Durability Of Proton Exchange Membrane Fuel Cells Research Articles

Study on the effect of NO2 impurity gas on the performance and local current density distribution of PEMFC

The performance of proton exchange membrane fuel cells (PEMFCs) is affected by impurities, and airborne NO2 is a potential factor in the degradation of the performance and durability of PEMFCs. Herein, the effect of 50 ppb ∼ 5 ppm NO2 on PEMFC was investigated by the poisoning strategy of increasing concentration gradient, and the effect of NO2 on the local current density distribution was explored in both galvanostatic and potentiostatic states. The results showed that 2 ppm NO2 caused a significant voltage decay accompanied by an increase in activation impedance and mass transfer impedance. NO2 was decomposed into oxygen atoms and adsorbed NO on the Pt surface, occupying active sites, impeding oxygen reduction reaction, and further hindering mass transfer. Polarization curve results showed more pronounced voltage decay at high current densities. Polarization curve testing and clean air purging were effective in restoring the poisoned PEMFC. Moreover, it was proved that the poisoning effect is more severe in the inlet region, especially in potentiostatic state. Hence, it is suggested to operate in galvanostatic state, which has a positive impact on reducing the uneven performance caused by NO2. This study provides a reference for the prevention of PEMFC poisoning and performance recovery after poisoning.

Efficient water-related failure detection in PEM fuel cells: Combining a PEMFCs fractional order impedance model with FFT-PWM techniques and artificial neural network classification

Water management and early detection of faults in proton exchange membrane fuel cells (PEMFCs) are among the most critical constraints that limit the optimal spread of this type of energy. Consequently, it is necessary to enhance the reliability and durability of PEMFCs by developing an approach to diagnose and identify water failure modes. This paper proposes an effective and simple method to detect, diagnose, and classify various water failure modes in PEMFCs using a hybrid diagnostic approach. This approach combines the PEMFC fractional order impedance model (FOIM) with fast Fourier transform pulse width modulation (FFT-PWM) techniques and artificial neural network pattern recognition (ANN-PR) classification. The results show an accurate match between the electrochemical impedance spectroscopy (EIS) experimental data, the Nyquist impedance spectra of FOIM, and the FFT-PWM algorithm as a proposed alternative technique to EIS measurements. Learning of ANN-PR was performed using the frequency spectrum amplitude (FSA) database of the voltage and current signals produced by the PEMFCs FOIM DC/DC boost converter, which was generated using the FFT-PWM algorithm. The ANN-PR achieved low values for error accuracy, with the Low Square Error and Learning Error reaching 6.676 × 10−19 and 1.888 × 10−16, respectively. The elements inside the confusion matrix and the rest of the matrices confirm that the proposed model's accuracy, precision, recall, and high F1 score reached 100%. Furthermore, all predictions made by the ANN-PR model were consistently accurate across all areas of failure detection. Overall, the proposed method helps in analyzing, diagnosing, and classifying fuel cell failure modes such as flooding and drying, which may simplify the health assessment of PEMFC.

Transformer Based Long-Term Prognostics for Dynamic Operating PEM Fuel Cells

Proton Exchange Membrane Fuel Cell (PEMFC) is considered as a clean alternative energy that has been widely used in many fields. However, the large-scale commercialization of PEMFC is still limited by its durability performance. Prognostics and Health Management (PHM) is considered as a helpful solution to improve the durability of PEMFC with degradation prediction and health-based control and maintenance methods. The long-term PEMFC prognostic task, as a primary component in PHM, has received extensive attention from both academia and industry. Recently, the combination of deep neural networks and PEMFC prognostics has expressed a broad research perspective. The deep-learning-based methods, such as Convolutional Neural Network (CNN), Echo State Network (ESN), and Recurrent Neural Network (RNN) family methods, have been well-studied by many researchers and have shown satisfactory performance in degradation prediction. However, the long-term prediction performance is still limited by the model structure and accumulative errors. This paper focuses on the degradation of the PEMFC and a Transformer-based PEMFC prognostic framework is proposed to predict the long-term degradation of the PEMFC system. The Transformer model is applied for the first time to predict the degradation of the PEMFC, and a series-attention mechanism is proposed to replace the self-attention mechanism in the Vanilla Transformer which could improve the health indicator (HI) prediction performance. Finally, the PEMFC dynamic durability test data is utilized to evaluate the performance of the proposed framework in both multi-step-ahead prediction and long-term prognostic conditions, and the experimental results illustrate the feasibility and effectiveness of the proposed method.

Intelligent diagnosis of proton exchange membrane fuel cell water states based on flooding-specificity experiment and deep learning method

Flood-related malfunctions stand out as a primary impediment, constraining the effective and consistent functioning of proton exchange membrane fuel cells (PEMFC). This study firstly confirmed the correlation between health characteristic and PEMFC watering based on flooding-specificity experiment of PEMFC. In addition, a new index of iterative power drop was calculated, which could reflect the effect of the set operation condition on the stack water states timely. Moreover, this study took into account that not only normal state and flooded state, but also the mutual transformation stages between the two have the monitoring significance. Finally, a data-driven method was deployed to further delineate the three-classification diagnosis of the water states inside the stack and the diagnostic accuracy had been reached to 99.5 %. The proposed new index and water states definition method could open up new ideas for improving the durability and hydrogen consumption economy of PEMFC.

Current status of research on composite bipolar plates for proton exchange membrane fuel cells (PEMFCs): nanofillers and structure optimization.

The proton exchange membrane fuel cell (PEMFC) is an efficient and clean energy source with promising applications. However, drawbacks such as high cost and low durability limit its application. Bipolar plates are an important component of PEMFCs, which not only account for a large proportion of the price and quality, but also affect the performance and durability of PEMFCs. Unlike traditional graphite and metal bipolar plates, composite bipolar plates have the advantages of easy processing, low cost, and corrosion resistance, but their lower performance limits their practical applications. This paper firstly summarizes the current research progress of various nanofillers used to improve the performance of composite bipolar plates, and discusses the improvement of the performance of composite bipolar plates by different forms and types of nanofillers. The morphological characteristics of different types of nanofillers and their effects on the improvement of conductive pathways are also analyzed. Subsequently, the means of structural optimization of composite bipolar plates are summarized, and specific optimization methods for phase interface, graphite/resin dispersion morphology, and conductive network structure are discussed in detail. Finally, challenges are discussed. Overall, this review can provide a reference for future research on composite bipolar plates.

Effect of Superhydrophobic Catalyst Layers on PEMFC Durability

High durability of proton exchange membrane fuel cells (PEMFCs) is one main objective of this technology nowadays. Among different ways, the use of a superhydrophobic catalyst layer in the cathode may help to increase the stability of the cell under operation. Superhydrophobic cathodic layers improve water management in the cell by enhancing the back-diffusion transport from cathode to anode. As a consequence, anode humidification is favored whereas flooding of the cathode is avoided, leading to higher cell response at intermediate and high current densities [1]. Superhydrophobic catalyst layers can be obtained by adding specific agents to the precursor ink that is later deposited together with the catalyst and the ionomer. Another possibility is the use of electrospray deposition, which does not require additives. Electrospray is a dry deposition method where the ink is deposited under an electric field, yielding particular ionomer distribution inside the pores of the layer as a consequence of electrostatic interactions.Accelerated stress tests (AST) are well stablished protocols to analyze durability of PEMFCs in a systematic and reduced time frame [2]. Protocols for stressing different components of the cell have been proposed. In this work, different cell configurations have been mounted, using electrosprayed catalyst layers in cathode, anode, and both. The cells have been submitted to an AST that affects mainly the cathodic catalyst layer. The study is complemented with microscopy analysis (cross-sectional) and local mechanical properties (small-punch) (Fig. 1).The results show the effect of superhydrophobic cathodic catalyst layers on the durability of a PEMFC.AcknowledgementsFunding by PORHYDRO2 project (TED2021-131620B-C22, ‘Preparation and characterisation of catalyst layers fabricated by electrospray for proton exchange fuel cells with passive gas feed’) by the Spanish Ministry of Science and Innovation.[1] M.A. Folgado, J.J. Conde, P. Ferreira-Aparicio, A.M. Chaparro, Single Cell Study of Water Transport in PEMFCs with Electrosprayed Catalyst Layers, Fuel Cells. 18 (2018) 602–612. https://doi.org/10.1002/fuce.201700217.[2] S. Stariha, N. Macauley, B.T. Sneed, D. Langlois, K.L. More, R. Mukundan, R.L. Borup, Recent Advances in Catalyst Accelerated Stress Tests for Polymer Electrolyte Membrane Fuel Cells, J. Electrochem. Soc. 165 (2018) F492–F501. https://doi.org/10.1149/2.0881807jes.[3] R. Hernández, S. Merino, D. Plaza, L. Duque, M.A. Folgado, A.M. Chaparro, M. Serrano, G. de Diego, Study of Mechanical Properties of Membrane-Electrode Assemblies for Proton Exchange Membrane Fuel Cells By the Small-Punch Technique, ECS Meet. Abstr. MA2022-02 (2022) 1426–1426. https://doi.org/10.1149/ma2022-02391426mtgabs. Figure 1

Improving PEMFC Performance with Customized Catalyst Combinations and Advanced Mixing Techniques

Proton Exchange Membrane Fuel Cells (PEMFCs) are a popular choice for use in vehicles and buildings because they can operate at relatively low temperatures and have a simpler system compared to other types of fuel cells. The performance and durability of PEMFCs are influenced by the membrane electrode assembly (MEA).The cathode, where the oxygen reduction reaction occurs, is the component of the MEA that has the greatest influence on performance. The factors that affect high power performance are catalyst activity, proton conductivity, and mass transport resistance of fuels and products.Pt catalysts and PtCo catalysts have advantages and disadvantages at different current densities in PEMFCs. In low current density conditions, PtCo catalysts have been shown to exhibit higher catalytic activity compared to Pt catalysts for the oxygen reduction reaction (ORR). This can result in a more efficient fuel cell operation. However, in high current density conditions, the activity of PtCo catalysts can be reduced compared to Pt catalysts because of their larger particle sizes, which can limit their performance.The properties of the carbon support, such as its hydrophobicity and surface area, can also play an important role in determining the performance of the fuel cell. Hydrophobic carbon supports can facilitate gas diffusion and prevent flooding which can occur when water accumulates in the pores of the electrode and limits reactant transport. Moreover, such supports can limit the contact area between the water and catalyst, leading to prolonged catalyst activity and lifespan. On the other hand, high surface area supports can increase the number of sites available for catalyst anchoring and enlarge the electrode's effective surface area. However, achieving both hydrophobicity and high surface area can be challenging due to the trade-off between these properties.Because each catalyst has advantages and disadvantages at different current densities or operating conditions in PEMFCs, combining different catalystscan achieve improved performance across a wider range of operating conditions. However, each catalyst and carbon support has different affinity with ionomer. Therefore, it is impossible to achieve even ionomer distribution through simple mixing. This means that it is difficult to express the advantages of each catalyst through simple mixing because the transport properties of protons can be influenced by the distribution of the ionomer.To address this, two catalysts were mixed into thecathode electrodes separately, and it was confirmed that this approach improved their performance across a range of current densities. In particular, their high power characteristics were enhanced. To confirm these results, the MEA was tested using H2/air polarization curves, EIS analysis, and limit current density tests, and the porosity in the electrode structure was measured by the BET method and Mercury intrusion porosimetry (MIP).In conclusion, Pt and PtCo catalysts have unique advantages and disadvantages at different current densities in PEMFCs. The properties of the carbon support also play a crucial role in determining the fuel cell performance. Combining different catalysts can enhance the fuel cell's performance but achieving even ionomer distribution through simple mixing is challenging. Applying the two catalysts separately through a distribution process improved the fuel cell's performance across different current densities, especially high power characteristics.

Chemo-Mechanical Durability of Reinforced Fuel Cell Membranes in the Presence of Metallic Foreign Particles

High-throughput production is vital to achieve cost-effective proton exchange membrane fuel cells (PEMFCs) at scale1. The high-volume mass production of PEMFCs using industrial manufacturing machinery may however introduce unwanted material in the final product due to the wear and tear of the machinery. As an example, roll-to-roll processes applied to the manufacture of catalyst coated membrane (CCM) generally use Fe alloys such as stainless steel2 components that could release fine metallic particles or related debris that may affect the product quality3,4. Therefore, it is important to understand the fundamental impact of such non-uniformities on PEMFC performance and durability.This work focusses on the impact of slightly oxidized iron (Fe) and stainless steel 316L (SS316L) micro-particles entrapped between the cathode catalyst layer (CCL) and a GORE-SELECT® Membrane A. Fe cations are considered as Fenton’s catalyst/reagent which enhance harmful radical generation and ionomer attack, known to weaken its mechanical strength and ionic conductivity5. Therefore, membrane electrode assemblies (MEAs) containing solid Fe and SS316L particles were prepared to conduct in-situ PEMFC experiments and identify their impact on membrane degradation and durability. The chosen particles were placed carefully on the bare membrane at selected locations based on the flow field design of the graphite bipolar plates. Later, the assembled MEAs were tested using a small-scale fixture (SSF) fuel cell in a combined chemical and mechanical AST after beginning-of-life (BOL) conditioning and diagnostics6.X-ray computed tomography (XCT) has been shown to be a powerful and non-invasive 3D characterization tool for analyzing membrane degradation7,8. Thus, periodic same-location XCT visualization of the CCL-membrane interface was performed after every 10 AST cycles. According to the Fe Pourbaix diagram9, Fe oxidizes to Fe2+ at 0.77 V and indeed, in this work, complete dissolution of the Fe-50µm particles was observed leaving cavities at the CCL-membrane interface. This dissolution manifested as a distinct black spot in CT imaging, as highlighted by the enclosed red circle in Figure 1. In contrast, corrosion of SS316L particles is usually prevented by a native oxide layer formation during fuel cell operational conditions10. The Fe particle laden AST reached membrane failure within 30 cycles and indicates an escalation of degradation by global membrane thinning. This is substantially lower than the baseline AST without particles. The XCT images for Fe-50µm AST seen in Figure 1 show that severe global membrane thinning occurred in the Fe-50µm MEA, which contributed to a high electrochemical leak detection (ELDT) signal exceeding test failure criteria. In contrast, the SS316L MEA did not reach the threshold failure criteria for the AST duration, however, the average OCV remained lower as compared to the baseline MEA AST. XCT imaging showed that the SS316L- 50µm particles did not dissolve throughout the AST duration and the membrane thinning was more pronounced near the particle rather than globally. Additionally, we have evaluated whether chemically and mechanically mitigated GORE-SELECT Membrane® B could enable more robustness and minimize impact of multiple metallic particles. Analysis of combined chemo-mechanical AST with a larger dimension SS316L-500µm present on mitigated GORE-SELECT® Membrane B suggest that chemical and mechanical mitigation can reduce impact of large particles and enable lifetime response at the level close to baseline. In conclusion, the membrane lifetime and failure mode were found to be strongly dependent on the particle chemical composition and membrane degradation mitigation strategies, which are therefore should be considered at PEM design stages to reduce risks and improve CCM and MEA production quality. Keywords: PEM durability, quality control, cost reduction, XCT Acknowledgments This research was supported by the Natural Sciences and Engineering Research Council of Canada, Canada Foundation for Innovation, British Columbia Knowledge Development Fund, Western Economic Diversification Canada, Ballard Power Systems, and W.L. Gore & Associates. This research was undertaken, in part, thanks to funding from the Canada Research Chairs program. References H. Tsuchiya and O. Kobayashi, Int. J. Hydrogen Energy, 29, 985–990 (2004).J. Chen, H. Liu, Y. A. Huang, and Z. Yin, J. Manuf. Process., 23, 175–182 (2016).A. Phillips et al., Fuel Cells, 20, 60–69 (2020).A. Phillips, M. Ulsh, K. C. Neyerlin, J. Porter, and G. Bender, Int. J. Hydrogen Energy, 43, 6390–6399.J. G. Goodwin, K. Hongsirikarn, S. Greenway, and S. Creager, J. Power Sources, 195, 7213–7220 (2010).Y. Chen et al., J. Power Sources, 520, 230673 (2022).Y. Chen et al., J. Power Sources, 520, 230674 (2022).Y. Singh et al., J. Power Sources, 412, 224–237 (2019).R. Tolouei et al., Phys. Chem. Chem. Phys., 18, 19637–19646 (2016).N. Kumar et al., Int. J. Energy Res., 44, 6804–6818 (2020). Figure 1

Grooved Electrodes for High Power Density Fuel Cells

Proton exchange membrane fuel cells (PEMFCs) are a promising alternative to internal combustion engines, owing to their intrinsic power density, decoupled energy storage and generation, and relatively short refueling time. However, challenges related to cost, performance, and durability continue to prevent wide adoption of PEMFCs.1 Development of alternative electrode structures, which can enable smaller and less expensive PEMFCs with higher power and lower precious metal content, provides a promising path to overcome these challenges.2 Here, we report grooved electrodes, where the transport pathways of H+ and O2 were partitioned. Specifically, H+ are transported through electrode ridges with optimized ionomer content, and O2 is transported through the grooves that separate the electrode ridges. The grooved electrodes made with commercial electrode materials enhanced the performance up to 50%, and the enhancement becomes greater after accelerated durability tests. We verify via electrochemical impedance analyses, limiting current measurements, and multiphysics modeling that the enhancement is due to improved H+ and O2 transport. The work also demonstrates that the electrodes can be further improved by optimizing the electrode geometry, proven via machine learning investigations. These results inform next generation electrode designs for enhanced PEMFC performance and durability. Acknowledgement: This work was supported by the Hydrogen and Fuel Cell Technologies Office (HFTO), Office of Energy Efficiency and Renewable Energy, US Department of Energy (DOE) through the Million Mile Fuel Cell Truck (M2FCT) consortia, technology managers G. Kleen and D. Papageorgopoulos. Financial support for this work from the Laboratory Directed Research and Development (LDRD) program at Los Alamos National Laboratory (LANL) is gratefully acknowledged (Projects 2020200DR and 20210915PRD2). ChungHyuk Lee acknowledges the support of the Natural Sciences and Engineering Research Council of Canada (NSERC).

Simulation of Proton Exchange Membrane Durability Under Fuel Cell Vehicle Operation – a Fundamental Study

Proton exchange membrane fuel cells (PEMFCs) have been proven to be a promising candidate to replace combustion engines due to their zero-carbon emission and high power densities. Despite the recent success in PEMFC commercialization, a number of challenges such as high cost and difficulty in lifetime estimation still hinder their further development. PEMFC durability tests require a long time to complete; therefore, durability predicting models are increasingly important as a supporting tool for further development and implementation.Fuel cell membranes undergo a variety of dynamic conditions during regular operation such as varying temperature, humidity, current density, and cell potential. The cyclic variations of humidity and temperature (hygrothermal variations) during dynamic operation lead to swelling and contraction of the membrane. The fluctuating stress caused by the continuous expansion and contraction of the membrane when confined within the cell leads to mechanical membrane degradation. The recurring swelling and contraction of the membrane which stem from water content changes in the membrane cause fatigue and creep and ultimately the formation of pinholes, cracks, and tears [1-2].Chemical membrane degradation occurs when radicals such as hydroxyl and hydroperoxyl are formed and attack the membrane and is escalated by high operating cell potentials. Chemical degradation results in decay in the ionomer chemical structure, membrane thinning, increased gas crossover, and potential electrode shorting [3]. The outcomes of such degradation are aggravated in the presence of mechanical degradation [4]. Hence, the study of combined chemo-mechanical membrane degradation is crucial for overall fuel cell membrane durability [5].The objective of the present work is to establish a predictive membrane lifetime simulation tool designed to represent chemo-mechanical membrane degradation under various operating conditions for automotive fuel cell applications. To this end, a statistical model is developed based on the membrane fibrillar morphology presented by El Hannach et al. [6-7]. A network of fibre bundles is generated to represent the membrane structure where any bundle is assumed as the primary building block of the membrane [8-10]. Each bundle contains an aggregate of backbone chains with typical mechanical and chemical properties. Mechanical and chemical degradation rates are separately studied and coupled in the model. The thermally activated breaking rate of each fibre is calculated to evaluate the mechanical degradation rate at any given time. In order to calibrate the mechanical degradation rate in the model, the mechanical degradation of a reinforced membrane under cross-pressure accelerated mechanical stress tests ( p-AMST) [11] is investigated to obtain the membrane fatigue lifetime for a variety of cross pressures and temperatures. Then, the genetic algorithm is successfully applied to optimize the experimental parameters considering the least squares method. Furthermore, accelerated membrane durability tests (AMDT) carried out by Macauley et al. [12] are considered to calibrate the chemical degradation rate parameter in the model. Finally, the fully calibrated model is used to estimate the membrane lifetime under realistic fuel cell vehicle operating conditions (e.g. drive cycles).Fuel cell components experience different degradation mechanisms. In this regard, this modelling framework on the membrane lifetime can be used in conjunction with other methodologies on the cathode catalyst lifetime such as [13-14] to scrutinize the key factors and their impacts on fuel cell durability under similar operating conditions. 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.

Experimental study on flow boiling-based micro-channel configurations for the PEMFC cooling

Proton Exchange Membrane Fuel Cell (PEMFC) is one of the most promising energy conversion devices. Efficient thermal management is crucial for maintaining the PEMFC's efficiency and durability. However, cooling the PEMFC can be challenging due to the small temperature differences between the stack's operating temperature and the surrounding environment. In the present study, flow boiling is applied as a cooling technique for the PEMFC. A flow boiling experimental test bench with fluid flow visualization is built for PEMFC cooling. To relieve the negative effect of mal-distribution of working fluid in the micro-channels, the cooling configurations with orifice baffles are also tested. Flow boiling performance of HFE-7100 in the micro-channel-based cooling configuration for PEMFC is experimentally investigated. The flow boiling characteristics of HFE-7100 in the micro-channel are revealed, which is beneficial for the appropriate design of flow boiling-based cooling configuration for the PEMFC. Excellent temperature distribution uniformity of flow boiling-based cooling PEMFC is achieved and is further enhanced by adding orifice baffles.

Impacts of cathode catalyst layer defects on performance and durability in PEM fuel cells

During the manufacturing of proton exchange membrane fuel cells (PEMFCs), the cathode catalyst layer (CCL) may contain regions of partially missing material due to deficient deposition or unintentional removal. The present research objective is to understand how larger (4.0, 5.9, and 8.5%) CCL missing areas may affect the performance and durability of PEMFCs. Three different CCL missing area samples are prepared and compared to defect-free CCL baselines in this work. The results show that such CCL missing areas reduce the performance of the defective fuel cell in all regions of the polarization curve, compared to defect-free cells. At low current densities, these performance voltage reductions are linear with the current density rise, followed by an exponential reduction at high current densities. The linear slope and onset of exponential voltage reduction are related to the investigated CCL missing area. However, no significant difference in the electrochemical surface area is observed. Additionally, chemical/mechanical and electrochemical cycling tests show no significant variance in the degradation between the baseline and CCL missing area samples, indicating that CCL missing areas do not significantly influence membrane or cathode durability.

Immobilized hindered amine radical scavenger for durability enhancement of perfluorosulfonic acid membrane in PEMFCs

Membrane durability is one of the crucial considerations that restrict the development of proton exchange membrane fuel cells (PEMFCs). The widely used and inexpensive stabilizer hindered amine 4-amino-2,2,6,6-tetramethylpiperidine (TEMP) was selected as the free radical scavenger and tethered onto the skeleton of carboxyl-functionalized metal-organic frameworks for addressing its migration problem. The resulted inorganic-organic hybrid dopant (UIO-66-TEMP) was then incorporated into the Nafion matrix to alleviate the attacks of free radicals on the membrane in the fuel cell working circumstances. Besides the improved mechanical strength and oxidative stability, and restricted water swelling and hydrogen crossover, the resulted hybrid membranes also possess excellent proton conductivity up to 176 mS cm−1, endowing them with high power density up to 612.78 mW cm−2, 1.5 times higher than recast Nafion. After accelerated durability testing for 120 h, the OCV decay rate of the hybrid membranes decreased to 0.74 mV h−1, only 40% of recast Nafion (1.89 mV h−1). Meanwhile, the optimized hybrid membrane still maintained a high peak power density of 463.62 mW cm−2 and a low hydrogen crossover density of 4.44 mA cm−2, which were superior to recast Nafion after OCV durability tests. Hindered amines can be “regenerated” by the “Denisov cycle” to ensure that they can be used sustainably in the fuel cell. The results demonstrate that the novel UIO-66-TEMP decorated with hindered amine radical scavengers are promising nanofillers for mitigating the membrane degradation and improving the proton conductivity, thereby significantly enhancing the performance and durability of PEMFCs.

Enhanced radical scavenging performance of Pt@CeO2 via strong metal-support interaction effect for improving durability of proton exchange membrane fuel cell

Since scavenging free radical is regarded as an efficient strategy to enhance the durability of proton exchange membrane fuel cells (PEMFCs), strong metal-support interaction (SMSI) effect between metal and reducible oxide supports is employed as a strategy to moderate the number of accessible active sites for reduction-oxidation reaction. Enriched Pt–CeO2 interface to enhance SMSI effect is achieved as well via constructing multicore-shell structure Pt@CeO2. Theoretical calculation confirms that SMSI effect at Pt–CeO2 interface endows electrons flowing from Pt to CeO2 to reduce the formation energy of oxygen vacancies, while Pt@CeO2 with higher magnitude of lattice distortion plan provides enriched Pt–CeO2 interface that made more concentration of Ce3+ ions feasible. Results show that better free radical scavenging performance is achieved with higher concentration of Ce3+ ions in Pt@CeO2. Based on the open circuit voltage (OCV) test, the Pt@CeO2-modified membrane in this work decays at only 70% of the commercial membrane, while 65% of the maximum power is still maintained after the test. This superior performance to the commercial membrane indicates this designed structure with SMSI effect could be considered as a potential route to solve the free radical problem in PEM for enhanced durability of PEMFCs.

A Comprehensive Review of Degradation Prediction Methods for an Automotive Proton Exchange Membrane Fuel Cell

Proton exchange membrane fuel cells (PEMFCs) are an alternative power source for automobiles that are capable of being cleaner and emission-free. As of yet, long-term durability is a core issue to be resolved for the mass production of hydrogen fuel cell vehicles that requires varied research in the range from sustainable materials to the optimal operating strategy. The capacity to accurately estimate performance degradation is critical for developing reliable and durable PEMFCs. This review investigates various PEMFC performance degradation modeling techniques, such as model-based, data-driven, and hybrid models. The pros and cons of each approach are explored, as well as the challenges in adequately predicting performance degradation. Physics-based models are capable of simulating the physical and electrochemical processes which occur in fuel cell components. However, these models tend to be computationally demanding and can vary in terms of parameters between different studies. On the other hand, data-driven models provide rapid and accurate predictions based on historical data, but they may struggle to generalize effectively to new operating conditions or scenarios. Hybrid prediction approaches combine the strengths of both types of models, offering improved accuracy but also introducing increased computational complexity to the calculations. The review closes with recommendations for future research in this area, highlighting the need for more extensive and accurate prediction models to increase the reliability and durability of PEMFCs for fuel cell electric vehicles.

Grooved electrodes for high-power-density fuel cells

Proton exchange membrane fuel cells (PEMFCs) are leading candidates to decarbonize the transport sector, but widespread deployment will require improvements in lifetime, fuel economy and cost. Here we present the grooved electrode, an alternative electrode structure that enhances PEMFC performance and durability by coupling high ionomer (ion-conducting binder) content for improved H+ transport with grooves for rapid O2 transport. Grooved electrodes provide up to 50% higher performance than state-of-the-art conventional electrodes under standard operating conditions. Fuel cell diagnostics combined with multiphysics modelling demonstrate that grooved electrodes provide facile O2 transport despite their high ionomer content, enabling improved reaction rate uniformity. Grooved electrodes also provide improved durability, with less performance loss after carbon corrosion compared with baseline electrodes. Machine learning analysis demonstrates the potential to further optimize grooved structures for next-generation PEMFCs with enhanced performance and durability, enabling smaller and cheaper fuel cell stacks with higher fuel efficiency.

Effects of Cathode GDL Gradient Porosity Distribution along the Flow Channel Direction on Gas–Liquid Transport and Performance of PEMFC

The gas diffusion layer (GDL) is an important component of proton exchange membrane fuel cells (PEMFCs), and its porosity distribution has considerable effects on the transport properties and durability of PEMFCs. A 3-D two-phase flow computation fluid dynamics model was developed in this study, to numerically investigate the effects of three different porosity distributions in a cathode GDL: gradient-increasing (Case 1), gradient-decreasing (Case 3), and uniform constant (Case 2), on the gas-liquid transport and performance of PEMFCs; the novelty lies in the porosity gradient being along the channel direction, and the physical properties of the GDL related to porosity were modified accordingly. The results showed that at a high current density (2400 mA·cm-2), the GDL of Case 1 had a gas velocity of up to 0.5 cm·s-1 along the channel direction. The liquid water in the membrane electrode assembly could be easily removed because of the larger gas velocity and capillary pressure, resulting in a higher oxygen concentration in the GDL and the catalyst layer. Therefore, the cell performance increased. The voltage in Case 1 increased by 8% and 71% compared to Cases 2 and 3, respectively. In addition, this could ameliorate the distribution uniformity of the dissolved water and the current density in the membrane along the channel direction, which was beneficial for the durability of the PEMFC. The distribution of the GDL porosity at lower current densities had a less significant effect on the cell performance. The findings of this study may provide significant guidance for the design and optimization of the GDL in PEMFCs.

Operatable and Efficient Mitigation Strategies for H2S Poisoning in Proton Exchange Membrane Fuel Cells: Releasing Pt Reactive Sites for Hydrogen Oxidation

The anode feed for hydrogen fuel cell electric vehicles (FCEVs) currently still relies on the reformed fuel that inevitably contains contaminants (e.g., CO, H2S, and NH3). As one of the most sensitive impurities, trace H2S in hydrogen significantly deteriorates the durability of proton exchange membrane fuel cells (PEMFCs), while there is still a lack of effective strategies to mitigate H2S poisoning in PEMFCs. Herein, we present two kinds of facile, operatable, and efficient strategies to mitigate a H2S-poisoned anode, with the aim of improving the durability of PEMFCs by releasing more Pt reactive sites for hydrogen oxidation reaction (HOR) catalysis. The first mitigation strategy is conducted by increasing the cell temperature temporarily when purging with pure hydrogen after H2S poisoning by means of accelerating H2S desorption on Pt sites under high temperatures and thus releasing more available Pt reactive sites for HOR catalysis. A higher temporary temperature leads to a larger recovery percentage of performance, outperforming the effect of the generally adopted pure hydrogen purging operation. Another mitigation strategy is called “internal oxygen permeation”, based on the oxidation of sulfur-adsorbed anode by compelling air diffusion through thin PEM via constructing a pressure differential between the cathode and the anode. The cell was found to be recovered more at a high pressure differential due to the fact that more sulfur species are oxidized by a larger content of permeated oxygen, showing ∼88.7% performance recovery for 0.40 bar pressure differential. The proposed strategies with simplicity, operability, and resilience show promising potential in the application of long-term PEMFCs, which is critical for the durability improvement of FCEVs and cost reduction of hydrogen purification.

Quantification and evolution on degradation mechanisms of proton exchange membrane fuel cell catalyst layer under dynamic testing conditions

The catalyst layer is one of the core components of the Proton Exchange Membrane Fuel Cell (PEMFC). Studying its degradation mechanism is very important to improve the durability of PEMFC. Therefore, the degradation of the catalyst layer after the 100 h, 225 h, and 650 h durability tests are studied quantitatively in this paper. The results show that the agglomeration of Pt particles is the main reason for the degradation of the catalyst layer in the first 100 h, accounting for 80%. Catalyst dissolution and the loss of proton connectivity caused by the ionomer are the main factors for the degradation of the catalyst layer between 225 and 650 h, which increases from 23% in the initial stage to 46%. In addition, the corrosion degree of the carbon support inside the catalyst layer gradually intensified with the test time. This study reveals the dominant degradation mechanism of the catalyst layer in different degradation stages and the evolution of the whole degradation process, which has important guiding significance for the structural design of the catalyst layer for long-life fuel cells.

Effect of hydrogen impurities on hydrogen oxidation activity of Pt/C catalyst in proton exchange membrane fuel cells

AbstractHigh-purity of hydrogen is vital to the guarantee of end usage in proton exchange membrane fuel cell (PEMFC) electric vehicles (EVs) with superior durability and low expense. However, the currently employed hydrogen, primarily from fossil fuel, still contains some poisoning impurities that significantly affect the durability of PEMFCs. Here, we investigate the poisoning effect of several typical hydrogen impurities (S2–, Cl–, HCOO– and CO32–) on the hydrogen oxidation reaction (HOR) of the state-of-the-art carbon-supported platinum (Pt/C) catalyst used in the PEMFC anode. Electrochemical results indicate that the electrochemically active surface area of Pt/C is hampered by these hydrogen impurities with reduced effective Pt reactive sites due to the competitive adsorption against hydrogen at Pt sites showing the extent of the poisoning on Pt sites in the order: S2– > Cl– > HCOO– > CO32–. Density functional theory calculations reveal that the adsorption energy of S2– on Pt (111) is greater than that of Cl–, HCOO– and CO2, and the electronic structure of Pt is found to be changed due to the adsorption of impurities showing the downshift of the d-band centre of Pt that weakens the adsorption of hydrogen on the Pt sites. This work provides valuable guidance for future optimization of hydrogen quality and also emphasizes the importance of anti-poisoning anode catalyst development, especially towards H2S impurities that seriously affect the durability of PEMFCs.