Mark H. Engelhard

A Soft Approach to Encapsulate Sulfur: Polyaniline Nanotubes for Lithium‐Sulfur Batteries with Long Cycle Life

A novel vulcanized polyaniline nanotube/sulfur composite was prepared successfully via an in situ vulcanization process by heating a mixture of polyaniline nanotube and sulfur at 280 °C. The electrode could retain a discharge capacity of 837 mAh g(-1) after 100 cycles at a 0.1 C rate and manifested 76% capacity retention up to 500 cycles at a 1 C rate.

Facile and controllable electrochemical reduction of graphene oxide and its applications

Graphene oxide is electrochemically reduced which is called electrochemically reduced graphene oxide (ER-G). ER-G is characterized with scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. The oxygen content is significantly decreased and the sp2 carbon is restored after electrochemical reduction. ER-G exhibits much higher electrochemical capacitance and cycling durability than carbon nanotubes (CNTs) and chemically reduced graphene; the specific capacitance measured with cyclic voltammetry (20 mV s−1) is ∼165, ∼86, and ∼100 F g−1 for ER-G, CNTs, and chemically reduced graphene, respectively. The electrochemical reduction of oxygen and hydrogen peroxide are greatly enhanced on ER-G electrodes as compared with CNTs. ER-G has shown promising features for applications in energy storage, biosensors, and electrocatalysis.

High rate and stable cycling of lithium metal anode

Lithium metal is an ideal battery anode. However, dendrite growth and limited Coulombic efficiency during cycling have prevented its practical application in rechargeable batteries. Herein, we report that the use of highly concentrated electrolytes composed of ether solvents and the lithium bis(fluorosulfonyl)imide salt enables the high-rate cycling of a lithium metal anode at high Coulombic efficiency (up to 99.1%) without dendrite growth. With 4 M lithium bis(fluorosulfonyl)imide in 1,2-dimethoxyethane as the electrolyte, a lithium|lithium cell can be cycled at 10 mA cm−2 for more than 6,000 cycles, and a copper|lithium cell can be cycled at 4 mA cm−2 for more than 1,000 cycles with an average Coulombic efficiency of 98.4%. These excellent performances can be attributed to the increased solvent coordination and increased availability of lithium ion concentration in the electrolyte. Further development of this electrolyte may enable practical applications for lithium metal anode in rechargeable batteries.

Functionalized Graphene Oxide as a Nanocarrier in a Multienzyme Labeling Amplification Strategy for Ultrasensitive Electrochemical Immunoassay of Phosphorylated p53 (S392)

P53 phosphorylation plays an important role in many biological processes and might be used as a potential biomarker in clinical diagnoses. We report a new electrochemical immunosensor for ultrasensitive detection of phosphorylated p53 at Ser392 (phospho-p53(392)) based on graphene oxide (GO) as a nanocarrier in a multienzyme amplification strategy. Greatly enhanced sensitivity was achieved by using the bioconjugates featuring horseradish peroxidase (HRP) and p53(392) signal antibody (p53(392)Ab(2)) linked to functionalized GO (HRP-p53(392)Ab(2)-GO) at a high ratio of HRP/p53(392)Ab(2). After a sandwich immunoreaction, the HRP-p53(392)Ab(2)-GO captured onto the electrode surface produced an amplified electrocatalytic response by the reduction of enzymatically oxidized thionine in the presence of hydrogen peroxide. The increase of response current was proportional to the phospho-p53(392) concentration in the range of 0.02-2 nM with the detection limit of 0.01 nM, which was 10-fold lower than that of the traditional sandwich electrochemical measurement for p53(392). The amplified immunoassay developed in this work shows acceptable stability and reproducibility, and the assay results for phospho-p53(392) spiked in human plasma also show good recovery (92-103.8%). This simple and low-cost immunosensor shows great promise for detection of other phosphorylated proteins and clinical applications.

Polyelectrolyte-Induced Reduction of Exfoliated Graphite Oxide: A Facile Route to Synthesis of Soluble Graphene Nanosheets

Here we report that poly(diallyldimethylammonium chloride) (PDDA) acts as both a reducing agent and a stabilizer to prepare soluble graphene nanosheets from graphite oxide. The results of transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, atomic force microscopy, and Fourier transform infrared indicated that graphite oxide was successfully reduced to graphene nanosheets which exhibited single-layer structure and high dispersion in various solvents. The reaction mechanism for PDDA-induced reduction of exfoliated graphite oxide was proposed. Furthermore, PDDA facilitated the in situ growth of highly dispersed Pt nanoparticles on the surface of graphene nanosheets to form Pt/graphene nanocomposites, which exhibited excellent catalytic activity toward formic acid oxidation. This work presents a facile and environmentally friendly approach to the synthesis of graphene nanosheets and opens up a new possibility for preparing graphene and graphene-based nanomaterials for large-scale applications.

Controlling SEI Formation on SnSb-Porous Carbon Nanofibers for Improved Na Ion Storage

Porous carbon nanofiber (CNF)-supported tin-antimony (SnSb) alloys are synthesized and applied as a sodium-ion battery anode. The chemistry and morphology of the solid electrolyte interphase (SEI) film and its correlation with the electrode performance are studied. The addition of fluoroethylene carbonate (FEC) in the electrolyte significantly reduces electrolyte decomposition and creates a very thin and uniform SEI layer on the cycled electrode surface, which an promote the kinetics of Na-ion migration/transportation, leading to excellent electrochemical performance.

Degradation Mechanisms of La-Sr-Co-Fe-O3 SOFC Cathodes

The long-term stability of anode-supported YSZ electrolyte SOFCs utilizing (La0.6Sr0.4)0.98Co0.2Fe0.8O3-? (LSCF-6428) cathodes was assessed. Samples tested for 500 hours at 750 C and 0.7V indicated ?50% degradation. While scanning electron microscopy (SEM) and energy dispersive x-ray (EDX) analysis indicated no obvious microstructural or chemical phenomena that could explain the high degradation, x-ray photon spectroscopy (XPS) revealed that enrichment of Sr at the cathode-electrolyte and cathode-current collector interfaces was at least partially responsible for the observed degradation.

Manipulating surface reactions in lithium–sulphur batteries using hybrid anode structures

Lithium-sulphur batteries have high theoretical energy density and potentially low cost, but significant challenges such as severe capacity degradation prevent its widespread adoption. Here we report a new design of lithium-sulphur battery using electrically connected graphite and lithium metal as a hybrid anode to control undesirable surface reactions on lithium. Lithiated graphite placed in front of the lithium metal functions as an artificial, self-regulated solid electrolyte interface layer to actively control the electrochemical reactions and minimize the deleterious side reactions, leading to significant performance improvements. Lithium-sulphur cells incorporating this hybrid anodes deliver capacities of >800 mAh g(-1) for 400 cycles at a high rate of 1,737 mA g(-1), with only 11% capacity fade and a Coulombic efficiency >99%. This simple hybrid concept may also provide scientific strategies for protecting metal anodes in other energy-storage devices.

Supercritical fluid synthesis and characterization of catalytic metal nanoparticles on carbon nanotubes

A rapid, convenient and environmentally benign method has been developed for the fabrication of metal nanoparticle–multiwall carbon nanotube (MWCNT) composites. Nanoparticles of palladium, rhodium and ruthenium are deposited onto functionalized MWCNTs through a simple hydrogen reduction of metal–β-diketone precursors in supercritical carbon dioxide, and are characterized by transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) analyses. These highly dispersed nanoparticles, with a narrow range of size distribution and good adhesion on MWCNT surfaces, are expected to exhibit promising catalytic properties for a variety of chemical reactions. Preliminary experiments demonstrate that Pd nanoparticles supported on MWCNTs are effective catalysts for hydrogenation of olefins in carbon dioxide. The Pd nanoparticle–MWCNT composite also shows a high electrocatalytic activity in oxygen reduction for potential fuel cell application.

Hollow core–shell structured porous Si–C nanocomposites for Li-ion battery anodes

Hollow core–shell structured porous Si–C nanocomposites with void space up to tens of nanometres are designed to accommodate the volume expansion during lithiation for high-performance Li-ion battery anodes. An initial capacity of ∼760 mA h g−1 after formation cycles (based on the entire electrode weight) with ∼86% capacity retention over 100 cycles is achieved at a current density of 1 A g−1. Good rate performance is also demonstrated.