Durability Of Membrane Electrode Assembly Research Articles

Improvement of durability of membrane electrode assembly by frame sealing structure in temperature shock

Improvement of durability of membrane electrode assembly by frame sealing structure in temperature shock

Elucidating Fundamental Structure-Function Relationships for Iridium Oxide Catalysts in PEM Water Electrolyzers

Proton exchange membrane water electrolysis (PEMWE) will contribute substantially towards decarbonization efforts and is expected to make up 40% of the green hydrogen market.1 A primary barrier for PEMWE scale-up is the detrimentally high usage of iridium for the oxygen evolution reaction catalyst. To achieve large-scale PEMWE deployment, loading reductions from 2-3 mgIr cm-2 to 0.10 mgIr cm-2 must occur.2 Such a feat can only be achieved through significant improvements in activity and durability. However, there exists a lack of fundamental understanding in how catalyst properties correlate to performance, thus hindering optimization efforts. The phenomena of catalyst activity/durability are frequently treated with purely empirical approaches, and thus the foundational knowledge needed for improved catalyst design—such as understanding how crystallinity and oxidation states impact performance in a membrane electrode assembly (MEA)—has not been well investigated.3 This work serves to bridge this gap in knowledge by correlating extensive structural characterization data with MEA activity and durability for six commercial IrOx catalysts. Properties such as oxidation states, chemical composition, local atomic/electronic configuration, crystallinity, surface area, and particle size distribution were elucidated for each catalyst in powder and/or MEA form. Following MEA conditioning, catalyst activity was benchmarked via polarization curves and Tafel analysis. Lastly, durability was evaluated by performing a 500h accelerated stress test (adapted from the H2New consortium), with electrochemical characterization conducted every 100h. The presence of amorphous character and the Ir3+ oxidation state was the best determinant of activity. Durability, on the other hand, was associated with greater crystalline character and more redox-stable cyclic voltammogram profiles. Correlations regarding chemical composition, local atomic/electronic configurations, particle size, and surface area will be discussed as well. Smolinka, T.; Wiebe, N.; Sterchele, P.; Palzer, A.; Lehner, F.; Jansen, M.; Kiemel, S.; Miehe, R.; Wahren, S.; Zimmermann, F. Studie IndWEDe: Industrialisierung Der Wasserelektrolyse in Deutschland: Chancen Und Herausforderungen Für Nachhaltigen Wasserstoff Für Verkehr, Strom Und Wärme.; 2018.Clapp, M.; Zalitis, C. M.; Ryan, M. Perspectives on Current and Future Iridium Demand and Iridium Oxide Catalysts for PEM Water Electrolysis. Catal Today 2023, 420 (March), 114140. https://doi.org/10.1016/j.cattod.2023.114140.Lazaridis, T.; Stühmeier, B. M.; Gasteiger, H. A.; El-Sayed, H. A. Capabilities and Limitations of Rotating Disk Electrodes versus Membrane Electrode Assemblies in the Investigation of Electrocatalysts. Nat Catal 2022, 5 (5), 363–373. https://doi.org/10.1038/s41929-022-00776-5.

Study of the Durability of Membrane Electrode Assemblies in Various Accelerated Stress Tests for Proton-Exchange Membrane Water Electrolysis.

In this work, we focus on the degradation of membrane electrode assemblies (MEAs) in proton-exchange membrane water electrolysis (PEMWE) induced by different accelerated stress tests (ASTs), including constant-current mode, square-wave mode, and solar photovoltaic mode. In constant-current mode, at continuous testing for 600 h at 80 °C, a degradation of operating voltage increased by the enhanced current density from 22 µV/h (1 A/cm2) to 50 µV/h (3 A/cm2). In square-wave mode, we found that in the narrow fluctuation range (1-2 A/cm2), the shorter step time (2 s) generates a higher degradation rate of operating voltage, but in the wide fluctuation range (1-3 A/cm2), the longer step time (22 s) induces a faster operating voltage rise. In the solar photovoltaic mode, we used a simulation of 11 h sunshine duration containing multiple constant-current and square-wave modes, which is closest to the actual application environment. Over 1400 h ASTs, the solar photovoltaic mode lead to the most serious voltage rise of 87.7 µV/h. These results are beneficial to understanding the durability of the PEM electrolyzer and optimizing the components of MEAs, such as catalysts, membranes, and gas diffusion layers.

Variation in performance and characteristics of long-term operated gas diffusion layer in a fuel cell electric vehicle

Proton-exchange membrane fuel cells (PEMFCs) operate at low temperatures and are used in household appliances and vehicles because of their high power density and fast start-up/shut-down capabilities. Previous research has focused on improving the performance of PEMFCs by enhancing their structures and constituent materials of their components. However, as PEMFCs are being commercialized, their durability remains a critical challenge that needs to be addressed. Although numerous studies have evaluated the durability of membrane electrode assemblies (MEA), limited research has been conducted on the durability of gas diffusion layers (GDL). The GDL, with its nanometer-to micrometer-sized pores and thickness of hundreds of microns, is prone to mechanical degradation during long-term operation. Moreover, the GDL is susceptible to carbon corrosion because it primarily consists of carbon materials, similar to the catalyst layer. Therefore, to ensure the performance and longevity of PEMFCs, it is of utmost importance to investigate the durability of the GDL. This study quantitatively investigates the variations in the performance and mechanical and chemical characteristics of GDLs during an extended period of operation in a fuel cell electric vehicle (FCEV), and two types of GDLs are analyzed.

Highly Durable Membrane–Electrode-Assemblies Using High M w and Ether-Free Polyfluorene-Based Electrolytes for Anion Exchange Membrane Water Electrolyzer

Water electrolysis technology, which produces hydrogen through electrolysis of water using electricity derived from renewable energy, is attracting attention as a way to realize a carbon-neutral society. Among water electrolysis systems, anion exchange membrane water electrolysis (AEMWE) can achieve high energy conversion efficiency and quick response to fluctuating power supplies by using thin polymer electrolyte membranes, and operates in an alkaline environment, allowing the use of inexpensive non-precious metals for bipolar plates and electrodes. However, conventional AEMs and ionomers exhibit low durability in high-temperature and alkaline environments, which is a critical issue in realizing high-performance and highly durable membrane–electrode assemblies (MEAs) for AEMWE.Our group developed high-molecular-weight (M w) and ether-free, polyfluorene-based anion conducting polyelectrolyte (PFT-Cx-TMA, Cx represent the number of carbon atoms in the alkyl side chain) as shown in Fig. 1a.1 These polyelectrolytes show high OH− conductivity over 100 mS cm− 1, high chemical durability (stable in 8 M NaOH at 80 °C for 168 h), and high tensile strength (25–42 MPa, comparable to a Nafion membrane). This study applied PFT-Cx-TMA to AEMs and ionomers in MEAs to evaluate the durability against various AEMWE operations (constant current operation and start-stop operation in different voltage ranges), demonstrating MEAs with both high performance and high durability.Fig. 1b shows the constant current durability of the MEA with PFT-C8-TMA as AEM and ionomer.2 This test was performed at the constant current density of 0.2 A cm− 2 and 80 °C using a 1 M KOH aqueous solution fed to the anode. Here, to investigate the effects of AEMs and ionomers on MEA durability, conventional precious metal catalysts (anode: IrO2, cathode: Pt/C or PtRu/C) were used in the MEA. The MEA with PFT-C8-TMA exhibited a current density of 1.0 A cm− 2 at 1.79 V and there was almost no voltage change even after the constant current operation for over 100 h. It is noteworthy that the MEAs using PFT-C8-TMA and PFT-C10-TMA demonstrated high performance and high durability not only in the alkaline-fed operation but also in the pure-water-fed operation.Next, this study investigated the start-stop durability of MEAs using voltage cycles simulating the start-stop operation of water electrolyzer. Here, square-wave voltage cycling of holding at 1.8 V and 0.1 V for 1 min each was used for the start-stop test at 80 °C with a 1 M KOH solution fed to the anode. As a comparison, the MEA was prepared using a commercial AEM (Sustainion X37-50, 50 μm in thickness) and ionomer (Sustaionion XB-7). As shown in Fig. 1c, the MEA using a PFT-C10-TMA AEM (56 μm in thickness) and ionomer was highly durable in the start-stop test compared to the MEA using commercial Sustaionion. During the test, the elution of black solid particles from the catalyst layer and the increase in charge transfer resistance (Rct) were observed in the MEA with Sustaionion, whereas no elution of catalyst materials and no change in Rct were confirmed in the MEA with PFT-C10-TMA. These results suggest that nonlinear mechanical stress via rapid bubble formation and shutdown during start-stop cycles caused the leaching of catalysts, resulting in the performance loss of the MEA with Sustainion. The commercial ionomer (Sustainion XB-7) exhibits a large dimensional change (156%) compared to the PFT-C10-TMA membrane (34%) at 80 °C in a 1 M KOH aqueous solution. Catalyst particles covered with a highly swollen ionomer are easily detached from a catalyst layer by the nonlinear mechanical stress. On the other hand, the PFT-C10-TMA ionomer has a high molecular weight (M w = 240000 g mol−1), low swelling degree, and well-entangled polymer chains, hence preventing leaching of the catalyst particles.In summary, this study demonstrates that MEAs using high M w and ether-free polyfluorene-based electrolytes with both high chemical and mechanical durability have excellent durability for AEMWE operations including constant and dynamic (start-stop voltage cycling) operations. Acknowledgement This presentation is based on results obtained from a project, JPNP14021, commissioned by the New Energy and Industrial Technology Development Organization (NEDO). References (1) S. Miyanishi and T. Yamaguchi, Polym. Chem., 2020, 11, 3812–3820.(2) R. Soni, S. Miyanishi, H. Kuroki, and T. Yamaguchi, ACS Appl. Energy Mater., 2021, 4, 1053–1058. Figure 1

Performance and Durability of Membrane-Electrode Assemblies Using Non-Precious Metal Catalyst and a Hydrocarbon-Based Electrolyte for Anion Exchange Membrane Water Electrolysis

Anion exchange membrane water electrolysis (AEMWE) is operated in an alkaline environment and has a similar membrane-electrode assembly (MEA) structure to that of proton exchange membrane water electrolysis (PEMWE). The use of non-noble metals as the electrocatalysts and operation at high current densities are inherently possible, so they are expected to be low-cost, high-performance candidates for next-generation water electrolysis systems. Improving the anion conductivity of the AEM and the activity of the non-precious metal catalysts is essential for the practical application of AEMWEs.1 The non-noble electrocatalysts used in the MEA in this study were Ni0.8Co0.2O2 and Ni0.8Fe0.2O,3 which have a fused-aggregate network structure, and the electrolyte was a hydrocarbon-based AEM (QPAF-4)4, all of which were developed at the University of Yamanashi.The catalyst ink for the anodes was prepared by mixing the Ni0.8Co0.2O catalyst (University of Yamanashi) with solvent (water/methanol) and QPAF-4 (IEC = 2.0 meq g-1, University of Yamanashi) binder solution. The anode ink was coated by using pulse-swirl-spray (PSS, Nordson) on the QPAF-4 membranes (IEC = 1.5 meq g-1) to make the catalyst-coated membranes (CCMs) with the anode. Catalyst inks for the cathodes was prepared by mixing Ni0.8Fe0.2O catalyst (University of Yamanashi) or Pt/CB catalyst (TEC10E50E, Tanaka Kikinzoku) with solvent (water/methanol) and QPAF-4 (IEC = 2.0 meq g-1) binder solution. The cathode ink was coated by using PSS on the gas diffusion layer (GDL, TGP-H-120, Toray) to make the gas diffusion electrodes (GDEs) for the cathodes. Ni mesh (Bekaert.co.jp) was used for the anode GDLs. The single cell (Figure 1, cell structure developed by Yokohama National University) performances were measured while supplying 1 M KOH at 80 °C to both electrodes.Figure 2 (a) shows the I-V performance of cells using Ni0.8Co0.2O for the anode and Ni0.8Fe0.2O or Pt/CB for the cathode. The electrolysis voltage observed for the cell with non-noble metal catalysts on both electrodes was higher than that for the cell with Pt/C on the cathode but was below 2 V at a current density of 1.2 A cm-2. The value of the onset electrolysis voltage was nearly the same as that of the corresponding rotating disk electrode,3 suggesting that the intrinsic performance of the cathode catalyst is being realized in the MEA. Increasing the amount of the cathodic catalyst loading scarcely affected the polarization. It is supposed that the fused-aggregate network structure of the Ni0.8Fe0.2O catalyst contributes to the favorable mass transfer. Figure 2 (b) shows the time dependence of the cell voltage of these cells. The increased loading amount improved the durability of the cathode. It is considered that the increase in the thickness of the cathode catalyst layer alleviated the damage of the GDL fibers to the membrane.These results indicate the possibility of adopting non-precious metal catalysts for both electrodes in AEMWE and thereby significantly reducing the catalyst cost. Acknowledgement This work was partially supported by NEDO of Japan through the AWE-1 project. References 1) A. Lim et al., J. Ind. Eng. Chem., 76, 410 (2019).2) G. Shi et al., ACS Catal., 12, 14209 (2022).3) G. Shi et al., ACS Omega, 8, 13068 (2023).4) H. Ono et al., J. Mater. Chem. A, 5, 24804 (2017). Figure 1

Comparison of MEA Degradation through FCV Actual Driving Test and Load-Cycle Durability Test

Introduction In research and development of high-durability polymer electrolyte fuel cells (PEFCs) for fuel cell vehicles (FCVs), accelerated stress tests (ASTs) are employed to evaluate durability of materials with a short time [1-3]. In order to validate an AST, it is necessary to confirm that the degradation mechanisms in the AST and in actual FCV operation are consistent, and to elucidate quantitative correspondence of their degradation rates. In this study, we analyzed degradation of a membrane electrode assembly (MEA) after FCV real-world driving and compared the degradation factor with that of a load-cycle durability test in a laboratory. Experiments MEA samples were extracted from an FC stack of a Toyota MIRAI 2014 model which was operated in real-world driving of 200,000 km, about 6000 h. MEA performance and electrochemical properties of them were investigated using a small differential cell with a straight flow field. As a comparison, another MEA at beginning of life (BOL) was subjected to a load-cycle durability test following a protocol encouraged by New Energy and Industrial Technology Development Organization (NEDO), Japan. Cell temperature and relative humidity were controlled at 80°C and 100%, respectively. A square-wave potential cycle shown in Figure 1 was adopted. MEA performance was investigated after cycles of 500, 1000, 3000, 10,000, and 30,000. Structures of catalyst layers and catalyst particles were analyzed for the MEAs after driving test and 30,000 cycles of the load-cycle test using scanning electron microscope (SEM), transmission electron microscope (TEM), and X-ray absorption fine structure (XAFS). Results and discussion The performance of the MEA after 200,000 km driving is close to that of the MEA after 30,000 cycles of the load-cycle test as shown in Figure 2. The performance degradation is mainly attributed to degradation of the catalyst layer, and properties of a gas diffusion layer and a proton exchange membrane are unchanged from those of the BOL sample. Degradation mechanisms of the catalyst layers in the driving test and the load cycle test are well corresponding. First, mass activities of PtCo catalyst decay to about a half of the BOL value mainly due to the decrease in electrochemically effective surface areas (ECSAs) as represented in Figure 3. Decrease rates of the ECSAs are consistent with the increase in average particle sizes of the catalyst. The catalyst size distributions of the two samples are also comparable. Then, oxygen transport resistance in the catalyst layers is increased. The resistance of the samples after the driving test and 30,000 cycles of the load-cycle test are twice as large as the BOL value. As shown in Figure 4, the transport resistance obviously exhibits inverse proportion to the catalyst surface area. This relationship represents that the primary factor of the resistance is one at vicinity of catalyst particles including ionomer permeation [4], and increase in it is attributed to decrease in the catalyst surface area. A performance simulation based on a simple 1-dimensioal MEA model supports that the decrease in the ECSA causes most of the MEA performance degradation through the deterioration in the catalyst activity and the oxygen transport resistance. Conclusions The MEA performance degradation after the 200,000 km real-world driving with the system of MIRAI 2014 model is primarily caused by catalyst metal coarsening and is well simulated by NEDO load-cycle durability test of 30,000 cycles. This result has validated the test protocol and should contribute to a target-setting of durability of future MEAs.

A Finite Element Analysis Model-Based Study on the Effect of the Frame on Membrane Stresses in Proton Exchange Membrane Fuel Cells

The frame of a membrane electrode assembly (MEA) has an important impact on durability and reliability of a proton exchange membrane fuel cell (PEMFC). In this study, the finite element analysis method has been used to build a two-dimensional model that can quickly screen and compare different frame structures and improve the design. Simulation results show that the membrane in the gap between the frame and the active area will generate a large amount of stress, close to the yield strength of the membrane under this condition, after application of the pressure difference. Further, an appropriate frame structure can improve the structural consistency between the frame and the area with moving materials, reduce membrane stress and improve reliability. The problem of stress concentration on the membrane at the joint area is solved by introducing a double-layer frame structure to limit membrane deformation. Hence, this can effectively alleviate the impact of the gap at the joint area and improve the durability of MEA.

Double-Layer ePTFE-Reinforced Membrane Electrode Assemblies Prepared by a Reverse Membrane Deposition Process for High-Performance and Durable Proton Exchange Membrane Fuel Cells

To promote further commercialization of proton exchange membrane (PEM) fuel cells, developing a novel preparation method for high-performance and durable membrane electrode assemblies (MEAs) is imperative. In this study, we adopt the reverse membrane deposition process and expanded polytetrafluoroethylene (ePTFE) reinforcing technology to optimize the interface combination and durability of MEAs simultaneously for the preparation of novel MEAs with double-layer ePTFE reinforcement skeletons (DR-MEA). With the wet-contact between the liquid ionomer solution and porous catalyst layers (CLs), a tight 3D PEM/CL interface is formed in the DR-MEA. Based on this enhanced PEM/CL interface combination, the DR-MEA exhibits a significantly increased electrochemical surface area, reduced interfacial resistance, and improved power performance compared with a conventional MEA (C-MEA) based on a catalyst-coated membrane method. Furthermore, with the reinforcement of double-layer ePTFE skeletons and the support of rigid electrodes for the membranes, the DR-MEA demonstrates less mechanical degradation than the C-MEA after wet/dry cycle test, reflected in lower increase in hydrogen crossover current, interfacial resistance, and charge-transfer resistance and reduced power performance attenuation. With less mechanical degradation, the DR-MEA therefore shows less chemical degradation than the C-MEA after an open-circuit voltage durability test.

An ePTFE-reinforced membrane electrode assembly based on a wet-contact interface design strategy for high-performance proton exchange membrane fuel cells

The interfacial bonding between a proton exchange membrane (PEM) and catalyst layers (CLs) is a critical factor that dominates the power performance and durability of the membrane electrode assembly (MEA) in a proton exchange membrane fuel cell and therefore must be designed with considerable attention. On this basis, we present a novel MEA preparation approach by combining a wet-contact interface design strategy and expanded polytetrafluoroethylene (ePTFE) reinforcing technology to optimize the PEM/CL interfacial combination and durability of MEAs simultaneously. With a tight and robust three-dimensional PEM/CL interface, the MEAs based on the wet-contact process exhibit significantly reduced interfacial resistance and charge-transfer resistance and improved electrochemical surface area, resulting in superior power performance compared with conventional MEAs. Simultaneously, intercalating ePTFE reinforcement skeletons into the PFSA membrane obviously reduces the hydrogen crossover of the novel MEAs. Furthermore, due to the tighter PEM/CL interfacial bonding and the support of the rigid electrodes, the novel ePTFE-reinforced MEA shows less mechanical degradation than a conventional MEA based on the catalyst coated membrane method (with a Gore membrane) after a wet/dry cycle test. This is reflected by the lower increase in hydrogen crossover current, interfacial resistance, and charge-transfer resistance, as well as less power performance attenuation.

A Review of Accelerated Stress Tests for Enhancing MEA Durability in PEM Water Electrolysis Cells

During the past decades, a significant amount of excellent scientific results has been generated in the field of polymer electrolyte membrane water electrolysis (PEMWE). Compared to current state-of-the-art technologies, PEMWE offers the opportunity to produce green hydrogen with zero carbon emissions. However, the membrane electrode assembly (MEA), whose price is still high for a rather limited lifetime, needs further improvement in terms of performance, cost, and durability. In order to efficiently process novel materials, accelerated stress tests (ASTs) can be implemented to provoke and investigate cell ageing processes and assess failure modes under real-life conditions. In this review, the different accelerated stressors of the main components of the MEA are discussed, and recent publications of ASTs in the study of PEMWE cell durability are summarized. Furthermore, a concise review of the degradation mechanisms for the individual MEA components depicted in recent publications is presented. The different aspects identified in this review serve as a roadmap to further advance the durability of novel stack materials.

Enhanced chemical durability of polymer electrolyte membrane fuel cells by crown ether grafted carbon nanotube

Low chemical stability of membrane-electrode assembly (MEA) remains a major obstacle to commercialization of polymer electrolyte membrane fuel cells (PEMFCs) for fuel cell electric vehicles (FCEVs). In this study, we doubly anchored cerium-ion in the catalyst layer by forming a complex with the 15-crown-5-ether and additionally grafting to the multiwall carbon nanotube (Ce/CRE-graft-CNT) as a long-lasting radical scavenger. To confirm the effect of Ce/CRE-graft-CNT on chemical durability, the binding energy between the cerium-ion and crown ether was identified with DFT calculations. The incorporation of Ce/CRE-graft-CNT into catalyst layer decreases decay rate of open circuit voltage (OCV) by 4 times from 2.13 to 0.56 mV h−1 for 210 h operation. The performance retention of the Ce/CRE-graft-CNT (70.8 %) at 0.6 V is also higher than that of the Ce/CRE-blend-CNT (44.8 %). The results indicate that the doubly anchored Ce/CRE-graft-CNT has a more retention capability as a radical scavenger. Therefore, a tightly bounded cerium-ion/crown ether complex with CNT can provide a strategy to improve the chemical durability of MEAs.

An effective method of applying octahedral Pt-Ni/C to membrane electrode assembly and related in-situ X-ray absorption fine structures study

To further promote the commercialization of fuel cells, it is essential to develop high-performance catalysts and apply them to the membrane electrode assembly (MEA). Here, the octahedral Pt-Ni/C is successfully used in MEA by a double-layer structure to obtain a higher performance than commercial Pt/C. The design of double-layer catalyst layer structure effectively hinders the diffusion of non-noble metals and improves the durability of MEA. Meanwhile, the catalytic and failure mechanism in proton-exchange membrane fuel cells (PEMFCs) is also directly reflected by the in-situ X-ray absorption fine structure (XAFS) for the first time. Compared to commercial Pt/C, the addition of Ni can effectively protect Pt by significantly reducing the valence change of Pt. Besides, the variation of coordination number of Pt in the Pt-Ni/C is smaller than that in Pt/C when the potential rises. This proves that the synergistic effect between different metals can improve the stability of Pt and reduce the adsorption capacity of oxygen on the surface of Pt atoms. It can provide a theoretical reference for putting the shape-controlled catalysts into practical application in the future.

Improving the performance and durability of low Pt-loaded MEAs by adjusting the distribution positions of Pt particles in cathode catalyst layer

The durability and performance of membrane electrode assembly (MEA) compose the bottleneck of fuel cells industrialization. In this paper, the effects of Pt particles distribution positions in the catalyst layer of MEA are studied. Polarization curves are carried out to evaluate the performance of MEAs with different Pt dispersion. It is found that when the Pt particles in the cathode catalyst layer are dispersed close to the membrane, under the same relative humidity, the MEA has better performance (0.819 W/cm2) because of the smaller charge transfer resistance and mass transfer resistance. At the same time, by comparing the changes of the oxygen transport resistance in the catalyst layer, it is shown that this structure makes it easier for oxygen molecules to be transported to the surface of the Pt particles. Meanwhile, the accelerated stress test is conducted to explore the durability of these MEAs. The result shows that when Pt particles are dispersed near the membrane, the stability of MEA is the same as that of MEA when Pt particles are evenly distributed in the catalyst layer. Therefore, by dispersing the Pt particles in the cathode catalyst layer near the membrane, the performance and durability of MEAs can be effectively improved.

Life prediction of membrane electrode assembly through load and potential cycling accelerated degradation testing in polymer electrolyte membrane fuel cells

Accelerated degradation tests (ADTs) are commonly used to assess the durability of membrane electrode assembly (MEA) components consisting of polymer electrolyte membrane fuel cells (PEMFC) under harsh stress conditions, estimating their lifetime in actual use condition and uncovering their vital degradation mechanisms. ADTs apply mechanically, chemically, or thermally combined stressors to efficiently investigate the durability of MEAs. However, combined stressors for ADTs might cause biased lifetime prediction because major deterioration mechanisms of MEA components are mixed with each other. This work proposes a method to accurately predict the lifetime of MEA through empirical modeling of its performance degradation through ADTs under potential cycle (carbon corrosion) and load cycle tests (electrocatalysts). To simulate operation modes of fuel cell electric vehicles, MEAs are tested under continuous on-off cycle testing (24 h operating and 1 h break) for 5000 h. Degradation patterns of MEAs are first modeled by the empirical model. The relationship between ADTs (potential and load cycle) and continuous on-off condition is then closely examined to accurately predict MEA lifetime under actual operation environments. The proposed idea has a potential to resolve critical durability issues of MEAs by identifying intermingling effects from other constituents.

Effect of dispersing solvents for ionomers on the performance and durability of catalyst layers in proton exchange membrane fuel cells

The microstructure of catalyst layers (CLs) plays a crucial role in determining the performance and durability of membrane electrode assemblies (MEAs) in proton exchange membrane fuel cells (PEMFCs). The microstructure substantially influences electrochemical reactions occurring at CLs due to the effect of triple-phase boundary formed by the physicochemical interaction of electrocatalyst, ionomer binder, and dispersing solvent. In catalyst inks comprising of the aforementioned three main components, dispersing solvents could be a key parameter for the formation of the optimal microstructure. In this study, the effect of the solvents in ionomer dispersions on the performance and durability of CLs for PEMFCs is investigated. Commercially available (water based) and laboratory-made (glycol based) ionomer dispersions are used. As a result, the physicochemical and electrochemical evaluation of the MEAs using glycol solvent based ionomer dispersions shows the thinner ionomer layer surrounding electrocatalyst and the crack-free surface of CLs, compared with that of the MEA using water based ionomer dispersion as expected. Among the MEAs using various glycol solvent based ionomer dispersions, ethylene glycol based ionomer dispersion results in the highest mobility of the main chain of ionomer in the corresponding solvent and the highest performance and durability for PEMFCs due to the lowest viscosity. This study provides useful knowledge in the selection of dispersing solvents for CLs with enhanced performance and durability in PEMFCs.

Effects of Relative Humidification on Durability of Membrane Electrode Assembly of Proton Exchange Membrane Fuel Cells

Membrane electrode assembly (MEA) is a core component of fuel cells, and its durability constitutes the bottleneck of fuel cells commercialization. In this paper, the effects of relative humidification (RH) on durability of membrane electrode assembly (MEA) are studied by the limiting current method. In-situ durability tests are carried out for 2040 h under constant current density of 800 mA cm−2 and relative humidification (RH) of 70%. The results are then compared to those of our previously published 1465h-MEA obtained for 1465 h under 100% humidification. The degradation in the voltage during the process is analyzed, and degradation mechanisms are investigated by electrochemical impedance spectroscopy and limiting current methods to analyze the change in oxygen transport resistance of the gas diffusion layer. The data suggest that the decline in the humidification can greatly improve the durability of MEAs, especially from 0 to 1000 h. The voltage decay rate of 2040h-MEA is half that of 1465h-MEA. The main degradation occurs in the substrate layer after durability tests for 2040 h under 70%RH. By comparison, 1465h-MEA operating at 100% RH shows a serious decay not only in the substrate layer but also in the MPL, as confirmed by the changes in contact angles.

Effect of catalyst layer with zeolite on the performance of a proton exchange membrane fuel cell operated under low-humidity conditions

Proton exchange membrane fuel cells (PEMFCs) employ a proton conductive membrane as the separator to transport a hydrogen proton from the anode to the cathode. The membrane's proton conductivity depends on the water content in the membrane, which is affected by the operating conditions. A membrane electrode assembly (MEA) that can self-sustain water is the key component for developing a light-weight and compact PEMFC system without humidifiers. Hence, zeolite is employed to the anode catalyst layer in this study. The effect of the gas diffusion layer (GDL) materials, catalyst loading, binder loading, and zeolite loading on the MEA performance is investigated. The MEA durability is also investigated through the electrochemical impedance spectroscopy (EIS) method. The results suggest that the MEA with the SGL28BCE carbon paper, Pt loadings of 0.1 and 0.7 mg cm−2 in the anode and cathode, respectively, Nafion-to-carbon weight ratio of 0.5, and zeolite-to-carbon weight ratio of 0.3 showed the best performance when the cell temperature is 60 °C and supplies with dry hydrogen and air from the environment. According to the impedance variation measured by EIS, the MEA with zeolite in the anode catalyst layer shows higher and more stable performance than those without zeolite.

Platinum-Nickel Nanotubes Array As Cathode for PEM Fuel Cell

Keywords: PEMFC, Anodic Alumina Oxide, Ni Nanowires, PtNi Alloy, Oxygen Reduction Reaction, Carbon-free electrode.Fuel cells technology have attracted great attention for future energy conversion and storage applications (1). The commercialization of polymer electrolyte membrane fuel cells (PEMFC) technologies is still a challenge due to durability and cost limitations of the catalyst (2). In order to enhance their achievement on the market, it is mandatory to optimize the high costly catalyst and improve its durability and stability or to innovate a new structure of electrodes.Commercial Pt/C catalysts (nanoparticles 3–5 nm) supported carbon black are considered as the current standard catalyst offering high surface areas and high specific activity. Unfortunately, they are limited by corrosion of the C and Pt dissolution/agglomeration through Electrochemical Ostwald ripening mechanism, which is reflected by a fast and significant loss of electrochemical surface area (ECSA) over time during fuel cell operation(3). This work focuses on reducing the amount of platinum and improving the performance and durability of membrane electrode assemblies (MEAs), aiming to reduce cost and thus encouraging the development of PEMFCs. Pt-based catalysts such as Pt-Co, Pt-Cu, and Pt-Ni etc. have shown to exhibit higher oxygen reduction reaction (ORR) activity than platinum for PEMFC. Accordingly, we aspire to develop and control a new carbon-free architecture of the cathode, made only with vertically aligned PtNi nanotubes supported onto a Nafion® membrane.Previous studies have demonstrated the benefits of platinum carbon-free nanostructures such as nanostructured thin films (NSTF) by 3M Company, USA (4), platinum opal nanostructures (5), or vertically aligned platinum nanotubes (6). They have shown very promising performance and stability for low Pt loading.A new carbon-free structure of electrodes made of vertically aligned PtNi nanotubes has been developed to improve performance and durability of PEMFC at low noble metal catalyst content. The process is based on an electrochemistry route of Ni electrodeposition inside anodic alumina oxide (AAO) mold, followed by a step of controlled spontaneous galvanic displacement (Figure 1), thermal treatment and acid treatment leading to the formation of nanotubes (~50nm in diameter and ~400nm in length). Ultraviolet spectrophotometric determination of platinum content showed a loading of ca. 0,1mg/cm². The latter are transferred onto a Nafion® membrane using an optimized hot pressing process. Finally, electrodes were integrated in a complete Membrane Electrode Assembly (MEA) in order to characterize their electrochemical and transport limitations in real operating conditions.The catalyst specific area estimated form the integration of Hupd desorption peaks at 30°C 100%RH in complete MEA, is approximately 6,7 cm²Pt/cm²geo. For comparison, we have elaborated a Pt/C standard cathode (Tanaka 50 wt.% catalyst onto Vulcan support) with low Pt loading (~20µg/cm²) which exhibits a close catalyst surface area of ~6,5 cm²Pt/cm²géo.The performance of the MEA was quantified by recording polarization curve under H2/O2 80°C (Figure 2 below). Promising results are obtained at a relative humidity of 80% at the anode side and 100% at the anode side, under a pressure of 1,38 bar / 1,5 bar respectively. Indeed, fully humified conditions at both anode and cathode lead to severe decay in performance as current density increases, ascribed to flooding. In addition, as shown in Figure 2, higher activities, estimated from the value of current density at 0.8V extracted from the polarization curve corrected from ohmic drop, are achieved with PtNiNTs comparing to Pt/C 20µg/cm². Figure 1

On the origin of deactivation of reversal-tolerant fuel cell anodes under voltage reversal conditions

Over the past decade, extensive efforts have been carried out to increase the durability of polymer electrolyte fuel cells (PEFCs) under voltage reversal conditions primarily caused by hydrogen starvation. One common strategy is the use of reversal tolerant anodes (RTAs) that incorporate oxygen evolution reaction (OER) catalysts (e.g., IrO2) to promote harmless water electrolysis over carbon oxidation and delay severe carbon support degradation. The present study investigates the RTA catalyst deactivation mechanism under hydrogen starvation conditions and the relative humidity (RH) dependence of the OER and carbon oxidation reactions to understand the relatively quick failure of an RTA at a high RH. The comparison of the OER durability of membrane electrode assemblies with and without carbon under hydrogen starvation conditions shows that the presence of carbon deactivates the OER catalyst through carbon oxidation species poisoning. The catalytic activity of IrO2 measured by the current density response shows a linear dependence on RH, while the rate of carbon oxidation reactions increases exponentially with RH, suggesting that the decreased durability of RTAs is related to the exponentially increased rate of carbon oxidation reactions. These findings can be used to design more robust electrodes for automotive fuel cells under hydrogen starvation conditions.