James M. Fenton's research while affiliated with University of Central Florida and other places

Publications (121)

Chapter
The practical application of theory to experiment and data analysis is a crucial component of effective advancement of electrochemical systems. This chapter takes the fundamental principles of fuel cell operation and the underlying scientific and engineering principles and applies them to laboratory experiments. Topics covered include experiments s...
Article
Full-text available
The ability to determine the state of charge of vanadium solutions is critical to understanding reaction mechanisms and charge transport dynamics. This paper describes in detail the methods used to generate quantitative concentrations of three of the four species in an all-vanadium flow battery. The UV-Vis method was shown to provide concentration...
Conference Paper
The Florida Solar Energy Center (FSEC) has led the U.S. Department of Energy (DOE) High Temperature Membrane Working Group (HTMWG) since 2006. The HTMWG investigates membrane performance at elevated temperature/low relative humidity conditions. For the final three years of the project, FSEC has worked with six teams to develop membrane electrode as...
Conference Paper
The lifetime of proton exchange membrane (PEM) fuel cells depends largely on the durability of the PEM and is a critical issue in the commercialization of PEM fuel cell technology (1, 2). Perfluorosulfonated acid (PFSA) membranes, such as Nafion®, are the most widely used electrolyte material for PEM fuel cells. Many factors can cause PEM failure...
Conference Paper
An important step in achieving fundamental understanding of fuel cell failure mechanisms and development of technology to mitigate these failures is accomplished by analysis of directed lifetime and failure test results. Several lifetime, accelerated stress, and drive cycle test protocols have been developed and carried out. The two major ASTs that...
Article
The determination of hydrogen permeation through a polymer electrolyte membrane is often achieved through electrochemical methods, under the assumption of no oxygen at the working electrode. However, multiple experiments utilizing low hydrogen crossover conditions have shown reduction currents resulting from trace amounts (2–3 ppm) of oxygen. For c...
Article
Cost, durability, performance, reliability, efficiency, and size are some of the requirements that must be met before proton exchange membrane (PEM) fuel cells can be used more extensively. The steady, moderate loss of performance is usually a result of steady electrode degradation, due to carbon corrosion, platinum dissolution and deposition insid...
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To establish a universal procedure to determine and predict the durability of components of PEM fuel cells in practical applications, it is desirable to assess the extent to which accelerated stress tests amplify cell degradation compared to lifetime tests. Experimental data from performance evaluation tests and open circuit voltage accelerated str...
Article
Poly(ether ether ketone) (PEEK) was sulfonated by electrophillic aromatic substitution to produce a highly water soluble polymer. With an equivalent weight (EW) of 381g/eq, the polymer is capable of a proton conductivity of 0.2S/cm at 80°C and 100% relative humidity (RH). High proton conductivity in polymer electrolyte membranes is a key factor for...
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Carbon corrosion is an important degradation mechanism that impairs PEMFC performance through destruction of catalyst connectivity, collapse of pore structure, and loss of hydrophobic character. In this study, carbon corrosion was quantified in situ by measurement of carbon dioxide in fuel cell exhaust gases through non-dispersive infrared spectros...
Conference Paper
PEM fuel cell electrode performance is shown to be influenced by catalyst ink application methods in a spray-type setup. As the spray parameters are varied, diffusion resistance changes significantly. SEM images reveal particles of ionomer and catalyst are formed with different sizes. Larger particles are formed when the ink has a greater amount of...
Conference Paper
To circumvent conductivity and therefore performance losses due to hot pressing, proton exchange membranes (PEMs) were immersed in high-boiling point solvents prior to hot pressing. It was hypothesized that the presence of the high boiling point solvents during hot pressing would prevent collapse of the hydrophilic domains because, unlike water, th...
Article
Sulfonated poly(etheretherketone) (SPEEK), with 577 g per equivalent proton, was made by the direct sulfonation method using sulfuric acid. Composite membranes were prepared by the addition of 0, 5, 15, 30, and 40 wt % phosphotungstic acid (PTA) to the nonwater soluble SPEEK. After Cs(+) stabilization of the solid acid-containing composites was don...
Article
The durability of polymer electrolyte membrane (PEM) fuel cells is a major barrier to the commercialization of these systems for stationary and transportation power applications. Commercial viability depends on improving the durability of the fuel cell components to increase the system reliability. The aim of this work is to separate ionomer degrad...
Article
Durability studies were carried out on membrane electrode assemblies (MEA)s containing commercial Nafion® membranes. Fuel cells were run under hydrogen/air for 100 hours at 10 to 100% relative humidity, 90 and 100 oC, and open circuit voltage. The voltage was monitored during the durability test, as was the condensate water for presence of fluoride...
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Full-text available
Molecular H2 and O2 reacting on the surface of Pt catalyst to form the membrane degrading species is the dominating membrane degradation mechanism in PEMFCs; not the formation of active oxygen species from H2O2 decomposition or the direct formation of active oxygen species in the oxygen reduction reaction. The source of H2 or O2 is from the reactan...
Article
750 EW perfluorosulfonic acid composite membranes with 15% phosphotungstic acid (FSEC3) were prepared and characterized for high temperature/low relative humidity PEM fuel cell. The membranes at different stages of fabrication, i.e., as cast, Cs treated, and protonated were evaluated with FTIR, XRD, TGA, water uptake, TEM and SEM. By using a low re...
Article
Two different fabrication procedures of catalyst coated membranes (CCMs) using 750 EW poly [perfluorosulfonic acid] ionomer composite membranes that contain phosphotungstic acid are discussed in this study. Cell polarization was obtained at three operating conditions: 80/100/75, 100/70/70, and 120/35/35 (cell temperature {degree sign}C/anode %RH/ca...
Article
Durability studies were carried out on membrane electrode assemblies (MEA)s containing commercial Nafion® and perfluorinated ionomer/PTFE composite membranes that include the incorporation of phosphotungstic acid (PTA). Fuel cells were run for 100 hours at 30% relative humidity, 90 and 100 oC, and open circuit voltage. The voltage was monitored dur...
Article
Two types of composite membrane were prepared by incorporating phosphotungstic acid (PTA) into host NafionO` membranes; one with 1100 EW of NafionO` and 15% PTA, namely FSEC1, and the other with 750 EW of NafionO` and 15% PTA, namely FSEC3. Catalyst-coated membranes (CCMs) were made using the composite membranes with the 32 wt.% and 25 wt.% ionomer...
Article
Perovskite-type BaCeO3 has been investigated to study the effects of preparation method and cation doping on the particle size and sintering in the fabrication of dense perovskite membranes. A variety of preparation methods including solid-state reactions, coprecipitation, microemulsion, and molten salt reactions have been studied. In coprecipitati...
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Full-text available
Organic sulfonated poly(ether ketone ketone) (SPEKK) membranes with different ion-exchange capacities (IECs), and composite membranes prepared by the addition of 20 wt % phosphotungstic acid (PTA) to SPEKK were used to prepare membrane electrode assemblies (MEAs). The proton conductivity of the membranes increased with increasing IEC of the SPEKK,...
Article
In the evaluation of membranes for use in high temperature PEM fuel cells, the membrane conductivity at the higher temperature and an associated low relative humidity (RH) is a primary property of consideration. However, an electrolyte, or ionomer, must also be within the electrodes to provide for the electrochemical reactions. The properties of th...
Article
Based on experimental findings it is suggested that formation of active oxygen species from H2O2 decomposition or the direct formation of active oxygen species in the oxygen reduction reaction are not the dominating membrane degradation mechanisms in PEMFCs, instead it is the molecular H2 and O2 that react on the surface of the Pt catalyst to form...
Article
Polarization losses of proton exchange membrane (PEM) fuel cells at 120°C and reduced relative humidity (RH) were analyzed. Reduced RH affects membrane and electrode ionic resistance, catalytic activity and oxygen transport. For a cell made of Nafion® 112 membrane and electrodes that have 35wt.% Nafion® and 0.3mg/cm2 platinum supported on carbon, m...
Article
The effects of lower equivalent weight (EW) perfluorosulfonic acid (PFSA) ionomers and catalyst on the cathode performance of proton exchange membrane fuel cells (PEMFCs) were investigated at two atmospheric pressure operating conditions: low temperature/high relative humidity (RH), RH, and high temperature/low RH, RH. Cell voltage at a curre...
Article
Surface oxidation of Pt cathode of proton exchange membrane (PEM) fuel cells at different relative humidities (RHs) was studied using cyclic voltammetry. The degree of platinum oxidation increased significantly with an increase in RH from 20% to 72%. Holding the cathode at high potentials and exposing it to air instead of N-2 resulted in the format...
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Full-text available
The organically treated montmorillonite (MMT) clays incorporated into the Nafion matrix by means of solution intercalation using dimethylacetamide (DMA) as a solvent have been tested. The diffraction patterns of the nanocomposite Nafion/MMT membranes indicated a disordered and exfoliated nanocomposite structure. The transmission electron microscopy...
Article
Carbon monoxide (CO) in the hydrogen (H2) stream can cause severe performance degradation for an H2 polymer electrolyte membrane (PEM) fuel cell. The on-board removal of CO from an H2 stream requires a process temperature less than 80 °C, and a fast reaction rate in order to minimize the reactor volume. At the present time, few technologies have be...
Article
Composite membranes consisting of Nafion-Teflon- phosphotungstic acid (NTPA) were developed for high temperature/low RH operation and demonstrate a 20% higher conductivity than that of Nafion. A fuel cell using an NPTA membrane was tested at 100{degree sign}C, 25% RH, and 150kPa total pressure for 1000 hours. The membrane resistance and hydrogen cr...
Article
The effects of lower equivalent weight (EW) PFSA ionomers on the cathode performance of PEM fuel cells were investigated at two atmospheric pressure operating conditions: low temperature/high relative humidity (RH), 80 oC/100% RH, and high temperature/low RH, 120 oC/35% RH. The optimized content in the electrode changed with the ionomer EW, from 32...
Article
Water transport induced by heat flow across polymer electrolyte fuel cell (PEFC) membranes has been studied under well-controlled thermal conditions. The investigation showed that water can be transferred across a membrane electrode assembly (MEA) that is subjected to a through-plane temperature differential. Thermo-osmotic water transport is a mem...
Article
Sulfonic acid modified perfluorocarbon polymer proton exchange membrane (PEM) fuel cells operated at elevated temperatures (120–150°C) can greatly alleviate CO poisoning on anode catalysts. However, fuel cells with these PEMs operated at elevated temperature and atmospheric pressure typically experience low relative humidity (RH) and thus have incr...
Article
Modules are described that provide experimental/analytical investigation of traditional chemical engineering concepts within the framework of a solar/hydrogen renewable energy cycle. Module lessons cover photovoltaics, thermodynamics, stoichiometry, characteristic current-voltage curves/efficiency, kinetics and transport. A self-contained solar pan...
Article
Sulfonated poly(ether ether ketone) (SPEEK) membranes were synthesized and investigated in direct methanol fuel cells (DMFCs). Single-layer SPEEK membrane with a sulfonation degree in the range from 40 to 60% showed good properties for DMFC applications. DMFC performance of pure SPEEK membranes with higher sulfonation degree (60%) decreased as temp...
Article
Organic/inorganic composite membranes with different inorganic heteropolyacid (HPA) additives maintain sufficient proton conductivities for elevated temperature (>100 °C) low relative humidity (<50%) operation. However, membrane and membrane electrode assembly (MEA) processing is severely curtailed because of the solubility of the HPA additives in...
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The carbon monoxide (CO) poisoning effect on carbon supported catalysts (Pt–Ru/C and Pt/C) in polymer electrolyte membrane (PEM) fuel cells has been investigated at higher temperatures (T>100°C) under different relative humidity (RH) conditions. To reduce the IR losses in higher temperature/lower relative humidity, Nafion®–Teflon®–Zr(HPO4)2 composi...
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Membrane degradation and failure is one of the factors limiting the overall durability of the polymer electrolyte membrane fuel cell. The fluoride emission rate (FER), which was calculated from the fuel cell effluent water analysis, was used to quantify the membrane degradation. The FER was found to decrease with an increase in load in the range fr...
Article
A quantitative investigation has been carried out to examine the effect of through-plane temperature gradients on water transport across the membrane-electrode assembly (MEA) of a Proton Exchange Membrane (PEM) fuel cell. The presence of a temperature gradient across the cell was found to cause a significant amount of water to transport through the...
Article
The membrane degradation in a polymer electrolyte membrane fuel cell (PEMFC) has been believed to occur due to formation of H2O2 and its decomposition to radicals (·OH, ·HO2) in the presence of bivalent metal cations, which can be present as impurities in the membrane. This mechanism is mainly based on the study of H2O2 formation in the oxygen redu...
Article
The involvement of H2 O2 in the membrane degradation mechanism in a polymer electrolyte membrane fuel cell (PEMFC) was investigated. Measurement of fluoride concentration in the effluent water was used as an indicator of the membrane degradation rate. It was found that H2 O2 is formed in the fuel cell in small concentrations but is not the main sou...
Article
Operating a proton exchange membrane (PEM) fuel cell at elevated temperatures (above 100 °C) has significant advantages, such as reduced CO poisoning, increased reaction rates, faster heat rejection, easier and more efficient water management and more useful waste heat. Catalyst materials and membrane electrode assembly (MEA) structure must be cons...
Article
Composite silica/Nafion® membranes were prepared using a tetraethylorthosilicate (TEOS) hydrolysis sol–gel reaction followed by solution casting. Physico-chemical properties of the composite membranes were characterized by TGA, XRD, FT-IR, SEM-EDX and water uptake. Membranes were investigated in direct methanol fuel cells (DMFCs). Lower silica load...
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Nafion membrane degradation was studied in a polymer electrolyte membrane fuel cell (PEMFC) under accelerated decay conditions. Fluoride emission rate (FER) determined by fuel cell effluent water analysis was used to quantify the membrane degradation. Membrane degradation is most likely caused either directly or indirectly by the species formed as...
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Full-text available
A quantitative investigation has been carried out to examine the effect of through-plane temperature difference on water transport across the membrane electrode assembly (MEA) of a proton exchange membrane (PEM) fuel cell. The presence of a temperature difference across the cell was found to cause a significant amount of water to transport through...
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The effect of reducing additive particle size on the conductivity of Nafion®/phosphotungstic acid composite membranes was evaluated. The additive particle size was reduced by nearly two orders of magnitude from 1 to 2 μm to 30 nm by appropriately modifying the casting procedure. The membranes prepared were characterized by transmission electron mic...
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An approach is presented to combine existing heteropolyacid (HPA) additive and membrane electrode assembly (MEA) stabilization techniques to yield a stabilized MEA for operation at 120°C and 35% relative humidity (RH). MEAs were prepared using Nafion®/phosphotungstic acid composite membranes with a phosphotungstic acid (PTA) particle size of 30–50n...
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Sulfonated poly(ether ether ketone)s (SPEEKs) with various sulfonation degrees were prepared and characterized for the intention of fuel cell applications. Two distinct water vapor activity regions characterized by different water vapor uptake behaviors were observed. Proton conductivity of SPEEK membranes increases with increasing sulfonation degr...
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As a measure of catalytic activity, , the current density at 0.3 V overpotential, was chosen to evaluate the oxygen reduction reaction (ORR) at elevated temperatures and various relative humidities (RH) for polymer exchange membrane (PEM) fuel cells. The purely kinetic reaction order of the ORR with respect to oxygen partial pressure is less tha...
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Electrochemical impedance spectroscopy (EIS) of the electrochemical oxidation of and mixtures on the proton exchange membrane fuel cell anode ( or electrocatalysts) was performed at higher temperature and ambient pressure. Anode polarization studies were also conducted with the same mixture-fed streams. Both impedance and anode polarizat...
Article
Research and development was conducted on a proton exchange membrane (PEM) fuel cell stack to demonstrate the capabilities of Ionomem Corporation's composite membrane to operate at 120°C and ambient pressure for on-site electrical power generation with useful waste heat. The membrane was a composite of polytetrafluoroethylene (PTFE), Nafion®, and p...
Article
The importance of the blend microstructure and its effect on conductivity and structural integrity of proton exchange membranes (PEM) were investigated. Sulfonated poly(ether ketone ketone) (SPEKK) was selected as the proton-conducting component in a blend with either poly(ether sulfone) (PES) or SPEKK with a different sulfonation level. The second...
Article
Proton exchange membrane (PEM) fuel cells with optimized cathode structures can provide high performance at higher temperature (120°C). A “pore-forming” material, ammonium carbonate, applied in the unsupported Pt cathode catalyst layer of a high temperature membrane electrode assembly enhanced the catalyst activity and minimized the mass-transport...
Article
A step-by-step technique to evaluate six sources of polarization, mainly associated with the cathode, in hydrogen/air proton exchange membrane fuel cells is demonstrated. The six sources of polarization were nonelectrode ohmic overpotential, electrode ohmic overpotential, nonelectrode concentration overpotential, electrode concentration overpotenti...
Article
Organic/inorganic composite membranes with different inorganic heteropolyacid (HPA) additives maintain sufficient proton conductivities for atmospheric pressure elevated temperature (>100 °C) polymer electrolyte fuel cell (PEFC) operation. However, membrane and membrane electrode assembly (MEA) processing is severely curtailed because of the solubi...
Article
Operating proton exchange membrane fuel cells (PEMFCs) at elevated temperatures (> 100 degrees C reduces the effect of CO poisoning, simplifies heat rejection, and results in more useful waste heat. Membrane electrode assemblies were developed to obtain high-performance PEMFCs at elevated temperatures and low relative humidity (RH) using the commer...
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Full-text available
Palladium (Pd)-impregnated Nafion membranes that reduce methanol crossover were synthesized via a supercritical fluid route. The method involved impregnation of Nafion membranes with palladium(II) hexafluoroacetylacetonate from a supercritical CO2 (scCO(2)) solution, followed by subjecting the impregnated membranes to hydrogen. Membrane morphology...
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The development of fuel cells for commercial applications is discussed. A fuel cell uses an electrochemical process to directly convert chemical energy to electricity and are characterized by their electrolytes. Due to safety and operational advantages the proton exchange membrane (PEM) fuel cell is amenable for use as an undergraduate laboratory e...
Article
Polymer electrolyte fuel cells (PEFC), which represent an environmentally friendly technology involving electrochemical oxidation of fuels using air to produce water and electricity, are analyzed. Their ability to operate continuously obviates the need for recharging, which represents a significant advantage over batteries. These unique features ma...
Article
Polarization tests were conducted on proton exchange membrane fuel cells (PEMFCs) at cell temperatures between 60 and 80 °C with various reactant humidification levels; varied from no external humidification to fully saturated on both the anode and the cathode. Elimination of cathode external humidification, while maintaining a fully humidified ano...
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Full-text available
In proton-exchange membrane fuel cells (PEMFC), gas diffusion layers serve as current collectors that allow ready access of fuel and oxidant to the anode and the cathode catalyst surfaces, respectively. Critical properties of five commercial and one in-house gas diffusion layers have been characterized and compared to determine factors limiting the...
Article
In this study, transition metal complexes of amines and macrocycle ligands like cyclam, porphyrin, and phthalocyanine were studied as catalysts with Pt for electrochemical oxidation of hydrogen containing CO. These complexes are believed to act as redox mediators in generating species that oxidize CO. A systematic approach was used to improve CO to...
Article
Tolerance to small amounts of CO is important for proton exchange membrane fuel cells (PEMFCs) operating on hydrogen obtained by reforming carbon-based fuels. Platinum-based catalysts used today suffer high anode polarization losses, reducing performance and fuel efficiency. Here, findings in the search for CO-tolerant catalysts are reported. Novel...
Article
Nafion membranes suffer high resistance due to dehydration when they are used at elevated temperatures and atmospheric pressures (Nafion at and 31% relative humidity). Thinner composite membranes containing Nafion and zirconium hydrogen phosphate, were prepared and showed lower resistance at these conditions. Thermogravimetric analysis sh...
Article
Nafion®-based organic/inorganic composite membranes with different inorganic heteropolyacid (HPA) additives such as phosphotungstic acid, silicotungstic acid phosphomolybdic acid and silicomolybdic acid were investigated for high temperature (120°C) low relative humidity (35%) operation. A mechanism is proposed to explain possible pathways for cond...
Article
Trilayer membranes (50 μm thick) composed of one central methanol-barrier layer and two conductive layers were developed to suppress methanol crossover in liquid-fed direct methanol fuel cells (DMFCs). Nafion-(poly)vinylidene fluoride (PVDF) was used as a central methanol-barrier layer with two outside Nafion layers. Both proton conduction and meth...
Article
Characterization of our electroenzymatic membrane reactors with respect to transport and reaction processes has been accomplished. Both batch and flow configurations were evaluated using the biosynthesis of lactate from pyruvate as a model system. A key feature is the in situ regeneration of the coenzyme nicotinamide adenine dinucleotide (NADH). Cy...
Article
In-situ AC impedance based diagnostics of H2 dissociative adsorption, oxidation, and CO poisoning were performed at higher temperatures (> 100°C) and ambient pressure conditions. CO adsorption on the electrode surface increased significantly with higher CO concentrations; thus, the H2 dissociative adsorption impedance increased. CO adsorption on th...