Cathode Catalyst Degradation Research Articles

Quantification of Hydrogen and Transition Metals in the Cathode Catalyst Layer of Anion Exchange Membrane Electrolyzer By Ion Beam Techniques

Anion Exchange Membrane Water Electrolyzer (AEMWE) has increased interest in H2 production at low cost and high scalability. The efficiency is strongly dependent on the membrane electrode assembly (MEA) with appropriate ionomer and catalyst layers. Herein, we report AEMWE with MoNi4-MoO2 cathode catalyst layer in ionomer-free Catalyst Coated Substrate (CCS) configuration. The optimized MEA for AEMWE demonstrated the superior performance of 225 mA/cm2 at 2V with more than 48 hours of durability. The X-ray diffraction confirmed the NiMoO4 phase transformation to MoNi4-MoO2 and SEM-EDS was used to study the morphology and elemental composition of the deposited catalyst. X-ray photoelectron Spectroscopy demonstrated the dominant metallic MoO2 formed after H2/Ar annealing. Rutherford Backscattering Spectroscopy (RBS) was also employed to measure the depth composition profile of the catalyst layer exhibiting the reduction of Ni concentration in the bulk after annealing. Further, we introduce hydrogen depth profiling by Nuclear Reaction Analysis (NRA) via the resonant 1H(15N,αγ)12C reaction as a versatile method for the highly depth-resolved visualization of hydrogen(H) in the near-surface region, including transitions of hydrogen between the surface and the bulk, and between shallow interfaces of the nanostructured cathode catalyst layer. The diffusion of the H atoms was observed with a 40% atomic percent of Hydrogen after H2/Ar annealing of the catalyst for 180 minutes (about 3 hours) and decreased to 10% atomic percent of hydrogen after 24 hours of electrolyzer operation. This technique also enabled the measurement of the zero-point vibrational energy of hydrogen atoms absorbed on the surfaces of the catalyst layer. Overall, this work better explains the cathode catalyst degradation effects and hydrogen diffusion in the cathode catalyst layer responsible for voltage and mass transfer losses in AEM electrolyzers.

In-Situ Characterization of Cathode Catalyst Degradation in PEM Fuel Cells

The composition and morphology of the cathode catalyst layer (CCL) have a significant impact on the performance and stability of polymer electrolyte membrane fuel cells (PEMFC). Understanding the primary degradation mechanism of the CCL and its influencing factors is crucial for optimizing PEMFC performance and durability. Within this work, we present comprehensive in-situ characterization data focused on cathode catalyst degradation. The dataset consists of 36 unique durability tests with over 4000 testing hours, including variations in the cathode ionomer to carbon ratio, platinum on carbon ratio, ionomer equivalent weight, and carbon support type. The applied accelerated stress tests were conducted with different upper potential limits and relative humidities. Characterization techniques including IV-curves, limiting current measurements, electrochemical impedance spectroscopy, and cyclic voltammetry were employed to analyse changes in performance, charge and mass transfer, and electrochemically active surface area of the catalyst. The aim of the dataset is to improve the understanding of catalyst degradation by allowing comparisons across material variations and provide practical information for other researchers in the field.

Heterogenous Degradation of Cathode Catalyst Layers: Influence of O2 Partial Pressure and Various Stressors Under Load Cycling Conditions

Proton exchange membrane fuel cells (PEMFCs) are an important technology to reduce greenhouse gas emissions in the heavy-duty vehicle automotive fleet. Of particular importance is achieving high performance and durability of the cathode catalyst layer (CCL) which uses platinum group metals (PGMs) to catalyze the kinetically sluggish oxygen reduction reaction (ORR).1 Understanding limits of performance under specific stressors and correlating stressors to changes in the microstructure of the membrane electrode assembly (MEA) and properties of the catalyst will enable better understanding of potential pathways to enhance durability of the PEMFCs.Transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS) studies have demonstrated through-plane differences in the local Pt content and nanoparticle size with regard to the gas diffusion layer (GDL)-catalyst layer interface, middle of the catalyst layer, and membrane (PEM)-catalyst layer interface.2,3 We have previously shown that there are spatial through-plane differences (e.g., F/Pt profile as a benchmark and nanoparticle size assessment) throughout the CCL depth of MEAs when ran under potential cycling accelerated stress test (AST) conditions under N2 with varied stressors (i.e., temperature, relative humidity, dwell time at upper and lower potential limits, etc.).3 It has also been demonstrated that adjusting these stressors can either mitigate or enhance the rate of degradation under potential cycling conditions.4 Historically, N2-based ASTs have been used, including in our past work, to characterize aging behavior in the CCL. Here, we present an analysis on the effect of oxygen presence in the cathode, more similar to real load/unload PEMFC operation. The elucidation of the through-plane spatial degradation with focus on influence of varied O2 partial pressure and comparison to lower temperature, relative humidity, and upper potential limit at 21% O2 will be discussed. More specifically, the differences in the F/Pt profile, nanoparticle size, depletion layer thickness, Pt band location within the membrane, etc. and its implications on real-world PEMFC testing will be presented.References(1) Cullen, D. A.; Neyerlin, K. C.; Ahluwalia, R. K.; Mukundan, R.; More, K. L.; Borup, R. L.; Weber, A. Z.; Myers, D. J.; Kusoglu, A. New Roads and Challenges for Fuel Cells in Heavy-Duty Transportation. Nat. Energy 2021, 6 (5), 462–474. https://doi.org/10.1038/s41560-021-00775-z.(2) Schneider, P.; Batool, M.; Godoy, A. O.; Singh, R.; Gerteisen, D.; Jankovic, J.; Zamel, N. Impact of Platinum Loading and Layer Thickness on Cathode Catalyst Degradation in PEM Fuel Cells. J. Electrochem. Soc. 2023, 170 (2), 024506. https://doi.org/10.1149/1945-7111/acb8df.(3) Coats, M.; Medina, S.; Braaten, J.; Cheng, L.; Craig, N.; Johnston, C.; Pylypenko, S. Quantitative Analysis of Fuel Cell Cathode Catalyst Layer Degradation Using Scanning Transmission Electron Microscopy and Energy Dispersive Spectroscopy. ECS Meet Abstr 2022, MA2022-02 1434. https://doi.org/10.1149/MA2022-02391434mtgabs.(4) Kneer, A.; Wagner, N. A Semi-Empirical Catalyst Degradation Model Based on Voltage Cycling under Automotive Operating Conditions in PEM Fuel Cells. J. Electrochem. Soc. 2019, 166 (2), F120–F127. https://doi.org/10.1149/2.0641902jes.

Mechanisms of Stabilization and Degradation of Transition Metal Oxygen Electroreduction Catalysts with in-Situ Electrochemical Flow Cell ICP-MS

Proton exchange membrane hydrogen fuel cell (PEMFC) deployment is presently limited by the high material cost of oxygen reduction reaction (ORR) electrocatalysts at the cathode. Developing low-cost, earth-abundant alternatives for use in acidic environments presents a material stability challenge, especially for long-term device operation. Platinum (Pt)-based materials are used in typical commercial PEMFC cathode formulations due to their simultaneous high performance and long-term stability despite the prohibitively high material cost. Developing lower-cost, longer-life catalyst materials based on earth abundant transition metals can accelerate the adoption of PEMFC technology. The impact of potential, current density, and local microenvironment has been shown to cause degradation of non-Pt materials but standard ex situ measurements can only probe surface restructuring and cumulative dissolution after operation. Material-specific degradation mechanisms that are strong functions of the operating conditions cannot be ascertained without in situ quantification of material degradation under PEMFC-relevant conditions. Information about the degradation pathways of these non-precious catalysts can assist with material design for devices; however, most efforts towards developing an in-situ understanding of PEMFC cathode catalyst degradation under operating conditions are generally limited to Pt-based materials. Extensive in situ characterization has revealed Pt-specific mechanistic information about corrosion pathways as well as conditions that exacerbate Pt alloy leaching. It has been hypothesized that the Pt degradation processes are related to oxide formation under potential cycling. With this critical in-situ information, Pt conditioning protocols have been developed to enhance material lifetime; however, investigations on non-precious materials are less common. Insights into non-precious catalyst degradation in PEMFC operating conditions are not as well-established but could be essential in enabling low-cost materials for commercial use. There is a need for more insights into a vast array of materials which necessitates the development of faster, preferably benchtop techniques for degradation analysis.In this work, we use an in situ electrochemical flow cell assembly and coupled it with an inductively coupled plasma-mass spectrometer (ICP-MS) to quantify the loss of material in real time for several non-Pt materials under reaction conditions. The flow cell is fed by a peristaltic pump at 2.5 mL/min of gas-saturated acidic electrolyte for optimal mass transport. The cell has a three-electrode configuration with a compression-mounted metal foil working electrode, silver/silver chloride reference electrode, and Pt counter electrode downstream of other components. We evaluate a variety of transition metals across the spectrum of ORR activity: palladium, silver, nickel, copper, manganese, and cobalt. Each metal is tested under oxygen and nitrogen saturation in five electrolytes of identical pH: perchloric acid, sulfuric acid, nitric acid, hydrochloric acid, and hydrobromic acid. This setup allows for nearly real time measurement of ORR kinetics and in situ element-specific dissolution rates as a function of time. With careful design of experimental conditions and controlled variables, we are able to suggest mechanisms of degradation with specific reference to conditions under which material loss occurred such as high/low potential, oxygen-saturated/nitrogen-saturated electrolyte, or faradaic/non-faradaic current. We find some metals are stable under nitrogen-saturated electrolyte but corrode more under oxygen-saturated electrolyte only while ORR active. Furthermore, other metals are stable in nitrogen saturated electrolyte at all tested electrochemical conditions but unstable under oxygen saturated electrolyte but only outside the ORR range, implying that cathodic faradaic processes might be stabilizing the surface at low potentials. This stabilization where a thermodynamically unstable material (based on its Pourbaix diagram) exhibits greater immunity while performing ORR in certain electrolytes could inform the development stability mechanisms that direct the design of next generation, non-precious PEMFC cathode catalyst materials. With combined in situ catalyst stability analysis in five pH 1 electrolytes, we can recommend specific conditions for optimizing activity and stability based on the potential range of operation and the electrolyte composition/saturation. We can also distill mechanistic insights from these experiments by creating models that validate causes of catalyst degradation. These models are built using “graphical causal modeling”, which is a mathematical field that goes beyond correlative predictions by venturing into causal inference. We hope to expand this framework into other electrocatalytic reactions of interest. The in-situ ICP-MS electrochemical flow cell setup exhibits promise for accelerating materials stability analysis for enabling next generation Pt-free ORR electrocatalysts through practical experiments and direct comparability to established electrochemical techniques.

Simulation of cathode catalyst durability under fuel cell vehicle operation –Effects of stack size and temperature

In this work, a fundamental cathode catalyst degradation model is developed in order to simulate fuel cell stack durability under realistic vehicle operation. A dynamic platinum degradation model featuring platinum dissolution and redeposition is developed to account for the Ostwald ripening phenomenon. The model is then calibrated for a variety of accelerated stress test data with different upper and lower potential limits and temperatures. Next, a case study of fuel cell transit bus operation in the city of Victoria, B.C., Canada is carried out to investigate the effects of stack size and temperature on the cathode catalyst durability. To this end, the required power density and cell voltage are calculated from the drive cycle considering vehicle dynamics and specifications. Larger stacks are found to experience higher upper potential limits; thus, showing lower lifetimes. The cathode lifetime is predicted to grow 379% at 80°C if the stack nominal power is lowered from 396 to 132 kW while the performance requirement is met. The temperature is also shown to have a tremendous impact on the cathode lifetime. A temperature drop from 80 to 60°C results in 154% cathode lifetime enhancement for a stack nominal power of 264 kW.

The Effect of Ionomer to Carbon Ratio and Relative Humidity on Cathode Catalyst Degradation in PEM Fuel Cells

The effect of ionomer to carbon (I/C) weight ratio and relative humidity (RH) on cathode catalyst degradation was investigated by comprehensive in situ characterization. Membrane electrode assemblies (MEA) with I/C ratios of 0.5, 0.8 and 1.2 were subjected to an accelerated stress test performed at 40, 70 and 100% RH. The results show an increasing loss in electrochemical active surface area (ECSA) for both higher I/C ratios and RH during voltage cycling. To differentiate between ionomer and water connected ECSA, carbon monoxide stripping measurements were performed at varying RH. Before degradation, all MEAs show comparable total ECSA values, while higher I/C ratios lead to a larger fraction of ionomer connected ECSA. After degradation, ECSA measurements of the lowest I/C ratio showed a relatively higher loss of Pt in contact with ionomer than Pt in contact with water, while an opposite trend was observed for higher I/C ratios. H2/N2 impedance measurements showed drastically increasing protonic catalyst layer resistances for decreasing RH especially at low I/C ratios, which might hinder Pt2+ ion diffusion towards the membrane, hence decreasing the ECSA loss. Limiting current measurements show increasing molecular O2 diffusion resistances at end of test for samples with higher I/C ratios and higher ECSA loss.

Elucidating the Mechanisms of Oxygen Depolarized Cathode Catalyst Degradation

Fe-N-C has shown to be a viable low-cost, PGM-free catalyst to replace RhS/C for oxygen-depolarized cathode applications. Though it possesses high intrinsic ORR activity and relatively good immunity towards chloride ion poisoning, further studies must be conducted to explore the degradation pathways of Fe-N-C in a wide pH range to realize its capabilities in concentrated hydrochloric acid and Chlor-alkali electrolysis1.Moreover, Fe-N-C has been shown to maintain performance after being in operation for more than one hour with three uncontrolled shutdowns, nearly matching RhS/C at a current density of 0.5 A/cm2 with a cell potential of 1.38 V1. Thus, we will perform long-term durability tests under Raman and X-ray absorption spectroscopy (XAS). Furthermore, a single electrochemical flow cell will be designed for both spectrochemical methods to characterize the interaction between the catalyst and the formation of products during the uncontrolled shutdown. Specifically, Raman spectroscopy will be utilized to detect changes in the catalyst structure if any Fe-N4 bonds are broken or changed due to chloride anions upon shutdown. XAS-Fe edge will be employed to elucidate the formation of Fe-Cl bonds due to crossover anions during operation and when the cell is removed from the power supply. By determining the degradation pathways or lack of, we can truly assess the viability of Fe-N-C as a replacement for RhS/C in hydrochloric acid and Chlor-alkali electrolysis. These techniques provide a platform to reduce experimental uncertainty and gain further insight into the degradation of both catalyst and membrane-electrode assembly performance.

Environmental Impact Assessment of PEM Fuel Cell Combined Heat and Power Generation System for Residential Application Considering Cathode Catalyst Layer Degradation

Recently, fuel cell combined heat and power systems (FC-CGSs) for residential applications have received increasing attention. The International Electrotechnical Commission has issued a technical specification (TS 62282-9-101) for environmental impact assessment procedures of FC-CGSs based on the life cycle assessment, which considers global warming during the utilization stage and abiotic depletion during the manufacturing stage. In proton exchange membrane fuel cells (PEMFCs), platinum (Pt) used in the catalyst layer is a major contributor to abiotic depletion, and Pt loading affects power generation performance. In the present study, based on TS 62282-9-101, we evaluated the environmental impact of a 700 W scale PEMFC-CGS considering cathode catalyst degradation. Through Pt dissolution and Ostwald ripening modeling, the electrochemical surface area transition of the Pt catalyst was calculated. As a result of the 10-year evaluation, the daily power generation of the PEMFC-CGS decreased by 11% to 26%, and the annual global warming value increased by 5% due to the increased use of grid electricity. In addition, when Pt loading was varied between 0.2 mg/cm2 and 0.4 mg/cm2, the 10-year global warming values were reduced by 6.5% to 7.8% compared to the case without a FC-CGS.

Impact of Platinum Loading and Layer Thickness on Cathode Catalyst Degradation in PEM Fuel Cells

In this work we investigate the effect of platinum loading and layer thickness on cathode catalyst degradation by a comprehensive in situ and STEM-EDS characterization. To decouple the effect of the platinum loading and layer thickness from each other, the experiments were categorized in two sets, each with cathode loadings varying between 0.1 and 0.4 mgPt cm−2: (i) Samples with a constant Pt/C ratio and thus varying layer thickness, and (ii) samples with varying Pt/C ratios, achieved by dilution with bare carbon, to maintain a constant layer thickness at different platinum loadings. Every MEA was subjected to an accelerated stress test, where the cell was operated for 45,000 cycles between 0.6 and 0.95 V. Regardless of the Pt/C ratio, a higher relative loss in electrochemically active surface area was measured for lower Pt loadings. STEM-EDS measurements showed that Pt was mainly lost close to the cathode—membrane interface by the concentration driven Pt2+ ion flux into the membrane. The size of this Pt-depletion zone has shown to be independent on the overall Pt loading and layer thickness, hence causing higher relative Pt loss in low thickness electrodes, as the depletion zone accounts for a larger fraction of the catalyst layer.

Simulation of Cathode Catalyst Durability Under Fuel Cell Vehicle Operation - the Effect of Temperature

Fuel cell vehicles (FCVs) emerge to be promising candidates to produce clean power for the transportation sector in order to tackle climate change issues. Although the commercialization of polymer electrolyte membrane fuel cells (PEMFCs) has progressed in the past few decades, there are still obstacles to address, including high cost and limited hydrogen infrastructure. For heavy duty transportation applications, the PEMFC durability is also not yet proven, and extrapolating from lab data to real-world field operating conditions remains a significant challenge [1].In this work, the cathode catalyst degradation in PEMFCs is studied to make an estimation of fuel cell durability in the FCV application. The well-known Butler-Volmer approach is utilized to model platinum dissolution and redeposition, platinum oxidation and platinum ion formation during the fuel cell operation [2]. First, the model is calibrated with the results presented by Ferreira et al. [3] at 80℃; the calibrated model is then validated with Kocha’s results [4] to demonstrate the model’s capability of generating reliable results at different temperatures. In order to realistically predict the cathode degradation pattern and lifetime, the real-life fuel cell operating conditions should be obtained. Therefore, a drive cycle recorded based on a real-life transit bus operation in the city of Victoria is utilized to calculate the input fuel cell voltage profile. The procedure to calculate fuel cell operating voltage profile using the drive cycle has been thoroughly explained by Ahmadi and Kjeang [5]. This procedure employs Newton’s second law to calculate the required cell power density considering the air flow drag force counteracting the vehicle thrust. Finally, polarization curves representing the fuel cell performance are used to calculate the fuel cell voltage profile with the determined required cell power density. Polarization curves measured under a range of temperatures are employed to adequately reflect the effect of temperature on the fuel cell performance. The cell active area is considered to be 500 cm2 and the stack is assumed to contain 225 cells, representing a nominal stack power of 74 kW at 80℃. The fuel cell operation and degradation are simulated at three different temperatures: 60, 70, and 80℃. The change of remaining electrochemically active surface area (ECSA) with time is calculated as the output of the model.Temperature highly affects the electrochemical reactions of platinum dissolution in several ways. First, it affects the Tafel slope in the platinum dissolution reaction. Second, it substantially impacts on platinum degradation reaction rate constant [6]. The Arrhenius approach is taken in this study to apply the effect of temperature on the reaction rate constants. Fuel cell voltage loss over time is determined by assuming simple Tafel kinetics. The cathode lifetime is calculated at 0.6 A/cm2 and is estimated by considering 10% voltage drop as the failure criterion. Fig. 1 shows the simulated change of remaining ECSA over time and the resulting fuel cell lifetime for the three different cell temperatures. The results indicate that the cathode lifetime increases 168% when the cell temperature drops from 80℃ to 60℃ due to a significantly lower platinum degradation rate at 60℃. The results show relatively low cathode catalyst lifetimes for a transit bus. The reason is attributed to the bus drive cycle used as the model input. The drive cycle contains a great portion of deceleration and idling time which leads to a fuel cell operation close to open circuit voltage (OCV), thus experiencing a high degradation rate.In this regard, the present modeling framework could become a useful tool for fuel cell and FCV developers to predict lifetime for new products and systems prior to commercial release. Scientifically, the present model can also be used to further explore key influencing factors on fuel cell durability and develop more durable cell, stack, and system designs for a targeted FCV application. Acknowledgements This research was supported by the Natural Sciences and Engineering Research Council of Canada, Canada Research Chairs, and Simon Fraser University Community Trust Endowment Fund.

Platinum Dissolution Induced Catalyst Layer Degradation in Polymer-Electrolyte Fuel Cells for Heavy-Duty-Vehicle Applications

Interest in electrifying the transportation sector has intensified as the value in reducing carbon emissions is recognized globally. Polymer-electrolyte fuel cells (PEFCs) provide an option for electrifying transportation if hydrogen is produced electrolytically from water and without carbon emissions if the electricity is provided by renewable energy resources. Though research in fuel cell powered vehicles has been ongoing, hydrogen infrastructure and concerns about hydrogen storage safety limit the technology’s uptake in the passenger vehicle market. However, fuel cells applied to heavy-duty-vehicle (HDV) transportation may address these shortcomings. HDV provide predictable routes allowing for more simple hydrogen infrastructure and larger cargo allowance in HDV allows for more secure hydrogen storage and safety. Fuel-cell-powered-HDV require higher operating temperature, pressure, and potential to realize the power-demands of the vehicle, therefore, durability requirements increase, and a better understanding of degradation is a priority. A major cause of performance degradation is due to catalyst dissolution, migration, and reprecipitation. This causes a loss of electrochemically active surface area (ECSA) which reduces the activity of the catalyst and is particularly detrimental in the cathode where the limiting factor for performance is often sluggish oxygen reduction kinetics. This loss in ECSA is due to an overall broadening of the particle size distribution (PSD) within the catalyst layer and a net loss of catalyst to the formation of a Pt band in the membrane. In this work, a Pt catalyst degradation model is developed which considers particle size dependent Pt oxidation and dissolution kinetics, Pt migration, and reprecipitation of Pt within the cell. This work interrogates the particle size dependence of these processes to explain experimentally observed loss in ECSA and changes in PSD. The degradation model is coupled with a PEFC performance model through the ECSA loss to study how the HDV-relevant operating conditions impact the cathode catalyst degradation behavior observed in PEFCs.

Simulation of Cathode Catalyst Durability Under Fuel Cell Vehicle Operation - the Effect of Fuel Cell Stack Size

The concerns regarding climate change have made the researchers seek a clean alternative for the fossil fuel vehicles. Fuel cell vehicles (FCVs) are considered to be promising candidates owing to their efficient energy conversion and zero-carbon emission. However, a number of obstacles such as high cost and limited hydrogen infrastructure have made the FCVs commercialization process challenging. Polymer electrolyte membrane fuel cells (PEMFCs) have been proven promising for transportation applications. For heavy duty transportation applications, the PEMFC durability is also not yet proven, and extrapolating from lab data to real-world field operating conditions remains a significant challenge [1].In this work, the cathode catalyst degradation in PEMFC is studied to estimate the effect of stack size on fuel cell durability in the FCV application. Platinum dissolution and redeposition, platinum oxidation and platinum ion formation during the fuel cell operation are modeled using the Butler-Volmer approach presented in [2]. A drive cycle recorded based on a real-life transit bus operation in the city of Victoria is utilized to calculate the input fuel cell voltage profile based on the methodology presented by Ahmadi and Kjeang [3]. According to this methodology, the required cell power density is calculated using Newton’s second law considering the air flow drag force as a counteracting force against the vehicle movement. Then, the required voltage cycle is obtained by employing a polarization curve characterizing the fuel cell performance. Finally, the change of remaining electrochemically active surface area (ECSA) with time is calculated as the output of the model. The fuel cell is assumed to operate at 80 ℃ and the cell active area is considered to be 500 cm2. Simple Tafel kinetics is then used to determine the fuel cell voltage loss. A 10% voltage drop at 0.6 A/cm2 is considered as the failure criterion for the cathode lifetime. Moreover, the effect of the fuel cell stack size is studied. By increasing fuel cell stack size, the required cell power density drops, leading to a decrease in the voltage cycle amplitude while the voltage cycle period remains the same. According to the empirical kinetic rate equation, the catalyst degradation exponentially increases with increasing the voltage. Therefore, a higher degradation rate is observed for a catalyst operating on a voltage cycle with a lower amplitude while the period and the upper potential limit (UPL) are maintained the same, causing a significant platinum ion generation. Fig. 1 shows the change of remaining ECSA over time and resulting fuel cell lifetime for three stack sizes which are represented by the stack nominal powers. The results show that the fuel cell lifetime will be roughly doubled when the stack size is reduced by half. Stack sizing is thus an important consideration for fuel cell durability in the FCV application.In this regard, predicting fuel cell lifetime is a crucial step in commercializing FCVs. The present modeling framework could be utilized by FCV developers to predict lifetime for new products instead of carrying out time-consuming lifetime experiments. The factors influencing fuel cell durability can also be investigated using the present model framework to develop durables cells and stacks for a targeted FCV application. Acknowledgements This research was supported by the Natural Sciences and Engineering Research Council of Canada, Canada Research Chairs, and Simon Fraser University Community Trust Endowment Fund.

Mitigation of PtCo/C Cathode Catalyst Degradation via Control of Relative Humidity

Maintaining the high performance of proton-exchange membrane fuel cells (PEMFC) over the course of its lifetime is a key enabling factor for its successful commercialization as a primary power source in zero-emission transportation applications. In this context, it is important to mitigate the degradation of PtCo-alloy based cathode catalysts used for oxygen reduction reaction (ORR). PtCo-alloy catalysts exhibit high activity at beginning-of-life (BOL) which tends to decrease during operation due to loss of electrochemical surface area (ECSA) and dissolution-contamination related effects of the Co-alloying component. Here, we demonstrate the use of relative humidity (RH) of the inlet gases as a controllable parameter to mitigate the degradation of PtCo-alloy catalyst degradation. We employ a catalyst-specific voltage cycling accelerated stress test (AST) durability protocol as a function of inlet RH to degrade PtCo catalysts. A series of in situ electrochemical diagnostics and ex situ characterizations have been carried out to investigate the catalyst layer characteristics at end-of-test (EOT). Our results show that at sub-saturated conditions of durability protocol operation, PtCo catalyst sustains higher EOT H2/air performance due to better retention of ECSA and smaller impact of Co2+ dissolution/contamination.

Investigating low and high load cycling tests as accelerated stress tests for proton exchange membrane water electrolysis

In this paper, novel accelerated stress protocols have been proposed based on polarization and electrochemical impedance spectroscopy characterization conducted on three single cell assemblies: one for reference at constant load of 1 A cm −2 and two dynamic loads consisting of a high load cycling between 1.2 A cm −2 and 2 A cm −2 and a low load cycling between 0 A cm −2 (open circuit voltage) and 0.5 A cm −2. Results showed that the degradation rate is 29.8 µV h−1 for constant load test, 51.4 µV h−1 for low load cycling test and -55.8 µV h−1 for high load cycling test. Compared to the constant load operation, low load cycling operation could accelerate the cell performance decrease mainly due to cathode catalyst degradation. The high load cycling could lead to increased cell performance by reducing the ohmic resistance but degrades the anode catalyst significantly, which could compromise the cell's long-term stability. Besides, it is believed that this dynamic condition could accelerate the cell aging by accelerating the membrane thinning.

Effects of Pt particle on structure and protons transport of Nafion membrane

With proton exchange membrane fuel cell (PEMFC) running, Pt particles are re-deposited in proton exchange membrane PEM after the degradation and migration of Pt cathode catalyst. Classic molecular dynamics simulations are conducted to study the effects of Pt particle on the structure and protons transport of Nafion membrane. The structure of membrane around a Pt particle is observed to present a core–shell structure. The Pt particle is the core coated by the shell of Nafion polymers, with the side-chains of polymers wrapping snugly around the particle. In that structure, some hydronium ions locate in inner shell owing to the electrostatic action with sulfonic acid groups, and few water molecules near particle due to few voids in the structure and hydrophobicity of the backbone of polymers. Besides, the diffusion for hydronium ions irregularly changes over the number of Pt atoms thanks to irregular changes of water channels. While the hopping of protons is to decline over Pt atoms due to greater loss of hydrogen bonding acceptable sites caused by larger particle.

Electrochemical impedance spectroscopy of catalyst and carbon degradations in proton exchange membrane fuel cells

Wide–scale commercialisation of proton exchange membrane fuel cell (PEMFC) is hindered by the degradation of cathode catalyst and carbon support, making it crucial to understand these mechanisms. This study compares the cathode catalyst and carbon support degradations mechanisms using commercial gas diffusion electrode in operating PEMFCs. The impact of the accelerated stress tests (ASTs) is monitored by recording the polarisation, electrochemical surface area (ECSA) and mass activity. Furthermore, the electrochemical impedance spectroscopy (EIS) is monitored at seven operating points from 0.05 to 1 A cm−2. For both phenomena, the charge transfer resistance increases at high current densities, which is attributed to the losses in activity observed with the ECSA and the mass activity degradations. In the carbon–corroded PEMFC, the mass transport resistance first reduces by 45% (0–100 cycles), suggesting an increase in electrode porosity due to carbon corrosion. At a later stage (200–5000 cycles), the mass transport resistance increases by 225% as the electrode collapses. On the other hand, in the catalyst–degraded PEMFC, the mass transport resistance uniformly reduces while the charge transfer resistance increases by 30%. Altogether, EIS provides additional sensitivity to differentiate catalyst and carbon support degradation within PEMFCs.

Pt–Co/C Cathode Catalyst Degradation in a Polymer Electrolyte Fuel Cell Investigated by an Infographic Approach Combining Three-Dimensional Spectroimaging and Unsupervised Learning

Catalyst degradation at the cathode of a membrane electrode assembly (MEA) remains a critical issue for practical polymer electrolyte fuel cell (PEFC) operation, but such wet systems impede detaile...

Operando Time-Resolved X-ray Absorption Fine Structure Study for Pt Oxidation Kinetics on Pt/C and Pt3Co/C Cathode Catalysts by Polymer Electrolyte Fuel Cell Voltage Operation Synchronized with Rapid O2 Exposure

The oxidation of a cathode catalyst surface is one of the major factors for cathode catalyst degradation under polymer electrolyte fuel cell (PEFC) operating conditions; however, the oxidation kinetics of Pt cathode catalysts in a membrane electrode assembly with O2 has not been investigated. We have investigated operando Pt LIII-edge time-resolved X-ray absorption fine structure analysis for the Pt oxidation processes on Pt/C and Pt3Co/C cathode catalysts controlled by transient PEFC voltage operation (0.4 V → 0.7–1.0 V) synchronized with the rapid exchange of cathode gas (N2 → 10% O2 in N2). We plotted Pt valence and the coordination numbers of Pt–Pt and Pt–O bonds every 20 ms, and the rate constants of the structural parameters for the Pt oxidation were successfully estimated. The structural kinetics of the Pt oxidation at the cathode suggested differences in the Pt oxidation kinetics between the Pt/C and Pt3Co/C cathode catalysts, showing the kinetic control of the Pt oxidation rate by the alloying wi...

(Invited) Instability of Pt-Based Catalysts for Fuel Cell Applications

I am delighted to join this symposium and celebrate not only the scientific accomplishments of R. Adzic and but also his contributions to the mentoring of generations of scientists in the electrochemistry and electrocatalysis community. Without formal training in electrochemistry, learning and making high-quality electrochemical measurements is not straightforward. R. Adzic not only has trained a large number of students and postdocs but also has opened his laboratory to other research groups throughout his career, shaping and mentoring future generations of researchers. My own involvements in electrocatalysis in the past decade would not be possible without individuals like R. Adzic who is committed to mentoring and collaborating with researchers coming from other disciplines. In this talk, I will discuss the mechanisms of Pt and Pt alloy catalyst instability and activity loss in fuel cells (1-2), limiting the lifetime of fuel cells, and how morphologies of Pt alloy particles can influence activity and stability (3-4). Chen, S., H.A. Gasteiger, K. Hayakawa, T. Tada, and Y. Shao-Horn, Platinum-Alloy Cathode Catalyst Degradation in Proton Exchange Membrane Fuel Cells: Nanometer-Scale Compositional and Morphological Changes, Journal of the Electrochemical Society, 157, A82–97 January 2010.Ferreira, P.J., G.J. la O’, Y. Shao-Horn, D. Morgan, R. Makharia, S. Kocha and H. Gasteiger, Instability of Pt/C Electrocatalysts in Proton Exchange Membrane Fuel Cells: A Mechanistic Investigation, Journal of the Electrochemical Society, 152, A2256–A2271 2005.Chen, S., W.C. Sheng, N. Yabuuchi, P.J. Ferreira, L.F. Allard and Y. Shao-Horn, The Origin of Oxygen Reduction Activity of “Pt3Co” Nanoparticles: Atomically Resolved Chemical Compositions and Structures, Journal of Physical Chemistry C, 113, 1109–1125 2009.Han, B., C.E. Carlton, A. Kongkanand, R.S. Kukreja, B.R.C. Theobald, L. Gan, R. O'Malley, P. Strasser, F.T. Wagner, and Y. Shao-Horn, Record Activity and Stability of Dealloyed Bimetallic Catalysts for Proton Exchange Membrane Fuel Cells, Energy & Environmental Science, 8, 258-266 2015.

Degradation mitigation effects of pressure swing in proton exchange membrane fuel cells with dead-ended anode

High cost remains to be one of the primary obstacles for the commercialization of proton exchange membrane fuel cells (PEMFCs). To simplify the fuel cell system and reduce cost, dead-ended anode (DEA) is widely used. However, water and nitrogen can accumulate in the dead-ended anode, resulting in cell performance decrease and severe cell degradation. Anode pressure swing supply is a new technology which has been shown to be effective in reducing local water and nitrogen accumulation in the anode channel. In this work, the effects of pressure swing supply on fuel cell degradation have been experimentally studied. Two sets of experiments on the same fuel cell are conducted, one under conventional constant pressure operation and the other under pressure swing operation. Polarization curves show that pressure swing supply can significantly mitigate cell degradation during DEA operations. Electrochemical characterizations are performed to study the mechanisms of mitigations in cell degradation. The cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) results show that pressure swing supply can significantly reduce electrolyte membrane degradation, but has no significant mitigation effect on the cathode catalyst degradation during DEA operation. Further examinations of the membrane-electrode-assembly (MEA) by scanning electron microscope (SEM) confirm the significant difference in membrane degradations since there is a very large difference in average thickness of the membranes after the degradation tests.