1,721,006 research outputs found
Experimental and FEM investigation into early gasket failure and its correlation to the clamping load and HT-PEMFC performance
No full textPerformance and degradation tests on high temperature proton exchange membrane fuel cells (HT-PEMFCs)
No full textMethanol steam reforming process can be a good solution for hydrogen generation in the case of fuel cells. The use of hydrogen generated by such process to fuel a fuel cell can eliminate the issues related to infrastructure and storage. But the hydrogen obtained through methanol steam reforming is not pure, containing impurities such as carbon dioxide, carbon monoxide, water vapor and unconverted methanol. Researches have been conducted on HT-PEM fuel cells to study the effects of fuel impurities. The current work investigates experimentally the effects of methanol-water vapor mixture concentrations in a H3PO4 doped PBI-based HT-PEM fuel cell. To isolate the effects of methanol-water vapor mixture from the whole reformate gas, the carbon dioxide and carbon monoxide are excluded from the experimental matrix. Two types of experiments are conducted: performance tests and degradation tests. The performance tests are realized in order to study the effect of temperature and the different vapor mixture concentrations on the fuel cell. The effect of startup-shutdown cycles is studied during the degradation tests. The analysis of these effects is made based on the impedance spectra measurements, polarization curves and cyclic voltammetry measurements. The results showed that temperature and methanol-water vapor mixture variations have an effect on the fuel cell performance. The increase in temperature increases the cathode catalyst active area and decreases the charge transfer resistance. Methanol-water vapor variations have an effect on the membrane conductivity when the cell is operated for longer times and cause a decrease in the catalyst active area of the cathode. During the startup/shutdown cycles performed with pure hydrogen the total voltage decay was of -46.3 mV, while the degradation rate for the case with methanol at a concentration of 3% was of -7.9 mV/h
Modelling and Experimental Analysis of a Polymer Electrolyte Membrane Water Electrolysis Cell at Different Operating Temperatures
Full text linkIn this paper, a simplified model of a Polymer Electrolyte Membrane (PEM) water electrolysis cell is presented and compared with experimental data at 60 °C and 80 °C. The model utilizes the same modelling approach used in previous work where the electrolyzer cell is divided in four subsections: cathode, anode, membrane and voltage. The model of the electrodes includes key electrochemical reactions and gas transport mechanism (i.e., H2, O2 and H2O) whereas the model of the membrane includes physical mechanisms such as water diffusion, electro osmotic drag and hydraulic pressure. Voltage was modelled including main overpotentials (i.e., activation, ohmic, concentration). First and second law efficiencies were defined. Key empirical parameters depending on temperature were identified in the activation and ohmic overpotentials. The electrodes reference exchange current densities and change transfer coefficients were related to activation overpotentials whereas hydrogen ion diffusion to Ohmic overvoltages. These model parameters were empirically fitted so that polarization curve obtained by the model predicted well the voltage at different current found by the experimental results. Finally, from the efficiency calculation, it was shown that at low current densities the electrolyzer cell absorbs heat from the surroundings. The model is not able to describe the transients involved during the cell electrochemical reactions, however these processes are assumed relatively fast. For this reason, the model can be implemented in system dynamic modelling for hydrogen production and storage where components dynamic is generally slower compared to the cell electrochemical reactions dynamics
Advances in Hydrogen Energy
Full text linkThis book, which is a reprint of articles published in the Special Issue "Advances in Hydrogen Energy" in Energies, seeks to contribute to disseminating the most recent advancements in the field of hydrogen energy. It does so by presenting scientific works from around the world covering both modeling and experimental analysis. The focus is placed on research covering all aspects of the hydrogen energy, from production to storage and final use, including the development of other easy to transport and versatile hydrogen-based energy carriers via the power-to-x (PtX) route, such as ammonia and methanol.Hydrogen energy research and development has attracted growing attention as one of the key solutions for clean future energy systems. In order to reduce greenhouse gas emissions, governments across the world are developing ambitious policies to support hydrogen technology, and an increasing level of funding has been allocated for projects of research, development, and demonstration of these technologies. At the same time, the private sector is capitalizing on the opportunity with larger investments in hydrogen technology solutions.While intense research activities have been dedicated to this field, several issues require further research prior to achieving full commercialization of hydrogen technology solutions. This book addresses some of these issues by presenting detailed models to optimize design strategies and operating conditions for the entire hydrogen value chain, covering production via electrolysis, storage and use in different types of fuel cells and in different forms of energy carriers
Modelling of stand alone micro-grid using hybrid energy storage Solar - Battery - Hydrogen
No full textImpedance characterization of high temperature proton exchange membrane fuel cell stack under the influence of carbon monoxide and methanol vapor
No full textThis work presents a comprehensive mapping of electrochemical impedance measurements under the influence of CO and methanol vapor contamination of the anode gas in a high temperature proton exchange membrane fuel cell, at varying load current. Electrical equivalent circuit model parameters based on experimental evaluation of electrochemical impedance spectroscopy measurements were used to quantify the changes caused by different contamination levels. The changes are generally in good agreement with what is found in the literature. It is shown that an increased level of CO contamination resulted in an increase in the high frequency and intermediate frequency impedances. When adding CO and methanol to the anode gas, the low frequency part of the impedance spectrum is especially affected at high load currents, which is clearly seen as a result of the high load current resolution used in this work. The negative effects of methanol vapor are found to be more pronounced on the series resistance. When CO and methanol vapor are both present in anode gas, the entire frequency spectrum and thereby all the equivalent circuit model parameters are affected. It is also shown that the trends of contamination effects are similar for all the test cases, namely, CO alone, methanol alone and a mix of the two, suggesting that effects of methanol may include oxidation into CO on the catalyst layer
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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