128 research outputs found
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
Impedance 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
saraya209/Araya_etal_2021_SOIL_Data_and_Code: Long-Term Impact of Cover Crop and Reduced Disturbance Tillage on Soil Pore Size Distribution and Soil Water Storage
No full textData* and Code for The Research Paper:
Long-Term Impact of Cover Crop and Reduced Disturbance Tillage on Soil Pore Size Distribution and Soil Water Storage
About The Project
We studied the long-term impact of contrasting tillage and cover cropping systems on soil structure and soil hydraulic properties. We measured water retention and conductivity properties and analyzed the implication of these changes on water storage using numerical simulations in HYDRUS-2D software. Our study concludes that the long-term practices of no-till and cover crop systems were beneficial in terms of changes to the pore size distribution. No-till and cover cropping systems made marginal improvements in soil water conductivity and water storage.
Contents and Folder Structure
The analysis was done primarily in R. For each *.R code file, I have compiled a report with the corresponding file name in markdown (.md) and HTML file formats. The folder structure and description are outlined here:
Data_Processed/: Data tables in .csv and/or .rds format that have been processed from raw data
Data_Raw/: Raw data exported from lab instruments (KSAT and HYPROP) and HYDRUS-2D simulation output files
Plots/: Contains plots and figures from analysis of data in .pdf and/or png file formats.
Reports/: Compiled reports of the processing .R codes with corresponding file names.
".R" files: R codes:
Files starting with "01" to "04" are for analyzing laboratory data,
Files starting with "H2D" are for analyzing Hydrus-2D data
License
Distributed under the Creative Commons Attribution 4.0 (CC BY 4.0) License.
Contact
Samuel Araya - @SamuelA209 - https://samuelna.netlify.app/
* HYDRUS-2D Mesh-level data are not available in this repository due to GitHub file size limits. Please contact author for access.</sub
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
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 text
High Temperature PEM Fuel Cells - Degradation and Durability
Full text linkA harmonious mix of renewable and alternative energy sources, including fuel cells is necessary to mitigate problems associated with the current fossil fuel based energy system, like air pollution, Greenhouse Gas (GHG) emissions, and economic dependence on oil, and therefore on unstable areas of the globe. Fuel cells can harness the excess energy from other renewable sources, such as the big players in the renewable energy market, Photovoltaic (PV) panels and wind turbines, which inherently suffer from intermittency problems. The excess energy can be used to produce hydrogen from water or can be stored in liquid alcohols such as methanol, which can be sources of hydrogen for fuel cell applications. In addition, fuel cells unlike other technologies can use a variety of other fuels that can provide a source of hydrogen, such as biogas, methane, butane, etc. More fuel flexibility combined with wider range of applications than any other available technology make them suitable candidates for powering a sustainable future. This work analyses the degradation issues of a High Temperature Proton Exchange Memebrane Fuel Cell (HT-PEMFC). It is based on the assumption that given the current challenges for storage and distribution of hydrogen, it is more practical to use liquid alcohols as energy carriers for fuel cells. Among these, methanol is very attractive, as it can be obtained from a variety of renewable sources and has a relatively low reforming temperature for the production of hydrogen rich gaseous mixture. The effects on HT-PEMFC of the different constituents of this gaseous mixture, known as a reformate gas, are investigated in the current work. For this, an experimental set up, in which all these constituents can be fed to the anode side of a fuel cell for testing, is put in place. It includes mass flow controllers for the gaseous species, and a vapor delivery system for the vapor mixture of the unconverted reforming reactants.Electrochemical Impedance Spectroscopy (EIS) is used to characterize the effects of these impurities. The effects of CO were tested up to 2% by volume along with other impurities. All the reformate impurities, including ethanol-water vapor mixture, cause loss in the performance of the fuel cell. In general, CO2 dilutes the reactants, if tested alone at high operating temperatures (180 C), but tends to exacerbate the effects of CO if they are tested together. On the other hand, CO and methanol-water vapor mixture degrade the fuel cell proportionally to the amounts in which they are tested. In this dissertation some of the mechanisms with which the impurities affect the fuel cell are discussed and interdependence among the effects is also studied. This showed that the combined effect of reformate impuritiesis more than the arithmetic sum of the individual effects of reformate constituents. The results of the thesis help to understand better the issues of degradation and durability in fuel cells, which can help to make them more durable and competitive with traditional devices to revolutionize the current energy systems
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