Search

To date, several high-performing anion exchange membrane fuel cells (AEMFCs) have been demonstrated, but most these studies have focused on Pt containing cathodes with high loadings. Here, we explore and compare the performance and perform electrochemical diagnostics on three leading AEMFC cathode electrocatalysts: Pt/C, Ag/C, and Fe–N–C with electrodes that have been processed with either powder or dispersion-based ionomers using perfluorinated anion exchange polymers. Pt/C had the highest performance but also showed a strong dependence on ionomer type, with powder ionomer exhibiting much higher performance. These results were consistent with the observations for Ag/C but did not hold for the Fe–N–C catalyst where almost no change was observed between powder and dispersion-based ionomers. This is the first-time the impact of powder and dispersion ionomer with different classes of cathode electrocatalysts on the fuel cell performance have been compared, and the results have strong implications for the ability to achieve high performance at low loadings and for better understanding catalyst-ionomer interactions within AEMFCs.

Proton-exchange membrane water electrolysis (PEMWE) produces hydrogen with high efficiency and purity but uses high-loading platinum-group metal (PGM) catalysts. Such concerns call for the development of novel electrode architectures to improve catalyst utilization and mass activity, thus promoting PEMWE cost competitiveness for large-scale implementation. In this study, we demonstrated, for the first time, a novel two-dimensional (2D)-patterned electrode with edge effects to address these challenges. The edge effect was induced by membrane properties, potential distribution, and counter electrode coverage and could be optimized by tuning the catalyst layer dimensions. To achieve identical PEMWE performance, the optimal pattern saved the 21% anode PGM catalyst compared with the conventional catalyst fully covered electrode. The PGM catalyst could be further reduced by 61% to boost mass activity with no significant performance loss. The results also indicated that the electrode uniformity in PEMWE cells might not be as critical as that in PEM fuel cells. The novel 2D-patterned electrode could effectively reduce PGM catalyst loading, accelerating affordable and large-scale production of hydrogen and other value-added chemicals via electrolysis.

Partially fluorinated poly(arylene ether) copolymer having reactive functional group are used to fabricate the MEA to improve the interfacial adhesion between membrane and electrode. The optimum MEA processing procedure was studied using different hot pressing temperature and crosslinking. Good interfacial adhesion between hydrocarbon membrane and Nafion bonded electrode produced excellent fuel cell performance which was comparable to the MEA using Nafion 212.

Fuel cell operation under reduced humidity is highly desirable for automotive applications. Unfortunately, sulfonated polymer electrolytes tend to lose proton conductivity with decreasing water activity. It has been observed in our studies that proton conductivity of polymer electrolytes is critically related to nanostructured (phase separated) morphology. In this study, we focus on morphological effects on proton conductivity, particularly at a low relative humidity. Two copolymer systems - . multiblock copolymers and traditional random copolymers were used in the study. Water sorption, proton conductivity and morphology of the systems are compared and H2/air fuel cell performance was evaluated at high temperature and low relative humidity.

The performance of polymer electrolyte membrane (PEM) fuel cells as a function of cathode inlet relative humidity (RH) and gas diffusion layer (GDL) properties has been characterized. The performance of 50 cm2 fuel cells at high current densities was a strong function of the polytetrafluoroethylene (PTFE) content in the cathode GDL microporous layer (MPL). The voltage at a current density of 1.4 A cm-2 decreased at all inlet RHs as the PTFE content in the cathode MPL increased from 5 % by weight to 23 % by weight. This was associated with a corresponding increase in the mass transport resistance as measured by AC impedance. The low frequency resistance also increased with increasing cathode inlet RH. These results were validated by high-resolution neutron radiography on specially designed 2.25 cm2 cells that showed increased water content in the GDLs at high inlet RHs and high microporous layer PTFE content. High-resolution neutron imaging also revealed higher water concentrations at the outlets, cathode GDL, anode flow channel, and MEA/GDL above the land when compared to the inlets, anode GDL, cathode flow channel, and MEA/GDL above the channel respectively.

The performance of single-PEM fuel cells at sub-freezing temperatures has been characterized. Fully humidified fuel cells that were subjected to multiple freeze/thaw cycles down to -40 oC showed degradation in performance associated with mass transport problems at the gas diffusion layer. The performance loss was negligible for cloth GDLs and slow cooling rates while fast cooling rates and paper GDLs showed significant degradation. When a single-fuel cell was operated at -10 oC at a constant voltage, the current first increased to a maximum value, then started decaying due to ice formation. This ice formation was monitored using neutron radiography and was found to be concentrated near the inlets, outlets and cell edges resulting in a significant increase in mass transport resistance as revealed by AC impedance spectroscopy. Cyclic voltammograms at -10 oC show no change in catalyst electrochemical surface area associated with this decreased performance. Finally the cell did not exhibit any degradation in performance at 80 oC even after 5 separate operations at -10 oC, where the cell was allowed to completely clog with ice each time until no further current was produced.

The oxygen reduction reaction (ORR) at the interface between platinum and recast Nafion with 1100 equivalent weight was studied using voltammetry utilizing interdigitated microelectrode arrays (IDAs). At high relative humidity (RH) (60-100%), peroxide generation was found to decrease with scan rate. The opposite behavior was observed at low RH (10%), with a more complex response at an intermediate RH (35%). Peroxide generation was found to significantly increase with temperature at 60% RH, but the effect of temperature was not as well defined at other humidities. The effects of humidity, scan rate and temperature on peroxide generation are explained by the occurrence of two phenomena. At high humidity, peroxide generation results mainly from the blocking of Pt surface by the hydrophobic component of Nafion, in agreement with previously postulated interfacial restructuring of ionomer (1-3). While at low humidity, peroxide generation originates predominantly from dehydration of the hydrophilic component of Nafion at the interface

When polymer electrolyte membrane (PEM) fuel cells are exposed to sub-freezing temperatures, the water present in the various components can freeze resulting in ice formation. In this study we examine the effect of freeze/thaw cycling on fully humidified fuel cells frozen to various sub-freezing temperatures. The cells showed negligible performance degradation when cycled up to 40 times to as low as -40C. However, the cells started to fail with an associated increase in the high frequency cell resistance within 10 freeze/thaw cycles down to -80C. In this paper we also report the conductivity and state of water of the Nafion(r) membrane at sub-freezing temperatures. A change in activation energy associated with the freezing of water in the ionomer was observed at high relative humidities. This change in activation energy and associated phase transition was avoided at low relative humidities or when the water is replaced with a non-freezing solvent.

In this study, interfacial degradation under DMFC operating conditions was systematically investigated using series of alternative sulfonated poly(sulfone) membranes. In-situ cell high frequency resistance measurement indicated that membrane dimensional stability was the key parameter for interfacial delamination. Based on this result, less water swollen sulfonated poly(sulfone) membranes were prepared by introducing fluorine and other polar groups such as benzonitirle or phenyl phosphine oxide in the backbone of poly (sulfone) copolymer. Long-term fuel cell performance of an interface-optimized poly (sulfone) membrane showed a stable interfacial resistance and an excellent cell performance for 3,000h under continuous DMFC operation at fixed voltage of 0.5 V.

Due to its ability to perform clean, efficient processes, hydrogen has long been promoted as the energy carrier of the future, but recent activity and advances suggest a tipping point has been reached as hydrogen is now being recognized by much of the world for its unique capabilities to strongly support global efforts in achieving climate neutrality. The coming decades will require a massive increase in the amount of hydrogen used in the energy system as well as a transition from largely thermochemical to predominantly electrochemical processes involving hydrogen. For this to happen, hydrogen will need to globally approach the gigaton-scale on an annual basis. Thus, before hydrogen can fully achieve its potential, challenges that need to be addressed include achieving scale and further research and development (R&D) advances.

The societal energy system is evolving rapidly as the impacts of our existing energy system are better appreciated and technological advances have dramatically decreased the cost of renewable resources. Simultaneously, the importance of energy transfer across timeframes and the difficulty of decarbonizing the industrial loads and transportation demands using electricity are being recognized. At the center of this need is achieving low-cost clean hydrogen. The U.S. Department of Energy launched the Hydrogen Energy EarthShot which seeks to reduce the cost of clean hydrogen to $1 per 1 kilogram in one decade. Reaching the $1/kg goal is dependent on the evolution of the electrical energy system to increase renewable energy deployment and low electricity costs; advances in electrolysis technology and manufacturing readiness; and infrastructure build-out and hydrogen market establishment that results in the ability to make, move, store, and use clean hydrogen economically while spurring job creation.

This paper establishes baseline performance of several platinum group metal (PGM) and non-PGM catalysts in alkaline oxygen evolution (OER). As OER catalyst development efforts increase, there is a need to standardize testing and baseline performance to compare catalysts between different studies, better direct materials development, and understand how performance improvements translate to the device. Of the catalysts tested, metals tend to have higher half-cell activity than their fully oxidized counterparts. In single-cells, however, metal activities approach oxides, likely due to the elevated temperature, higher potential, and longer time needed to condition membrane electrode assemblies (MEAs) relative to rotating disk electrodes (RDEs). In RDEs, cobalt (Co) and ruthenium nanoparticles are the most OER active. Due to high ruthenium dissolution rates, however, iridium (Ir) is used as a PGM baseline. Activity differences between materials in RDE (Ir 320 A g‒1, Co 12 A g‒1at 1.55 V) further appear to translate to MEAs (Ir 1370 A g‒1, Co 101 A g‒1at 1.5 V), indicating that half-cell testing can be useful in the early stages of catalyst development to predict kinetics at the device-level.

Anion exchange membranes (AEMs) are a promising technology for fuel cell applications. Most of the research done to date was focused on membrane development, electrode fabrication, or cell performance. Studies of the polymer catalyst interface are needed in order to advance the science of these devices and achieve further improvements. Here we have studied these interfacial properties using grazing-incidence small-angle x-ray scattering (GISAXS). Thin films of a perfluorinated anion exchange polymer were spin cast onto bare, or silver or platinum coated flat silicon substrates. From the GISAXS data, we can conclude that the polymer chains align parallel to the plain silicon or silver coated substrate at higher thicknesses, >17 nm and, >13 nm respectively. However, on the coated platinum substrate the alignment is somewhere between parallel and perpendicular. The in-plane alignment of ionomer on the surface constrains the swelling of water channels which affects the transport of reactants and products.

Alkaline fuel cells and electrolyzers are of interest because they have potential advantages over their acid counterparts. High-conductivity anion conducting membranes were analyzed and used in alkaline hydrogen/oxygen fuel cells. The membranes were composed of reinforced block copolymers of poly(norbornenes) with pendant quaternary ammonium head-groups. It was found that membranes with light cross-linking provided excellent mechanical stability and allowed very high ion exchange capacity polymers to be used without penalty of excessive water uptake and swelling. The optimum membrane and fuel cell operating conditions were able to achieve a peak power density of 3.4 W/cm2using hydrogen and oxygen. The performance increase was greater than expected from minimizing ohmic losses. Mechanical deformations within the membrane due to excess water uptake can disrupt full cell operation. Cells were also run for over 500 h under load with no change in the membrane resistance and minimal loss of operating voltage.

One of the hurdles in Anion exchange membrane fuel cell technology is weaker understanding of CO2poisoning observed when they are exposed to air. Our previous work suggests that OH-ions depletes in approximately 15 min to form CO32-and HCO3-ions when exposed to ambient air at 30 °C and 95%RH (1). However, an actual fuel cell device is operated at a much higher temperature. In this study we have reported the CO2absorption data at different temperatures and different CO2concentration environment. Our data suggest that the air equilibrated AEM concentration of CO32-increases at higher temperatures whereas HCO3-concentration follows a decreasing trend. The OH-ion has a very insignificant change at higher temperatures but we observe that the equilibrium OH-concentration is higher at lower ppm level of CO2environment. This indicates that the CO2reaction is dependent on CO2concentration in air.

Chemical degradation of perfluorinated sulfonic acid membranes, such as Nafion®viaradical attack represents one of the current challenges with fuel cell durability. Ce and Mn have been used to decompose radicals, but migration of these species results in loss of chemical stability efficacy. Herein we report on a recent breakthrough in chemical durability that has been achieved through using heteropoly acids (HPAs) as both the proton conducting acid and the radical decomposition catalyst. Exceptional chemical durability is reported for a thin film and a mechanism is purposed where the W atoms in the HPA reversibly change oxidation state from W(VI) to W(V) while decomposing radical species. It is concluded that covalently tethered HPA should be considered as a next generation chemical stabilization strategy for polymer electrolyte fuel cells.

Anion Exchange Membrane Fuel Cells (AEMFCs) have experienced a significant rise in attention in recent years, largely motivated by the potential to overcome the costs that have plateaued for proton exchange membrane fuel cells. However, despite significant advances in power generation, membrane conductivity, membrane stability, and catalyst activity, the vast majority of high performing AEMFCs are fabricated with a high PGM loading (0.4-0.8 mg cm-2). This work demonstrates an electrode fabrication method that reduces the anode catalyst loading by 85 % while still achieving performance ca. 1 W cm-2– accomplished by designing a multi-layered electrode comprised of an optimized ionomer:carbon:PGM ratio catalyst layer coupled with a hydrophobic microporous layer. If paired with a high-performing PGM-free cathode, this new anode can meet existing DOE PGM loading and performance targets.

Platinum-nickel nanowire (PtNiNW) catalysts have shown exceptionally high oxygen reduction mass activity in rotating disk electrode measurements. However, the ability to successfully incorporate PtNiNWs into high performance membrane electrode assemblies (MEAs) has been challenging due to their size, shape, density, dispersion characteristics, and corrosion-susceptible nickel core. We have investigated the impact of specific processing steps and electrode composition on observed fuel cell performance and electrochemical properties in order to optimize performance. We have found that nickel ion contamination is a major concern for PtNiNWs that can be addressed through ion exchange in fabricated/tested MEAs or by acid leaching of catalyst materials prior to MEA incorporation, with the latter being the more successful method. Additionally, decreased ionomer incorporation has led to the highest performance demonstrating 238 mA/mgPt(0.9 V IR-free) for PtNiNWs (pre-leached to 80 wt% Pt) with 9 wt% ionomer incorporation.

Chemical degradation of perfluorinated sulfonic acid membranes, such as Nafion, via radical attack, represents one of the current challenges of fuel cell durability. Here we report on a recent breakthrough in chemical durability that has been achieved through using covalently attached heteropoly acid (HPA) moieties as both the proton conducting acid and the radical decomposition catalyst. Exceptional chemical durability is reported for a thin (25 μm) film in an accelerated stress test that eventually had an open circuit voltage decay rate of 520 μV h−1, which was shown to be a result of the formation of an electrical short after thinning due to mechanical stresses. A mechanism is proposed using density functional theory in which the W atoms in the HPA reversibly change oxidation state from W(VI) to W(V) while decomposing radical species. Using rate constants found in the literature and realistic concentrations of scavenging species, it is hypothesized that the rate of radical decomposition can be >35x faster for HPA containing membranes than it is for Ce doped films. It is concluded that covalently tethered HPA should be considered as a next generation chemical stabilization strategy for polymer electrolyte fuel cells.

Anion Exchange Membrane Fuel Cells (AEMFCs) have experienced a significant rise in attention in recent years, largely motivated by the potential to overcome the costs that have plateaued for proton exchange membrane fuel cells. However, despite significant advances in power generation, membrane conductivity, membrane stability, and catalyst activity, the vast majority of high performing AEMFCs are fabricated with a high PGM loading (0.4–0.8 mg cm−2). This work demonstrates an electrode fabrication method that reduces the anode catalyst loading by 85% while still achieving performance ca. 1 W cm−2– accomplished by designing a multi-layered electrode comprised of an optimized ionomer:carbon:PGM ratio catalyst layer coupled with a hydrophobic microporous layer. If paired with a high-performing PGM-free cathode, this new anode shows the potential to meet existing DOE PGM loading and performance targets.

This paper fills a significant gap in the literature for alkaline hydrogen evolution (HER) and oxidation (HOR) baseline performance, while reviewing the different variables that influence observed properties. Although high-performing HER-HOR catalysts in acidic electrolytes are too active to measure kinetic in rotating disk electrode (RDE) half-cells, under alkaline conditions RDE kinetics evaluations are relevant and half-cell performances are comparable to hydrogen pump data. This paper focuses on best practices to ensure that half-cell tests don't unnecessarily lower platinum group metal (PGM) performance or improve non-PGM performance. Specific aspects examined include experiments on PGMs minimizing the impact of impurities (electrolyte, cell material) and experiments on non-PGMs minimizing the impact from test protocols (counter electrode).

Anion exchange membranes (AEMs) are of high interest for a number of electrochemical device applications including fuel cells, electrolyzers, and flow batteries. Perfluorinated sulfonic acid polymers have been the standard polymer used in the much more established area of proton exchange membrane based devices due to specific advantageous attributes including chemical stability, high conductivity, high water mobility, and the ability to create high performance electrodes. These attributes would make for desirable AEMs, but synthesizing perfluorinated AEMs has been limited and has significant challenges. Here, we report our efforts to develop novel synthesis routes to sulfonamide-linked alkyl ammonium perfluorinated AEMs. We have demonstrated the ability to achieve both high levels of ion exchange and membrane conductivity. We have achieved improved durability by extending the length of the alkyl tether from 3 to 6 carbons, and we have demonstrated the ability to process these polymers into membranes, ionomer solutions/dispersions, and fuel cells with reasonable performance.

The increased interest in the use of anion exchange membranes (AEMs) for applications in electrochemical devices has prompted significant efforts in designing materials with robust stability in alkaline media. Most reported AEMs suffer from polymer backbone degradation as well as cation functional group degradation. In this report, we provide comprehensive experimental investigations for the analysis of cation functional group stability under alkaline media. A silver oxide-mediated ion exchange method and an accelerated stability test in aqueous KOH solutions at elevated temperatures using a Parr reactor were used to evaluate a broad scope of quaternary ammonium (QA) cationic model compound structures, particularly focusing on alkyl-tethered cations. Additionally, byproduct analysis was employed to gain better understanding of degradation pathways and trends of alkaline stability. Experimental results under different conditions gave consistent trends in the order of cation stability of various QA small molecule model compounds. Overall, cations that are benzyl-substituted or that are near to electronegative atoms (such as oxygen) degrade faster in alkaline media in comparison to alkyl-tethered QAs. These comprehensive model compound stability studies provide valuable information regarding the relative stability of various cation structures and can help guide researchers towards designing new and promising candidates for AEM materials.

Anion-exchange membrane fuel cells (AME-FCs) are of increasingly popular interest as they enable the use of non-Pt fuel cell catalysts, the primary cost limitation of proton exchange membrane fuel cells. Benzyltrimethyl ammonium (BTMA) is the standard cation that has historically been utilized as the hydroxide conductor in AEMs. Herein we approach AEMs from two directions. First and foremost we study the stability of several different cations in a hydroxide solution at elevated temperatures. We specifically targeted BTMA and methoxy and nitro substituted BTMA. We've also studied the effects of adding an akyl spacer units between the ammonium cation and the phenyl group. In the second approach we use computational studies to predict stable ammonium cations, which are then synthesized and tested for stability. Our unique method to study cation stability in caustic conditions at elevated temperatures utilizes Teflon Parr reactors suitable for use under various temperatures and cation concentrations. NMR analysis was used to determine remaining cation concentrations at specific time points with GCMS analysis verifying product distribution. We then compare the experimental results with calculated modeling stabilities. Our studies show that the electron donating methoxy groups slightly increase stability (compared to that of BTMA), while the electron withdrawing nitro groups greatly decrease stability in base. These results give insight into possible linking strategies to be employed when tethering a BTMA like ammonium cation to a polymeric backbone; thus synthesizing an anion exchange membrane.

The role of system contaminants in the performance degradation of Proton Exchange Membrane (PEM) fuel cells has been underappreciated to date. This work seeks to identify potential contaminants derived from balance of plant (BOP) system components with the ultimate goal of tying contaminant exposure to changes in PEMFC performance and durability. After accelerated aging of select assembly aid materials in DI water at 90{degree sign}C, the resulting leachant solutions were qualitatively and quantitatively characterized through a suite of analytical methods for organic and inorganic components. By design, the materials studied fall into a wide range of 'clean' and 'dirty' solutions. Potential routes of entry for species were examined for plausibility of identification, and determination of model compounds. Systematic identification and selection of model compounds provide the basis for in-situ and ex-situ testing to determine the potential degradation mechanisms and effects of these system contaminants on catalysis and membrane performance.

Supportless platinum nanotubes are synthesized by the decomposition of a platinum acetylacetonate vapor within anodic alumina templates at 210 {degree sign}C. As synthesized, the nanotubes are nanoparticulate aggregates composed of Pt crystallites approximately 3 nm in diameter and with a range of lengths from 1 μm to 20 μm. Annealing treatments result in crystallite growth and morphological evolution of the tubular nanostructures. The oxygen reduction activity of the PtNTs was investigated using the rotating disc electrode method at room temperature. PtNTs annealed at 500 {degree sign}C exhibited a specific activity of 2084 μA/cm2Pt at 0.9 V, a value approaching that of polycrystalline Pt. The electrochemical surface area of the annealed structures was found to be quite low, from 5-10 m2/g, resulting in moderate overall mass activity of up to 177 mA/mgPt.

Partially fluorinated poly(arylene ether) copolymer having reactive functional group are used to fabricate the MEA to improve the interfacial adhesion between membrane and electrode. The optimum MEA processing procedure was studied using different hot pressing temperature and crosslinking. Good interfacial adhesion between hydrocarbon membrane and Nafion bonded electrode produced excellent fuel cell performance which was comparable to the MEA using Nafion 212.

The performance of single-PEM fuel cells at sub-freezing temperatures has been characterized. Fully humidified fuel cells that were subjected to multiple freeze/thaw cycles down to -40 oC showed degradation in performance associated with mass transport problems at the gas diffusion layer. The performance loss was negligible for cloth GDLs and slow cooling rates while fast cooling rates and paper GDLs showed significant degradation. When a single-fuel cell was operated at -10 oC at a constant voltage, the current first increased to a maximum value, then started decaying due to ice formation. This ice formation was monitored using neutron radiography and was found to be concentrated near the inlets, outlets and cell edges resulting in a significant increase in mass transport resistance as revealed by AC impedance spectroscopy. Cyclic voltammograms at -10 oC show no change in catalyst electrochemical surface area associated with this decreased performance. Finally the cell did not exhibit any degradation in performance at 80 oC even after 5 separate operations at -10 oC, where the cell was allowed to completely clog with ice each time until no further current was produced.