Polymer electrolyte membrane fuel cells provide an alternative option to fossil fuel-based energy... more Polymer electrolyte membrane fuel cells provide an alternative option to fossil fuel-based energy conversion devices. However, the corrosion of fuel cell components, specifically the bipolar plates, introduces contaminants (e.g., Fe, Ni) into the membrane electrode assembly (MEA). These contaminants accelerate the ionomer degradation by acting as a Fenton’s reagent, decreasing the fuel cell’s durability. This study presents the mechanism and the diffusion media properties affecting the transport of cation contaminants into the MEA. Cation contaminant transport was studied after altering the gas diffusion layers (GDLs) wettability, emulating the GDL properties after prolonged operation, by ex situ hydrogen peroxide treatment or in situ electrochemical potential cycling. A GDL with crack-free microporous layer (MPL) showed a lower cation transport rate to the catalyst layer than MPL with cracks after both ex situ and in situ treatment. A novel GDL was developed from modification of th...
Page 1. J. Phys. Chem. 1989, 93, 3087-3089 3087 Comparison between the Geometric and Harmonic Mea... more Page 1. J. Phys. Chem. 1989, 93, 3087-3089 3087 Comparison between the Geometric and Harmonic Mean Electronegativity Equilibration Techniques Mahlon S. Wilson and Shinichi Ichikawa* Department of Chemical and ...
Proceedings of 11th Annual Battery Conference on Applications and Advances
The benefits provided by Polymer Electrolyte Fuel Cells (PEFC) for power generation (e.g. low ope... more The benefits provided by Polymer Electrolyte Fuel Cells (PEFC) for power generation (e.g. low operating temperatures, and non-corrosive and stable electrolyte), as well as advances in recent years in lowering their cost and improving anode poisoning tolerance, are stimulating interest in the system for stationary power applications. A significant market potentially exists for PEFCs in certain stationary applications where PEFC technology is a more attractive alternative to other fuel cell technologies. A difficulty with the PEFC is its operation on reformed fuels containing CO, which poisons the anode catalyst. This difficulty can be alleviated in several ways. One possible approach is described whereby the product reformate is purified using a relatively low cost, high-throughput hydrogen permselective separator. Preliminary experiments demonstrate the utility of the concept.
CeOx is an excellent free radical scavenger to improve polymer electrolyte membrane durability. H... more CeOx is an excellent free radical scavenger to improve polymer electrolyte membrane durability. However, this metal oxide will dissolve during accelerated stress testing (AST), with the resulting cations transporting to the cathode catalyst layer (CCL) leading to performance reduction/degradation of the PEMFC. Controlling the rate of CeOx dissolution is therefore of great importance, as it may be possible to maintain sufficient Ce cations for free radical scavenging while minimizing the impact of these cations on the CCL. Here the effect of CeOx crystallite size on CeOx dissolution was investigated. Three CeOx additives were prepared having crystallite sizes of 6, 13, or 25 nm. An ex-situ method was used to evaluate the chemical stability of these three CeOx samples, as well as one commercially available CeOx. It was determined that surface area, rather than crystallite size, is the best predictor of chemical stability. In-situ membrane electrode assembly AST cycling was then performed, demonstrating that when low loadings of CeOx (0.006 mg/cm 2) are used, the ex-situ method correctly predicts trends in end of life (EOL) performance. Finally, it is shown that increasing the anode RH during AST cycling leads to significantly higher EOL performance losses.
removal from a mould, resulting in long cycle USA times. A novel composite material for fuel cell... more removal from a mould, resulting in long cycle USA times. A novel composite material for fuel cell bipolar plates is described which is lowcost, lightweight, impermeable, strong, tough, corrosion-resistant and easily processable. These composites overcome some of the major disadvantages of traditiona bipolar plate materials while maintaining comparable performance in fuel cells.
Improve tolerance to carbon monoxide (CO) and study the effect of other fuel and air impurities. ... more Improve tolerance to carbon monoxide (CO) and study the effect of other fuel and air impurities. • Improve the efficiency of the fuel cell electrodes while lowering the dependence on Pt loadings. • Improve overall polymer electrolyte membrane (PEM) fuel cell operating efficiency.
Polymer electrolyte fuel cell membranes are degraded by oxygen free radical attack. The addition ... more Polymer electrolyte fuel cell membranes are degraded by oxygen free radical attack. The addition of cerium oxide and doped cerium oxide nanoparticles improves membrane stability as measured by open circuit voltage and low humidity accelerated stress testing. In this work we varied the crystallite size of ceria nanoparticles and investigated their role in enhancing durability of the PEM fuel cell. We found that the ratio of the free radical production to hydrogen peroxide decomposition rates provides a novel approach to characterize the efficiency of free radical scavenging catalysts. Nanoparticle crystallite size and doping plays a significant role in determining the surface area normalized efficiency of ceria based free radical scavengers.
Platinum surface area was chemically and electrochemically characterized using X-ray diffraction ... more Platinum surface area was chemically and electrochemically characterized using X-ray diffraction (XRD), H 2 S adsorption, and electrochemical techniques including halfcells and fuel cells. Electrode ink processing and composition were found to have a strong impact on observed surface area with increased processing leading to a reduction in platinum surface area. Fuel cell electrode measurements show a significant portion of the platinum may not be available. This unutilized Pt may be due to either ionic or electronic connectivity as evidence exists to support both ionic and electronic isolation.
ABSTRACTThe most costly and problematic components of fuel cell stacks may be bipolar plates. Bes... more ABSTRACTThe most costly and problematic components of fuel cell stacks may be bipolar plates. Besides meeting cost constraints, bipolar plates must possess a host of other properties including low gas permeability, corrosion resistance, low weight, high strength, and manufacturability. While we have developed a baseline composite material that meets these requirements, further optimization and development have resulted in significant improvements in properties and processability.
Metal hexaborides demonstrate the unusual ability to spontaneously deposit noble metals from solu... more Metal hexaborides demonstrate the unusual ability to spontaneously deposit noble metals from solution without the need for separate reducing agents or pretreatments. A range of deposition thicknesses are possible and uniform and strongly adherent 30 nm thick metal films on lanthanum hexaboride sputter- coated glass are easily and quickly achieved. Full and uniform coverages of hexaboride powders are obtained even with deposits only ca. 1 nm thick. Cyclic voltammetry for 4 wt% Pt on a roughly 1 m2/g EuB6 powder show electrochemically active Pt surface area, derived from the area under the hydrogen absorption curve, to be 39 m2/g Pt and is exceptional considering the low hexaboride support surface area. This result suggests that the entire support area is covered with Pt (approximately 1 nm thick) and that the entire Pt surface is electrochemically active.
A compelling market segment for the introduction of fuel cells is in small battery types of appli... more A compelling market segment for the introduction of fuel cells is in small battery types of applications. While in other applications (e.g. transportation), fuel cells need to compete with relatively effective and low-cost technologies, batteries are easier to compete with because they are expensive and have low energy densities. Even with modest hydrogen storage densities such as metal hydrides, fuel cells can provide higher energy densities than batteries and the values can increase substantially further with an increase in the energy to power ratio of the system (which is fixed for batteries). However, the fuel cells will still have to compete with batteries on reliability and cost. As such, the typical polymer electrolyte fuel cell system with its heavy reliance on subsystems for cooling, humidification and air supply would not be practical in small battery applications. Instead, the fuel cell system should ideally be simple, inexpensive, and reliable. In response, Los Alamos Na...
An inexpensive sample transfer system suitable for surface studies with in situ prepared model ca... more An inexpensive sample transfer system suitable for surface studies with in situ prepared model catalysts is described. Experiments from ultrahigh vacuum to 10 atm and 50-cm travel with negligible pressure spikes were made possible by the use of double-seal glands with spring-loaded Teflon O-rings and a guided rotational transport rod.
A fuel cell produces electrical energy via an electrochemical reaction. Unlike a conventional bat... more A fuel cell produces electrical energy via an electrochemical reaction. Unlike a conventional battery, the "fuel" and oxidant are supplied to the device from external sources. The device can thus be operated until the fuel (or oxidant) supply is exhausted, which can provide very high energy densities for the overall system. Historically, fuel cells have been of principle interest to the space program because of their high intrinsic conversion efficiencies and benign reaction product (water). Because of these various advantages and ever increasing environmental concerns, most types of fuel cells are attracting greater commercial and government interest. However, the popularity of a relatively new type of fuel cell, the polymer electrolyte membrane (PEM) fuel cell, is rapidly outpacing the others. Unlike most other types of fuel cells, which use liquid electrolytes, the PEM fuel cell uses a quasi-solid electrolyte based on a polymer backbone with side-chains possessing acid-...
Described is the most recent configuration of a segmented cell used to measure current distributi... more Described is the most recent configuration of a segmented cell used to measure current distribution across the surface of an electrode in a polymer electrolyte fuel cell (PEFC). In this fourth generation cell design, measurement and data collection capabilities have been modified to significantly improve ease of use and quality of information obtained. The current configuration allows examination of spatial resolution of the cell current and cell voltage with respect to well-defined baseline reference measurements, as well as measurement of the high frequency resistance (HFR) distribution and spatial ac impedance spectroscopy. This specially designed cell is intended for use in studies on time and location resolved carbon monoxide poisoning, humidification and flow-field design effects on fuel cell performance.
... Xiaoming Ren, Mahlon S. Wilson, Shimshon Gottesfeld. Abstract. Direct methanol fuel cells (DM... more ... Xiaoming Ren, Mahlon S. Wilson, Shimshon Gottesfeld. Abstract. Direct methanol fuel cells (DMFCs) using Pt‐Ru electrocatalysts and perfluorosulfonic acid membranes provide high performances if operated above 100°C with optimized catalyst layers. ...
Spontaneous Deposition of Noble Metal Films onto Hexaboride Surfaces. [Journal of The Electrochem... more Spontaneous Deposition of Noble Metal Films onto Hexaboride Surfaces. [Journal of The Electrochemical Society 154, D623 (2007)]. Francisco A. Uribe, Fernando H. Garzon, Eric L. Brosha, Christina M. Johnston, Steven D. Conradson, Mahlon S. Wilson. Abstract. ...
Polymer electrolyte membrane fuel cells provide an alternative option to fossil fuel-based energy... more Polymer electrolyte membrane fuel cells provide an alternative option to fossil fuel-based energy conversion devices. However, the corrosion of fuel cell components, specifically the bipolar plates, introduces contaminants (e.g., Fe, Ni) into the membrane electrode assembly (MEA). These contaminants accelerate the ionomer degradation by acting as a Fenton’s reagent, decreasing the fuel cell’s durability. This study presents the mechanism and the diffusion media properties affecting the transport of cation contaminants into the MEA. Cation contaminant transport was studied after altering the gas diffusion layers (GDLs) wettability, emulating the GDL properties after prolonged operation, by ex situ hydrogen peroxide treatment or in situ electrochemical potential cycling. A GDL with crack-free microporous layer (MPL) showed a lower cation transport rate to the catalyst layer than MPL with cracks after both ex situ and in situ treatment. A novel GDL was developed from modification of th...
Page 1. J. Phys. Chem. 1989, 93, 3087-3089 3087 Comparison between the Geometric and Harmonic Mea... more Page 1. J. Phys. Chem. 1989, 93, 3087-3089 3087 Comparison between the Geometric and Harmonic Mean Electronegativity Equilibration Techniques Mahlon S. Wilson and Shinichi Ichikawa* Department of Chemical and ...
Proceedings of 11th Annual Battery Conference on Applications and Advances
The benefits provided by Polymer Electrolyte Fuel Cells (PEFC) for power generation (e.g. low ope... more The benefits provided by Polymer Electrolyte Fuel Cells (PEFC) for power generation (e.g. low operating temperatures, and non-corrosive and stable electrolyte), as well as advances in recent years in lowering their cost and improving anode poisoning tolerance, are stimulating interest in the system for stationary power applications. A significant market potentially exists for PEFCs in certain stationary applications where PEFC technology is a more attractive alternative to other fuel cell technologies. A difficulty with the PEFC is its operation on reformed fuels containing CO, which poisons the anode catalyst. This difficulty can be alleviated in several ways. One possible approach is described whereby the product reformate is purified using a relatively low cost, high-throughput hydrogen permselective separator. Preliminary experiments demonstrate the utility of the concept.
CeOx is an excellent free radical scavenger to improve polymer electrolyte membrane durability. H... more CeOx is an excellent free radical scavenger to improve polymer electrolyte membrane durability. However, this metal oxide will dissolve during accelerated stress testing (AST), with the resulting cations transporting to the cathode catalyst layer (CCL) leading to performance reduction/degradation of the PEMFC. Controlling the rate of CeOx dissolution is therefore of great importance, as it may be possible to maintain sufficient Ce cations for free radical scavenging while minimizing the impact of these cations on the CCL. Here the effect of CeOx crystallite size on CeOx dissolution was investigated. Three CeOx additives were prepared having crystallite sizes of 6, 13, or 25 nm. An ex-situ method was used to evaluate the chemical stability of these three CeOx samples, as well as one commercially available CeOx. It was determined that surface area, rather than crystallite size, is the best predictor of chemical stability. In-situ membrane electrode assembly AST cycling was then performed, demonstrating that when low loadings of CeOx (0.006 mg/cm 2) are used, the ex-situ method correctly predicts trends in end of life (EOL) performance. Finally, it is shown that increasing the anode RH during AST cycling leads to significantly higher EOL performance losses.
removal from a mould, resulting in long cycle USA times. A novel composite material for fuel cell... more removal from a mould, resulting in long cycle USA times. A novel composite material for fuel cell bipolar plates is described which is lowcost, lightweight, impermeable, strong, tough, corrosion-resistant and easily processable. These composites overcome some of the major disadvantages of traditiona bipolar plate materials while maintaining comparable performance in fuel cells.
Improve tolerance to carbon monoxide (CO) and study the effect of other fuel and air impurities. ... more Improve tolerance to carbon monoxide (CO) and study the effect of other fuel and air impurities. • Improve the efficiency of the fuel cell electrodes while lowering the dependence on Pt loadings. • Improve overall polymer electrolyte membrane (PEM) fuel cell operating efficiency.
Polymer electrolyte fuel cell membranes are degraded by oxygen free radical attack. The addition ... more Polymer electrolyte fuel cell membranes are degraded by oxygen free radical attack. The addition of cerium oxide and doped cerium oxide nanoparticles improves membrane stability as measured by open circuit voltage and low humidity accelerated stress testing. In this work we varied the crystallite size of ceria nanoparticles and investigated their role in enhancing durability of the PEM fuel cell. We found that the ratio of the free radical production to hydrogen peroxide decomposition rates provides a novel approach to characterize the efficiency of free radical scavenging catalysts. Nanoparticle crystallite size and doping plays a significant role in determining the surface area normalized efficiency of ceria based free radical scavengers.
Platinum surface area was chemically and electrochemically characterized using X-ray diffraction ... more Platinum surface area was chemically and electrochemically characterized using X-ray diffraction (XRD), H 2 S adsorption, and electrochemical techniques including halfcells and fuel cells. Electrode ink processing and composition were found to have a strong impact on observed surface area with increased processing leading to a reduction in platinum surface area. Fuel cell electrode measurements show a significant portion of the platinum may not be available. This unutilized Pt may be due to either ionic or electronic connectivity as evidence exists to support both ionic and electronic isolation.
ABSTRACTThe most costly and problematic components of fuel cell stacks may be bipolar plates. Bes... more ABSTRACTThe most costly and problematic components of fuel cell stacks may be bipolar plates. Besides meeting cost constraints, bipolar plates must possess a host of other properties including low gas permeability, corrosion resistance, low weight, high strength, and manufacturability. While we have developed a baseline composite material that meets these requirements, further optimization and development have resulted in significant improvements in properties and processability.
Metal hexaborides demonstrate the unusual ability to spontaneously deposit noble metals from solu... more Metal hexaborides demonstrate the unusual ability to spontaneously deposit noble metals from solution without the need for separate reducing agents or pretreatments. A range of deposition thicknesses are possible and uniform and strongly adherent 30 nm thick metal films on lanthanum hexaboride sputter- coated glass are easily and quickly achieved. Full and uniform coverages of hexaboride powders are obtained even with deposits only ca. 1 nm thick. Cyclic voltammetry for 4 wt% Pt on a roughly 1 m2/g EuB6 powder show electrochemically active Pt surface area, derived from the area under the hydrogen absorption curve, to be 39 m2/g Pt and is exceptional considering the low hexaboride support surface area. This result suggests that the entire support area is covered with Pt (approximately 1 nm thick) and that the entire Pt surface is electrochemically active.
A compelling market segment for the introduction of fuel cells is in small battery types of appli... more A compelling market segment for the introduction of fuel cells is in small battery types of applications. While in other applications (e.g. transportation), fuel cells need to compete with relatively effective and low-cost technologies, batteries are easier to compete with because they are expensive and have low energy densities. Even with modest hydrogen storage densities such as metal hydrides, fuel cells can provide higher energy densities than batteries and the values can increase substantially further with an increase in the energy to power ratio of the system (which is fixed for batteries). However, the fuel cells will still have to compete with batteries on reliability and cost. As such, the typical polymer electrolyte fuel cell system with its heavy reliance on subsystems for cooling, humidification and air supply would not be practical in small battery applications. Instead, the fuel cell system should ideally be simple, inexpensive, and reliable. In response, Los Alamos Na...
An inexpensive sample transfer system suitable for surface studies with in situ prepared model ca... more An inexpensive sample transfer system suitable for surface studies with in situ prepared model catalysts is described. Experiments from ultrahigh vacuum to 10 atm and 50-cm travel with negligible pressure spikes were made possible by the use of double-seal glands with spring-loaded Teflon O-rings and a guided rotational transport rod.
A fuel cell produces electrical energy via an electrochemical reaction. Unlike a conventional bat... more A fuel cell produces electrical energy via an electrochemical reaction. Unlike a conventional battery, the "fuel" and oxidant are supplied to the device from external sources. The device can thus be operated until the fuel (or oxidant) supply is exhausted, which can provide very high energy densities for the overall system. Historically, fuel cells have been of principle interest to the space program because of their high intrinsic conversion efficiencies and benign reaction product (water). Because of these various advantages and ever increasing environmental concerns, most types of fuel cells are attracting greater commercial and government interest. However, the popularity of a relatively new type of fuel cell, the polymer electrolyte membrane (PEM) fuel cell, is rapidly outpacing the others. Unlike most other types of fuel cells, which use liquid electrolytes, the PEM fuel cell uses a quasi-solid electrolyte based on a polymer backbone with side-chains possessing acid-...
Described is the most recent configuration of a segmented cell used to measure current distributi... more Described is the most recent configuration of a segmented cell used to measure current distribution across the surface of an electrode in a polymer electrolyte fuel cell (PEFC). In this fourth generation cell design, measurement and data collection capabilities have been modified to significantly improve ease of use and quality of information obtained. The current configuration allows examination of spatial resolution of the cell current and cell voltage with respect to well-defined baseline reference measurements, as well as measurement of the high frequency resistance (HFR) distribution and spatial ac impedance spectroscopy. This specially designed cell is intended for use in studies on time and location resolved carbon monoxide poisoning, humidification and flow-field design effects on fuel cell performance.
... Xiaoming Ren, Mahlon S. Wilson, Shimshon Gottesfeld. Abstract. Direct methanol fuel cells (DM... more ... Xiaoming Ren, Mahlon S. Wilson, Shimshon Gottesfeld. Abstract. Direct methanol fuel cells (DMFCs) using Pt‐Ru electrocatalysts and perfluorosulfonic acid membranes provide high performances if operated above 100°C with optimized catalyst layers. ...
Spontaneous Deposition of Noble Metal Films onto Hexaboride Surfaces. [Journal of The Electrochem... more Spontaneous Deposition of Noble Metal Films onto Hexaboride Surfaces. [Journal of The Electrochemical Society 154, D623 (2007)]. Francisco A. Uribe, Fernando H. Garzon, Eric L. Brosha, Christina M. Johnston, Steven D. Conradson, Mahlon S. Wilson. Abstract. ...
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