Advanced Materials Research Vols. 724-725

Abstract: A series of sulfonated polyphosphazene-organic montmorillonite hybrid membranes for direct methanol fuel cells (DMFCs) were prepared. The structure and characteristics of the obtained membranes were studied by testing their X-ray diffraction (XRD), water uptake, water swelling ratio, proton conductivity, thermal properties, methanol permeability and mechanical properties. The morphological analysis of the composite membranes indicated that the organic montmorillonite was uniformly distributed throughout the polymer matrix. Compared to the native sulfonated polyphosphazene membranes, the hybrid membranes showed better mechanical properties and selectivity for proton ions over methanol. The selectivity indicates that polyphosphazene-montmorillonite membranes may be promising electrolyte candidate for direct methanol fuel cells.

Abstract: A visible light photocatalytic system consisting of Eosin Y containing trace vitamin B₁₂ (VB₁₂) as a light harvesting unit, multiwalled carbon nanotubes (MWCNTs) as an electron transfer channel and CuO as a hydrogen evolution center (abbreviated to Eosin Y/VB₁₂-MWCNTs-CuO) was prepared on the basis of the synergistic effect between Eosin Y and VB₁₂ under visible light irradiation. The Eosin Y/VB₁₂-MWCNTs-CuO system exhibits a higher photocatalytic activity of hydrogen evolution than the Eosin Y-MWCNTs-CuO system. The improvement of the photocatalytic activity is probably due to the effective transfer of photogenerated electrons and stabilization of VB₁₂ to excited Eosin Y.

Abstract: It is the objective of this study to present the 3-dimensional comprehensive computational fuel cell dynamics (CFCD) model of a scaled-down single PEM cell featuring a nominal active surface of 0.0004 m² for both conventional and serpentine flow field designs. The performance of these two designs are then analysed and compared keeping both anode and cathode inlet gases fully humidified. Then the parallel flow field was modelled under different inlet gas relative humidities (RH_a/RH_c) representing saturated, moderate, and dry conditions to observe the gain in cell performance. The higher pressure drop of the serpentine flow-field was demonstrated and the magnitude of which might seem to be negligible in the range of 100 Pascal. The simulation results show that a parallel flow-field design with appropriate humidity level can compete with the serpentine counterpart and gives considerably lower pressure drop across the cell. With a grid-independency analysis, it is suggested for the computational power available, the percentage error of important variables (species concentration and averaged current density) between the reference and finer mesh is negligible (< 3%) and the solution time is considerably less.

Abstract: Dual-chamber microbial fuel cells (MFCs) were established to study the effect of seed sludge, carbon sources, buffering solution and stirring on power generation performance. Scanning electron microscope (SEM) and polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) technologies were used to investigate the spatial distribution characteristics of bacterial community. The results showed that the MFC feeding with lactic acid obtained 0.57V of electromotive force, and 1.57 W/m³ of volumetric power density. It reached 0.62V and 2.07 W/m³ when the carbon source was changed to acetic acid. Compared with anaerobic sludge, aerobic sludge had higher maximum voltage and longer high voltage duration. The stirring and the adding buffer solution improved electricity generation. SEM and DGGE profiles indicated that a large number of bacilli were tightly bound to the anode surface. Microbial community structure on the membrane surface was more similar to suspended sludge than sediment and seed sludge. In conclusion, MFCs perform better with incubating aerobic sludge, feeding acetic acid, adding PBS buffer (50mmol/L) and stirring.

Abstract: The reaction thermodynamics of sorption enhanced steam reforming (SESR) of acetic acid as a model compound of bio-oil for hydrogen production were investigated and contrasted with acetic acid steam reforming (SR). The most favorable temperature for SR is approximately 650 °C. However, the optimum temperature for SESR is around 550 °C, which is about 100 °C lower than that for SR. The highest hydrogen concentration from SR is only 67%, which is below the basic requirement of hydrogen purity for fuel cells. In SESR, hydrogen purities are over 99% in 500-550 °C with a calcium oxide to acetic acid molar ratio (CAMR) of 4 and a water to acetic acid molar ratio (WAMR) greater than 6. The results show that hydrogen production from sorption enhanced steam reforming of acetic acid should be a promising direction.

Abstract: The hydrolysis reaction of sodium borohydride (NaBH₄) can generate highly pure hydrogen. In this paper, the Co-Y-B catalyst is prepared using the simple chemical reduction method. Its catalytic reactivity is investigated for different NaBH₄ concentrations, NaOH concentrations, the catalyst amounts and the reacting temperatures. When the Y/(Co+Y) mole ratio in catalyst arrives at 40 %, the catalysts show the best catalytic ability. There is an optimum range, around 8 wt.% for NaBH₄ concentration and also 8 wt.% for NaOH concentration, respectively, in which the hydrogen generation rate performed best. Both the large catalyst amount and the high reacting temperature are beneficial to promote the hydrogen generation rate. Structural characterizations of the fibrillar catalysts are carried out in SEM and XRD analysis. The value of activation energy for the hydrogen generation process is calculated to be 48.02 kJ/mol and it compares favorably with some other previously reported values.

Abstract: The demand for ever more functions and higher processing speed in mobile devices has raised the energy consumption of such devices beyond the capability of low-energy-density and long-charging-hour lithium batteries. As an energy source, fuel cells are much better than lithium batteries due to their higher energy density and faster charging speed. Of the many types of fuel cell, the DBFC appears to be the best alternative for mobile devices because of its higher energy density, better performance at low temperature and more compact structure. This research will study such DBFC parameters as the proportions of membranes, catalyst, fuel and temperature in order to achieve the best result for supplying power to mobile devices, and compare these characteristics with the popular DMFC to further develop the most suitable fuel cell for portable electronic products.

Abstract: This paper focus on the mass transportation in integrited μDMFC stack. The situation that simply increasing the integrity of stack will deteriorate the performance of single cell, was confirmed by implementing and testing a highly-integrated μDMFC power supply system. Based on works above, a centrual-inlet μDMFC stack using new structure of mass transportation was fabricated. To prevent a long serial path or highly paralleled paths, the methanol and O₂ were supplied from central-inlet and transported through a serial-parallel-hybrid mass transportation path. Compareing with the traditional structure, the new stack has about 25% performance enhancing and considerable stability improvement.

Abstract: The Li-ion battery has high discharge voltage, long cycle life, good safety performance, no memory effect and other advantages. So it has being more and more used and concerned. This paper reviews various aspects of recent research and developments in Li-ion battery prognostics and health monitoring,and summarizes the techniques,algorithms and models used for state-of-charge estimation,voltage estimation,capacity estimation and remaining-useful-life prediction. Especially for state-of-charge estimation, this paper summed up many methods, such as current integration method, open circuit voltage method, Fuzzy logic, Autoregressive moving average model, Electrochemical impedance spectroscopy, Support vector machine and support vector machine based on Extended Kalman filter. And their advantages and disadvantages are summarized.

Abstract: The power lithium-ion battery with its high specific energy, high theoretical capacity and good cycle-life is a prime candidate as a power source for electric vehicles (EVs) and hybrid electric vehicles (HEVs). Sacurity is especially important for large-scale lithium-ion batteries, especially the thermal analysis is essential for their development and design. Mathematical model and thermal model for Li-ion battery were built to analyze the effects of discharge rate on the peak temperature and on the homogeneity of temperature field, and to compare the calculated and the simulated results.