Huimin Shi

Porous ultrathin carbon nanobubbles formed carbon nanofiber webs for high-performance flexible supercapacitors

Development of novel and scalable high-performance carbon nanomaterials and nanostructures is of critical importance for practical applications of flexible supercapacitors. In this study, we report a unique type of all-carbon nanofibrous non-woven web, in which carbon nanofibers are formed from well-connected porous ultrathin carbon nanobubbles. The foamed porous structures are achieved using ethanol as a carbon source coating on an electrospun ZnO nanofiber template followed by removing the ZnO template via a reduction and evaporation process. As a candidate for flexible supercapacitor applications, the fabricated integrated carbon nanofiber webs exhibit a long cycling life with 94.1% capacitance retention even after 35 000 cycles at a current density of 10 A g−1 with a three-electrode configuration. The symmetric supercapacitors also show a high rate performance with 81.4% capacitance retention when the current density is increased 70 times from 0.5 to 35 A g−1. Furthermore, electrochemical testing of the flexible symmetric devices displays almost the same capacitive behavior in different bending states. These excellent electrochemical performances are attributed to the interconnected porous and bubbled structures of the carbon nanofiber webs.

Uniform Gold-Nanoparticle-Decorated {001}-Faceted Anatase TiO2 Nanosheets for Enhanced Solar-Light Photocatalytic Reactions

The {001}-faceted anatase TiO2 micro-/nanocrystals have been widely investigated for enhancing the photocatalysis and photoelectrochemical performance of TiO2 nanostructures, but their practical applications still require improved energy conversion efficiency under solar-light and enhanced cycling stability. In this work, we demonstrate the controlled growth of ultrathin {001}-faceted anatase TiO2 nanosheets on flexible carbon cloth for enhancing the cycling stability, and the solar-light photocatalytic performance of the synthesized TiO2 nanosheets can be significantly improved by decorating with vapor-phase-deposited uniformly distributed plasmonic gold nanoparticles. The fabricated Au-TiO2 hybrid system shows an 8-fold solar-light photocatalysis enhancement factor in photodegrading Rhodamine B, a high photocurrent density of 300 μA cm-2 under the illumination of AM 1.5G, and 100% recyclability under a consecutive long-term cycling measurement. Combined with electromagnetic simulations and systematic control experiments, it is believed that the tandem-type separation and transition of plasmon-induced hot electrons from Au nanoparticles to the {001} facet of anatase TiO2, and then to the neighboring {101} facet, is responsible for the enhanced solar-light photochemical performance of the hybrid system. The Au-TiO2 nanosheet system addresses well the problems of the limited solar-light response of anatase TiO2 and fast recombination of photogenerated electron-hole pairs, representing a promising high-performance recyclable solar-light-responding system for practical photocatalytic reactions.

Osiers-sprout-like heteroatom-doped carbon nanofibers as ultrastable anodes for lithium/sodium ion storage

We report an in situ carbothermic reduction process to prepare osiers-sprout-like heteroatom-doped carbon nanofibers. The dosage of copper salts and a unique annealing process have a crucial effect on the development of this unique carbon structure. A systematic analysis is performed to elucidate the possible mechanism of synthesis of the carbon nanofibers decorated with carbon bubbles. As anodes for rechargeable lithium/sodium ion batteries, the heteroatom-doped nanofibers exhibit high reversible capacities and satisfactory long-term cycling stabilities. The osiers-sprout-like heteroatom-doped carbon nanofiber electrodes deliver an ultrastable cycling performance with reversible capacities of 480 and 160 mAh·g−1 for lithium-ion and sodium-ion batteries after 900 cycles at a current density of 800 mA·g−1, respectively.

Transmissive structural color filters using vertically coupled aluminum nanohole/nanodisk array with a triangular-lattice

We demonstrate a configuration to generate transmissive structural colors through triangular-lattice square nanohole arrays in aluminum (Al) film with Al nanodisks on the bottom of the nanoholes. By using a simple nanofabrication process, colors covering the entire visible light with different brightness and saturation are achieved by tuning both the period of arrays and the size of nanoholes. The optical behaviors of the structures are systematically investigated by both experimental and theoretical methods. The results indicate that the localized surface plasmon resonance of nanohole arrays plays the key role in the extraordinary transmission and meanwhile the coupling of disks and holes is also of importance for the enhanced transmission. With the wide color gamut, these kinds of vertically coupled Al nanohole/nanodisk arrays show the capabilities for high-resolution full-color printing. Compared to existing transmissive plasmonic color filters, the configuration in this work has the advantages of a simple fabrication process and using cheap aluminum materials.

Three-Dimensional-Stacked Gold Nanoparticles with Sub-5 nm Gaps on Vertically Aligned TiO2 Nanosheets for Surface-Enhanced Raman Scattering Detection Down to 10 fM Scale

Seeking for ultrasensitive and low-cost substrates is highly demandable for practical applications of surface-enhanced Raman scattering (SERS) technology. In this work, we report an ultrasensitive SERS-active substrate based on wet-chemistry-synthesized vertically aligned large-area TiO2 nanosheets (NSs) decorated by densely packed gold nanoparticles (Au NPs) with sub-5 nm gaps. Via a multistep successive deposition process, three-dimensional-stacked Au NPs sandwiched by a 3 nm SiO2 layer were assembled onto the TiO2 NS, enabling numerous hotspots due to the formation of both ultratiny plasmonic gaps and semiconductor/metal interfaces. Experimental results show that the fabricated substrate displays a detection limit down to 10 fM (10-14 M) without involving any condensation process by using the crystal violet as probe molecules. Control experiments and electromagnetic simulations indicate that the nanogaps defined by the 3 nm spacer are essential for the obtained excellent SERS performance. With its ultrasensitive detection capability, we demonstrate that the fabricated SERS substrate can be used for the trace analysis of melamine in milk.

Split-orientation-modulated plasmon coupling in disk/sector dimers

The coupled asymmetric plasmonic nanostructures allow more compact nanophotonics integration and easier optical control in practical applications, such as directional scattering and near-field control. Here, we carried out a systematic and in-depth study on the plasmonic coupling of an asymmetric gold disk/sector dimer, and investigated the light-matter interaction in such an asymmetric coupled complex nanostructures. The results demonstrated that the positions and the intensity of plasmon resonance peak as well as the spatial distribution of electric fields around the surface in the coupled disk/sector dimer can be tuned by changing the azimuth angle of the gold sector. Based on Simpson-Peterson approximation, we proposed a model to understand the obtained plasmon properties of asymmetric coupled disk/sector dimers by introducing an offset parameter between the geometry center and dipole center of the sector. The experimental results agree well with the simulations. Our study provides an insight to tune ...