrRuO3 and GQDs contributes to more active catalytic sites as well as faster ion diffusion and electron transfer than a pristine SrRuO3 CE, thereby resulting in increased electrocatalytic ability towards I3− reduction. As a result, our fabricated DSSCs based on the optimized SRO–GQD CE achieve an impressive PCE of 8.05%, much higher than that of the reference device assembled with a conventional platinum (Pt) CE (7.44%). The SRO–GQD CE also exhibits an excellent long-term electrochemical stability in I3−/I− electrolyte. Overall, the SRO–GQD hybrid can be considered as a highly efficient Pt-free CE for practical applications of DSSCs.

Continuously prepared highly conductive and stretchable SWNT/MWNT synergistically composited electrospun thermoplastic polyurethane yarns for wearable sensing

Highly conductive and stretchable yarns have attracted increasing attention due to their potential applications in wearable electronics. The integration of conductive yarns with large stretching capability renders the composite yarns with new intriguing functions, such as monitoring human body motion and health. However, simultaneously endowing the yarns with high conductivity and stretchability using an easily scalable approach is still a challenge. Here, highly conductive and stretchable yarns based on electrospun thermoplastic polyurethane (TPU) fiber yarns successively decorated with multi-walled carbon nanotubes (MWNTs) and single-walled carbon nanotubes (SWNTs) were prepared by a combined electrospinning, ultrasonication adsorbing, and bobbin winder technique. The improved thermal stability of the SWNT/MWNT/TPU yarn (SMTY) indicated strong interfacial interactions between the CNTs and electrospun TPU fibers. The synergism between the successively decorated SWNTs and MWNTs significantly enhanced the conductivity of the TPU yarns (up to 13 S cm−1). The as-fabricated yarns can be easily integrated into strain sensors and exhibit high stretchability with large workable strain range (100%) and good cyclic stability (2000 cycles). Moreover, such yarn can be attached to the human body or knitted into textiles to monitor joint motion, showing promising potential for wearable electronics, such as wearable strain sensors.

An overview of metamaterials and their achievements in wireless power transfer

Metamaterials have been deployed for a wide range of fields including invisible cloak, superlens, electromagnetic wave absorption and magnetic resonance imaging, owing to their peculiar electromagnetic properties. However, few investigations on metamaterials were focused on wireless power transfer (WPT). WPT is the transmission of electrical energy from a power source to an electrical load without conductors like wires or cables. Metamaterials can enhance the transfer efficiency and enlarge the transfer distance due to their ability of focusing magnetic flux, which opens up a novel approach to promoting the development and application of WPT. This review paper aims to provide an overview of the fabrications, exotic properties, and their applications especially in the WPT field. Meanwhile, the perspective and future challenges of metamaterials and WPT are proposed.

Silica microsphere templated self-assembly of a three-dimensional carbon network with stable radio-frequency negative permittivity and low dielectric loss

Percolative composites always suffer from their unstable and filler-loading dependent microstructures and negative electromagnetic parameters. Here, stable negative permittivity is achieved by in situ constructing a three-dimensional carbon network in the silica spherical matrix after a self-assembly and pyrolysis process. An electrical percolation phenomenon appears with the formation of a carbon network. Once the carbon network is formed, further increasing carbon loadings will only influence the porosity rather than the connectivity due to the nature of the porous carbon itself. Hence, the microstructure and plasma-like negative permittivity are not sensitive to carbon loading, leading to a negligible carbon loading dependent permittivity behavior. Moreover, negative permittivity with small values (−100 < e′ < 0), beneficial for matching with permeability, was effectively adjusted by changing the carbonization temperature. The carbon composites with negative permittivity showed an extremely low dielectric loss (tanu2006δ = 1–7) compared with metal composites (usually tanu2006δ = 10–100). This work provides a convenient means to obtain stable negative permittivity properties. The carbon composites can be regarded as a promising candidate for metamaterials and will facilitate the applications of materials with negative electromagnetic parameters.

Correction: An overview of metamaterials and their achievements in wireless power transfer

Correction for ‘An overview of metamaterials and their achievements in wireless power transfer’ by Kai Sun et al., J. Mater. Chem. C, 2018, DOI: 10.1039/c7tc03384b.

In-situ grown nickel selenide onto graphene nanohybrid electrodes for high energy density asymmetric supercapacitors

Nickel selenide (NiSe) nanoparticles uniformly supported on graphene nanosheets (G) to form NiSe-G nanohybrids were prepared by an in situ hydrothermal process. The uniform distribution of NiSe on graphene bestowed the NiSe-G nanohybrid with faster charge transport and diffusion along with abundant accessible electrochemical active sites. The synergistic effect between NiSe nanoparticles and graphene nanosheets for supercapacitor applications was systematically investigated for the first time. The freestanding NiSe-G nanohybrid electrode exhibited better electrochemical performance with a high specific capacitance of 1280 F g-1 at a current density of 1 A g-1 and a capacitance retention of 98% after 2500 cycles relative to that of NiSe nanoparticles. Furthermore, an asymmetric supercapacitor device assembled using the NiSe-G nanohybrid as the positive electrode, activated carbon as the negative electrode and an electrospun PVdF membrane containing 6 M KOH as both the separator and the electrolyte delivered a high energy density of 50.1 W h kg-1 and a power density of 816 W kg-1 at an extended operating voltage of 1.6 V. Thus, the NiSe-G nanohybrid can be used as a potential electrode material for high-performance supercapacitors.