PEM Fuel Cell performance at sub-zero temperatures

In this work a study of the performance of a low power fuel cell at sub-freezing temperatures has been undertaken. Knowledge in this area is still scarce. After global characterization of the stack on a wide range of temperatures and relative humidity’s the behaviour at negative temperatures (-5ºC -10ºC, -15ºC) has been established. Furthermore, performance was evaluated after the cell was submitted to cycles from -25ºC to + 25ºC. At the end of 10 cycles only marginal loss in performance was registered, when testing at + 2.5ºC and + 25ºC. On the basis of the obtained results a strategy for start-up and shut-down has been designed in order to be implemented for operation at low temperatures. A failure analysis of the membrane and catalyst layers and GDLs is under way in order to evaluate material degradatio

Solar hydrogen production from aqueous solutions of ethanol at near ambient temperatures

Nanostructured semi-conductor materials based on titanium dioxide, with effective photo-catalytic properties under UV illumination, were synthesized using sol-gel technology and characterized by X-Ray diffraction and scanning electron microscopy, with the objective of studying the photo-catalytic hydrogen production from water. The need to decrease the electron-hole recombination rate was accounted for by metal doping and the addition of ethanol as a hole trap. Aqueous suspensions of the semiconductor powders, with noble metal loadings (Pt) of 1.5 wt% were used and the effect of solution pH and temperature (20-70ºC) on hydrogen production were studied, for a selected catalyst concentration. Hydrogen production rates were found to be linear with solution temperature with values larger than published literature data

Gravitational radiation in d>4 from effective field theory

Some years ago, a new powerful technique, known as the Classical Effective Field Theory, was proposed to describe classical phenomena in gravitational systems. Here we show how this approach can be useful to investigate theoretically important issues, such as gravitational radiation in any spacetime dimension. In particular, we derive for the first time the Einstein-Infeld-Hoffman Lagrangian and we compute Einstein's quadrupole formula for any number of flat spacetime dimensions.Comment: 32 pages, 10 figures. v2: Factor in eq. (3.11) fixed. References adde

Fuel Starvation: irreversible degradation mechanisms in PEM Fuel Cells

PEM fuel cell operates under very aggressive conditions in both anode and cathode. Failure modes and mechanism in PEM fuel cells include those related to thermal, chemical or mechanical issues that may constrain stability, power and lifetime. In this work, the case of fuel starvation is examined. The anode potential may rise to levels compatible with the oxidization of water. If water is not available, oxidation of the carbon support will accelerate catalyst sintering. Diagnostics methods used for in-situ and ex-situ analysis of PEM fuel cells are selected in order to better categorize irreversible changes of the cell. Electrochemical Impedance Spectroscopy (EIS) is found instrumental in the identification of fuel cell flooding conditions and membrane dehydration associated to mass transport limitations / reactant starvation and protonic conductivity decrease, respectively. Furthermore, it indicates that water electrolysis might happen at the anode. Cross sections of the membrane catalyst and gas diffusion layers examined by scanning electron microscopy indicate electrode thickness reduction as a result of reactions taking place during hydrogen starvation. Catalyst particles are found to migrate outwards and located on carbon backings. Membrane degradation in fuel cell environment is analyzed in terms of the mechanism for fluoride release which is considered an early predictor of membrane degradation

Hydrogen production from sodium borohydride on a Ni-Ru catalyst : an electrochemical study

Previous work by the authors has demonstrated a high rate and high yield hydrolysis of sodium borohydride, in the presence of a Ni-Ru catalyst synthesized by wet chemistry. The catalyst has been fully characterized and utilized more than 300 times exhibiting high stability and durability. In this work, results of an electrochemical study are reported using the powder catalyst supported on a Ni foam in order to measure the open circuit potential during hydrogen production and to study the reaction using voltammetry and ac impedance. Production rates were as high as 10 Lmin-1gcat -1 at 65ºC. Electrochemical studies indicated that the hydrogen evolution mechanism corresponds to a Volmer- Heyrovsky type, suggested by a Tafel slope of 117 mVdec-1. Tafel region potentials are in agreement with values found for hydrolysis at the open circuit. The Langmuir-Hinshelwood mechanism explains the hydrolysis of sodium borohydride using a Ni-Ru catalyst. The role of Ni and Ru is briefly discussed

Optimization of production of extracellular polymeric substances by Arthrobacter viscosus and their interaction with a 13X zeolite for the biosorption of Cr(VI)

In this work we aimed to optimize the production of extracellular polymeric substances (EPS) by an Arthrobacter viscosus biofilm supported on 13X zeolite to be used in the biosorption of Cr(VI). The optimization parameters were agitation rate, work volume, pH and glucose concentration. Following the optimization of EPS production, the biofilm was used in the biosorption of hexavalent Cr from liquid solutions. Differences between the use of dead or active biomass and between the performance of zeolite in powder or in pellet form were also studied. The optimized EPS production allowed values of metal uptake between 2.72 mg/gbiosorbent and 7.88 mg/gbiosorbent for initial Cr(VI) concentrations of 20–60 mg/L. For an initial concentration of 20 mg/L, the optimal conditions of EPS production allowed an increase of 10% on the removal percentage of total Cr, and the use of zeolite as a powder rather than the pelleted form produced an increase of 46.5% in the removal percentage. For the initial concentration of 60 mg/L, the use of active biomass compared to dried biomass allowed a reduction of the time required for the total removal of Cr(VI) from 20 to 13 days.The authors would like to gratefully acknowledge the financial support of this project by the Fundacao para a Ciencia e Tecnologia, Ministerio da Ciencia e Tecnologia, Portugal. Bruna Silva and Hugo Figueiredo thank FCT for a PhD grant and Cristina Quintelas thanks FCT for a Post Doctoral grant

Prevalence and pattern of cognitive impairment in rural and urban populations from Northern Portugal

<p>Abstract</p> <p>Background</p> <p>Despite worldwide recognition of the burden of dementia, no epidemiological data is yet available in Portugal. The objective of this study is to estimate the prevalence and describe the pattern of cognitive impairment with dementia or no dementia (CIND) in rural and urban populations from Northern Portugal.</p> <p>Methods</p> <p>Two random samples of residents aged 55 to 79 years in rural and urban communities were drawn from the health centres registries to be screened for cognitive impairment. The screening criteria for dementia were an abnormal Mini-Mental State Examination (MMSE) score or a Blessed Dementia Scale score. After excluding those who tested positive for dementia, cut-off points for CIND were set at 1 standard deviation below the mean of the MMSE according to educational level. All those who screened positive either for dementia or CIND were examined by a neurologist for establishing a definitive diagnosis.</p> <p>Results</p> <p>The prevalence of cognitive impairment was higher in rural than in urban populations, 16.8% (95% CI: 14.3-19.8%) vs. 12.0% (95%CI: 9.3-15.4%), with a rural/urban prevalence ratio (PR) of 2.16 (95% CI: 1.04-4.50) in the eldest and 2.19 (95% CI: 1.01-4.76) in persons with vascular risk factors. The prevalence of dementia was 2.7% (95% CI: 1.9-3.8%) with a rural/urban PR = 2.1 and the prevalence of CIND was 12.3% (95% CI: 10.4-14.4%) and PR = 1.3. The prevalence of dementia increases exponentially with age and in those with cerebrovascular disease or other comorbid conditions while the prevalence of CIND, besides these factors, is also higher in persons with low levels of education or vascular risk factors. Alzheimer's and vascular disease were equally likely aetiologies of dementia (38.7%), the later more common in men PR(F:M = 0.3) as opposed to the former PR(F:M = 2.0). Vascular CIND, associated either with cerebrovascular disease or vascular risk factors was more frequent (39.7%) then depression (18.4%) or any other aetiology.</p> <p>Conclusions</p> <p>The prevalence of cognitive impairment is higher in rural compared with urban populations. This is shown in the synergy between age and rurality, with the rural/urban prevalence ratio increasing with age. In this relatively young population from Northern Portugal, cerebrovascular disease as well as vascular risk factors account for 48% of overall cognitive impairment.</p