Towards Improved Understanding of Mass Transport in Polymer Electrolyte Membrane Water Electrolysers PDF Download
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Author: Maximilian Maier
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author: Maximilian Maier
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author: Jude Olaoluwa Majasan
Publisher:
ISBN:
Category :
Languages : en
Pages : 199
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Polymer Electrolyte Membrane Water Electrolysers (PEMWEs) are considered a promising candidate for large-scale renewable energy storage and green hydrogen production. To improve efficiency and minimize cost for large-scale deployment, operation at high current densities is necessary. However, a consequence of high current density operation is increased mass transport hindrance which degrades performance. Two components are critical to mass transport in PEMWEs, namely the porous transport layer (PTL) and the flow-field plates. Both are expected to transport liquid water, product gases, electrons, and heat with minimal fluidic, thermal and voltage losses. However, the influence of morphology and configuration of both these components and operating conditions on cell performance are not well understood. This research investigates the mass transport phenomena in the PTL and in the flow-field channels in relation to performance in PEMWEs. The influence of flow-field configuration and two-phase flow characteristics in the flow channels on performance was studied by combined high-speed optical imaging and electrochemical characterization at various operating conditions. Results showed a strong correlation of performance with the flow path length and flow regime. Further, a correlative ex-situ X-ray tomography and in-situ electrochemical characterization approach was used to investigate the influence of PTL microstructural parameters such as mean pore diameter, pore size distribution, porosity, tortuosity, and porosity distribution on performance. Results indicated that minimizing contact resistance is most beneficial for improved performance over the range of current density studied. The influence of flow channel depth on performance was investigated by electrochemical impedance spectroscopy and a design of experiment (DoE) approach was employed to investigate the relative importance and interaction effects of mass transport factors on cell performance. Results showed the water feed rate and two-way interaction between the flow-field and PTL are most significant. This study provides enhanced understanding of the mass transport characteristics in PEMWEs for optimized design and improved performance.
Author: Dmitri Bessarabov
Publisher: Academic Press
ISBN: 0081028318
Category : Science
Languages : en
Pages : 140
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Book Description
PEM Water Electrolysis, a volume in the Hydrogen Energy and Fuel Cell Primers series presents the most recent advances in the field. It brings together information that has thus far been scattered in many different sources under one single title, making it a useful reference for industry professionals, researchers and graduate students. Volumes One and Two allow readers to identify technology gaps for commercially viable PEM electrolysis systems for energy applications and examine the fundamentals of PEM electrolysis and selected research topics that are top of mind for the academic and industry community, such as gas cross-over and AST protocols. The book lays the foundation for the exploration of the current industrial trends for PEM electrolysis, such as power to gas application and a strong focus on the current trends in the application of PEM electrolysis associated with energy storage. - Presents the fundamentals and most current knowledge in proton exchange membrane water electrolyzers - Explores the technology gaps and challenges for commercial deployment of PEM water electrolysis technologies - Includes unconventional systems, such as ozone generators - Brings together information from many different sources under one single title, making it a useful reference for industry professionals, researchers and graduate students alike
Author: Nan Ge
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Understanding the species transport in polymer electrolyte membrane (PEM) fuel cells is critical for improving the cell performance. Poor performance stems from inefficient species transport. Particularly, excess accumulation of liquid water in the gas diffusion layer (GDL) substrate hinders transport of the reactant gases; the membrane dehydrates with increasing current density, leading to ohmic losses; the catalyst carbon support corrodes in the presence of water and high local potentials. In this thesis, these phenomena were investigated for improving the cell performance. In addition, imaging procedures for synchrotron radiography were improved to accurately visualize the water evolution in PEM fuel cells. The roles of undesired secondary scattering and harmonic photons on imaging accuracy were numerically determined. Both the secondary scattering and harmonic components increased with increasing water thickness, leading to a decrease in the calibrated attenuation coefficient and subsequent decrease in imaging accuracy. Next, the GDL substrate land and channel region contributions to oxygen transport resistance were resolved. Both the substrate oxygen transport resistance and the mass transport resistance of the fuel cell were more sensitive to the local saturation in the substrate channel region than that in the substrate land region. In a related study, membrane dehydration under high relative humidities (above 70%) caused significant membrane shrinkage. Via experimental visualization and performance testing techniques, the dehydration was attributed to increases in the local temperature. Lastly, a novel diagnostic method was developed to measure the electrode performance for the real-time detection of carbon corrosion in dead-ended anode operation. The accumulation of nitrogen in the corroded cathode led to sudden increases in cathode polarization resistance, and this performance characteristic was identified as a new indicator for a corroded cathode. The main findings in this thesis advance the understanding of species transport as a basis for developing next-generation high-performance PEM fuel cells.
Author: ChungHyuk Lee
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Effective two-phase transport is a prerequisite for achieving high efficiency operation for polymer electrolyte membrane electrolyzers since the undesired accumulation of gaseous oxygen leads to mass transport losses. In this thesis, two-phase flow in the PTL and flow channels were investigated via experimental and numerical techniques to inform new designs and optimize operating conditions. The effect of gas compressibility on displacement behaviour in the PTL was elucidated by studying gas invasion in liquid-saturated microfluidic cells. Smaller pore throat sizes led to larger pore burst velocities, which inspired a new PTL design with engineered pore throat sizes for enhanced gas removal. Next, the gas transport behaviour in the PTL was investigated via a custom microfluidic cell that was based on a realistic PTL microstructure. A unique pore throat was identified where gas snap-off occurred, and the location of this pore throat governed the average gas saturation in the PTL. Next, the temperature-dependent gas saturation in the PTL was investigated using in operando neutron imaging. Increasing the operating temperature led to lower gas saturation near the catalyst layer and PTL interface, resulting in a decrease in mass transport overpotential. To increase the accuracy of anode flow channel visualizations, the nitrogen purging rate was optimized to minimize the impact of purging on cell performance. Excessive cathode purging led to undesired changes in performance, and a minimal purge rate was recommended to achieve accurate through-plane imaging. Lastly, temperature effects on two-phase quality in the anode flow channels were investigated via neutron imaging. A more uniform reactant distribution across the flow channels was observed at higher temperatures, enabling a uniform operating current density across the active area. The main findings in this thesis inform the design of novel PTL microstructure and explain the benefits of higher operating temperature for enhanced mass transport in PEM electrolyzers.
Author: Dmitri Bessarabov
Publisher: CRC Press
ISBN: 1482252325
Category : Science
Languages : en
Pages : 401
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Book Description
An ever-increasing dependence on green energy has brought on a renewed interest in polymer electrolyte membrane (PEM) electrolysis as a viable solution for hydrogen production. While alkaline water electrolyzers have been used in the production of hydrogen for many years, there are certain advantages associated with PEM electrolysis and its relevan
Author: Keonhag Lee
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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The design of a porous transport layer (PTL) that exhibits effective two-phase transport characteristics and rigid contact at the catalyst layer (CL)-PTL interface is a prerequisite for improving the efficiency of polymer electrolyte membrane (PEM) water electrolyzers at high current densities (i > 4 A/cm2). In this thesis, key design considerations were presented based on extensive investigations performed via comprehensive numerical models and in operando imaging. A numerical investigation was performed to determine the impact of PTL structures on reactant liquid water delivery to reaction sites. A comprehensive model for designing PTLs was presented, where a stochastic model was used to numerically generate PTLs with realistic morphologies and tunable PTL structures, and a pore network model was used to perform two-phase flow calculations and determine their transport properties. A trade-off relationship was observed between achieving an effective CL-PTL interfacial contact and favourable reactant transport behaviour. Finer powder diameters and lower porosities improved the CL-PTL interfacial contact but led to the reduced permeability of liquid water. Conversely, increasing either powder diameter or porosity improved permeability but deteriorated the CL-PTL interfacial contact. Therefore, it is crucial to consider the operating conditions of an electrolyzer when designing PTLs. Mass transport behaviour in an electrolyzer operating at high current densities was studied using in operando imaging techniques. A sufficient reactant flow rate was essential for mitigating electrolyzer cell failures at high current densities. Specifically, the critical current density was observed when inadequate reactant water was supplied at high current densities. Both gas content in the PTL and mass transport overpotential significantly increased at the critical current density, and the electrolyzer failed to operate beyond the critical current density. Moreover, mass transport in the PTL surprisingly improved when patterned through-pores (PTPs) were implemented with a commercial PTL. The usage of a novel PTP PTL led to the reduced accumulation of product gas at the CL-PTL interface by 43.5%. Furthermore, PTPs led to more frequent gas removal, which subsequently improved water intake to the reaction sites. The findings in this thesis provide valuable insights for designing novel PTLs in PEM electrolyzers operating at high current densities.
Author: Yong Hun Park
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Fuel cell performance was obtained as functions of the humidity at the anode and cathode sites, back pressure, flow rate, temperature, and channel depth. The fuel cell used in this work included a membrane and electrode assembly (MEA) which possessed an active area of 25, 50, and 100 cm2 with the Nafion(R) 117 and 115 membranes. Higher flow rates of inlet gases increase the performance of a fuel cell by increasing the removal of the water vapor, and decrease the mass transportation loss at high current density. Higher flow rates, however, result in low fuel utilization. An important factor, therefore, is to find the appropriate stoichiometric flow coefficient and starting point of stoichiometric flow rate in terms of fuel cell efficiency. Higher air supply leads to have better performance at the constant stoichiometric ratio at the anode, but not much increase after the stoichiometric ratio of 5. The effects of the environmental conditions and the channel depth for an airbreathing polymer electrolyte membrane fuel cell were investigated experimentally. Triple serpentine designs for the flow fields with two different flow depths was used. The shallow flow field deign improves dramatically the performance of the air-breathing fuel cell at low relative humidity, and slightly at high relative humidity. For proton exchange membrane fuel cells, proper water management is important to obtain maximum performance. Water management includes the humidity levels of the inlet gases as well as the understanding of the water process within the fuel cell. Two important processes associated with this understanding are (1) electro-osmotic drag of water molecules, and (2) back diffusion of the water molecules. There must be a neutral water balance over time to avoid the flooding, or drying the membranes. For these reasons, therefore, an investigation of the role of water transport in a PEM fuel cell is of particular importance. In this study, through a water balance experiment, the electro-osmotic drag coefficient was quantified and studied. For the cases where the anode was fully hydrated and the cathode suffered from the drying, when the current density was increased, the electro- osmotic drag coefficient decreased.
Author: Jin-Soo Park
Publisher: MDPI
ISBN: 303650690X
Category : Science
Languages : en
Pages : 128
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Book Description
This book consists of the nine sections: i) the first three sections are related to polymeric electrolyte composites; ii) the next two sections relate to gas diffusion layers (GDLs); iii) the next two sections relate to membrane¬–electrode assembly (MEA); iv) and the final two sections deal with the numerical simulation of flow fields for polymer electrolyte fuel cells (PEFCs). All sections describe recent results of the study of the main components of PEFC stacks. The studies provide the underlying material, electrochemical, and/or mechanical aspects that enhance the mass transport of gas, ions (liquid), and electrons for a better performance of PEFCs and the electrochemical reactions at the triple-phase boundary in electrodes. Each study offers the fundamentals, a comprehensive background, and cutting-edge technology on the aforementioned materials and mass transport phenomena.
Author: Jeff Gostick
Publisher:
ISBN:
Category :
Languages : en
Pages : 203
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Book Description
A detailed understanding of mass transport and water behavior in gas diffusion layers (GDLs) for polymer electrolyte membrane fuel cells (PEMFCs) is vital to improving performance. Liquid water fills the porous GDL and electrode components, hindering mass transfer, limiting attainable power and decreasing efficiency. The behavior of liquid water in GDLs is poorly understood, and the specific nature of mass transfer of multiphase flow in GDLs are not known. There is no clear direct correlation between easily measurable ex-situ GDL material properties and mass transfer characteristics. This thesis addresses this knowledge gap through a combination of test procedure development, experimentation and numerical pore scale modeling. Experimental techniques have been developed to measure permeability and capillary properties of water and air in the GDL matrix. Pore network modeling is used to estimate transport properties as a function of GDL water saturation since these are extremely difficult to determine experimentally. A method and apparatus for measuring the relationship between air-water capillary pressure and water saturation in PEMFC gas diffusion layers is described. The developed procedure of Gas Controlled Porosimetry is more effective for understanding the behaviour of water in GDL material then traditional methods such as the method of standard porosimetry and mercury intrusion porosimetry. Capillary pressure data for water injection and withdrawal from typical GDL materials are obtained, which demonstrated permanent hysteresis between water intrusion and water withdrawal. Capillary pressure, defined as the difference between the water and gas pressures at equilibrium, is positive during water injection and negative during water withdrawal. The results contribute to the understanding of liquid water behavior in GDL materials which is necessary for the development of effective PEMFC water management strategies and the design of future GDL materials. The absolute gas permeability of GDL materials was measured. Measurements were made in three perpendicular directions to investigate anisotropic properties of various materials. Most materials were found to be significantly anisotropic, with higher in-plane permeability than through-plane permeability. In-plane permeability was also measured as the GDL was compressed to different thicknesses. Typically, compression of a sample to half its initial thickness resulted in a decrease in permeability by an order of magnitude. The relationship between measured permeability and compressed porosity was compared to various models available in the literature, one of which allows the estimation of anisotropic tortuosity. The results of this work will be useful for 3D modeling studies where knowledge of permeability and effective diffusivity tensors is required. A pore network model of mass transport in GDL materials is developed and validated. The model idealizes the GDL as a regular cubic network of pore bodies and pore throats following respective size distributions of the pores. With the use of experimental data obtained the geometric parameters of the pore network model were calibrated with respect to porosimetry and gas permeability measurements for two common GDL materials. The model was subsequently used to compute the pore-scale distribution of water and gas under drainage conditions using an invasion percolation algorithm. From this information, transport properties of GDLs that are very difficult to measure were estimated, including the relative permeability of water and gas, and the effective gas diffusivity as functions of water saturation. Comparison of the model predictions with those obtained from constitutive relationships commonly used in current PEMFC models indicates that the latter may significantly overestimate the gas phase transport properties. The pore network model was also used to calculate the limiting current in a PEMFC under operating conditions for which transport through the GDL dominates mass transfer resistance. The results suggest that a dry GDL does not limit the performance of a PEMFC, but water flooding becomes a significant source of concentration polarization as the GDL becomes increasingly saturated with water. This work has significantly contributed to the understanding of mass transfer in gas diffusion layers in PEMFC through experimental investigation and pore scale modeling.
