Proton Exchange Membrane Fuel Cell Applications Research Articles

Exergy performance analysis of hydrogen recirculation ejectors exhibiting phase change behaviour in PEMFC applications

A comprehensive analysis of flow behavior and exergy performance was conducted in hydrogen recirculation ejector, taking into account the phase change of humid hydrogen for proton exchange membrane fuel cell (PEMFC) systems. A two-phase nonequilibrium condensation CFD model integrating the entropy transport equations was established. The effect of phase change on ejectors’ performance under various primary pressure, secondary pressure and temperature, and back pressure were analyzed. When primary pressure was adjusted into 3.0 bar, a liquid fraction of 4.56 % was observed at the outlet, while the liquid fraction will increase to 15.35 % when the inlet pressure got to 5.0 bar. Then, the values of mass flow rate and liquid mass fraction on different sections under variable secondary temperature and back pressure were calculated. Finally, it is found that a larger primary pressure brought an increase in exergy destruction. So was exergy destruction ratio. However, increasing secondary pressure leads to the opposite result. With the increase of secondary temperature from 60 to 80 °C, exergy destruction increases from 330.28 to 390.23 kJ/kg but the destruction ratio decreases from 29.85 % to 26.19 %.

Nanostructure Engineering of Cathode Layers in Proton Exchange Membrane Fuel Cells: From Catalysts to Membrane Electrode Assembly.

The membrane electrode assembly (MEA) is the core component of proton exchange membrane fuel cells (PEMFCs), which is the place where the reaction occurrence, the multiphase material transfer and the energy conversion, and the development of MEA with high activity and long stability are crucial for the practical application of PEMFCs. Currently, efforts are devoted to developing the regulation of MEA nanostructure engineering, which is believed to have advantages in improving catalyst utilization, maximizing three-phase boundaries, enhancing mass transport, and improving operational stability. This work reviews recent research progress on platinum group metal (PGM) and PGM-free catalysts with multidimensional nanostructures, catalyst layers (CLs), and nano-MEAs for PEMFCs, emphasizing the importance of structure-function relationships, aiming to guide the further development of the performance for PEMFCs. Then the design strategy of the MEA interface is summarized systematically. In addition, the application of in situ and operational characterization techniques to adequately identify current density distributions, hot spots, and water management visualization of MEAs is also discussed. Finally, the limitations of nanostructured MEA research are discussed and future promising research directions are proposed. This paper aims to provide valuable insights into the fundamental science and technical engineering of efficient MEA interfaces for PEMFCs.

Transfer learning-based deep learning models for proton exchange membrane fuel remaining useful life prediction

Proton exchange membrane fuel cells (PEMFCs) offer power generation capabilities for diverse applications including commercial enterprises, industrial sectors, and residential technologies. Nevertheless, the comprehensive integration of PEMFC applications could be improved by challenges related to degradation and durability. The imperative development of efficient performance prognostic models assumes a pivotal role in the prognosis of remaining useful life (RUL), health monitoring, and effective utilization of PEMFCs. This paper centers on the prognostication of critical components within PEMFCs and introduces a transfer learning approach based on variational autoencoder and bi-directional long short-term memory with an attention mechanism (Bi-LSTM-AM) model. This approach combines feature fusion, knee-point detection, and a sophisticated deep-learning-based predictive model. Notably, incorporating the variational autoencoder as the framework for feature fusion introduces a novel perspective previously unexplored. Identifying the knee point and knowing the start point on the training data, facilitates optimized parameter computation. The application of transfer learning facilitates the transfer of optimal model parameters and weights from a source to a target dataset. Conclusively, the estimation of stack voltage degradation and real-time RUL prediction based on the test dataset is executed by implementing our proposed method. The stack voltage prediction findings showcase the Bi-LSTM-AM model’s superior performance relative to comparison models. The proposed online rolling prediction model, utilizing a sliding window technique for RUL prediction, yields significantly enhanced accuracy, culminating in a relative error margin ranging from approximately 1.69% to 5.04%.

Boron-alloyed porous network platinum nanospheres for efficient oxygen reduction in proton exchange membrane fuel cells

Alloying (or doping) non-metals with platinum (Pt) is an advanced solution for the development of high-performance Pt-based electrocatalysts for oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs). Herein, we report boron (B)-alloyed Pt nanospheres (B-PtNSs) with a porous network nanostructure by a combination strategy of confinement reduction and post-boronation. B-alloying can induce effective electronic/geometric structures, strong Pt-B coordination, and lowered d-band center to weaken the binding energy of oxygenated intermediates on the Pt surface. The H2-O2 PEMFC with such a B-PtNSs/C as the cathode catalyst can reach a maximum power density of 1.49 W cm−2, about 1.28 times higher than that of Pt/C. After 30,000 voltage cycles in the range of 0.6 ∼ 0.95 V, only a 14.1 % loss of initial peak power density can be observed, while that with Pt/C declines 45.7 %. Non-metals alloying with Pt-based nanostructures can enable high-performance ORR electrocatalysts for their practical application in PEMFCs.

A Review of Proton Exchange Membrane Degradation Pathways, Mechanisms, and Mitigation Strategies in a Fuel Cell

Proton exchange membrane fuel cells (PEMFCs) have the potential to tackle major challenges associated with fossil fuel-sourced energy consumption. Nafion, a perfluorosulfonic acid (PFSA) membrane that has high proton conductivity and good chemical stability, is a standard proton exchange membrane (PEM) used in PEMFCs. However, PEM degradation is one of the significant issues in the long-term operation of PEMFCs. Membrane degradation can lead to a decrease in the performance and the lifespan of PEMFCs. The membrane can degrade through chemical, mechanical, and thermal pathways. This paper reviews the different causes of all three routes of PFSA degradation, underlying mechanisms, their effects, and mitigation strategies. A better understanding of different degradation pathways and mechanisms is valuable in producing robust fuel cell membranes. Hence, the progress in membrane fabrication for PEMFC application is also explored and summarized.

Optimizing design of catalyst layer structure with carbon-supported platinum weight ratio mixing method for proton exchange membrane fuel cells

The design of catalyst structure of proton exchange membrane fuel cells (PEMFCs) functions a crucial role in water and reactants transport. In this work, catalyst layer is designed to mixing strategy of commercial Pt/C catalysts with various weight ratios (20 wt%, 40 wt%, and 20 + 40 wt%). Our mixing strategy demonstrates beneficial effects for optimized catalyst structure, leading to improved electrochemical performance and durability. Mix weight ratio Pt/C (as we abbreviated 20 + 40 wt% to Mix wt%) confirmed the optimized morphology through physical characterization and verified through electrochemical characterization under varying relative humidity (RH) conditions. Remarkably, Mix wt% Pt/C showed the highest electrochemical performance at 40–120 % RH, with a maximum power density elevation of ∼42 % and charge transfer resistance improvement of ∼40 % under low humidity conditions. This enhancement can be attributed to the improved mass transport resulting from increased pore size and reduced distortion in transport pathways. Additionally, we performed a 5,000 cycle accelerated stress test (AST), demonstrating enhanced durability in Mix wt% Pt/C. Our strategy provides a reproducible and simplified process to achieve higher fuel efficiency. Moreover, we anticipate that this offers the potential to enhance both performance and durability in commercial PEMFC applications.

Advancing heat management in proton-exchange membrane fuel cells through hybrid nano-composite phase change materials

Heat management challenges in proton-exchange membrane fuel cells (PEMFC) leads to performance degradation, particularly during operational fluctuations and vehicle downtime. This study examines the use of Nano-additive phase change materials (PCMs) as an innovative approach to thermal management in PEMFCs. It addresses a research gap, as PCMs' advantages in batteries and electronics are well-known, but their application in PEMFCs remained relatively unexplored. Hence, using the ChtMultiRegionFoam solver from OpenFOAM, two heat transfer aspects in PEMFCs are studied. The first examines PEMFC cooling under normal conditions, combining liquid cooling with a hybrid Nano-composite phase change material (HNCPCM). The results indicate the HNCPCM cools the PEMFC for 11 min before reaching saturation, after which liquid cooling starts. Moreover, with HNCPCM, the PEMFC's thermal efficiency and temperature uniformity enhance by 7.04 % and 39.76 %, respectively. Therefore, the HNCPCM contributes to cooling as the temperature and voltage fluctuate under real conditions. The second aspect evaluates PCM and insulation to maintain the PEMFC stack's operating temperature range (OTR) during downtime. Using 4 mm PCM and 11 mm insulation, the stack stays within the OTR for nearly 4 h, extending the OTR duration by 49.2 %. Consequently, the waste energy stored by PCM ensures the stack remains within the OTR, averting performance degradation upon restart.

High-Loading Platinum-Cobalt Intermetallic Compounds with Enhanced Oxygen Reduction Activity in Membrane Electrode Assemblies

Platinum-based intermetallic compounds (IMCs) are emerging as promising oxygen reduction reaction (ORR) catalysts in proton exchange membrane fuel cells (PEMFCs). However, large-scale synthesis of supported IMCs catalysts with small particle size and high loading remains a significant challenge, greatly hindering the applications of IMCs in PEMFCs. Herein, carbon-supported PtCo IMCs with a metal loading of ∼40% and a mean size of ∼5 nm were successfully prepared via a simple impregnation method and display excellent performances in membrane electrode assemblies (MEA). The ordering degree of the PtCo IMCs can be tuned by carefully manipulating the annealing conditions. X-ray photoelectron spectroscopy characterizations demonstrate that the electronic interactions between Pt and Co are strengthened due to highly ordered structure of PtCo IMCs, thus promoting the ORR performance. The optimized PtCo IMCs exhibit an excellent ORR performance with a specific activity of 2.02 mA cm−2 and mass activity of 0.92 A mgPt−1 at 0.9 V (vs. RHE), which are approximately 5 times and 6 times higher than those of the commercial Pt/C. More importantly, the PtCo IMCs also display enhanced performance in MEA, and the power density at 1.5 A cm−2 and 2.5 A cm−2 is 0.949 W cm−2 and 1.244 W cm−2, respectively, thus reducing the Pt usage by 40% compared to Pt/C. This work offers a facile route for the scale preparation of platinum-based intermetallic compounds and promotes their practical applications in PEMFCs.

SYNTHESIS OF POLYMER ELECTROLYTE MEMBRANES BASED ON IONIC LIQUID DOPED SPEEK

The sustainable and environmentally benign energy demand of the world has been increasing. Among the various options, proton exchange membrane fuel cell is an attractive choice for energy supply due to its high efficiency and application conditions without waste. In this research, triazole-based ionic liquid doped sulfonated polyether ether ketone (SPEEK) composite membranes were presented for proton exchange membrane fuel cell (PEMFC) applications. Composite membranes were prepared by incorporating 1,2,3-triazole-based ionic liquids (TIL 1-2-3) into poly(ether ether ketone) (PEEK) matrices. The mechanical, structural, and thermal properties of both composite membranes and the triazole-based ionic liquids were thoroughly characterized using dynamic mechanical analysis (DMA), Fourier transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA). The performance and viability of composites for PEMFC applications that involve elevated temperatures were conducted by proton conductivity test across a broad range of temperatures (30-180 oC). High-temperature proton conductivity was measured as 1.73x10-2 S/cm for SPEEK/TIL-3(1.0). According to the proton conductivity test results, it was concluded that the composite membranes may exhibit improved performance in PEMFC applications due to increased proton conductivity values.

(Invited) Designing Advanced Low-PGM Core-Shell Electrocatalysts for Fuel Cells and Electrolyzers

The low-content Pt-based core-shell catalysts potentially alleviate the drawback in the existing Pt catalysts (i.e., high cost, slow kinetics, poor stability, etc.) and further improve the oxygen reduction reaction (ORR) activity and stability for the proton exchange membrane fuel cells (PEMFCs).1 There have been remarkable advances in both the development of promising core−shell catalysts and the understanding of the fundamental catalytic mechanisms, and it is clear that some of the low platinum-group-metal (PGM) core−shell catalysts with enhanced activity and stability have great potential for use in PEMFCs. Nevertheless, various issues still need to be clearly addressed for the advanced core−shell catalysts of the future. On the other hand, PEM electrolyzers (ELs) are desirable large-scale energy devices to produce green hydrogen toward a net-zero carbon economy. The technologies require the availability of effective catalysts, particularly for the oxygen evolution reaction (OER). However, Ir- and Ru-based catalysts are currently the best-performing OER catalysts and their cost and limited availability hamper the widespread commercialization/deployment of PEMELs. Therefore, there is also an urgent need for developing highly durable and inexpensive catalysts for the OER. This talk first focuses on synthetic strategies, catalytic mechanisms, and influencing factors of Pt- and Ir-based catalysts used for PEMFCs and PEMELs. We will then discuss effective and solid strategies/designs to employ transition-metal-nitride-based cores for the development of highly advanced low-PGM core-shell catalysts for the ORR, particularly in heavy-duty vehicle (HDV) PEMFC applications, and for the OER in PEMEL applications. R. Zhao and K. Sasaki, Advanced Pt-Based Core-Shell Electrocatalysts for Fuel Cell Cathodes, Accounts of Chemical Research. 55 (2022) 1226-1236.

Taking Advantage of the Operating Heterogeneities in PEMFC: Numerical Study with a Pseudo-3D Model

A Proton Exchange Membrane Fuel Cell (PEMFC) is an open system. Its operation is therefore inherently heterogeneous. Indeed, in a cell, electrochemical reactions do not take place homogeneously on the active surface area. It has already been pointed out that operating heterogeneities over a large cell active area can cause a decrease of performance and durability. In fact, studies to date have focused on the relation between operating heterogeneities and local degradation on the active surface area for a small selection of operating conditions.The objective of our study is to find a way to control the current, temperature and water distributions by adjusting the operating conditions to, hopefully, optimize performance and improve durability. In order to define those control strategies, a better understanding of the heterogeneities for a wide range of operating conditions is necessary. To that end, a first numerical approach seems to be the most appropriate.This numerical study is based on a pseudo-3D multi-physics and single-phase model of a large cell, developed on COMSOL Multiphysics®. One novelty of our study, from a methodological point of view, is the calibration of the model. Instead of calibrating the model with the electrochemical response of a large cell for some chosen operating conditions as per usual, it has been calibrated with the electrochemical response of a small cell (1.8 cm²), called differential cell, emulating local operating conditions on a larger cell. Three areas of the large cell were emulated for different operating conditions: inlet, middle and outlet. Once calibrated, the pseudo-3D model was used to calculate the distributions for 108 operating conditions, which were chosen from a full factorial design of experiment defined according to the automobile application of PEMFC. The statistical analysis of these simulation results will give the influence of operating conditions (gases pressure, the magnitude and orientation of the thermal gradient of the cooling fluid, gases temperature and relative humidity) on the current density, temperature and water distributions on the active surface area. These results will later be useful for the design of strategies for controlling heterogeneities, which will be finally tested on PEM stack. Figure 1

New Advances in Graded PEMFC Catalyst Layers

Ohmic and mass transport overpotentials remain investigation and optimization areas for Proton Exchange Membrane Fuel Cell (PEMFC) applications. One potential optimization approach involves the preferential distribution of the chemical substituents spatially in the catalyst layer. This would ultimately result in graded catalyst layers (GCLs). The spatial grading directions can thereby be in the in plane and/or through plane direction(s). Chemical constituents often graded in both directions include the binder and the catalyst[1, 2]. The ionomer, an essential constituent for PEMFC applications has also been a key focus area for many research institutes and groups. Novel optimization approaches include finding new ionomers with low equivalent weights (EWs).Typically, in a PEMFC, the highest proton conduction rate is at the membrane interface and decreases towards the GDL[3, 4]. Hence, previous studies with gradients containing high ionomer contents close to the membrane and lower ones at the GDL interface resulted in improved performances. The higher ionomer content at the membrane interface resulted in better protonic conductions, and the bigger void spaces in the GDL interface resulted in improved mass transport properties[1, 5]. Though precise electrochemical analysis is lacking, it is commonly agreed that the graded layers have lower mass transport and ohmic resistances. However, the studies encountered in the literature are almost exclusively based on high EW ionomers, such as Nafion. In contrast, low EW ionomers, which have higher protonic conductivity and water uptake capabilities have not yet been a focus of researchers. Additionally, the few reports encountered in the literature focus solely on GCLs while often disregarding other contributing effects to the overall cell voltage such as the equivalent weight.Low EW ionomers offer a wider operation range for PEMFCs in terms of relative humidities. By combining the low EW ionomers with graded catalyst layers, the operation range becomes even more flexible, and the limits are further stretched. In this study, we push the operating range limits of low EW graded catalyst layers and compare them to non-graded ones. We investigate different manufacturing techniques and use suitable scalable coating methods for the manufacturing of the electrodes. Afterwards, suitable in situ and ex situ analysis techniques are used in detail to trace down the improvements for the gradients. Among the key findings, we notice that potential improvements for low EW ionomer graded catalyst layers become apparent at considerable low relative humidities. The improvements are visible in the kinetic, ohmic, and mass transport regions.

Non-destructively incorporating ceria in Nafion membrane as hydroxyl radical scavenging agent for long-term PEMFC application

Aiming at enhancing the long-term operation of proton exchange membrane fuel cell (PEMFC), Nafion as a typical example of perfluorosulfonic acid proton exchange membrane is non-destructively modified by sulfonated ceria (CeO2-DS) nanoparticles via a swelling-filling strategy. CeO2-DS nanoparticles in Nafion matrix can not only act as radical scavenging agent to improve the durability of Nafion, but also assist the re-construction of the efficient proton conduction channel in the composite Nafion membrane. Both oxidative stability and proton conductivity of the Nafion membrane are therefore remarkably improved with the great mechanical and thermal stability of Nafion maintained. PEMFC equipped with the modified Nafion membrane therefore outperforms that with the pristine Nafion membrane in terms of both power output and durability. Specifically, the maximum power density of the PEMFC equipped with modified Nafion after Fenton accelerated degradation test was significantly improved by ca. 25 % compared with that of the pristine Nafion membrane. This work hence provides a facile way to improve the durability of the PEMFC for practical applications.

The Recent Progress of Oxygen Reduction Electrocatalysts Used at Fuel Cell Level.

Proton exchange membrane fuel cells (PEMFCs) are gaining significant interest as an attractive substitute for traditional fuel cells, with higher energy density, lower environmental pollution, and better operation efficiency. However, the cathode reaction, i.e., the oxygen reduction reaction (ORR), is widely proved to be inefficient, and therefore an obstacle to the widespread development of PEMFCs. The requirement for affordable highly-efficient ORR catalysts is extremely urgent to be met, especially at fuel cell level. Unfortunately, most previous reports focus on the ORR performance at rotating disk electrodes (RDE) level instead of membrane electrode assembly (MEA) level, making it harder to evaluate ORR catalysts operating under real vehicle conditions. Obviously, it is extremely necessary to develop an in-depth understanding of the structure-activity relationship of highly-efficient ORR catalysts applied at MEA level. In this work, an overview of the latest advances in ORR catalysts is provided with an emphasis on their performance at MEA level, hoping to cover the novel and systemic insights for innovative and efficient ORR catalyst design and applications in PEMFCs.

Thermal management of an open-cathode PEMFC based on constraint generalized predictive control and optimized strategy

The application of open-cathode proton exchange membrane fuel cell (PEMFC) has been extended to unmanned aerial vehicles (UAVs), light duty vehicles and other fields, but its performance is highly affected by the temperature fluctuation of stack and ambient temperature. This paper aims to design a thermal management system to achieve higher stack performance and lower fan power consumption by considering ambient temperature and practical application. To do that, a new temperature control strategy is first proposed by studying the relationship between optimal operating temperature and ambient temperature. Then, a model of 1000 W stack including thermal system is built for designing a temperature controller based on constraint generalized predictive control (CGPC). After that, the CGPC controller is enhanced by adding optimized strategy and control rules related to practical application to avoid irreversible damage especially when the current density increases. Finally, the control system with enhanced CGPC is effectively reduce the average error compared with PI control, which is only 0.032 °C. The proposed control strategy with additional control rules is valid by experiments and shows higher performance and lower fan duty cycle of 28.9 % compared with manufacture's default strategy. Thus, the proposed method has significant for widespread application of PEMFC.

Empirical correlation of water diffusivity in hollow fiber membrane humidifier by measuring latent effectiveness

A hollow fiber membrane serves as a crucial component for the membrane humidifier in proton-exchange membrane fuel cell applications. This study established an empirical correlation of a fundamental characteristic, water diffusivity in the annulus membrane, employing a latent effectiveness-number of transfer units approach under isothermal conditions. Initially, experiments are conducted on a specifically designed membrane humidifier, considering temperature, flow rates, relative humidity, and pressure to determine the latent effectiveness. Subsequently, the overall mass transfer coefficient of a hollow fiber tube bundle, possessing latent effectiveness, is utilized to determine the water diffusivity in the hollow fiber membrane.The empirical correlation of water diffusivity is established through dimensionless parameters, including Reynold and Schmidt numbers. Using measured water diffusivity data, the regression coefficients of the empirical correlation were calibrated. The deviation of the correlation was assessed in terms of the coefficient of determination (R2), which exceeded 0.87, demonstrating a high degree of accuracy upon comparing the correlated diffusivity and experimental data. As substantiated by the results, this correlation provides reliable predictions for an actual membrane humidifier, with a mean deviation of only 7.72% during the validation process. Thus, the present findings will aid the design and operation of membrane humidifiers in fuel cells, improving their performance and efficiency by facilitating precise control of water diffusivity.

FEA Assessment of Contact Pressure and Von Mises Stress in Gasket Material Suitability for PEMFCs in Electric Vehicles

Ensuring the safety of electric vehicles is paramount, and one critical concern is the potential for hazardous hydrogen fuel leaks caused by the degradation of Proton-Exchange Membrane Fuel Cell (PEMFC) gasket materials. This study employs advanced techniques to address this issue. We leverage Finite Element Analysis (FEA) to rigorously assess the suitability of gasket materials for PEMFC applications, focusing on two crucial conditions: ageing and tensile stress. To achieve this, we introduce a comprehensive “dual degradation framework” that considers the effects of contact pressure and von Mises stress. These factors are instrumental in evaluating the performance and durability of Liquid Silicon Rubber (LSR) and Ethylene Propylene Diene Monomer (EPDM) materials. Our findings reveal the Yeoh model as the most accurate and efficient choice for ageing simulations, boasting a minimal Mean Absolute Percentage Error (MAPE) and computational time of just 0.27 s. In contrast, the Ogden model, while accurate, requires more computational resources. In assessing overall model performance using MAE, Root Mean Square Error (RMSE), and R-squared metrics, both LSR and EPDM materials proved promising, with LSR exhibiting superior performance in most areas. Furthermore, our study incorporates uniaxial tensile testing, which yields RMSE and MAE values of 0.30% and 0.40%, respectively. These results provide valuable insights into material behaviour under tensile stress. Our research underscores the pivotal role of FEA in identifying optimal gasket materials for PEMFC applications. Notably, LSR is a superior choice, demonstrating enhanced FEA modelling performance under ageing and tensile conditions. These findings promise to significantly contribute to developing safer and more reliable electric vehicles by advancing gasket material design.

Design of PGM-Free Cathode Catalyst Layers for PEMFC Applications: The Impact of Electronic Conductivity

The impact of the electronic resistance of platinum-group-metal-free cathode catalyst layers (PGM-free CCLs) for proton-exchange-membrane fuel cells (PEMFCs) was systematically investigated. Here we selected two different PGM-free catalysts (having high and low electronic conductivity) and integrated them into CCLs without and with conductive carbon fiber additives. To investigate the impact of the electronic resistivity () of PGM-free catalysts and CCLs, their through-plane values were quantified by an in situ electrochemical impedance spectroscopy (EIS) approach based on a one-dimensional transmission line model. The results indicate that the electronic conductivity of PGM-free CCLs can be increased by adding carbon additive, resulting in a significant improvement of the fuel cell performance (by ∼60 mV at 1 A cm−2 in H2/O2 configuration). Ex situ four-point probe measurements of the in-plane values of some of the CCLs were found to differ vastly from the through-plane values. This difference is attributed to the anisotropic morphology of the CCLs, caused by preferential fiber orientation and/or cracks in the CCLs. In the end, we suggest guidelines for the design and evaluation of PGM-free CCLs and for assessing and improving their electronic resistance.

Accelerated Stress Test Study on PtRu Anode Catalysts for Reformate PEM Fuel Cells

Proton-exchange membrane fuel cells (PEMFCs) are interesting candidates for heavy duty applications, e.g. in the maritime or bus and truck sector, since they convert renewable fuels into electricity efficiently [1]. Moreover, PEMFCs are flexible with respect to fuels, since they can be operated not only with hydrogen but also with reformate gas, originating from steam reforming of carbohydrates such as renewable methanol [2]. Compared to state-of-the-art carbon-supported Platinum catalysts (Pt), which are severely poisoned by CO, a side product from reforming, carbon-supported Platinum-Ruthenium catalysts (PtRu) prevail in reformate applications due to their promoting effects towards CO oxidation [3]. However, PtRu catalysts are less stable than Pt catalysts due to a higher susceptibility to dissolution [4]. Since the durability of materials in heavy duty applications is crucial to reach long operating times (> 30000 h), major efforts have to be taken to improve the stability of PtRu anode catalysts.To be able to evaluate the stability of catalysts and to investigate, identify, and understand degradation mechanisms with little time and costs, so-called accelerated stress tests (ASTs) are deployed, which induce fast electrode aging and ideally simulate electrode degradation that can be transferred to real operating conditions. For Pt cathode catalysts in PEMFC application, the U.S Department of energy proposed an AST based on square wave potential cycling between 0.6 V and 0.95 V for 30000 cycles [5]. As Ru and possibly PtRu have different dissolution potentials than Pt and are used on the anode side (therefore exposed to different potentials compared to the cathode), an AST designed for PtRu anode catalysts is required.In this work, several AST protocols based on square cycling the anode potential for 30000 cycles were developed and tested on cells with the same material composition. The carbon-supported PtRu anode electrodes were manufactured in-house with a patented technique [6], while for membranes, cathode catalysts, and GDLs commercial available products were applied. The ASTs differ by the upper potential limit, which was chosen at 0.2 VRHE, 0.65 VRHE, 0.8 VRHE, and 1.0 VRHE, respectively. The lower potential limit was set at 0.06 VRHE, (cf. Figure 1b). Before, during, and after the AST, electrochemical characterization was conducted via cyclic voltammetry, CO-stripping, and recording U-I curves (cf. Figure 1a). After the AST, post-mortem analyses were performed by means of transmission electron microscopy, X-ray diffraction, and cross-sectional scanning electron microscopy coupled with energy dispersive X-ray spectroscopy to analyze the prominent degradation mechanisms occurring for the different testing conditions.Strong differences in the degradation of the cells between the different ASTs could be observed. With increasing upper potential limit, the severity of degradation and the observed degradation phenomena increased. For example, Ru leaching occurred at ASTs with upper potentials beyond 0.65 VRHE, and increased with increasing potential, resulting in a reduced CO-tolerance. At the same time, the consequent Ru crossover to the cathode, which lowers the overall cell performance, could be only detected by EDX for ASTs beyond 0.8 VRHE, implying a correlation between Ru crossover and upper potential limit. Moreover, the data indicate that an upper potential limit of 1.0 VRHE may be too high to investigate the stability of Ru in PtRu catalysts, as an additional strong Pt degradation makes the evaluation difficult. Future work will address the correlation of these ASTs to long-term testing at constant potential.

Advanced ORR Catalysts Based on Intermetallic Nanoparticles and Metal Organic Frameworks

Over the past decade, substantial resources have been devoted to developing proton exchange membrane fuel cells (PEMFCs). The high cost and insufficient durability of oxygen reduction reaction (ORR) catalysts are the main factors delaying the commercialization of high-efficiency fuel cells. Development of new catalysts with enhanced activity and durability would have a transformative effect on fuel cells and related energy devices. Catalyst design for ORR requires creation of catalytic sites with high ORR activity, but these sites must also have good accessibility for transport of reactants (oxygen, protons, electrons) and products (water). They must also have high durability, with lifetimes of up to 30,000 hours required for heavy duty vehicle applications. The most successful ORR catalysts for PEMFCs are PtM/C, i.e., nanoparticles of Pt alloys with a base metal (e.g., Co, Ni) dispersed on a nanostructured carbon catalyst support. Tuning properties of both the PtM nanoparticles and the C support is necessary to achieve high performance and durability. In recent years, intermetallic PtM nanoparticles in which Pt and M occupy distinct sites in a highly ordered structure have emerged as a leading candidate for PEMFC applications. However, development of nanostructured carbon supports with improved control of morphology and pore properties is needed to fully reap the benefits of advanced intermetallic nanoparticle catalysts. Herein, we report recent advances in development of both intermetallic PtM nanoparticles and nanostructured carbon supports with controlled morphology and pore seize distribution. By combining novel nanostructured materials synthesis with advanced characterization and fuel cell testing, we demonstrate a path to produce highly active catalysts with sufficient durability to meet the challenging requirements of heavy duty trucking applications.