Evaluation of water transport in PEMFC gas diffusion layers using image analysis

Liquid water transport through the gas diffusion layer (GDL) of a proton exchange membrane fuel cell (PEMFC) was investigated through three interrelated studies utilizing the tools of image processing. First, a new framework and model for the digital generation and characterization of the microstructure of GDL materials with localized binder and polytetrafluoroethylene (PTFE) distributions were developed using 3D morphological imaging processing. The new generation technique closely mimics manufacturing processes and produces realistic 3D phase-differentiated digital microstructures in a cost- and time- effective manner. The generated distributions of hydrophobic (PTFE) and hydrophilic (carbon) regions representative of commercial GDL materials provides water transport modeling efforts with more accurate geometries to improve PEMFC water management. Second, through-plane transport in an operating PEMFC was investigated by developing and testing a transparent (visible and infrared) fuel cell. Visible observations and subsequent video processing revealed condensation of microdroplets on the GDL and implied the existence of condensation within the GDL. Temperature gradients across the cathode GDL under realistic operating conditions were obtained in a noninvasive manner using infrared imaging and subsequent image analysis. Recommendations for improving accuracy of PEMFC temperature measurements using infrared imaging were made. The final contribution of this work was the measurement and analysis of water breakthrough dynamics across GDL materials with and without microporous layers (MPLs). Dynamic breakthrough events, or recurrent breakthroughs, were observed for all GDL material investigated indicating the breakdown and re-build of water paths through the GDL caused by an intermittent water drainage process from the GDL surface. GDL materials without an MPL exhibited a dynamic breakthrough location phenomenon and significantly elevated water saturations. The results suggest that the MPL not only limits the number of water entries into the GDL substrate but also stabilizes the water paths. These dynamic breakthrough events were explained in terms a Haines jump transport mechanism. The main contributions of this work are: (1) Development of a new digital GDL microstructure generation algorithm, (2) Evaluation of infrared temperature measurements in the through-plane direction of a PEMFC, and (3) Identification of a new water transport mechanism in GDL materials

Development of Zinc Slurry Air Flow Battery

Batteries have gained large interest in past few decades as energy storage systems because their merits such as relatively high efficiency, good durability of battery and unique power and energy output design. There are many types of batteries which can be used as reversible, or secondary, energy storage systems like redox flow batteries or metal-air batteries. The hybrid of those two types of batteries which is the Zinc slurry air flow battery uses zinc particles suspended in highly alkaline solution as the electrolyte and electrode for the negative compartment, whereas air is flowing in and out of the positive compartment for the oxygen reaction. As this is a relatively new concept of battery, there are two important factors which needs to be investigated. First, the discharge performance of the battery is the primary problem to be solved and the second challenge is the rechargeability of the battery to make it a secondary battery. In order to achieve those two goals, the bipolar plates are one of the key components to be studied in redox flow batteries as they require not only a good electrical conductivity, but also good mechanical durability with high corrosion resistance. Furthermore, this component is also important as the electrolyte flow can be improved by carving a flow field on the bipolar plate. Hence, this study aims first to improve the discharge performance of the Zinc Slurry Air Flow Battery. To do this, several types of flow field designs and material compositions have been tested as they play an important role in the performance of the redox flow battery, especially when using highly viscous liquids. To enhance the discharge power density of zinc slurry air flow batteries, an optimum slurry distribution in the cell is key. Hence, several types of flow fields (serpentine, parallel, plastic flow frames) were tested in this study to improve the discharge power density of the battery. The serpentine flow field delivered a power density of 55 mW·cm−2, while parallel and flow frame resulted in 30 mW·cm−2 and 10 mW·cm−2, respectively. Moreover, when the anode bipolar plate material was changed from graphite to copper, the power density of the flow frame increased to 65 mW·cm−2, and further improvement was attained when the bipolar plate material was further changed to copper–nickel. These results show the potential to increase the power density of slurry-based flow batteries by flow field optimization and design of bipolar plate materials. The second aim of this work is to improve the rechargeability of the battery. In the last section of this study, carbon additives were introduced to achieve a rechargeable zinc slurry flow battery by minimizing the zinc plating on the bipolar plate that occurs during charging. When no carbon additive was present in the zinc slurry, the discharge current density was 24mA·cm−2 at 0.6 V, while the use of carbon additives increased it to up to 38 mA·cm−2. The maximum power density was also increased from 16 mW·cm−2 to 23 mW·cm−2. Moreover, the amount of zinc plated on the bipolar plate during charging decreased with increasing carbon content in the slurry. A rheological investigation revealed that the elastic modulus and yield stress are directly proportional to the carbon content in the slurry, which is beneficial for redox flow battery applications, but comes at the expense of an increase in viscosity (two-fold increase at 100s−1). These results show how the use of conductive additives can enhance the energy density of slurry-based flow batteries

Modern Surface Engineering Treatments

Surface engineering can be defined as an enabling technology used in a wide range of industrial activities. Surface engineering was founded by detecting surface features which destroy most of pieces, e.g. abrasion, corrosion, fatigue, and disruption; then it was recognized, more than ever, that most technological advancements are constrained with surface requirements. In a wide range of industry (such as gas and oil exploitation, mining, and manufacturing), the surfaces generate an important problem in technological advancement. Passing time shows us new interesting methods in surface engineering. These methods usually apply to enhance the surface properties, e.g. wear rate, fatigue, abrasion, and corrosion resistance. This book collects some of new methods in surface engineering

Development of advanced diagnostic techniques for water management in polymer electrolyte fuel cells

Polymer electrolyte fuel cells (PEFCs) are a potential solution to the increasing demand for sustainable energy conversion technologies. One of the long-standing challenges to ensuring efficient and reliable PEFC performance is accomplishing effective internal water management. Here, advanced diagnostic techniques are employed to optimize the water management of PEFCs. Neutron radiography is applied to evaluate the water management of PEFCs under different levels of compression. The PEFC compressed at 1.0 MPa demonstrates ∼3.2 % and ∼7.8 % increase in the maximum power density over 1.8 MPa and 2.3 MPa, respectively. Water droplet number and median droplet surface area rapidly increase with higher compression pressure, showing the ineffective water removal. A systematic comparison is presented of liquid water distribution within the single-, double- and quad-channel serpentine flow-fields. The single-channel serpentine flow-field not only provides the best performance, but also attains the most uniform water profile distribution. The water management of the metal foam and serpentine flow-field based PEFCs have been investigated using neutron radiography. The absence of a land/channel configuration in the metal foam flow-field designs improves the uniformity in reactant distribution across the electrode, contributing to a ~101% increase in maximum power density than the serpentine design. The peak power density of 853 mW cm-2 was recorded for a PEFC with medium compressed metal foam flow-field, followed by maximum (780 mW cm-2) and minimum compression (568 mW cm-2). X-ray computed tomography and simulation results indicate that the compression process significantly decreases the mean pore size and narrows the pore size distribution of metal foams, whereas it leads to larger pressure drop and more effective water removal. A novel transfer function based neutron radiography technique, hydro-electrochemical impedance imaging (HECII) is presented, providing a complementary view to that of conventional neutron imaging in that it highlights the location of nascent water generation

Degradation aspects of water formation and transport in Proton Exchange Membrane Fuel Cell: A review

This review paper summarises the key aspects of Proton Exchange Membrane Fuel Cell (PEMFC) degradation that are associated with water formation, retention, accumulation, and transport mechanisms within the cell. Issues related to loss of active surface area of the catalyst, ionomer dissolution, membrane swelling, ice formation, corrosion, and contamination are also addressed and discussed. The impact of each of these water mechanisms on cell performance and durability was found to be different and to vary according to the design of the cell and its operating conditions. For example, the presence of liquid water within Membrane Electrode Assembly (MEA), as a result of water accumulation, can be detrimental if the operating temperature of the cell drops to sub-freezing. The volume expansion of liquid water due to ice formation can damage the morphology of different parts of the cell and may shorten its life-time. This can be more serious, for example, during the water transport mechanism where migration of Pt particles from the catalyst may take place after detachment from the carbon support. Furthermore, the effect of transport mechanism could be augmented if humid reactant gases containing impurities poison the membrane, leading to the same outcome as water retention or accumulation. Overall, the impact of water mechanisms can be classified as aging or catastrophic. Aging has a long-term impact over the duration of the PEMFC life-time whereas in the catastrophic mechanism the impact is immediate. The conversion of cell residual water into ice at sub-freezing temperatures by the water retention/ accumulation mechanism and the access of poisoning contaminants through the water transport mechanism are considered to fall into the catastrophic category. The effect of water mechanisms on PEMFC degradation can be reduced or even eliminated by (a) using advanced materials for improving the electrical, chemical and mechanical stability of the cell components against deterioration, and (b) implementing effective strategies for water management in the cell

Space Electrochemical Research and Technology (SERT)

The conference provided a forum to assess critical needs and technologies for the NASA electrochemical energy conversion and storage program. It was aimed at providing guidance to NASA on the appropriate direction and emphasis of that program. A series of related overviews were presented in the areas of NASA advanced mission models (space stations, low and geosynchronous Earth orbit missions, planetary missions, and space transportation). Papers were presented and workshops conducted in a variety of technical areas, including advanced rechargeables, advanced concepts, critical physical electrochemical issues, and modeling

Recent advances in acoustic diagnostics for electrochemical power systems

Over the last decade, acoustic methods, such as acoustic emission and ultrasonic testing, have been increasingly deployed for process diagnostics and health monitoring of electrochemical power devices including batteries, fuel cells, and water electrolysers. These acoustic are non-invasive, highly sensitive, and low cost, while also providing a high level of spatial and temporal resolution, and practicality. The application of these tools in electrochemical devices is based on identifying changes in acoustic signals due to physical, structural, and electrochemical properties change within the material which are then correlated to critical processes and the health status of the devices. This review discusses recent progress in the use of acoustic methods for process and health-monitoring of major electrochemical energy conversion and storage devices. First, the fundamental concepts and principles of acoustic emission and ultrasonic testing are introduced, followed by a discussion of the range of electrochemical energy conversion and storage systems, and how acoustic techniques are being used to study relevant materials and devices. Conclusions and future perspectives highlighting some of the unique challenges and potential commercial and academic applications of the devices are also discussed. It is expected that, with further developments, acoustic techniques will form a key part of the suite of diagnostic techniques routinely used to monitor electrochemical devices across various processes including fabrication, on-board maintenance, post-mortem examination and second life or recycle decision support to aid the deployment of these devices in increasingly demanding applications