Construction of ultrathin MnO2 decorated graphene/carbon nanotube nanocomposites as efficient sulfur hosts for high-performance lithium-sulfur batteries.

Lithium-sulfur batteries are attracting significant attention due to their high theoretical specific capacity and low cost. However, their applications are hindered by the poor conductivity of sulfur and capacity fading caused by the shuttle effect. Here, ultrathin manganese dioxide decorated graphene/carbon nanotube nanocomposites are designed as sulfur hosts to suppress the shuttle effect and improve the adsorption efficiency of polysulfides. The graphene/carbon nanotube hybrids, with extraordinary conductivity and large surface area, function as excellent channels for electron transfer and lithium ion diffusion. The ultrathin manganese dioxide nanosheets enable efficient chemical interaction with polysulfides and promote the redox kinetics of polysulfides. As a result, an ultrathin manganese dioxide decorated graphene/carbon nanotube sulfur composite with high sulfur content (81.8 wt%) delivers a high initial specific capacity of 1015.1 mA h g-1 at a current density of 0.1C, high coulombic efficiency approaching 100% and high capacity retention of 84.1% after 100 cycles. The nanocomposites developed in this work have promising applications in high-performance lithium-sulfur batteries.

Fluorinated graphene/sulfur hybrid cathode for high energy and high power density lithium primary batteries.

It is a great challenge to obtain high performance carbon fluoride (CF x ) cathodes with high specific capacity and good rate performance due to the electronic conductivity of CF x being known to decrease with an increase in the specific capacity. Herein, we propose a novel fluorinated graphene (FG)/sulfur hybrid cathode to enhance both the energy density and power density of lithium/carbon fluoride (Li/CF x ) batteries. Impressive enhancements of the specific capacity, discharge voltage, and rate capability are demonstrated with the novel FG/sulfur hybrid cathode. In comparison with the pristine FG cathode, the hybrid cathode exhibits higher electrochemical activity, lower overpotential, and faster ion transfer over the main discharge range. Furthermore, when the melt-diffusion method is used to prepare the hybrid cathode, the uncommon monoclinic sulfur is presented under ambient temperature. A significant synergistic effect which reduces the reaction resistance effectively is demonstrated with the presence of monoclinic sulfur, leading to the highest energy density of 2341 W h kg-1 and a power density up to 13 621 W kg-1 at 8.0 A g-1. Our results are expected to introduce a new generation of high energy and high power density lithium primary cells, based on a simple and effective strategy employing FG/S hybrid cathodes.

A gemini quaternary ammonium poly (ether ether ketone) anion-exchange membrane for alkaline fuel cell: design, synthesis, and properties.

To reconcile the tradeoff between conductivity and dimensional stability in AEMs, a novel Gemini quaternary ammonium poly (ether ether ketone) (GQ-PEEK) membrane was designed and successfully synthesized by a green three-step procedure that included polycondensation, bromination, and quaternization. Gemini quaternary ammonium cation groups attached to the anti-swelling PEEK backbone improved the ionic conductivity of the membranes while undergoing only moderate swelling. The grafting degree (GD) of the GQ-PEEK significantly affected the properties of the membranes, including their ion-exchange capacity, water uptake, swelling, and ionic conductivity. Our GQ-PEEK membranes exhibited less swelling (≤ 40 % at 25-70 °C, GD 67 %) and greater ionic conductivity (44.8 mS cm(-1) at 75 °C, GD 67 %) compared with single quaternary ammonium poly (ether ether ketone). Enhanced fuel cell performance was achieved when the GQ-PEEK membranes were incorporated into H2 /O2 single cells.

Nonionic surfactant greatly enhances the reductive debromination of polybrominated diphenyl ethers by nanoscale zero-valent iron: mechanism and kinetics.

Nanoscale zero-valent iron (nZVI) has been considered as an effective agent for reductive debromination of polybrominated diphenyl ethers (PBDEs). But the high lipophilicity of PBDEs will hinder their debromination owing to the inefficient contact of PBDEs with nZVI. In this study, different ionic forms of surfactants were investigated aiming to promote PBDE debromination, and the beneficial effects of surfactant were found to be: nonionic polyethylene glycol octylphenol ether (Triton X-100, TX)>cationic cetylpyridinium chloride (CPC)>anionic sodium dodecyl benzenesulfonate (SDDBS). Except for with SDDBS, the promotion effect for PBDE debromination was positively related to the surfactant concentrations until a critical micelle concentration (CMC). The debromination process of octa-BDE and its intermediates could be described as a consecutive reaction. The corresponding rate constants (k) for the debromination of parent octa-BDE (including nona- to hepta-BDEs), the intermediates hexa-, penta-, and tetra-BDEs are 1.24 × 10(-1) h(-1), 8.97 × 10(-2) h(-1), 6.50 × 10(-2) h(-1) and 2.37 × 10(-3) h(-1), respectively.

[Reductive debromination of polybrominated diphenyl ethers in aquifier by nano zero-valent iron: debromination kinetics and pathway].

Nano-zerovalent iron (nZVI) approach is effective in the debromination of polybrominated biphenyl ethers (PBDEs). The kinetics and degradation pathway are the key issues to understand the PBDEs degradation mechanisms. In this study, nZVI, synthesized through liquid phase reduction method, coupled with Triton X-100, could completely debrominate the highly brominated congeners of a commercial octa-BDEs mixture within 46 h. The debromination of octa-BDEs could be described by means of pseudo-first-order kinetics with the reaction constant (k) of 0.106 h(-1). In case of lacking the PBDE standards, an effective approach has been developed to determine the unknown PBDE congeners using the quantitative-structure retention relationship (QSRR) model. The retention time of all 39 PBDE congeners in a standard mixture was firstly analyzed with gas chromatography coupled with an electron capture detector (GC-ECD), and the relative retention time (RRT) for each standard was obtained after normalizing the RT by the average RT of BDE47 and BDE183. Then a QSRR model was developed by fitting the RRT of each PBDE congener and its specific RRT index. The debromination products of octa-BDEs were identified using this QSRR model and the degradation pathway of octa-BDEs was elucidated. The results showed that in the stepwise reductive debromination process of PBDEs by nZVI, meta-debromin was facile to be degraded.

Evaluating the interfacial reaction kinetics of the bipolar membrane interface in the bipolar membrane fuel cell.

A reaction kinetic model of the bipolar membrane interface in the bipolar membrane fuel cell (BPMFC) was proposed based on the p-n junction theory and chemical reaction kinetics. It verified the self-humidification feasibility of the BPMFC successfully.

Nernst-ping-pong model for evaluating the effects of the substrate concentration and anode potential on the kinetic characteristics of bioanode.

Understanding the electron-transfer mechanism and kinetic characteristics of bioanodes is greatly significant to enhance the electron-generating efficiencies in bioelectrochemical systems (BESs). A Nernst-ping-pong model is proposed here to investigate the kinetics and biochemical processes of bioanodes in a microbial electrolysis cell. This model can accurately describe the effects of the substrate (including substrate inhibition) and the anode potential on the current of bioanodes. Results show that the half-wave potential positively shifts as the substrate concentration increases, indicating that the rate-determining steps of anodic processes change from substrate oxidation to intracellular electron transport reaction. The anode potential has negligible effects on the enzymatic catalysis of anodic microbes in the range of -0.25 V to +0.1 V vs. a saturated calomel electrode. It turns out that to reduce the anodic energy loss caused by overpotential, higher substrate concentrations are preferred, if the substrate do not significantly and adversely affect the output current.

Enhancement of hydrogen production in a single chamber microbial electrolysis cell through anode arrangement optimization.

Reducing the inner resistances is crucial for the enhancement of hydrogen generation in microbial electrolysis cells (MECs). This study demonstrates that the optimization of the anode arrangement is an effective strategy to reduce the system resistances. By changing the normal MEC configuration into a stacking mode, namely separately placing the contacted anodes from one side to both sides of cathode in parallel, the solution, biofilm and polarization resistances of MECs were greatly reduced, which was also confirmed with electrochemical impedance spectroscopy analysis. After the anode arrangement optimization, the current and hydrogen production rate (HPR) of MEC could be enhanced by 72% and 118%, reaching 621.3±20.6 A/m3 and 5.56 m3/m3 d respectively, under 0.8 V applied voltage. A maximum current density of 1355 A/m3 with a HPR of 10.88 m3/m3 d can be achieved with 1.5 V applied voltage.