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Abstract In this study, a multi-phase, two-dimensional model that integrates the bipolar plate (BP) and gas diffusion layer (GDL) interfacial morphology was developed to understand the effects of this interface on mass, charge and heat transport and performance of polymer electrolyte fuel cells (PEFCs). Two different case studies were performed. The first case assumes a perfect contact interface between the BP and GDL, whereas in the second case, the BP|GDL interfacial layer was incorporated as a separate domain based on the measured BP|GDL morphology. In the BP|GDL interface case, the interfacial voids were assumed to be filled with liquid water to investigate the role of the interfacial voids. For both cases, the effects of different current densities on the in-plane temperature, saturation, and oxygen concentration distribution in the GDL were investigated. Simulations indicate that the Ohmic and concentration losses are increased due to the inclusion of the realistic BP|GDL interface. The electrical contact resistance contribution of the BP|GDL interface was predicted to be 3.8 mΩcm 2 . The saturation in the GDL was found to be higher for the BP|GDL interface case, which results in higher concentration losses. The temperature was predicted to be slightly higher for the BP|GDL interface case, which could be attributed to the higher thermal contact resistance due to the fewer contact regions at the interface.

Abstract Hybrid TiO2/SiO2 thin films deposited by material printing technique on flexible substrates were prepared, characterized and tested for solar photocatalytic disinfection. Effect of surface hydrophilicity/hydrophobicity of printed coatings on photocatalytic disinfection was studied by means of (i) drinking water contaminated with natural consortia of fecal bacteria (gram-negative: Escherichia coli and total coliforms; gram-positive: Enterococci), and (ii) seawater containing pathogenic gram-negative bacteria (Vibrio owensii, Vibrio alfacsensis and Vibrio harveyi). Inactivation of gram-negative bacteria in drinking water with fecal contamination by solar photocatalysis was slightly more efficient than solar disinfection, while for gram-positive bacteria similar efficiency was observed. These results, in combination with observed release of titanium from coatings (detected by means of inductively coupled plasma atomic emission spectrometer), indicate that TiO2/SiO2 needs further improvements for solar photocatalytic disinfection of drinking water. Efficiency of seawater disinfection towards gram-negative Vibrio spp. (Vibrio owensii, Vibrio alfacsensis and Vibrio harveyi) was significantly enhanced when TiO2/SiO2 coatings were used under natural solar light. Moreover, hydrophobic thin films led to faster Vibrio spp. inactivation as compared to hydrophilic ones, which was attributed to higher bacteria adhesion on hydrophobic coatings. However, decrease of photocatalytic activity of hydrophobic TiO2/SiO2 coatings was observed after ten experimental cycles mainly due to deposition of salts on the surface of photocatalyst. Generally, results of this study suggest that autochthonous bacteria such as Vibrio spp. in seawater are significantly more resistant to solar disinfection in comparison with not autochthonous bacteria such as Escherichia coli, total coliforms and Enterococci in contaminated drinking water.

Abstract To elucidate the gas generation mechanism due to electrolyte decomposition in commercial lithium-ion cells after long cycling, we developed a device which can accurately determine the volume of generated gas in the cell. Experiments on LixC6/Li1−xCoO2 cells using electrolytes such as 1 M LiPF6 in propylene carbonate (PC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are presented and discussed. In the nominal voltage range (4.2–2.5 V), compositional change due mainly to ester exchange reaction occurs, and gaseous products in the cell are little. Generated gas volume and compositional change in the electrolyte are detected largely in overcharged cells, and we discussed that gas generation due to electrolyte decomposition involves different decomposition reactions in overcharged and overdischarged cells.

Abstract When a lithium ion polymer battery (LiPB) is being cycled, one major cause for degradations is the irreversible side reactions between ions and solvent of electrolyte taking place at the surface of anode particles. SEM analysis of cycled battery cells has revealed that the deposits from the side reactions are dispersed not only on particles, but also between the composite anode and the separator. Thus, the solid electrolyte interface (SEI) becomes thicker and extra deposit layers are formed between composite anode and separator. Also, XPS analysis showed that the deposits are composed of Li 2 CO 3 , which is ionic conductive and electronic nonconductive. Based on the mechanisms and findings, we identified four degradation parameters, including volume fraction of accessible active anode, SEI resistance, resistance of deposit layer and diffusion coefficient of electrolyte, to describe capacity and power fade caused by the side reactions. These degradation parameters have been incorporated into an electrochemical thermal model that has been previously developed. The terminal voltage and capacity of the integrated model are compared with experimental data obtained for up to 300 cycles. Finally, the resistance of the deposit layer calculated by the model is validated against the thickness of the deposit layer measured by SEM.

Abstract The intention of the current flow model is to investigate the significance of bioconvection in stagnation point flow of third grade nanofluid containing motile microorganisms past a radiative stretching cylinder. The impacts of activation energy and stagnation point flow are also considered. In addition the behavior of thermophoresis diffusion and Brownian motion are observed. Nanofluid can be developed by dispersing the nanosized particles into the regular fluid. Nano-sized solid materials for example carbides, grephene, metal and alloyed CNT have been utilized for the preparation of nanofluid. Physically, regular fluids have low thermal proficiency. Therefore, nano-size particles can be utilized to enhance the thermal conductivity of the host fluid. Nanofluids have many features in hybrid power engine, heat transfer, and can be used in cancer therapy and medicine. The formulated system of flow problems are transformed into dimensionless coupled ordinary differential expressions system via appropriate transformation. The systems of converted governing expressions are computed numerically by employing well known bvp4c solver in MATLAB software. The outcomes of emerging physical flow parameters on the velocity profile, volumetric concentration of then nanoparticles, rescaled density of the motile microorganisms and nanofluid temperature are elaborated graphically and numerically. Furthermore, velocity of third-grade fluid intensifies for higher values of third-grade fluid parameter and mixed convection parameter while opposite behavior is detected for buoyancy ratio parameter and mixed convection parameter. Temperature distribution grows for higher estimation of temperature ratio parameter and Biot number. Higher amount of Prandtl number and Lewis number decreases the concentration of nanoparticles. Concentration of microorganisms reduces by growing the values of velocity ratio parameter and bioconvection Lewis number.

Background, Aim and Scope Societal assessment is advocated as one of the three pillars in the evaluation of, and movement toward, sustainability. As is the case with the well established LCA, and the emerging LCC, societal life cycle assessment should be developed in such as way as to permit relative product comparisons, rather than absolute analyses. The development of societal life cycle assessment is in its infancy, and important concepts require clarification including the handling of the more than two hundred social indicators. Therefore, any societal life cycle assessment methodology must explain why it is midpoint- or endpoint-based as well as its reasons to be complimentary with, or included within, life cycle assessment. Materials and Methods: A geographically specific midpoint based societal life cycle assessment methodology, which employs labour hours as an intermediate variable in the calculation has been developed and evaluated against an existing LCA comparing two detergents. The methodology is based on using an existing life cycle inventory and, therefore, has identical system boundaries and functional units to LCA. The societal life cycle assessment methodology, much like LCA, passes from inventory, through characterisation factors, to provide an ultimate result. In analogy to economics and cost estimation, societal life cycle assessment combines, into its statistics, both data as well as estimates, some of which are correlated to elements of the LCI. It focuses on the work hours required to meet basic needs.A geographically specific midpoint based societal life cycle assessment methodology, which employs labour hours as an intermediate variable in the calculation has been developed and evaluated against an existing LCA comparing two detergents. The methodology is based on using an existing life cycle inventory and, therefore, has identical system boundaries and functional units to LCA. The societal life cycle assessment methodology, much like LCA, passes from inventory, through characterisation factors, to provide an ultimate result. In analogy to economics and cost estimation, societal life cycle assessment combines, into its statistics, both data as well as estimates, some of which are correlated to elements of the LCI. It focuses on the work hours required to meet basic needs. Results: The societal life cycle assessment of an appended case study indicates that Detergent 2 generates, relative Detergent 1, approximately 20% less employment in Russia, 35% less in France, and approximately five times more in Canada and South Africa, the latter derived from its higher aluminium content. There is essentially no difference in the employment in the use country (Switzerland) nor in Morocco, where some of the waste disposal was assumed to take place. Discussion: Given that housing is more affordable, in terms of shelter units per labour hour, in South Africa, compared to Europe, it is, therefore, of no surprise that Detergent 2 provides a societal benefit in terms of housing. Detergent 2 does, however, result in dematerialization, in that its environmental impact is lower (LCI). Therefore, as less resources are employed and labour required, in extraction, production and transport, the societal benefits in health care, education and necessities, a grouped variable, are lower for Detergent 2. This is despite the employment shift away from Europe and to less 'developed' regions. Conclusions: The assessment of societal impacts involves several hundred specific indicators. Therefore, aggregation is, if not impossible, at least heavily value laden and, therefore, not recommended. The impact of a societal action, derived from a product purchase or otherwise, is also highly local. Given this, societal life cycle assessment, carried through to the midpoints, and based on an existing LCI, has been developed as a methodology. The results, for an existing LCA-detergent case, illustrate that societal life cycle assessment provides a means to investigate how policy and policy makers can be linked to sustainable development. The sensitivity analyses also clarify the decisions in regards to product improvement. Recommendations and Perspectives: The goal of societal life cycle assessment is not to make decisions, but rather to point out tradeoffs to decision- or policy-makers. This case, and the methodology that it is based on, permit such a comparison. Substituting Detergent 2 for Detergent 1 reduces resource use at the expense of an increase in atmospheric and terrestrial emissions. Access to housing is improved, though at the expense of education, health care and necessities. As a recommendation, one would look at the fact that the majority of indicators are superior for Detergent 2 relative to Detergent 1and seek to improve the aqueous emissions in Detergent 2 via a change in the formulation. An energy or fossil fuel substitution at the site of production could also improve the societal benefits in terms of education and health care. While societal life cycle assessment remains in its infancy, a methodology does exist. The field can, therefore, be viewed in a similar way to LCA in the early 1990s, with a need to validate, consolidate and, ultimately, built toward a standard. The contribution is aimed at contributing to such a discussion and therefore proposes that a societal life cycle assessment be LCI-derived, geographically specific, based on mid-points, and use employment as an intermediate variable.

The electrical conductivity of fluoride–chloride electrolytes for solar silicon electrolysis was investigated using impedance spectroscopy. Electrolytes containing potassium fluoride, potassium chloride, cesium chloride, potassium hexafluorosilicate, and silicon oxide were studied. The influence of the electrolyte composition on the electrical conductivity was examined.

PurposeThe purpose of this paper is to study a fractional grey model FAGM(1,1,tα) based on the GM(1,1,tα) model and the fractional accumulated generating operation, and then predict the national health expenditure, the government health expenditure and the out-of-pocket health expenditure of China.Design/methodology/approachThe presented univariate grey model is systematically studied by using the grey modelling technique, the fractional accumulated generating operation and the trapezoid approximation formula of definite integral. The optimal system parametersrandαare evaluated by the particle swarm optimisation algorithm.FindingsThe expressions of the time response function and the restored values of this model are derived. The GM(1,1), NGM(1,1,k,c) and GM(1,1,tα) models are particular cases of the FAGM(1,1,tα) model with deterministicrandα. Compared with other forecasting models, the results of the FAGM(1,1,tα) model have higher precision.Practical implicationsThe superiority of the new model has high potential to be used in the medicine and health fields and others. Results can provide a guideline for government decision making.Originality/valueThe univariate fractional grey model FAGM (1,1,tα) successfully studies the China’s health expenditure.

Many of the premature failures in the PEM fuel cells are attributed to crossover of the reactant gas from pinholes or through-the-thickness flaws in the membranes. The formation of these pinholes is not fully understood, although mechanical stress is often considered one of the major factors in their initiation and/or propagation. This paper reports evidence of pinhole failure from mechanical stress by cycling between wet and dry conditions in a normally built single 50cm2 fuel cell. In an effort to understand the source of the mechanical stress, to quantify the magnitude, and to correlate its role in membrane failure, a membrane stress model based on linear viscoelastic theory was developed. The effects of temperature, water content, and time are accounted for in the membrane stress model. To satisfy the inputs for the membrane model and to characterize the mechanical behavior of the polymer electrolyte membrane, a series of experiments was performed. Using commercially available Nafion® NR111 membrane as a model material, swelling of 15% and shrinkage of 4% were found from a hydration and de-hydration cycle. Data on elastic moduli versus relative humidity showed discontinuity at the vapor and liquid water transition. We also found that creep compliance master curves can be obtained by double-shifting the compliance curves according to the time-temperature-moisture superposition principle, which significantly simplifies the modeling effort. Combining data on hygro-expansion, elastic moduli, and creep compliance data through the membrane stress model, it was found that the de-hydration process induces significant stress in the membrane. Due to fluctuations in fuel cell operating conditions, the membrane and the associated components are subject to mechanical fatigue which may mechanically degrade the membrane of PEM fuel cells and eventually lead to pinhole formation.