1,721,162 research outputs found
Modelling analysis of heterogeneity of ageing in high temperature polymer electrolyte fuel cells: insight into the evolution of electrochemical impedance spectra
No full textDegradation of catalyst electrochemical active surface is a major issue that hinders polymer electrolyte fuel cells commercialization. Several degradation mechanisms that have been reported in the literature are known to result in heterogeneity of ageing, whose effects on performance loss have not been previously investigated. In this work experimental and theoretical methodologies are combined to provide an insight between the effects of heterogeneity of ageing and the evolution of electrochemical impedance spectra. Experimental results collected during a 6000 hours degradation test indicate an increase of cathode charge transfer and mass transport resistances, consistently with cyclic voltammetry that reveals about 60% loss of cathode catalyst active surface. A physical based model is developed and validated to demonstrate that uniform cathode ageing does not to affect the evolution of impedance spectra. On the other side, it is shown that non-uniform ageing of cathode active area improves the agreement with experimental data. The evolution of the polarization curves and impedance spectra recorded during 6000 hours degradation test is critically discussed by including heterogeneity of ageing
Effects of flooding on DMFC performance: 1D+1D model development and experimenatl validation
No full textPlayers at home: Physical activity and quality of life in 12–17 years-old football (soccer) players during the Covid-19 lockdown
No full textBACKGROUND: Aggressive preventive actions were required to face the Covid-19 outbreak. However, from March 2020 on, many healthy youth football players have seen their sporting activities disrupted by the restrictions on outdoor exercise. This study describes physical activity and quality of life during April 2020 lockdown of young people participating in organized football. METHODS: 1163 young football players aged 12–17 years (185 girls) completed a web-based questionnaire including the Youth Physical Activity and the Youth Quality of Life-Short Form Questionnaires; information on lifestyle and football-specific activity were also collected. Differences according to sex, urban/rural context and élite/non-élite club level were tested using a 2 [Formula: see text] 2 [Formula: see text] 2 MANOVA (age considered as a covariate). RESULTS: We found that: (i) on average, exposure to football accounted for 3.2 hours/week, was higher in élite clubs and changed in nature, being mainly performed individually; 19% of participants practiced football <1 hour/week; (ii) only 56% of the participants reported 7 or more hours/week of moderate-to-vigorous physical activity, which decreased with age and changed according to the geographical context; (iii) perceived quality of life was lower in youth playing for non-elite clubs and in older girls; (iv) coaches, rather that official initiatives, were the primary source of football exercises practiced at home. CONCLUSION: A status of limited physical activity emerged; this might lead to deconditioning and susceptibility to injuries when football could restart. Governing bodies, football Associations and clubs could exploit these results to take informed decisions and support evidence-based interventions during and after the Covid-19 pandemic
Physical modelling of cathode impedance in low temperature fuel cells
No full textLow temperature Polymer Electrolyte Membrane (PEM) fuel cells are a promising energy source for stationary and automotive applications, mainly due to high efficiency and low emissions. However the widely use of this technology is still hindered by some technological issues, among which severe cathode flooding and degradation. The most common technique to monitor system internal losses during real operation is the Electrochemical Impedance Spectroscopy (EIS). Despite the potentiality of this in-situ measurement technique, the interpretation of impedance data is still object of discussion in the literature and physical modelling becomes crucial to analyze experiments.
In this work, the development of a physically based model of cathode impedance is described and validated with respect to Direct Methanol Fuel Cell (DMFC) technology. The presented
approach will be also applied to simulate cathode behavior in hydrogen fed PEM
Experimental and modeling analyses of Vanadium Redox Flow Battery
No full textVanadium redox flow battery is a promising and interesting storage technology that in a carbon-free scenario will have a key role in stabilizing the electric grid. Experimental activity presented in this work makes use of half-cell configuration, where the working electrode is fed with Vanadium solutions, while the other works as reference hydrogen electrode. Experimental characterization of both anode and cathode electrode with flow by feeding is presented, varying flow rate and state of charge. Moreover a 1D+1D Flow Battery model has been developed in Comsol Multiphysics, describing a single cell derived from fuel cell technology, composed by electrodes, membrane and flow field. The model includes Butler-Volmer kinetic equations, cross contamination fluxes through the membrane and mass transport phenomenon occurring in the pore of the carbon electrode. Discharge polarization curve was fitted to estimate kinetic rate constant and transfer coefficients
On the effect of gas diffusion layers hydrophobicity on direct methanol fuel cell performance and degradation
Full text linkMitigation of capacity decay in vanadium redox flow batteries through initial imbalance of electrolytes state of charge
Full text linkCapacity decay due to vanadium cross-over is a key technical challenge for Vanadium Redox Flow Batteries (VRFBs). To mitigate this effect this study investigates an operating strategy based on the imbalance of electrolyte solutions State of Charge (SoC). The strategy was conceived starting from the analysis of a VRFB during charge-discharge cycles adopting through-plate Reference Hydrogen Electrodes (RHE), which allowed to continuously monitor the evolution of the electrolytes SoCs during the operation. The obtained information, combined with a modelling analysis to estimate cross-over fluxes and net-vanadium transfer, suggested that starting the operation of the battery with positive electrolyte at a higher SoC compared to the negative one can be an effective strategy. Simulations of battery operation with different initial values of positive electrolyte SoC confirmed that this approach mitigated both battery capacity decay and net vanadium transfer. Model results were then validated by experimental testing. Starting the operation of the battery with negative and positive electrolyte SoC equal to 0 % and 15 % respectively, permitted to increase the discharged energy per cycle by 15 % and to reduce the net vanadium transfer by over 30 % without penalizing the efficiency of the battery
Effects of anode MPL on DMFC mass transport phenomena and electrochemical impedance spectroscopy: experimental and modeling analyses
No full textMASS TRANSPORT ISSUES IN LOW PLATINUM LOADING CATALYST LAYERS FOR POLYMER FUEL CELLS
No full textState of art cathode catalyst layers for polymer electrolyte fuel cells require the use of Platinum based catalysts to promote the sluggish oxygen reduction reaction, with a Platinum loading of approximately 0.2 mg cm-2. The main goal of research in long term deals with the necessity to reduce the Platinum loading that still impacts the cost of the system. Even though this topic has been researched intensively, low Platinum catalyst layers present mass transport limitations that strongly affect performance. In the present work mass transport overpotential in low Platinum polymer fuel cells is investigated with the aid of a quasi 2D single cell continuum based model
- …
