Chun Han Hsu

High performance of transferring lithium ion for polyacrylonitrile- interpenetrating crosslinked polyoxyethylene network as gel polymer electrolyte

A polyacrylonitrile (PAN)-interpenetrating cross-linked polyoxyethylene (PEO) network (named XANE) was synthesized acting as separator and as gel polymer electrolytes simultaneously. SEM images show that the surface of the XANE membrane is nonporous, comparing to the surface of the commercial separator to be porous. This property results in excellent electrolyte uptake amount (425 wt %), and electrolyte retention for XANE membrane, significantly higher than that of commercial separator (200 wt %). The DSC result indicates that the PEO crystallinity is deteriorated by the cross-linked process and was further degraded by the interpenetration of the PAN. The XANE membrane shows significantly higher ionic conductivity (1.06-8.21 mS cm(-1)) than that of the commercial Celgard M824 separator (0.45-0.90 mS cm(-1)) ascribed to the high electrolyte retention ability of XANE (from TGA), the deteriorated PEO crystallinity (from DSC) and the good compatibility between XANE and electrode (from measuring the interfacial-resistance). For battery application, under all charge/discharge rates (from 0.1 to 3 C), the specific half-cell capacities of the cell composed of the XANE membrane are all higher than those of the aforementioned commercial separator. More specifically, the cell composed of the XANE membrane has excellent cycling stability, that is, the half-cell composed of the XANE membrane still exhibited more than 97% columbic efficiency after 100 cycles at 1 C. The above-mentioned advantageous properties and performances of the XANE membrane allow it to act as both an ionic conductor as well as a separator, so as to work as separator-free gel polymer electrolytes.

Stabilization of Embedded Pt Nanoparticles in the Novel Nanostructure Carbon Materials

An extremely durable and highly active Pt catalyst has been successfully prepared by embedding Pt(0) nanoparticles inside the pores of the nitrogen-dotted porous carbon layer surrounding carbon nanotubes (Pt@NC-CNT). The Pt@NC-CNT catalyst has a high BET surface area of 271 m(2) g(-1) (62 m(2) g(-1) for Pt/XC-72) and comparably high electrochemically active surface area of 64.3 m(2) g(-1) (68.2 m(2) g(-1) for Pt/XC-72). The prepared Pt nanoparticles are small in size (2.8 ± 1.3 nm) and have a strong interaction of nitrogen to platinum, as evidenced by the binding energy observed at 399.5 eV. The maximum current densities (I(f)) during methanol oxidation observed for Pt@NC-CNT (13.2 mA cm(-1)) is 1.2 times higher than that of Pt/XC-72 (10.8 mA cm(-1)) catalysts. Remarkably, in the long term durability test, the I(f) after 1000 cycles for Pt@NC-CNT decreased to 10.6 mA cm(-1) compared with Pt/XC-72, which decreased to 2.6 mA cm(-2). This means that the Pt@NC-CNT catalyst has a tremendously stable electrocatalytic activity for MOR because of the unique structure of Pt@NC-CNT formed in this novel synthesis technique.

Benzylamine-assisted noncovalent exfoliation of graphite-protecting Pt nanoparticles applied as catalyst for methanol oxidation.

A novel method has been developed to physically exfoliate graphite and uniformly disperse Pt nanoparticles on graphite nanoplates without damaging the graphene structures. A stable aqueous suspension of graphite nanoplates was achieved by benzylamine-assisted noncovalent fuctionalization to graphite and characterized by transmission electron microscopy, X-ray diffraction and Raman spectroscopy. A uniform dispersion of Pt nanoparticles was then prepared on the graphite nanoplates, where the benzylamine acts as a stabilizer. These Pt loaded graphite nanoplates were then prepared as an electrode, which significantly increased catalytic activity toward the methanol oxidation reaction, resulting in a 60% increment in mass activity compared to that of E-TEK.

Nitrogen-doped mesoporous carbon hollow spheres as a novel carbon support for oxygen reduction reaction

Novel nitrogen-doped mesoporous carbon hollow spheres (NMCs) as a catalyst support are prepared using polyaniline as both a carbon and a nitrogen source, where the amount of doped nitrogen is controllable (N/C ratio 7.81–16.83 wt%). The prepared NMCs are characterized via scanning electron microscopy, transmission electron microscopy, conductivity and nitrogen adsorption and desorption isotherms. For fuel cell application, a uniform dispersion of Pt nanoparticles with a diameter of 3.8 ± 1.3 nm is anchored on the surface of the NMCs by ethylene glycol reduction. In a single cell test, the Pt/NMC catalyst is found to have superior catalytic activity to better support the oxygen reduction reaction, resulting in an enhancement of about 19% in mass activity compared with that of the commercial Pt/C catalyst, E-TEK.

Stable Lithium Deposition Generated from Ceramic-Cross-Linked Gel Polymer Electrolytes for Lithium Anode

In this work, a composite gel electrolyte comprising ceramic cross-linker and poly(ethylene oxide) (PEO) matrix is shown to have superior resistance to lithium dendrite growth and be applicable to gel polymer lithium batteries. In contrast to pristine gel electrolyte, these nanocomposite gel electrolytes show good compatibility with liquid electrolytes, wider electrochemical window, and a superior rate and cycling performance. These silica cross-linkers allow the PEO to form the lithium ion pathway and reduce anion mobility. Therefore, the gel not only features lower polarization and interfacial resistance, but also suppresses electrolyte decomposition and lithium corrosion. Further, these nanocomposite gel electrolytes increase the lithium transference number to 0.5, and exhibit superior electrochemical stability up to 5.0 V. Moreover, the lithium cells feature long-term stability and a Coulombic efficiency that can reach 97% after 100 cycles. The SEM image of the lithium metal surface after the cycling test shows that the composite gel electrolyte with 20% silica cross-linker forms a uniform passivation layer on the lithium surface. Accordingly, these features allow this gel polymer electrolyte with ceramic cross-linker to function as a high-performance lithium-ionic conductor and reliable separator for lithium metal batteries.

Mesoporous SiO2/carbon hollow spheres applied towards a high rate-performance Li-battery anode

Mesoporous SiO2/C hollow spheres have been successfully synthesized via a one-step template process and carbonization of a mesoporous SiO2/poly(ethylene oxide)/phenolic formaldehyde resin hollow nanocomposite, and then evaluated as anode materials for lithium-ion batteries. The continuous carbon framework significantly led the SiO2/C hollow spheres to reach a high conductivity (3.9 × 10−4 S cm−1) compared with the SiO2 hollow spheres (<10−9 S cm−1), furthermore, the unique hollow nanostructure with a large volume interior and numerous mesopores plugged with carbon in the silica shell, could accommodate the volume variation and improve the structural strain for Li ion conduction, as well as allow rapid access of Li ions during charge–discharge cycling. For battery applications, at 100 mA g−1 charge/discharge rates, the reversible capacity of this mesoporous SiO2/C anode (624 mA h g−1) is over ten times higher than that of the SiO2 anode (61 mA h g−1). More specifically, even under the high discharge rate of 3000 mA g−1, this SiO2/C hollow nanostructure exhibits a specific capacity of 582 mA h g−1, featuring a high retention of more than 90% of its low discharge rate of 100 mA g−1. This demonstrates that the effective conduction of electrons through the continuous carbon network and the fast transport of Li ions through the nanoscale SiO2 shell significantly contribute to the high-rate performance.

The intensively enhanced conductivity of polyelectrolytes by amphiphilic compound doping

As pyrenesulfonic acid (PSA) is added to sulfonated poly(styrene-b-isoprene-b-styrene) (s-SIS), a novel effect on the conductivity of polyelectrolytes results. In this study, s-SIS was sulfonated to two different degrees to obtain s-SISL (ion-exchange capacity (IEC): 0.92) and s-SISH (IEC: 1.20). After PSA was added to the s-SISL, the proton conductivity increased significantly and reached an optimum at a PSA addition of 4% (s-SISL4.0), where the conductivity (0.6 × 10−2 S cm−1) was 6.0 times higher than s-SISL without PSA (0.1 × 10−2 S cm−1). Similarly, when PSA was added to s-SISH (IEC: 1.20), the proton conductivity achieved an optimum at a PSA addition of 2% (s-SISH2.0), at which point the proton conductivity (5.3 × 10−2 S cm−1) was 26 times that of s-SISH without PSA (0.2 × 10−2 S cm−1). From the TEM analyses of the s-SISH membrane in the presence of different PSA concentrations, this doping PSA effect can be interpreted by means of the interaction between the aromatic ring on the PSA and the aromatic ring on the hydrophobic polystyrene segments of the s-SIS block copolymer. This effect of doping an amphiphilic compound to polyelectrolytes to intensify the conductivity can be widely applied to numerous kinds of polyelectrolytes.