Lifeng Zhang

Electrospun carbon nanofibers as low-cost counter electrode for dye-sensitized solar cells.

Electrospun carbon nanofibers (ECNs) have been explored as an electrocatalyst and low-cost alternative to platinum (Pt) for triiodide reduction in dye-sensitized solar cells (DSCs). The results of electrochemical impedance spectroscopy (EIS) and cyclic voltammetry measurements indicated that the ECN counter electrodes exhibited low charge-transfer resistance (Rct), large capacitance (C), and fast reaction rates for triiodide reduction. Although the efficiency (η) of ECN-based cells was slightly lower than that of Pt-based cells, their short circuit current density (Jsc) and open circuit voltage (Voc) were comparable. The ECN-based cells achieved an energy conversion efficiency (η) of 5.5 % under the AM 1.5 illumination at 100 mW cm(-2). The reason for lower cell performance using the ECN electrode was because of its lower fill factor (FF) than that of Pt-based cells, probably caused by high total series resistance (RStot) at ∼15.5 Ω cm2, which was larger than that of ∼4.8 Ω cm2 in the Pt-based devices. Simulated results showed that the fill factor (FF) and η could be substantially improved by decreasing RStot, which might be achieved by using thinner and highly porous ECNs to reduce the thickness of the ECNs counter electrode.

A review: carbon nanofibers from electrospun polyacrylonitrile and their applications

Carbon nanofibers with diameters that fall into submicron and nanometer range have attracted growing attention in recent years due to their superior chemical, electrical, and mechanical properties in combination with their unique 1D nanostructures. Unlike catalytic synthesis, electrospinning polyacrylonitrile (PAN) followed by stabilization and carbonization has become a straightforward and convenient route to make continuous carbon nanofibers. This paper is a comprehensive and state-of-the-art review of the latest advances made in development and application of electrospun PAN-based carbon nanofibers. Our goal is to demonstrate an objective and overall picture of current research work on both functional carbon nanofibers and high-strength carbon nanofibers from the viewpoint of a materials scientist. Strategies to make a variety of carbon nanofibrous materials for energy conversion and storage, catalysis, sensor, adsorption/separation, and biomedical applications as well as attempts to achieve high-strength carbon nanofibers are addressed.

Electrospun Nanofibrous Membranes Surface-Decorated with Silver Nanoparticles as Flexible and Active/Sensitive Substrates for Surface-Enhanced Raman Scattering

The development of novel nanomaterials with well-controlled morphologies/structures to achieve excellent activities/sensitivities in surface-enhanced Raman scattering (SERS) is crucial in advancing the high-performance SERS detections of chemical and biological species. In this study, amidoxime surface-functionalized polyacrylonitrile (ASFPAN) nanofibrous membranes surface-decorated with silver nanoparticles (Ag NPs) were prepared via the technique of electrospinning followed by the method of seed-mediated electroless plating. High SERS activities/sensitivities were observed from the ASFPAN-Ag NPs nanofibrous membranes, while the density and size of Ag NPs had an important impact on the SERS activity/sensitivity. The results confirmed that the enhancement of Raman signals is due to the presence of hot spots between/among Ag NPs on the nanofiber surfaces. Electrospun nanofibrous membranes surface-decorated with Ag NPs were mechanical flexible/resilient and could be used as highly active/sensitive SERS substrates for a broad range of applications.

Dye-sensitized solar cells based on spray-coated carbon nanofiber/TiO2 nanoparticle composite counter electrodes

Electrospun carbon nanofiber (ECN)/TiO2 nanoparticle composite counter electrodes (CEs) for dye-sensitized solar cells (DSSCs) were successfully prepared by spray-coating an ECN/TiO2 (1 : 1 by weight) mixture on a fluorine doped tin oxide (FTO)-glass substrate. TiO2 particles (Degussa P25) were used to bind carbon nanofibers and adhere them to the FTO-glass substrate. Electrochemical impedance spectroscopy (EIS) measurements revealed that the spray-coated ECN/TiO2 composite CEs have lower charge transfer resistance (Rct) and higher interfacial capacitance (Q) than those of Pt CEs. Cyclic voltammograms (CV) further indicated that ECN/TiO2 composite CEs have a faster tri-iodide reduction rate than those of Pt CEs. DSSCs fabricated using ECN/TiO2 CEs showed a power conversion efficiency (η) of 7.25% under 100 mW cm−2 light intensity, which is comparable to that of thermally deposited Pt based DSSCs (η = 7.57%). Moreover, ECN/TiO2 composite CE based DSSCs demonstrated almost equal power conversion efficiency to that of Pt based cells by adding only 8 wt% Pt, which unveiled a cost-effective alternative of costly Pt CEs in DSSCs.

Graphene-embedded carbon nanofibers decorated with Pt nanoneedles for high efficiency dye-sensitized solar cells

Graphene-embedded carbon nanofibers (GCNFs) were developed as a new counter electrode nanomaterial for high efficiency dye-sensitized solar cells (DSCs). GCNFs were produced by electrospinning polyacrylonitrile (PAN) with graphene nanoplatelets followed by stabilization and carbonization. GCNFs decorated with surface-attached platinum nanoneedles (GCNFs-PtNNs) were subsequently prepared by a redox reaction and then deposited onto fluorine doped tin oxide (FTO) glass to make a counter electrode for DSCs. Graphene inside the carbon nanofibers and Pt nanoneedles on the surface demonstrated a synergistic effect to improve the DSC performance. Compared to DSCs with conventional planar Pt counter electrodes, the DSCs with GCNFs-PtNNs significantly improved the energy conversion efficiency from ∼8.63% to ∼9.70% using a mask under AM1.5 illumination. This is the highest conversion efficiency so far with a carbon nanofiber based counter electrode.

Monodisperse raspberry-like multihollow polymer/Ag nanocomposite microspheres for rapid catalytic degradation of methylene blue

Raspberry-like multihollow polymer microspheres were prepared by seeded swelling polymerization and decorated with silver nanoparticles (AgNPs) in the presence of polyvinylpyrrolidone (PVP) which acted as both reducing and stabilizing agent. Formation mechanism of the raspberry-like multihollow microsphere was discussed on the basis of water absorption of sulfonated groups in the seeded swelling polymerization. Effects of weight ratio of sodium 4-vinylbenzenesulfonate to styrene (NaSS/St) of the seed particles, the concentration of PVP and [Ag(NH3)2]+ ions on the properties of polymer/Ag nanocomposite microspheres were investigated by microscopic observation, nitrogen adsorption/desorption isotherms, UV-vis absorption spectra, X-ray diffraction patterns and thermogravimetric analysis. The results demonstrated that the raspberry-like multihollow microspheres were successfully fabricated by controlling over the NaSS/St of the seed particles in the seeded swelling polymerization by which the fabrication of hollow structure became simple and convenient. The spherical AgNPs were loaded on the polymer microsphere by in-situ chemical reduction due to the stabilization and reduction of PVP and the attraction between sulfonated groups and [Ag(NH3)2]+ ions. The raspberry-like multihollow polymer/Ag microspheres showed good catalytic activity and reusability in the degradation of methylene blue in the presence of NaBH4.

A metal matrix composite prepared from electrospun TiO2 nanofibers and an Al 1100 alloy via friction stir processing.

Electrospun TiO2 nanofibers, consisting of anatase phase TiO2 single-crystalline crystallites with sizes of approximately 10 nm, were impregnated into an Al 1100 alloy by the technique of friction stir processing (FSP). The studies of the resulting TiO2-Al composite revealed that the electrospun TiO2 nanofibers with diameters of approximately 200 nm were broken into nanoparticles during FSP; the in situ generated pristine surfaces led to the interfacial reaction between TiO2 and Al and resulted in the formation of strong interfaces between the electrospun TiO2 nanoparticles and the Al 1100 matrix. This was evidenced by the fact that the filler-matrix fracture always occurred on the Al matrix side in the interfacial region. Consequently, the TiO2-Al composite made from the electrospun TiO2 nanofibers possessed a significantly higher Vickers hardness than that made from a commercially available anatase phase TiO2 nanopowder, of which the organic and/or carbonaceous contaminants on the surface impeded the interfacial reaction between TiO2 and Al during FSP.

Multi-hollow polymer microspheres with enclosed surfaces and compartmentalized voids prepared by seeded swelling polymerization method

Multi-hollow particles have drawn extensive research interest due to their high specific areas and abundant inner voids, whereas their convenient synthesis still remains challenging. In this paper, we report a simple and convenient method based on seeded swelling polymerization to prepare the multi-hollow microspheres with enclosed surfaces and compartmentalized voids using monodisperse poly (styrene-co-sodium 4-vinylbenzenesulfonate) microspheres as seed particles. A formation mechanism of the multi-hollow structure was proposed involving the processes of water absorption, coalescence and stabilization of water domains, immobilization of multi-hollow structure, and coverage of surface dimples. The influencing parameters on the morphology of the microspheres, including weight ratio of sodium 4-vinylbenzenesulfonate to styrene in the seed particles, dosage of the swelling monomer and the crosslinking agent were systematically investigated. The internal structure of the resultant microspheres could be tuned from solid to multi-hollow by controlling over these parameters. Multi-hollow microspheres with compartmentalized chambers, smooth surfaces and narrow size distributions were obtained as a result.

A form-stable phase change material made with a cellulose acetate nanofibrous mat from bicomponent electrospinning and incorporated capric–myristic–stearic acid ternary eutectic mixture for thermal energy storage/retrieval

An innovative type of form-stable phase change material (PCM) was prepared by incorporating a capric–myristic–stearic acid (CMS) ternary eutectic mixture with a cellulose acetate (CA) nanofibrous mat that was derived from electrospinning a binary mixture of CA/polyvinylpyrrolidone (PVP) and subsequent selective dissolution of PVP component from the obtained bicomponent nanofibrous mat. PVP removal from the CA/PVP bicomponent nanofibers created nanoporous features on the resultant CA nanofiber surface and increased CMS incorporation capability of the nanofibrous mat. Morphology, thermal behavior and durability, and thermal energy storage/retrieval capacity of the prepared CMS/CA nanofibrous form-stable PCM were investigated. This form-stable PCM could maintain well the PCM characteristics even after multiple thermal cycle uses and demonstrated great thermal storage/retrieval capability and temperature regulation ability.

A photocurable leaky dielectric for highly electrical insulating electrohydrodynamic micro-/nanopatterns

This communication describes an innovative photocurable leaky dielectric for electrohydrodynamic patterning (EHDP). Based on the well-designed molecular structure, the material in its liquid state exhibits low viscosity, high homogeneity, and more importantly a leaky dielectric characteristic; meanwhile, UV light irradiation transforms it from a liquid leaky dielectric into a solid perfect dielectric instantaneously via an interfacial reaction. Two typical EHDP processes have confirmed that the beneficial properties of this material help to rapidly fulfill a higher aspect ratio and/or smaller feature size patterning compared to its perfect dielectric counterpart. Therefore, this material provides the potential in accessing high-performance EHDP towards fabricating electrically insulating micro-/nanostructures.