Fuel Cell Operating Conditions Research Articles

In-situ X-ray Fluorescence Analysis of In-plane Cerium-ion Distribution Under Humidity Gradients in Proton Exchange Membrane

Cerium ions are incorporated into proton exchange membranes (PEMs) of fuel cells to mitigate its chemical degradation caused by radical species. However, under fuel cell operating conditions, cerium ions move in in-plane direction in the cell by humidity gradient. This cerium ion transport results in cerium ion depletion leading to accelerated chemical degradation. This study developed an in-situ and operando measurement technique utilizing synchrotron high-energy X-ray fluorescence spectroscopy to monitor the cerium ion transport across the membrane under the in-plane humidity gradient. This method effectively tracks the dynamic behavior of cerium ions under fuel cell operating conditions.

Effects of Zr dopants on properties of PtNi nanoparticles for ORR catalysis: A DFT modeling.

Pt-based alloys, such as Pt3Ni, are among the best electrocatalysts for oxygen reduction reaction (ORR) in polymer electrolyte membrane fuel cells. Doping of PtNi alloys with Zr was shown to enhance the durability of the operating ORR catalysts. Rationalizing these observations is hindered by the absence of atomic-level data for these tri-metallic materials, even when not exposed to the fuel cell operation conditions. This study aims at understanding structure-property relations in Zr-doped PtNi nanoparticles as a key to their ORR function. In particular, we calculated, using a method based on density functional theory, the most stable chemical orderings of pristine and Zr-doped Pt3Ni particles containing over 400 atoms. We thus clarify (i) preferential location and charge states of Zr atoms in the Pt3Ni NPs; (ii) effect of doping Zr atoms on the stability of the Pt skin of the Pt3Ni NPs; (iii) charge redistribution induced by Zr dopants; (iv) layer-by-layer atomic ordering in the Pt3Ni/Zr NPs with the increasing Zr content; and (v) effect of Zr atoms on the adsorption energies of O and OH species as indicators of the ORR activity.

Biopolymers‐Based Proton Exchange Membranes For Fuel Cell Applications: A Comprehensive Review

AbstractNafion has been dominating the proton exchange membrane (PEM) market because of its adequacy for the proton exchange operation. However, because of its high cost, low performance at low relative humidity, and finally environmental unfriendliness, researchers have been developing and working on Nafion alternatives. In this review, we assess how biopolymers present an opportunity as an eco‐friendly material able to replace the conventional Nafion membrane in proton exchange membrane fuel cells (PEMFC). Chitosan and cellulose were the most studied in literature owing to their abundance in nature, low cost, and high affinity for water, which are sought‐after properties for PEM. In addition to that, their ease of modification through their hydroxyl or amine groups represents an opportunity to further enhance their characteristics and thus meet the criteria of diverse applications. The use of biopolymers as an adequate PEM is facing many challenges. Having a practical proton conductivity and securing the physicochemical stability of the biopolymers in fuel cell operating conditions are two of the most important challenges to overcome. Promising strategies to simultaneously address these challenges such as crosslinking, making interpenetrated networks, and making blends and composites are reported.

Highly Durable Electrocatalyst with Low-Loading Pt-Co Dispersed over Graphene Nanofiber for Oxygen Reduction Reaction Under PEMFC Condition

Proton exchange membrane fuel cell (PEMFC) has been demonstrated as a highly efficient energy conversion technology. The sluggish oxygen reduction reaction (ORR) at the fuel cell cathode requires 3 to 5 times more catalysts than the hydrogen oxidation reaction at the anode (1). Currently, platinum is still the catalyst material of choice. However, the heavy use of scarce Pt in the electrodes represents a major cost barrier to the commercialization of PEMFCs. Tremendous efforts have been dedicated to reduce or remove Pt usage through the development of Pt-transition metal catalysts, as highlighted recently by dealloyed PtNi (2), Mo-doped PtNi(3), and ordered PtCo (4); or through the development of transition metals-nitrogen-carbon based PGM-free catalysts (5, 6).In the fuel cell, catalysts should be highly dispersed over the electrode surface to be easily accessible by the reactants, especially at the high fuel cell current density where a large influx of O2 must be converted. For the Pt alloy catalyst of large crystallites, there won’t be enough crystallites available to spread over the electrode surface to encounter the incoming O2 if the total loading of platinum has to be maintained ultralow. Furthermore, unprotected Pt nano-alloys may lose their nanostructure and crystallinity from the dissolution and agglomeration during the ORR process. The PGM-free catalysts, on the other hand, have high catalytic site density with uniform distribution when prepared by homogenous precursors such as metal-organic framework or porous organic polymer, rendering them highly efficient in interacting with O2 flux. Their key drawback, however, is the poor stability operated under PEMFC condition.In this presentation, we will describe a method of preparing highly active yet stable electrocatalysts containing ultralow Pt content using polymer fiber containing cobalt zeolitic imidazolate framework as precursor. The new catalyst contains Pt-Co nanoparticels situated over the PGM-free catalystically active support (7,8). The ORR activities of the new catalyst was first tested in O2 saturated acidic electrolyte by rotating ring disk electrode (RRDE) before fabricated into the membrane electrode assembly (MEA) and evaluated under fuel cell operating condition. The synergistic catalysis between PtCo NPs and the PGM-free active substrate led to an unprecedented oRR performance in both RRDE and fuel cell. For example, the fuel cell test demonstrated a mess activity of 2.43 A/mgPt for the new catalysts and > 80% retention of the initial mass activity after 60000 continuous voltage cycles from 0.6 – 1.0 V.The characterizations of the fresh and the post-electrochemical test samples were investigated by x-ray photoelectron spectroscopy (XPS), x-ray diffraction (XRD), x-ray absorption near-edge structure (XANES), extended x-ray absorption fine structure (EXAFS), transmission electron microscopy (TEM), Raman spectroscopy and BET surface analysis. We also performed DFT calculation on the ORR thermodynamic barriers over both Pt-Co NPs and PGM-free site as the descriptors for reaction pathway. The results reveal that the synergistic interaction between Pt-Co and PGM active substrate contribute significantly to both activity and durability enhancements.Acknowledgments:This work was supported by Argonne National Laboratory through Maria Goeppert Mayer Fellowship, US; Overseas Outstanding Youth Fund project, shanghai Jiao Tong university, Shanghai, China, State Key Laboratory of Metal Matrix Composites, shanghai Jiao Tong university, Shanghai, China. The works performed at Argonne National Laboratory’s Center for Nanoscale Materials and Advanced Photo Source, and Hydrogen research center, shanghai Jiao Tong university.Reference: H. A. Gasteiger, N. M. Markovic, Just a Dream-or Future Reality? Science 324, 48-49 (2009).B. Han et al., Record activity and stability of dealloyed bimetallic catalysts for proton exchange membrane fuel cells. Energy & Environmental Science 8, 258-266 (2015).X. Huang et al., High-performance transition metal–doped Pt3Ni octahedra for oxygen reduction reaction. Science 348, 1230-1234 (2015).D. Wang et al., Structurally ordered intermetallic platinum-cobalt core-shell nanoparticles with enhanced activity and stability as oxygen reduction electrocatalysts. Nat Mater 12, 81-87 (2013).L. Chong et al., Investigation of Oxygen Reduction Activity of Catalysts Derived from Co and Co/Zn Methyl-Imidazolate Frameworks in Proton Exchange Membrane Fuel Cells. ChemElectroChem 3, 1541-1545 (2016).J. Shui, C. Chen, L. Grabstanowicz, D. Zhao, D. J. Liu, Highly efficient nonprecious metal catalyst prepared with metal-organic framework in a continuous carbon nanofibrous network. Proc Natl Acad Sci U S A 112, 10629-10634 (2015).L. Chong et al., Ultralow-loading platinum-cobalt fuel cell catalysts derived from imidazolate frameworks. Science, (2018).L. Chong et al., Highly durable fuel cell electrocatalyst with low-loading Pt-Co nanoparticles dispersed over single-atom Pt-Co-N-graphene nanofiber. Chem Catalysis 3, 100541.

Anode Defects’ Propagation in Polymer Electrolyte Membrane Fuel Cells Stack

Reliability and durability are key considerations to successfully deploy Proton Exchange Membrane Fuel Cells (PEMFCs). Defects induced by manufacturing processes and fuel cell operating conditions may shorten the lifetime of PEMFC due to membrane electrode assembly (MEA) components degradations. If the degradation mechanisms occurring along ageing are now well-known, the propagation of these defects to other materials or to other locations in the stack was poorly investigated in the literature. Recently, we investigated a defect-propagation in MEA via accelerated stress tests combining load and load-driven humidity cycling, and open-circuit voltage. Results highlighted a defect propagation in term of anode and cathode ECSA losses. Significant membrane thinning is also observed for the defective segments. If, the defect propagation was investigated at the cell scale, it has been barely studied in the literature at the stack level.The objective of this work is to quantify the impact of MEA manufacturing defects on the performance and durability in stack and to analyze how these defects can propagate within healthy areas of the same MEA or to healthies MEAs within a stack.Tests were carried out on two stacks with metallic bipolar plates. The stacks were assembled using 35 defect-free MEAs for the healthy stack and using 30 homogeneous MEAs and 5 MEAs with controlled anode defects over 25% of the active area (absence of anode catalyst layer) for the faulty one. The two stacks were operated on a test bench able to control operating conditions and electrochemical characterizations were regularly made in order to evaluate the impact of the defects on the stack behavior.The initial characterization of the stack contained faulty MEAs showed, as expected, that the defects in the anode active layers have a significant effect on the performance of the cells from the conditioning stage. The analysis of the degradation rate showed that the cells directly in contact with the defected MEAs were the ones whose performance degraded the fastest, which implies that the presence of defects within the stack induces a propagation of the performance decrease. This phenomenon could be linked to a significant increase in hydrogen leakage through the membrane identified both by off-line electrochemical characterization and by thermal camera measurements in post-mortem analysis. The mechanism of degradation is still difficult to understand but the presence of defects within the stack could lead to constriction of the current lines around the defect and to localized heating which could degrade the membrane relatively rapidly. Figure 1

Numerical Simulations for in-Plane Distribution of Platinum Degradation in Dynamic Operating Conditions of Polymer Electrolyte Membrane Fuel Cells

Predicting degradation of polymer electrolyte membrane fuel cells (PEMFCs) is an important issue from the viewpoint of durability and cost. In fact, in technical roadmaps regarding fuel cell of each country, high targets of durability and performance are set for transport applications especially for heavy duty vehicles. One of important degradation process takes place in catalyst layer. PEMFC catalysts are typically platinum or platinum alloys and consist of nanoparticles to increase the electrochemically active surface area (ECSA). However, these particles are not stable in dynamic operating conditions of the transport applications. A typical degradation mechanism of the catalyst is the electrochemical Ostwald ripening mechanism, and it is known that the platinum particle size distribution shifts to larger particle diameter, resulting in lower ECSA and lower performance. Therefore, predicting platinum catalyst degradation is important to enhance durability of the products.Various numerical models for catalyst degradation of PEMFC have been proposed and used to explore degradation mechanisms. Many of these are zero or one-dimensional models, but factors that affect catalyst degradation, such as temperature, potential, and humidity, have non-uniform distributions in the active area of large-size (several hundred cm2) cells. Furthermore, these factors change unsteadily due to the dynamic operating conditions. In order to predict the degradation of cells, it is necessary to analyze the dynamic behavior of large-area cells, but there are few spatially resolved catalyst degradation predictions [1].In this analysis, transient analysis of a large-area cell for a dynamic operating conditions is performed to predict in-plane distribution of catalyst degradation. Furthermore, we will analyze changes in the power generation performance of the cells when these degradations progress. A three-dimensional numerical simulation model based on our original methodology [2] was used as the performance prediction model for the PEMFC. Catalyst degradation considers the mechanisms of platinum dissolution, oxidation, and platinum oxide dissolution [3]. The in-plane distribution of platinum degradation is predicted from the time-series results of in-plane distributions of temperature, potential, humidity, etc., obtained by the performance prediction model. The performance of the PEMFC at the time of progressive degradation is analyzed by reflecting the effect of ECSA decrease due to platinum degradation in the performance prediction model. Although this method considers only a part of the catalyst degradation process, a path is presented to analyze the distribution of catalyst degradation under dynamic operating conditions in large-area cells.

Comprehensive understanding of oxygen transport at Gas/ionomer/electrocatalyst triple phase boundary in PEMFCs

Reducing Pt loading of proton exchange membrane fuel cells (PEMFCs) without sacrificing performance remains challenging due to the severe oxygen transport resistance in cathode, especially the local oxygen transport resistance (RLocal) at the gas/ionomer/electrocatalyst triple phase boundary (TPB). Here, the detailed oxygen adsorption mechanism at surface ionomer is quantified for the first time via a self-built characterization system based on quartz crystal microbalance (QCM). The results show that the surface oxygen adsorption amount quasi-logarithmically increases as oxygen partial pressure increases. The ionomer surface is further investigated by molecular dynamics simulations and it is found that there exists not only non-uniformity in morphology, but also separation of hydrophilic and hydrophobic phase, which leads an inhomogeneity of interaction with oxygen. As a consequence, the extended form of Toth model is proved to be more appropriate for the surface oxygen adsorption on ionomer film due to higher correlation coefficients R2, better applicability at low pressure and varying temperature. Ultimately, we successfully predict the oxygen adsorption amount and the corresponding trend of RLocal at practical fuel cell operating condition with the adsorption model disclosed in this work, which is potential to estimate the oxygen adsorption in other type of electrochemical devices.

Novel Strategy for Engineering Ultra-Thin Proton Exchange Membranes for Advanced PEM Fuel Cells

The energy needs of the modern world currently relies heavily on fossil fuels and energy conversion technologies that emit greenhouse gases (GHGs). These GHGs have been shown to have a detrimental impact on global climate. Climate change has created a vital shift in the way society thinks about energy conversion and storage. Today we are seeing huge increase in the demand for utilization of renewable energy sources (solar, wind, and etc.) as well as in their integration with zero-carbon emission energy conversion and storage devices such as fuel cells, water electrolyzers, and batteries. The renewable energy sources are intermittent by nature since the wind does not always blow and the sun does not always shine. This creates a need for a way to store excess green energy that would otherwise be wasted when the demand does not meet the production. Development of advanced Proton Exchange Membrane (PEM) water electrolyzers and fuel cells that can be integrated with renewable energy sources to convert the excess electricity to hydrogen, is the most efficient approach for sustainable energy storage and utilization. Development of such sustainable energy systems is of primary importance for implementation and widespread application of the green energy technologies in our everyday life and elimination of the GHG emissions. Low temperature Polymer Electrolyte Membrane Fuel Cells (PEMFC) are the most promising type of fuel cells for application in the transportation sector. Currently, the commercialization of these devices is hindered by their high cost and limited durability. Further research is needed to increase their efficiency, power output, catalyst utilization, and durability. Fabrication of thinner proton conductive membranes, is one of the strategies that are of particular research interest. Successful development of thinner PFSA membranes will result in reduction of the ohmic resistance of the MEAs, cost reduction, and will improve their performance. Fabrication of thinner PEM membrane is a challenging task that requires innovative engineering approaches that will allow to fabricate ultra-thin, pinhole free membranes with the desired mechanical stability and hydrogen crossover suppression properties. This work aims on development of novel approaches for engineering ultra-thin PEM membranes with thicknesses below 10µm, and to perform a systematic study of the membrane thickness impact on the MEAs cost, activity, and durability performance. In addition, the effect of various reinforcement materials on the membrane properties have been studied, and their optimal concentrations and position in the volume of the membrane has been investigated. All PEM membranes of interest have been fabricated with a state-of-the-art ultrasonic spray deposition method, designed, and developed at UConn. This methodology allows for precise control of the thickness and composition of the thin membranes, as well as of the thickness, composition, and precious metal loading in the catalysts layers. The newly designed MEAs have been tested at real fuel cell operating conditions, and the results will be presented and discussed in detail at the 243rd ECS meeting in Boston, MA.

A new and robust MnCo1.9Sb0.1O4 spinel cathode for proton-conducting solid oxide fuel cells

As a cathode material for proton-conducting SOFCs (H–SOFCs), a novel MnCo1.9Sb0.1O4 (MCSO) spinel material was suggested. The MCSO material was effectively produced, and it demonstrated excellent phase stability at elevated temperatures and chemical stability against CO2 and H2O. Doping Sb into the MnCo2O4 (MCO) allowed for enhanced proton diffusion and surface exchange, as evidenced by electrical conductivity relaxation tests. In addition, an oxygen-vacancy-rich surface was developed for the MCSO material, resulting in the possibility of a high cathode oxygen reduction reaction activity. The MCSO material was examined in the H–SOFC application, and the fuel cell with an MCSO cathode attained a high power density of 1380 mW cm−2 at 700 °C. At 700 °C, the cell employing the Sb-free MCO cathode, which had a comparable cell microstructure to the MCSO cell, only obtained a peak power density of 836 mW cm−2. The higher cell performance resulted from the Sb-modified MCO cathode's increased catalytic activity. In addition, the MCSO cell displayed excellent operational stability under fuel cell operating conditions, indicating that MCSO is a novel and effective spinel cathode for H–SOFCs.

Origin of High Activity and Durability of Confined Ordered Intermetallic PtCo Catalysts for the Oxygen Reduction Reaction in Rotating Disk Electrode and Fuel Cell Operating Conditions

Origin of High Activity and Durability of Confined Ordered Intermetallic PtCo Catalysts for the Oxygen Reduction Reaction in Rotating Disk Electrode and Fuel Cell Operating Conditions

Elucidating mechanistic background of the origin and rates of peroxide formation in low temperature proton exchange fuel cells

Degradation of electrode-membrane assembly of the low-temperature hydrogen fuel cells represents one of the main obstacles in wider adoption of these clean and efficient electrochemical sources of electrical energy. Chemical degradation of proton exchange membrane is initiated by hydrogen peroxide formation, which forms in the fuel cell as a by-product to water in oxygen reduction reaction and decomposes to reactive radical species, damaging to the membrane chemical structure. Depending on the operating conditions of the fuel cell, the source of hydrogen peroxide can be either cathode, anode, or, as we argue in the paper, also the Pt particles in the membrane, which originate from the cathode catalyst dissolution, diffusion into the membrane and redeposition of Pt ions inside the membrane. In the paper we propose a mathematical model of intertwined physical processes in membrane and catalyst layer, aimed at unifying the description of hydrogen peroxide formation throughout entire membrane-electrode assembly at any fuel cell operating conditions. The model results, compared to experimental data, indicate that Pt particles inside the membrane can indeed be an important source of hydrogen peroxide in aged fuel cells. For a fresh fuel cell, numerical simulation using proposed model show that hydrogen peroxide can be formed at either cathode or anode, depending on the fuel cell operating condition, but with anode production being more prominent in standard fuel cell operating conditions.

A Methodology to Design the Flow Field of PEM Fuel Cells

<div class="section abstract"><div class="htmlview paragraph">Proton Exchange Fuel Cells (PEMFCs) are considered one of the most prominent technologies to decarbonize the transportation sector, with emphasis on long-haul/long-range trucks, off-highway, maritime and railway. The flow field of reactants is dictated by the layout of machined channels in the bipolar plates, and several established designs (e.g., parallel channels, single/multi-pass serpentine) coexist both in research and industry. In this context, the flow behavior at cathode embodies multiple complexities, namely an accurate control of the inlet/outlet humidity for optimal membrane hydration, pressure losses, water removal at high current density, and the limitation of laminar regime. However, a robust methodology is missing to compare and quantify such aspects among the candidate designs, resulting in a variety of configurations in use with no justification of the specific choice. This contrasts with the large operational differences, especially regarding the pressure loss/stoichiometric factor trade-off and in the outlet humidity level.</div><div class="htmlview paragraph">In this paper a simple thermodynamic model (0D) is presented to evaluate pressure losses, stoichiometric factors, channel length, and humidity level for typical flow fields. Based on distributed and concentrated pressure losses and on a water balance between the humidified air, the electrochemically produced water, and the electro-osmotic water flux, the model indicates the optimal flow field for a given active area. The methodology is validated using 3D-CFD models, assessing the predictive capability of the simplified 0D model, and it is applied to small/medium/large active area cases. The presented method introduces a model-based guideline for the design of PEMFCs flow fields, providing design indications to optimize the humid flow dynamics. The study shows the impact of flow field design on fuel cell operating conditions, providing guidelines for fuel cell engineering. In the limits of laminar flows, the parallel channel design demonstrated the lowest pressure drop (∆<i>p</i> ≃ 1 × 10<sup>2</sup> − 10<sup>3</sup><i>Pa</i>, more than one order of magnitude lower than other designs) and the best capability of saturated outlet flows (i.e., ideal membrane hydration) for current densities in the range 0.5 − 2.0 <i>A</i>/<i>cm</i><sup>2</sup>, hence outperforming any other serpentine-type designs for medium-to-large active areas and with the focus on high current density operation.</div></div>

Simulation to analyze operation strategy of combined cooling and power system using a high-temperature polymer electrolyte fuel cell for data centers

With the development of the information and communication technology (ICT) industry, the energy consumption of data centers is continuously increasing. High-temperature polymer electrolyte fuel cells (HT-PEFC) have a high operating temperature of 120 °C or higher; thus, the heat generated from fuel cells stack is effectively used as a heat source for a absorption refrigerator (AR) to generate cooling. The combined cooling and power (CCP) system is proposed to satisfy the energy demand of data centers that require both power and cooling. The CCP system comprises an HT-PEFC and a double-effect AR that recovers the wasted heat of the fuel cell stack. As a result of analyzing the electrical and cooling efficiency of the CCP system according to the fuel cell operating conditions, the overall efficiency increased to 95%, which was significantly higher than the existing system. Based on the simulation of the developed model, coefficient of performance (COP) and cooling capacity depending on the temperature changes of chilled water and cooling water were calculated within the stack temperature range of 150–180 °C, and the COP changed from 1.1 to 1.58 depending on the conditions. The developed CCP system model can be used to plan strategies for flexible fuel cell operation according to the power and cooling demands required in the data center.

Operando X-Ray Fluorescence Measurement Method of Cerium Radical Quencher Distribution in through-Plane MEA

Hydroxyl and hydroperoxyl radicals produced by reacting impurities with hydrogen peroxide is one of the degradation factors of polymer electrolyte [1]. A method to suppress this degradation is the addition of cerium into the polymer electrolyte membrane (PEM), which serves as radical quencher [2,3]. However, cerium ion in PEM migrates from the initial state by fuel cell operation [4]. The lack of cerium ion in PEM causes degradation from radical species. Information on cerium migration in PEM is necessary to design the membrane electrode assembly (MEA) for long-term operation. Although the observation of cerium ion diffusion with in-plane direction of PEM has been reported [5], it is difficult to detect the distribution in through-plane of MEA under fuel cell operating condition due to the quite narrow thickness of PEM. This study reports an operando X-ray fluorescence analysis technique to detect cerium distribution in through-plane direction of MEA using high-energy X-ray nanobeam.MEAs were prepared by a conventional method using Pt/C catalyst and polymer electrolyte with the thickness of 12 mm. The active electrode area was 1 cm2. Single cells were assembled using custom-made end-plates that have an X-ray permeation window. Operando X-ray fluorescence spectroscopy measurements were performed at SPring-8, BL37XU (Japan). The monochromatized X-ray at an energy of 45 keV was focused to less than 200 nm by Kirkpatrick-Baez mirror. To detect the cerium distribution in MEA, Ce-Ka fluorescence intensity was counted using a Ge semiconductor detector with scanning the position of the cell. The cell temperature was 80 ℃. O2 and H2 gases with relative humidity of 100% were flew to cathode and anode, respectively.Figure 1 shows line-scan profile of Ce-Kα fluorescence X-ray intensity from the as-prepared MEA. The x-axis represents the through-plain position, where the positive and negative sides corresponds to cathode and anode sides, respectively. The two peaks are observed at 678 and 685 mm and the peak width is approximately 13 mm. This peak shows PEM containing cerium ion. During the fuel cell operation, the line-scan is repeated and cerium ion distribution can be analyzed. Acknowledgment Part of this work is based on results obtained from the project commissioned by the New Energy and Industrial Technology Development Organization (NEDO) of Japan.[1] R. Borup et al., Chem. Rev., 107 3904-3951 (2007).[2] E. Endoh et al., ECS Electrochem. Lett. 2 F73-F75 (2013).[3] P. Trogadas et al., Electrochem. Solid-State Lett. 11 B113-B116 (2008).[4] S.M. Stewart et al., ECS Electrochem. Lett. 3 F19-F22 (2014).[5] A.M. Baker et al., J. Electrochem. Soc. 164 F1272-F1278 (2017). Figure 1

Durability and Performance Study of Chemically Anchored Heteropoly Acid with Perfluorinated Sulfonic Acid-Expanded Polytetrafluoroethylene Composite Membrane for Proton Exchange Membrane Fuel Cells

Chemical degradation and mechanical degradation are the major challenges for heavy-duty vehicle fuel cell commercialization. Perfluorinated sulfonic acid is the benchmark material that has high proton conductivity and robust mechanical properties. However, chemical degradation can occur through radical formation during the fuel cell operation. Chemical degradation can also have a synergetic effect with mechanical degradation. Recent studies have used cerium and manganese additives to suppress the radical formation or chemical degradation caused by radicals. The limitation of the metal and metal oxide additives was the migration and agglomeration of the additives. Both migration and clustering can lead to changes in membrane morphology, resulting in a loss in proton conductivity. Our group has previously reported that immobilization of heteropoly acid to a fluoroelastomer can be used to both enhance proton conductivity and chemical degradation. The durability test has shown that the chemical durability was significantly enhanced, but the mechanical durability remained the challenge.In this study, we hypothesized that when a heteropoly acid can be chemically bound to the perfluorinated polymer and cast on a composite membrane with expanded polytetrafluoroethylene (e-PTFE) will enhance the chemical and mechanical durability without migration. Proton conductivity was measured using impedance spectroscopy. The structure-property relationship was studied using multi-scale morphology analysis methods such as scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), atomic force microscopy (AFM), and small-angle x-ray scattering (SAXS). The chemical degradation will be tested under the highly accelerated standard test (HAST) condition, a more severe fuel cell operation condition than the accelerated standard condition (AST). The mechanical durability of the composite membrane will also be tested on the HAST condition with humidity cycling.

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.

Modeling of Fuel Cells Characteristics in Relation to Real Driving Conditions of FCHEV Vehicles

Fuel cells are one of the zero-emission elements of modern automotive drive systems. This article presents theoretical identification of the component parameters of indicators for the fuel cell operating conditions. Activation, ohmic, and mass transport losses were identified. Current–voltage characteristics were provided along with an analysis of typical cell losses. The actual performance characteristics of fuel cells were analyzed for Toyota Mirai I and II generation vehicles. The fuel cells operating conditions were derived and analyzed in the context of real driving conditions. Therefore, urban, rural, and motorway conditions were used. The vehicles were equipped with PEM fuel cells supplying power equal to 114 kW (1st gen.) or 128 kW (2nd gen.). The average fuel cell stack power values depend on the driving conditions: urban (about 10 kW), rural (20 kW) and motorway (about 30–40 kW) driving modes. The different power ratings of fuel cells combined with different battery generations resulted in a variation in the cells operating conditions. Analyses conducted in various traffic conditions indicated the possibility of determining losses related to the fuel cells. The analysis of fuel cell losses shows the greatest values for activation losses when the cells are under high load (for both generations)—i.e., in motorway driving conditions. The voltage of resistive losses reached its maximum in urban driving conditions when the load on the fuel cells was small.

Lignocellulosic biomass based microbial fuel cells: Performance and applications

Lignocellulosic biomass has the potential to replace fossil fuels as a sustainable and renewable feedstock for energy generation . Microbial fuel cell technology offers an energy-producing system from lignocellulosic biomass. This review explores different microbial fuel cell designs i.e. membrane-less single chambered, double chambered and integrated microbial fuel cell along with their mode of operation. There are some compatibility issues with different microbial fuel cell designs in utilizing the lignocellulosic biomass as feed. Microbial fuel cell setup with integrated pre-treatment or simultaneous degradation of lignocellulosic biomass may provide a solution. A careful selection of microbial community according to the microbial fuel cell operation conditions along with upscaling of the system may help in efficient utilization of renewable energy sources . Thus, lignocellulosic biomass-based microbial fuel cell may potentially be used in the bioremediation, production of biofuels and industrially important value-added products along with simultaneous production of electricity. • Lignocellulosic biomass may be used as a renewable feedstock in microbial fuel cells. • Microbial fuel cell designs influence the substrate utilization efficiency. • Pre-treatment of lignocellulosic biomass is required to be used as feed. • Such eco-friendly technology may be used for several applications.

Improved Durability of High-Performance Intermediate-Temperature Solid Oxide Fuel Cells with a Ba-Doped La0.6Sr0.4Co0.2Fe0.8O3-δ Cathode.

As a device for direct conversion of chemical energy into electrical energy, the solid oxide fuel cell (SOFC) contributes positively to the sustainable development strategy. However, the commercialization of fuel cells is still impeded by severe cathode degradation caused by its limited stability at operating temperatures and being prone to Cr-poisoning from Cr-containing alloy interconnectors commonly used in these cells. This paper reports the development of a high-durability Ba-doped LSCF(La0.6Sr0.4Co0.2Fe0.8O3-δ) cathode material under realistic fuel cell operating conditions in the presence of the Cr alloy. In particular, when tested in a symmetrical cell constructed of Ba-doped LSCF, the polarization resistance of the cell remains very low at 0.06 Ω cm2 after being tested at 800 °C for 120 h exposed to Cr in 3% humidified air. In contrast, for the undoped LSCF under the same testing conditions, the polarization resistance of the cell increases ∼10 times from 0.22 Ω cm2 of the pristine cell to 2.18 Ω cm2 after Cr-exposure testing. Furthermore, when tested in an anode-supported complete cell as a cathode under typical SOFC operation conditions at 750 °C, the cell with the Ba-doped LSCF cathode displays significantly low degradation rates of 0.00056% h-1 (without Cr) and 0.00310% h-1 (with Cr); both are much lower than that of the cell using the undoped LSCF cathode (0.00124% h-1 without Cr and 0.01082% h-1 with Cr). This enhanced durability and Cr-tolerance exhibited by the Ba-doped LSCF cathode stem from its higher crystal structure stability and improved chemical resistance compared to undoped LSCF.

Mathematical Model of Hydrogen Peroxide Production in Anode, Cathode, and Membrane of LT-PEMFC

Degradation of proton exchange membrane in low-temperature fuel cells represents one of the main limiting factors for wider adoption of this clean, carbon emission free energy device. In combination with mechanical degradation caused by membrane swelling and shrinkage during water content change, chemical degradation of the membrane is considered to be the main mechanism leading to loss of membrane conductivity, membrane thinning and eventual pinhole formation.Chemical degradation is caused by the attack of reactive radical species on the perfluorinated polymer chains of the membrane, which are formed in Fenton reaction between hydrogen peroxide and ions of transition metals, which are inevitably present in the membrane in small traces. Since the metal ions are recycled in Fenton reactions, the rate of chemical degradation is mainly determined by the production of hydrogen peroxide, formed as a side product to water in reaction between oxygen and protons in the fuel cell. [1]The source of hydrogen peroxide production in low-temperature fuel cells have long been debated in scientific literature. On one hand, the abundance of oxygen in the cathode suggest that the production takes place there, but high local electric potential strongly promotes 4-electron reaction, forming water, over 2-electron reaction required for production of hydrogen peroxide [2]. The conditions in the anode are reversed, low electric potential is well suited for peroxide production, but the concentration of oxygen, present in the anode due to diffusion through the membrane, is in general expected to be quite low, making it a rate limiting factor for the peroxide production in the anode. The last possible source of hydrogen peroxide is closely related to the degradation of platinum (Pt) catalyst in the cathode. When Pt catalyst nanoparticles dissolve due to high local electric potential on the cathode, part of the dissolved ions diffuses into the membrane, where it is reduced by counter-diffusing hydrogen from the anode. These Pt particles in the membrane, the so-called Pt band, serve as a catalyst for the reaction between diffusing oxygen from cathode and hydrogen in anode. Since these particles are not electrically connected to either anode or cathode, their electric potential is determined by the rates of oxygen reduction and hydrogen oxidation on their surface, which result in production of water and potentially also hydrogen peroxide.The complex interplay between the processes determining the peroxide production, explained above, suggest that different sources of peroxide might be relevant in different fuel cell operation conditions and at different states of health of the fuel cell. To explore this question quantitatively, we propose a mathematical model of peroxide production which describes physical and electrochemical processes for hydrogen peroxide production in fuel cell catalysts and the membrane, relevant for hydrogen peroxide production: oxygen and hydrogen diffusion in the membrane, electrochemical oxygen reduction in the cathode, anode and on Pt band inside membrane, hydrogen oxidation on Pt band and electric charging of Pt particles in the band due to electrochemical reactions on their surface. To provide realistic internal states of the fuel cell during operation, the model is coupled with advanced spatially and temporally resolved model of the fuel cell operation. [3]Preliminary results of the model indicate that main source of peroxide production depends on the fuel cell operating conditions. In fresh fuel cell, where Pt band in membrane is not yet formed, low current densities and high fuel cell voltages promote the peroxide formation mainly on the anode from the diffused oxygen, while at high current densities the electric potential on the cathode is low enough to allow for significant peroxide production there, outweighing the production on the anode. The formation of the Pt band shifts the production of peroxide from anode to the Pt particles in the band, since large amount of the oxygen is consumed there and therefore its diffusion to the anode is reduced.The results indicate that the question of where the peroxide is formed cannot be resolved by a single answer and that the use of sufficiently complex models, coupling physical and electrochemical processes in different fuel cell components, are required to properly manage fuel cell operation in order to avoid or at least mitigate its detrimental effects of chemical membrane degradation.[1] Frühwirt, P., Kregar, A., Törring, J. T., Katrašnik, T., Gescheidt, G. (2020). Physical Chemistry Chemical Physics, 22(10), 5647–5666.[2] Sethuraman, V. A., Weidner, J. W., Haug, A. T., Motupally, S., Protsailo, L. V. (2008). Journal of The Electrochemical Society, 155(1), B50.[3] Kregar, A., Tavčar, G., Kravos, A., Katrašnik, T. (2020). Applied Energy, 263(March), 114547.