The Experts below are selected from a list of 6993 Experts worldwide ranked by ideXlab platform
Richard I. Masel - One of the best experts on this subject based on the ideXlab platform.
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Integrated Micro Fuel Cell with on-demand hydrogen production and passive control MEMS
Microfluidics and Nanofluidics, 2012Co-Authors: Vikhram V. Swaminathan, Richard I. Masel, Likun Zhu, Bogdan Gurau, Mark A. ShannonAbstract:An ever increasing demand for packaging more energy on-board to meet the needs of power hungry Microsystems is driving the miniaturization of power generators. We report a fully integrated Power MEMS, in the 10-μL size, designed to deliver high energy and power densities. On-board hydrogen production and an efficient control scheme that facilitates integration with a Fuel Cell membrane electrode assembly are key elements for Micro energy conversion. A millimeter-scale reactor produces hydrogen by hydrolysis of CaH_2 and LiAlH_4, to yield energy densities of the order of 200 Whr/L. A passive Microfluidic control scheme, incorporating surface tension to pump water in a Microchannel for hydrolysis and Microvalve control using hydrogen backpressure, facilitates delivery and regulation and eliminates bulky auxiliaries that consume parasitic power. We tested the ability of this control scheme to improve uniformity of power delivery during long periods of lower demand, with fast switching to mass transport regime on the order of seconds, and realized peak power density of up to 391.85 W/L. Prototypes have been tested for duty periods from 2–48 h, with multiple switching of power demand in order to establish performance across multiple regimes. Critical to the realization of the integrated power MEMS, and its energy and power density, are effects of water transport and byproduct hydrate swelling on hydrogen production in the Microreactor. While CaH_2 showed superior hydrogen release kinetics that enhances power density, LiAlH_4 provided greater energy density due to reduced byproduct expansion that permitted increased hydrogen production.
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An onboard hydrogen generation method based on hydrides and water recovery for Micro-Fuel Cells
Journal of Power Sources, 2009Co-Authors: Likun Zhu, Vikhram V. Swaminathan, Richard I. Masel, Bogdan Gurau, Mark A. ShannonAbstract:Abstract Micro-proton exchange membrane Fuel Cells are considered to be the next generation power sources for Micro-scale power applications, but onboard hydrogen storage and generation with high energy density at the small scale is still a technical barrier. This paper introduces a hydrogen generation method based on an onboard hydride Fuel and a byproduct water recovery mechanism for Micro-hydrogen PEM Fuel Cells. The water recovery is carried out by water diffusion from the more humid cathode side to the less humid anode side through the proton exchange membrane. The Micro-Fuel Cells based on this water recovery method were constructed and tested. The results demonstrate that the relative humidity has a significant affect on the Fuel Cell performance as well as the opening area on the cover layer, the type of hydrides, and the thickness of the Nafion membrane also can affect the Fuel Cell performance. A 10 mm 3 prototype water recovery Micro-Fuel Cell has been built and tested, and the device has produced a maximum power density of 104 W L −1 and a maximum energy density of 313 W h L −1 .
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A Novel Architecture for Micro Fuel Cells
2009Co-Authors: Kevin Lin, Richard I. Masel, Saeed Moghaddam, Eakkachai Pengwang, Mark A. ShannonAbstract:Development of a fully integrated millimeter-scale (3×3×1 mm 3 ) Fuel Cell with a completely passive control mechanism is reported in this study. Fabrication of this unique power source was enabled through development of a novel self-regulating Micro-hydrogen generator. The hydrogen generator stops generating hydrogen automatically when hydrogen is not consumed, enabling the Micro Fuel Cell to operate passively, similar to a battery. The implemented passive control mechanism occupies only 0.5% of the total device volume. The first generation of this device delivered an energy density of 254 W-hr/L. Subsequent generations of this device can potentially reach 1000 W-hr/L.
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Nanoporous Silicon Membrane Based Micro Fuel Cells for Portable Power Sources Applications
2006Co-Authors: Kuan-lun Chu, Mark A. Shannon, Richard I. MaselAbstract:In this paper the preparation of nanoporous silicon membranes and their usage for the solid electrolyte in Micro Fuel Cells compatible with silicon Micro-fabrication technology is presented. The effects of different membrane structures and Fuel concentrations were studied. And the Micro Fuel Cell design for improved performances is discussed.
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A nanoporous silicon membrane electrode assembly for on-chip Micro Fuel Cell applications
Journal of Microelectromechanical Systems, 2006Co-Authors: Kuan-lun Chu, Mark A. Shannon, Scott Alan Gold, Vaidyanathan Subramanian, Richard I. MaselAbstract:Silicon-based Fuel Cells are under active development for chip-scale electrical power supply. One of the greatest challenges in Micro-Fuel-Cell research is the development of a suitable proton conducting membrane material that is compatible with standard silicon Microfabrication technology. In this paper, the use of nanoporous silicon as a novel proton conducting membrane material in a Microscale Fuel Cell membrane electrode assembly (MEA) is demonstrated. The devices were fabricated by first creating 100-/spl mu/m-thick silicon windows in a standard silicon wafer, anodizing to create pores in the windows, and then painting catalyst layers and insulators onto the porous structures. Using 5 M formic acid and 0.5 M sulfuric acid as the Fuel, the Fuel Cell peak power density reached about 30 mW/cm/sup 2/ at current density level of about 120 mA/cm/sup 2/. These results represent the successful integration of a new class of protonic conductor into a Microfabricated silicon Fuel Cell.
Mark A. Shannon - One of the best experts on this subject based on the ideXlab platform.
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Integrated Micro Fuel Cell with on-demand hydrogen production and passive control MEMS
Microfluidics and Nanofluidics, 2012Co-Authors: Vikhram V. Swaminathan, Richard I. Masel, Likun Zhu, Bogdan Gurau, Mark A. ShannonAbstract:An ever increasing demand for packaging more energy on-board to meet the needs of power hungry Microsystems is driving the miniaturization of power generators. We report a fully integrated Power MEMS, in the 10-μL size, designed to deliver high energy and power densities. On-board hydrogen production and an efficient control scheme that facilitates integration with a Fuel Cell membrane electrode assembly are key elements for Micro energy conversion. A millimeter-scale reactor produces hydrogen by hydrolysis of CaH_2 and LiAlH_4, to yield energy densities of the order of 200 Whr/L. A passive Microfluidic control scheme, incorporating surface tension to pump water in a Microchannel for hydrolysis and Microvalve control using hydrogen backpressure, facilitates delivery and regulation and eliminates bulky auxiliaries that consume parasitic power. We tested the ability of this control scheme to improve uniformity of power delivery during long periods of lower demand, with fast switching to mass transport regime on the order of seconds, and realized peak power density of up to 391.85 W/L. Prototypes have been tested for duty periods from 2–48 h, with multiple switching of power demand in order to establish performance across multiple regimes. Critical to the realization of the integrated power MEMS, and its energy and power density, are effects of water transport and byproduct hydrate swelling on hydrogen production in the Microreactor. While CaH_2 showed superior hydrogen release kinetics that enhances power density, LiAlH_4 provided greater energy density due to reduced byproduct expansion that permitted increased hydrogen production.
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An onboard hydrogen generation method based on hydrides and water recovery for Micro-Fuel Cells
Journal of Power Sources, 2009Co-Authors: Likun Zhu, Vikhram V. Swaminathan, Richard I. Masel, Bogdan Gurau, Mark A. ShannonAbstract:Abstract Micro-proton exchange membrane Fuel Cells are considered to be the next generation power sources for Micro-scale power applications, but onboard hydrogen storage and generation with high energy density at the small scale is still a technical barrier. This paper introduces a hydrogen generation method based on an onboard hydride Fuel and a byproduct water recovery mechanism for Micro-hydrogen PEM Fuel Cells. The water recovery is carried out by water diffusion from the more humid cathode side to the less humid anode side through the proton exchange membrane. The Micro-Fuel Cells based on this water recovery method were constructed and tested. The results demonstrate that the relative humidity has a significant affect on the Fuel Cell performance as well as the opening area on the cover layer, the type of hydrides, and the thickness of the Nafion membrane also can affect the Fuel Cell performance. A 10 mm 3 prototype water recovery Micro-Fuel Cell has been built and tested, and the device has produced a maximum power density of 104 W L −1 and a maximum energy density of 313 W h L −1 .
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A Novel Architecture for Micro Fuel Cells
2009Co-Authors: Kevin Lin, Richard I. Masel, Saeed Moghaddam, Eakkachai Pengwang, Mark A. ShannonAbstract:Development of a fully integrated millimeter-scale (3×3×1 mm 3 ) Fuel Cell with a completely passive control mechanism is reported in this study. Fabrication of this unique power source was enabled through development of a novel self-regulating Micro-hydrogen generator. The hydrogen generator stops generating hydrogen automatically when hydrogen is not consumed, enabling the Micro Fuel Cell to operate passively, similar to a battery. The implemented passive control mechanism occupies only 0.5% of the total device volume. The first generation of this device delivered an energy density of 254 W-hr/L. Subsequent generations of this device can potentially reach 1000 W-hr/L.
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Nanoporous Silicon Membrane Based Micro Fuel Cells for Portable Power Sources Applications
2006Co-Authors: Kuan-lun Chu, Mark A. Shannon, Richard I. MaselAbstract:In this paper the preparation of nanoporous silicon membranes and their usage for the solid electrolyte in Micro Fuel Cells compatible with silicon Micro-fabrication technology is presented. The effects of different membrane structures and Fuel concentrations were studied. And the Micro Fuel Cell design for improved performances is discussed.
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A nanoporous silicon membrane electrode assembly for on-chip Micro Fuel Cell applications
Journal of Microelectromechanical Systems, 2006Co-Authors: Kuan-lun Chu, Mark A. Shannon, Scott Alan Gold, Vaidyanathan Subramanian, Richard I. MaselAbstract:Silicon-based Fuel Cells are under active development for chip-scale electrical power supply. One of the greatest challenges in Micro-Fuel-Cell research is the development of a suitable proton conducting membrane material that is compatible with standard silicon Microfabrication technology. In this paper, the use of nanoporous silicon as a novel proton conducting membrane material in a Microscale Fuel Cell membrane electrode assembly (MEA) is demonstrated. The devices were fabricated by first creating 100-/spl mu/m-thick silicon windows in a standard silicon wafer, anodizing to create pores in the windows, and then painting catalyst layers and insulators onto the porous structures. Using 5 M formic acid and 0.5 M sulfuric acid as the Fuel, the Fuel Cell peak power density reached about 30 mW/cm/sup 2/ at current density level of about 120 mA/cm/sup 2/. These results represent the successful integration of a new class of protonic conductor into a Microfabricated silicon Fuel Cell.
Herbert Reichl - One of the best experts on this subject based on the ideXlab platform.
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Optimization of efficiency and energy density of passive Micro Fuel Cells and galvanic hydrogen generators
2016Co-Authors: Robert Hahn, Steffen Krumbholz, Stefan Wagner, Herbert ReichlAbstract:A PEM Micro Fuel Cell system is described which is based on self-breathing PEM Micro Fuel Cells in the power range between 1 mW and 1W. Hydrogen is supplied with on-demand hydrogen production with help of a galvanic Cell, that produces hydrogen when Zn reacts with water. The system can be used as a battery replacement for low power applications and has the potential to improve the run time of autonomous systems. The efficiency has been investigated as function of Fuel Cell construction and tested for several load profiles.
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Design and evaluation of a passive self-breathing Micro Fuel Cell for autonomous portable applications
International Journal of Hydrogen Energy, 2013Co-Authors: Matthias Weiland, Stefan Wagner, Robert Hahn, Herbert ReichlAbstract:A Micro Fuel Cell system designed to power complex autonomous systems with dynamic pulse-shaped loads like wireless sensor nodes is presented in this work. The requirements posed by the corresponding pulse load profiles are considered for the design of the passive self-breathing Micro Fuel Cell. The performance of the Fuel Cell is mainly affected by the oxygen and water management which is influenced by the openings in the cathodic current collector. Due to the comparatively low average Cell current the performance can be strongly improved by retaining water within the Cell using a reduced opening ratio and thus improving the ionic conductivity of the electrolyte. The impact of the opening ratio is studied in the range between 54% and 0.007%. The total active area of the Fuel Cell is only 0.1 cm2. Prototypes are realized using printed circuit board technology and wet chemical etching of the Micro-structured current collectors. The Cells were characterized with an exemplary load profile with a 10 ms load pulse and a 1 s pulse period. Successful operation was demonstrated for all Cells for different current densities. A significant power improvement was achieved by reducing the opening ratio down to 0.3%. Under these circumstances a power density of 220 mW cm−2 could be generated during the pulse. This is more than twice in comparison to Cells with large opening ratios of 54% where only approx. 100 mW cm−2 was obtained.
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Study on the dynamic behavior of Zn-based hydrogen generating Cells as Fuel storage for a PEM Micro Fuel Cell system
Journal of Power Sources, 2010Co-Authors: Matthias Weiland, Stefan Wagner, S. Krumbholz, Herbert ReichlAbstract:Abstract Portable Fuel Cell systems consist of three essential parts: the Fuel Cell stack, the Fuel storage and the balance of plant (BOP) which contains all required peripheral components. Scaling down Fuel Cell systems to smaller dimensions in the power range of 1 mW to 1 W currently leads to an increased volume fraction of the peripheral components. Consequently it is necessary to forego peripheral components in small systems and develop passive systems. Furthermore Fuel storage is a challenging issue for portable Micro Fuel Cell systems. Common approaches for hydrogen storage, e.g. pressure cartridges or reversible metal hydrides yield a low energy density for the entire system. In our approach a gas evolving Cell (GEC) is used to generate hydrogen “on demand”. This allows to develop small Micro Fuel Cell systems with a high energy density. The GEC is electrically connected in series to the Fuel Cell. Hydrogen is generated through the electro catalytic Zn-H 2 O reaction and proportional to the Cell current according to Faraday's law, which leads to a simple and passive system. The dynamic and long-term behavior of the GEC is studied experimentally in this work. The electrical and chemical behavior of the GEC plays an important role in the design and operation of the Micro Fuel Cell system. Portable applications generally imply dynamic load profiles. Therefore the study focuses on the dynamic response of the GEC. The electric response of the GEC is examined for load pulses in the range of milliseconds with an amplitude of up to 150 mA for the lifecycle of a Cell. The results are compared to the behavior of the GECs under an equivalent static load in order to draw conclusions on the effect of the dynamic load. Furthermore the electrical and chemical capacity of the GECs is examined for different loads. The obtained results provide an insight into the dynamic behavior of the GEC and provide the basis for the design and operation of the Micro Fuel Cell system.
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Influence of structure dimensions on self-breathing Micro Fuel Cells
Journal of Power Sources, 2009Co-Authors: Stefan Wagner, Robert Hahn, S. Krumbholz, Herbert ReichlAbstract:In this paper a proton exchange membrane Micro Fuel Cell (PEMFC) with a passive air breathing cathode and Microstructured flow fields is studied comprehensively using a numerical model and experimental characterization. The design of the flow field structures is directly dependent on the fabrication technology. An optimization of structure dimensions is possible within the design space. A model is presented, which describes the influence of the aspect ratio of the channel width and the rib width of the Micro flow field for a structure were no gas diffusion layers are incorporated. The Fuel Cell performance is limited by electrical losses in the electrode layer for large channel widths and by reactant transport for small channel widths.
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Development of Micro Fuel Cells with organic substrates and electronics manufacturing technologies
2008 58th Electronic Components and Technology Conference, 2008Co-Authors: Robert Hahn, Stefan Wagner, S. Krumbholz, Herbert ReichlAbstract:A PEM Micro Fuel Cell system is described which is based on self-breathing PEM Micro Fuel Cells in the power range between 1 mW and 1 W. Micro patterned substrates were used as Micro flow fields and replacement of gas diffusion layers (GDL). An analytical model was developed to estimate the losses in such structures and optimize channel design and current collector metallization. A detailed comparison was made between two different designs: pin structures and channel structures. A variety of Micro Fuel Cells with variations of design parameters were tested to verify the model. As a result, Micro Fuel Cell fabrication can be optimized in terms of Cell performance and production costs. A maximum power density of 160 mW/cm2 has been achieved with the GDL-less design and a current collector pitch of 400 mum with commercial membrane electrode assemblies.
Chi-yuan Lee - One of the best experts on this subject based on the ideXlab platform.
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A novel integration approach for combining the Micro thermal sensor and stainless steel foil as gas diffusion layer in Micro Fuel Cell
Renewable Energy, 2010Co-Authors: Chi-yuan Lee, Chen-hen LinAbstract:Abstract Fuel Cells will be used extensively in the future as renewable energy sources and they are the subject of substantial research. However, various problems are encountered with their mass production, such as the bipolar plate, the flow channel, the catalyst, the membrane electrode assembly (MEA), and the gas diffusion layer (GDL). Given the present uneven gas reactions and the difficulty of obtaining information on the temperature in a Fuel Cell, this novel investigation utilized Micro-electro-mechanical-systems (MEMS) to integrate a Micro thermal sensor and a stainless steel foil as a gas diffusion layer. The reaction inside a Micro Fuel Cell must be controlled and adjusted in real time. The results of the experiment demonstrated that the accuracy and sensitivity of the Micro thermal sensor were 0.5 °C and 1.805 × 10−3/°C, respectively.
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Integration of silicon Micro-hole arrays as a gas diffusion layer in a Micro-Fuel Cell
International Journal of Hydrogen Energy, 2009Co-Authors: Chi-yuan Lee, Shuo-jen Lee, Wen-pin Shih, Wei-yuan Fan, Chih-wei ChuangAbstract:Abstract This work examines silicon Micro-hole arrays (Si-MHA) as a gas diffusion layer (GDL) in a Micro-Fuel Cell that was fabricated using Micro-electro-mechanical systems (MEMS) fabrication technique. Pt was deposited on the surface of the Si-MHA, to increase the conductivity of the Micro-Fuel Cell. The Si-MHA with three Micro-holes, replaces the traditional GDL, and the performance of the Micro-proton exchange membrane Fuel Cell was discussed. Wet etching was performed on a 500 μm-thick layer of silicon to yield Fuel channels with a depth of 450 μm and a width of 200 μm. The Si-MHA formed by deep reactive ion etching (DRIE) in the fabricated structure had diameters of 10 μm, 30 μm and 50 μm; the thickness of the structure was 50 μm. The experiment yielded results for 10 μm, 30 μm and 50 μm Micro-hole arrays, for various Fuel flow rates and under various operating conditions. The maximum power density was approximately 8.13 mW/cm2 with H2/O2 gas flow rates of 30/30 ml/min and 10 μm Micro-hole arrays at 20 °C.
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NEMS - Integration of Micro flow sensor and flexible substrate as GDL in Micro Fuel Cell
2009 4th IEEE International Conference on Nano Micro Engineered and Molecular Systems, 2009Co-Authors: Chi-yuan Lee, Shuo-jen Lee, Yu-ming Lee, Kuan-yu ChuAbstract:The production of useable energy is today a global issue and the search for alternative energy sources is very challenging. Therefore, scientists have' tried hard to identify new alternative energy sources. Fuel Cells have potential as an indispensable source of electrical power. However, the mass production of Fuel Cells encounters various problems, which are yet to be solved, such as determining the Fuel flow rate inside Fuel Cells. The product of the chemical reaction that proceeds in a Fuel Cell is water, which lowers the working efficiency of the Cell and affects the Fuel flow rate. No study of the Fuel flow rate within a Micro Fuel Cell has yet been published. Hence, in this work, Micro flow sensors are fabricated on a flexible substrate as the gas diffusion layer (GDL) using Micro-electro-mechanical systems (MEMS) within the Micro Fuel Cell. The fundamental concept of the Micro flow sensor is the use of two sets of Micro temperature sensors plus and a set of heaters. The temperature difference between the two sensors is measured. The heater is also used to increase the working temperature of the Fuel Cell when the actual temperature is not favorable. The experimental results show an accuracy and sensitivity of the Micro temperature sensor of 0.5°C and 1.31Ω/°C, respectively.
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Embedded flexible Micro-sensors in MEA for measuring temperature and humidity in a Micro-Fuel Cell
Journal of Power Sources, 2008Co-Authors: Chi-yuan Lee, Wei-jung HsiehAbstract:Abstract In this investigation, flexible sensors embedded in a membrane electrode assembly (MEA) are fabricated to measure the temperature and humidity of a Micro-Fuel Cell. Fuel Cell performance was determined by the temperature and humidity of the MEA. Restrictions on the sensor volume are such that in previous investigations the temperature and the humidity of the MEA have been measured only at the Fuel inlet and outlet. Hence, flexible Micro-thin film sensors were fabricated using Micro-electro-mechanical systems (MEMS) fabrication technology. The thin film flexible sensor was 2 μm thick. The temperature and humidity sensors had areas of 180 μm × 180 μm and 180 μm × 220 μm, respectively. A flow channel was integrated in a stainless-steel base (SS-304) with Micro-channels that are 300 μm wide and 200 μm deep using wet-etching technology. This study reveals the feasibility of utilizing flexible thin film sensors with Micro-Fuel Cells to measure local temperature and humidity in an MEA. We found that the maximum temperature difference between MEA and the outer surface of a bipolar plate is 5.7 °C. The optimal performance curves of the single Cell are obtained at 50 °C, 75%RH and H 2 /O 2 gas flow rates of 50 ml min −1 . The maximum power density of the Fuel Cell was 358 mW cm −2 and the current density was 796 mA cm −2 when the Cell voltage was 0.45 V.
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A novel integration approach for combining the components to minimize a Micro-Fuel Cell
2007Co-Authors: Chi-yuan Lee, Chih-wei ChuangAbstract:This work employs porous silicon as a gas diffusion layer (GDL) in a Micro-Fuel Cell. Pt catalyst is deposited on the surface of, and inside, the porous silicon by the physical vapor deposition (PVD) method, to improve the porous silicon conductivity. Porous silicon with Pt catalyst replaces traditional GDL, and the Pt metal that remains on the rib is used to form a Micro-thermal sensor in a single lithographic process. The GDL was replaced by porous silicon and used in a proton exchange membrane Fuel Cell (PEMFC). Wet etching is applied to a 500 μm thick layer of silicon to yield Fuel channels with a depth of 450 μm and a width of 200 μm. The pores in the fabricated structure had two diameters, 10 μm and less than 1 μm; its thickness was 50 μm. Accordingly, the GDLs of the Fuel Cell are fabricated using macro-porous silicon technology. Porous silicon was fabricated by photoelectrochemical porous silicon etching. The topside of the Fuel channel was exposed to light from a halogen lamp. The porous structure was fabricated at the bottom of the Fuel channel and patterned by anodization. The principles on which the method is based, the details of the fabrication flows, the set-up and the experimental results are all presented.
Stefan Wagner - One of the best experts on this subject based on the ideXlab platform.
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Optimization of efficiency and energy density of passive Micro Fuel Cells and galvanic hydrogen generators
2016Co-Authors: Robert Hahn, Steffen Krumbholz, Stefan Wagner, Herbert ReichlAbstract:A PEM Micro Fuel Cell system is described which is based on self-breathing PEM Micro Fuel Cells in the power range between 1 mW and 1W. Hydrogen is supplied with on-demand hydrogen production with help of a galvanic Cell, that produces hydrogen when Zn reacts with water. The system can be used as a battery replacement for low power applications and has the potential to improve the run time of autonomous systems. The efficiency has been investigated as function of Fuel Cell construction and tested for several load profiles.
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Design and evaluation of a passive self-breathing Micro Fuel Cell for autonomous portable applications
International Journal of Hydrogen Energy, 2013Co-Authors: Matthias Weiland, Stefan Wagner, Robert Hahn, Herbert ReichlAbstract:A Micro Fuel Cell system designed to power complex autonomous systems with dynamic pulse-shaped loads like wireless sensor nodes is presented in this work. The requirements posed by the corresponding pulse load profiles are considered for the design of the passive self-breathing Micro Fuel Cell. The performance of the Fuel Cell is mainly affected by the oxygen and water management which is influenced by the openings in the cathodic current collector. Due to the comparatively low average Cell current the performance can be strongly improved by retaining water within the Cell using a reduced opening ratio and thus improving the ionic conductivity of the electrolyte. The impact of the opening ratio is studied in the range between 54% and 0.007%. The total active area of the Fuel Cell is only 0.1 cm2. Prototypes are realized using printed circuit board technology and wet chemical etching of the Micro-structured current collectors. The Cells were characterized with an exemplary load profile with a 10 ms load pulse and a 1 s pulse period. Successful operation was demonstrated for all Cells for different current densities. A significant power improvement was achieved by reducing the opening ratio down to 0.3%. Under these circumstances a power density of 220 mW cm−2 could be generated during the pulse. This is more than twice in comparison to Cells with large opening ratios of 54% where only approx. 100 mW cm−2 was obtained.
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Study on the dynamic behavior of Zn-based hydrogen generating Cells as Fuel storage for a PEM Micro Fuel Cell system
Journal of Power Sources, 2010Co-Authors: Matthias Weiland, Stefan Wagner, S. Krumbholz, Herbert ReichlAbstract:Abstract Portable Fuel Cell systems consist of three essential parts: the Fuel Cell stack, the Fuel storage and the balance of plant (BOP) which contains all required peripheral components. Scaling down Fuel Cell systems to smaller dimensions in the power range of 1 mW to 1 W currently leads to an increased volume fraction of the peripheral components. Consequently it is necessary to forego peripheral components in small systems and develop passive systems. Furthermore Fuel storage is a challenging issue for portable Micro Fuel Cell systems. Common approaches for hydrogen storage, e.g. pressure cartridges or reversible metal hydrides yield a low energy density for the entire system. In our approach a gas evolving Cell (GEC) is used to generate hydrogen “on demand”. This allows to develop small Micro Fuel Cell systems with a high energy density. The GEC is electrically connected in series to the Fuel Cell. Hydrogen is generated through the electro catalytic Zn-H 2 O reaction and proportional to the Cell current according to Faraday's law, which leads to a simple and passive system. The dynamic and long-term behavior of the GEC is studied experimentally in this work. The electrical and chemical behavior of the GEC plays an important role in the design and operation of the Micro Fuel Cell system. Portable applications generally imply dynamic load profiles. Therefore the study focuses on the dynamic response of the GEC. The electric response of the GEC is examined for load pulses in the range of milliseconds with an amplitude of up to 150 mA for the lifecycle of a Cell. The results are compared to the behavior of the GECs under an equivalent static load in order to draw conclusions on the effect of the dynamic load. Furthermore the electrical and chemical capacity of the GECs is examined for different loads. The obtained results provide an insight into the dynamic behavior of the GEC and provide the basis for the design and operation of the Micro Fuel Cell system.
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Influence of structure dimensions on self-breathing Micro Fuel Cells
Journal of Power Sources, 2009Co-Authors: Stefan Wagner, Robert Hahn, S. Krumbholz, Herbert ReichlAbstract:In this paper a proton exchange membrane Micro Fuel Cell (PEMFC) with a passive air breathing cathode and Microstructured flow fields is studied comprehensively using a numerical model and experimental characterization. The design of the flow field structures is directly dependent on the fabrication technology. An optimization of structure dimensions is possible within the design space. A model is presented, which describes the influence of the aspect ratio of the channel width and the rib width of the Micro flow field for a structure were no gas diffusion layers are incorporated. The Fuel Cell performance is limited by electrical losses in the electrode layer for large channel widths and by reactant transport for small channel widths.
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Development of Micro Fuel Cells with organic substrates and electronics manufacturing technologies
2008 58th Electronic Components and Technology Conference, 2008Co-Authors: Robert Hahn, Stefan Wagner, S. Krumbholz, Herbert ReichlAbstract:A PEM Micro Fuel Cell system is described which is based on self-breathing PEM Micro Fuel Cells in the power range between 1 mW and 1 W. Micro patterned substrates were used as Micro flow fields and replacement of gas diffusion layers (GDL). An analytical model was developed to estimate the losses in such structures and optimize channel design and current collector metallization. A detailed comparison was made between two different designs: pin structures and channel structures. A variety of Micro Fuel Cells with variations of design parameters were tested to verify the model. As a result, Micro Fuel Cell fabrication can be optimized in terms of Cell performance and production costs. A maximum power density of 160 mW/cm2 has been achieved with the GDL-less design and a current collector pitch of 400 mum with commercial membrane electrode assemblies.