FC Performance Research Articles

Investigation of the Influence of Catalyst Layer and Carbon Structure for Cell Performance Using Reaction and Mass Transport Simulation of PEFC

The expectation of hydrogen is growing towards achieving a carbon-neutral society. In particular, further popularization of Polymer Electrolyte Fuel Cell (PEFC) is desired not only for passenger vehicles but also heavy duty vehicles. Therefore, high performance, high durability and cost reduction of the catalyst layer (CL) are becoming increasingly important. In recent years, research on mesoporous carbon (MPC) has become active [1, 2]. MPC exhibits high catalytic activity because this carbon is able to avoid sulfonic acid poisoning by reducing contact between the ionomer and Pt surface. However, it is disadvantage from the perspective of mass transport as it is necessary to supply oxygen and protons to the inside of the carbon support. Many studies have been conducted to balance sulfonic acid inhibition and mass transport of oxygen and protons of MPC. But it is still unclear which factors of the carbon structure play an important role for the performance and durability. Currently, carbon selection is being carried out by trial and error, and it is essential to provide design guidelines for CL and carbon structures to improve performance and durability.Our research group have developed a reaction and mass transport simulation within CL of PEFC and investigated the influence of CL structure for mass transport and cell performance [3, 4]. In this study, we have developed a model that takes into account the mass transport inside carbon support by extending the above CL scale model. Regarding the modeling of the internal carbon support, as reported in Chowdhury et al.'s research, the pore size distribution and surface wettability inside the carbon support are used to calculate the water uptake in the catalyst support, enabling the calculation of Electrochemical Surface Area (ECSA), proton conductivity, and gas diffusivity based on relative humidity (RH) [5]. By conducting such modeling, it became possible to simulate the polarization curve of CL using MPC. The calculated results, as reported in the studies by Ramaswamy [6] and Shinozaki [7], show that Pt utilization, proton conductivity, and gas diffusivity change depending on the RH inside the CL, and the polarization curve accurately match the experimental results.Furthermore, using this model, we simulated the effects of different MPC structures for FC performance. The relationship between carbon structures such as the ratio of Pt supported within the carbon interior and surface and depth from the carbon surface and cell performance will be reported in this presentation.Acknowledgements:This work is supported by the Junichi Miyamoto Hydrogen Research Award.

Performance constraints of high temperature polymer electrolyte membrane fuel cells by varying the Pt/C ratio of the catalyst

Electrodes prepared from catalysts with Pt weight percentages on the carbon support (Pt/C nanoparticles) ranging from 10 up to 60 wt% are used as cathodes of membrane electrode assemblies (MEAs) and tested in high temperature polymer electrolyte membrane fuel cells (HT-PEMFCs). For each Pt/C percentage in the catalyst, the cathode Pt-loading (which become proportional to the thickness of the electrode formed by the catalyst nanoparticles) is stepwise scanned from low to high loadings. Results show that when the Pt load increases, the MEA performance (measured by its power density at 0.6 V) rises initially (due to the increase in the number of active sites in the cathode) up to a maximum value limited by the mass transport of oxygen, associated to an optimum Pt-loading (different for each Pt/C ratio). Noteworthy, the peak performance is significantly different depending on the catalyst used (60 > 40 >> 20 > 10 wt% Pt/C), a fact that restricts the catalyst choice according to the performance required by the application. Furthermore, higher amounts of Pt in the cathode lead to a large catalyst waste as the FC performance even decreases as the cathode thickness increases.

Synergistic Integration of Hydrogen Peroxide Powered Valveless Micropumps and Membraneless Fuel Cells: A Comprehensive Review

AbstractCatalytic valveless micropumps, and membraneless fuel cells are the class of devices that utilize the decomposition of hydrogen peroxide (H2O2) into water and oxygen. Nonetheless, a significant obstacle that endures within the discipline pertains to the pragmatic open circuit potential (OCP) of hydrogen peroxide FCs (H2O2 FCs), which fails to meet the theoretical OCP. Additionally, bubble formation significantly contributes to this disparity, as it disrupts the electrolyte's uniformity and interferes with reaction dynamics. In addition, issues such as catalyst degradation and poor kinetics can impact the overall cell efficiency. The development of high‐performance H2O2‐FCs necessitates the incorporation of selective electrocatalysts with a high surface area. However, porous micro‐structures of the electrode impedes the transport of fuel and the removal of reaction byproducts, thereby hindering the attainment of technologically significant rates. To address these challenges, including bubble formation, the review highlights the potential of integrating electrokinetic and bubble‐driven micropumps. An alternative approach involves the spatiotemporal separation of fuel and oxidizer through the use of laminar flow‐based fuel cell (LFFC). The present review addresses multifaceted challenges of H2O2‐powered FCs, and proposes integration of electrokinetic and bubble‐driven micropumps, emphasizing the critical role of bubble management in improving H2O2 FC performance.

Evaluation of Achievement Development Management of Bhayangkara Precision Football Club

Evaluation of Bhayangkara Presisi Football Club Achievement Development Management. Thesis. Yogyakarta: Masters Program, Faculty of Sports and Health Sciences, Yogyakarta State University, 2024. The aim of this research is to find out the evaluation of the Bhayangkara Presisi Football Club's achievement development program, examining it from the context, input, Process and Product (CIPP) aspects as well as finding out whether the achievement development program that has been running at the Bhayangkara Presisi Football Club has been managed optimally. This research is a type of quantitative and qualitative research with the CIPP evaluation model. The sampling technique used purposive sampling technique to obtain a sample of three program administrators, three coaches and six players. Evaluation uses quantitative and qualitative approaches. Data collection uses research instruments in the form of observation, questionnaires, interviews and documentation. The results of the research, namely, Context evaluation of Bhayangkara Presisi FC's achievement coaching management, amounted to 2.91, which is in the good category. Based on the background indicators of the coaching program, it is 3.09 in the good category, the coaching program objectives are 2.60 in the good category, and the coaching program is 3.03 in the good category. The evaluation input for Bhayangkara Presisi FC's achievement coaching management, amounting to 2.75, is in the good category. Based on the human resources indicator, it is 3.07 in the good category, the trainer program is 3.05 in the good category, funding is 2.66 in the good category, facilities and infrastructure is 2.66 in the good category, and parental support is 2.29 in the poor category. Bhayangkara Presisi FC's achievement management evaluation process, amounting to 2.83, is in the good category. Based on the program implementation indicator, it is 3.06 in the good category, and coordination is 2.83 in the good category. Bhayangkara Presisi FC's performance management management evaluation product, amounting to 3.27, is in the good category. Based on the achievement indicator of 3.33 in the good category and welfare of 3.20 in the good category.

All-Perfluorosulfonated-Ionomer Composite Membranes Containing Blow-Spun Fibers: Effect of a Thin Fiber Framework on Proton Conductivity and Mechanical Properties.

In this study, thin fiber composite polymer electrolyte membranes (PEMs) were prepared using short side-chain perfluorosulfonic acid (PFSA) ionomers, Aquivion, to create composite PEMs with improved proton conductivity and improved mechanical properties. PFSA thin fiber webs prepared by blow spinning and successive hot pressing were used as the porous substrate. Herein, PFSA ionomers were used for both the substrate and the matrix of the composite PEMs, and their structures, properties, and fuel cell performance were characterized. By adding the PFSA thin fiber webs to the matrix, the proton conductivity was enhanced and the mechanical properties were slightly improved. The prepared PFSA thin fiber composite PEM showed better FC performance than that of the pristine PFSA one for the high-temperature low-humidity condition in addition to the low-temperature high-humidity one. To the best of our knowledge, this is the first report on the all PFSA composite membranes containing a PFSA thin fiber framework.

Impact of the Catalyst Type and Dopant Composition on the Performance of High-Temperature PEM Fuel Cell

Increasing interest in hydrogen-powered fuel cells for electric energy generation led to the identification of serious limitations of state-of-the-art technologies. In particular, low-temperature fuel cell with a proton-exchange membrane (LT-PEM FC), which is widely considered as an optimal type for mobility, is reaching its technological limits. This is due to its operating temperature up to 90 °C, defined by properties of perfluorinated, sulfonated membranes used as PEM, requiring liquid water for ensuring their ionic conductivity. In the case of heavy duty applications, high-power LT-PEMFC stacks suffer from local overheating, which is currently solved by intensive cooling. Ineffective heat-exchange and necessity of water regime control lead to limitations in total energy utilization. Such problem can be solved by increasing operating temperature up to 180 °C, which is suitable for heat cogeneration. This requires application of appropriate PEM conducting even at an elevated temperature.Current state-of-the-art high-temperature PEM fuel cells (HT-PEM FCs) utilize PEMs based on polymer doped with phosphoric acid. Polymers, such as polybenzimidazole or pyridine aromatic polyether, act as a matrix and a bonding agent for the phosphoric acid dopant. Such PEMs can operate within the temperature range of 120 to 180 °C. In terms of the catalyst, HT-PEM FCs use Pt-based, nanoparticle catalysts on carbon support as in LT-PEM FCs. However, due to the mobile nature of phosphoric acid, which is responsible for pronounced catalyst degradation, poisoning as well as local catalytic layer flooding, Pt loading used in HT-PEM FCs is within an order of magnitude higher than in LT-PEM FCs.Due to its high operating temperature, HT-PEM FC technology offers numerous advantages, such as heat and electric energy cogeneration, simple water regime and, due to improved tolerance to catalyst poisons like CO, the possibility of utilization of contaminated H2 produced from fossil fuels and biomass. However, degradation of components, in particular the catalyst and the membrane, remain the main bottlenecks for wide HT-PEM FC commercialization. With respect to the latest advances in technology, two critical aspects were identified. Firstly, the necessity of new catalysts immobilized on durable supports, with improved stability, activity and resistance against poisoning by phosphate anions. Secondly, membrane with improved fixation of phosphoric acid and greater durability. A special case of the membrane degradation is the reduction of phosphoric acid, by hydrogen or at low potentials on the anode, to phosphorous acid. This compound can poison the anode catalyst, incorporate into the membrane as well as oxidize on the cathode to phosphoric acid, completing dopant lifecycle. Nevertheless, the exact impact of phosphorous acid on HT-PEM FC performance is still not fully understood.Accordingly, the study had two major goals. A first one was to investigate the performance and degradation of Pt-based alloy catalyst on graphene-type support using thin-film modified rotating disc electrode, half-cell and single cell setups. All experiments have been performed at HT-PEM FC relevant conditions, i.e. in concentrated phosphoric acid electrolyte within temperature range of 120 to 180 °C. On the other hand, the second one goal investigated the influence of the dopant composition in terms of phosphorous acid addition to phosphoric acid electrolyte on the activity of the catalyst.Performance of experimental catalysts based on Pt-Co on various supports, including carbon black and graphene was compared to commercial Pt/C catalyst. Experimental catalysts exhibited superior activity for oxygen reduction. The overall performance of single cells with experimental catalyst on the cathode was better than the one with the commercial catalyst, with best results obtained for the graphene supported Pt-Co. The impact of phosphorous acid on oxygen reduction on commercial Pt/C catalyst was significant, due to simultaneous oxidation of acid and reduction of oxygen, as confirmed using rotating disc electrode and half-cell setups. Using the addition of phosphorous acid after single cell break-in on the cathode, the anode or both electrodes at once, it was determined that after stabilization the performance improved. Electrochemical impedance spectroscopy showed that addition of phosphorous acid decreases cell Ohmic resistance, but the comparative I-U curves and CO stripping analysis performed on cathode indicated significant decrease of available Pt surface. This reflects the ambivalent influence of phosphorous acid on HT-PEM FC.This study was supported by the Grant Agency of the Czech Republic under project No. 22-23668K.

Influence of the addition of nanoparticles on the oxygen reduction reaction characteristics of FeNC catalysts and the impact on the stability

Hydrogen peroxide is known to have a detrimental effect on the stability of FeNC catalysts, as previously concluded from the comparison of differently prepared FeNC catalysts. However, beside the release of hydrogen peroxide, the iron composition as well as the carbon morphology changes. Different iron species might cause varying degrees of demetallation (associated with Fenton reaction and reactive oxygen species), whereas the carbon morphology is characteristic of the ability to persist under oxidative conditions. Thus, the true effect of H2O2 is difficult to understand from the comparison of different FeNC catalysts. To overcome this, we explored the relation between H2O2 formation and FC performance for an FeNC catalyst and a series of catalysts obtained by modification of this catalyst with different precious group metal (PGM) nanoparticles (Pd, Ag, Ir, Au). At two catalyst loadings, we performed detailed electrochemical investigations to identify changes in the oxygen reduction reaction pathway induced by accelerated stress tests mimicking the load cycle conditions. Moreover, hydrogen peroxide oxidation and reduction experiments were used to identify changes in the kinetics before and after load cycles. The results were compared to FC activity and short stability tests. While all modified catalysts exhibited a higher degree of H2O2 formation, the addition of small quantities of PGM nanoparticles improved the stability in FC. The latter effect can be associated with an enhanced HPRR kinetic.

Alleviating Class-Imbalance Data of Semiconductor Equipment Anomaly Detection Study

Plasma-based semiconductor processing is highly sensitive, thus even minor changes in the procedure can have serious consequences. The monitoring and classification of these equipment anomalies can be performed using fault detection and classification (FDC). However, class imbalance in semiconductor process data poses a significant obstacle to the introduction of FDC into semiconductor equipment. Overfitting can occur in machine learning due to the diversity and imbalance of datasets for normal and abnormal. In this study, we suggest a suitable preprocessing method to address the issue of class imbalance in semiconductor process data. We compare existing oversampling models to reduce class imbalance, and then we suggest an appropriate sampling strategy. In order to improve the FC performance of plasma-based semiconductor process data, it was confirmed that the SMOTE-based model using an undersampling technique such as Tomek link is effective. SMOTE-TOMEK, which removes multiple classes and makes the boundary clear, is suitable for FDC to classify minute changes in plasma-based semiconductor equipment data.

Platinum group metal-free Fe−N−C catalysts for PEM fuel cells derived from nitrogen and sulfur doped synthetic polymers

• PGM-free Fe−N−C catalysts are produced from N or N/S co-doped porous organic gels. • S-doping alters fundamental properties of carbon materials vs S-free counterparts. • S co-doping induces extensive ultramicroporosity (pores of ∼0.6 nm) • Ultramicropores could enhance ORR via their strong adsorption potential. • S co-doped Fe−N−C catalysts achieve ∼0.15 W cm −2 peak power density in a H 2 –air FC. • Morphology dominates other Fe−N−C characteristics and determines FC performance. Fe−N−C electrocatalysts were obtained via pyrolysis of N- or N/S co-doped synthetic polymers impregnated with FeCl 3 . The influence of the presence/absence of sulfur co-doping, the initial FeCl 3 content and phenanthroline addition on the Fe−N−C–based cathode catalyst layers (CCLs) performance in H 2 -air PEM fuel cells was studied. To this end the Fe−N−C materials were first characterized concerning their chemical composition, surface chemistry, porosity and morphology. Sulfur and phenanthroline additions strongly affect these characteristics of Fe−N−C materials. This in turn determines (to various extents) the electrochemical properties as measured with a rotating ring-disk electrode and upon infusion in the cathode catalyst layer in H 2 -air PEM fuel cells. While simultaneous sulfur and phenanthroline addition yields Fe−N−C catalysts with high N-content and specific surface area, this does not translate into good electrochemical performance. We discuss the multitude of factors determining the catalysts’ and the final CCLs’ performances and conclude that the specific micro-colloidal morphology of the carbon gel-based materials dominates other Fe−N−C characteristics and determines overall FC performance. The best performing CCL provided peak power density of ∼0.15 W⋅cm −2 in a H 2 -air PEMFC.

Structural Aspects of Materials in Optimization of Fuel Cell Electrodes.

Today's energy problems, caused by the irrational consumption of fossil fuels and, as a result, terrible environmental consequences, require the global population to quickly introduce clean energy sources. Electrochemical power sources, which include the fuel cell, provide the technological basis for electrical energy production. While proton exchange membrane fuel cells (PEMFC) rely on platinum based catalysts, obtaining stable and earth abundant catalytic materials for the oxygen reduction reaction (ORR) is an important step towards large scale integration. Our work focusses on FeNC noble-metal free catalysts in PEMFC conditions. The reaction conditions are much more complex in comparison to half cells, as transport processes and e.g. carbon oxidation affect the performance data. Thus, it turns out to be extremely difficult to determine the most important factors affecting the catalytic activity and stability of the material and to optimize the structure of the membrane-electrode assembly as several factors are overlaying each other: For example, the pyrolysis temperature affects the surface area, degree of graphitization and iron-related composition as well as extent of surface functional groups [1]. The metal loading, pyrolysis temperature and a use of possible precursor templates effects the structure, surface area as well as ORR activity and selectivity of catalysts [2], [3].In our recent work, it was shown that in contrast to the electrochemical characteristics observed in rotating disc electrode (RDE) measurements, the best performing catalyst was prepared at the highest investigated temperature for both FC activity and stability [1]. In contrast, the dwell time had only a limited impact at low pyrolysis temperature, whereas a variation from 30 min to 90 min gave significant destruction of molecular FeNx moieties for the high temperature pyrolysis. [1]To gain further insights on the effect of preparation parameters on FC performance and in specific stability, we coupled a quadrupole mas-spectrometer to the cathode exhaust to follow possible release of CO2 depending on the applied conditions. The data are interpreted together with the structural characterization of the materials. We will discuss how the dwell time and pyrolysis temperature effected on morphology changes of the catalyst and to what extent this impacts the FC activity and short-term stability.AcknowledgementsA.O. would like to thank you the TU Darmstadt for the Future talent scholarship, UIK gratefully acknowledges financial support by the BMBF young research group StRedO (03XP0092), and we thank Y. Ostroverkh, and Z. L. Müller, for the consultation and assistance with the fuel cell setup.[1] J. Scharf, M. Kübler, V. Gridin, W.D.Z. Wallace, L. Ni, S.D. Paul, U.I. Kramm, Relation between half-cell and fuel cell activity and stability of FeNC catalysts for the oxygen reduction reaction, (2022) SusMat, accepted (doi: 10.1002/sus2.84).[2] P.Theis, W.D. Z. Wallace, L. Ni, M. Kübler, A. Schlander, R. W. Stark, N. Weidler, M, Gallei, U. I. Kramm. Systematic study of precursor effects on structure and oxygen reaction activity of FeNC catalysts, (2021) Philos. Trans. Royal Soc. A PHILOS T R SOC A, (doi: 10.6084/m9.figshare.c.5506708).[3] P. Boldrin, D. Malko, A. Mehmood, U. I. Kramm, S. Wagner, S. Paul, N. Weidler, A. Kucernak. Deactivation, reactivation and super-activation of Fe-N/C oxygen reduction electrocatalysts: Gas sorption, physical and electrochemical investigation using NO and O2., (2021) Appl. Catal. B, Vol. 292, 120169, (doi: 10.1016/j.apcatb.2021.120169).

Removing maturational influences from female youth swimming: the application of corrective adjustment procedures

Introduction: Common annual age-group competition structures unintentionally introduce participation inequalities, performance (dis)advantages and selection biases due to the effect of maturational variation between youth swimmers. On this basis, there are implications for improving performance evaluation strategies. Therefore the aim was to: (1) To determine maturity timing distributions in female youth swimming; (2) quantify the relationship between maturation status and 100-m FC performance; (3) apply Maturational-based Corrective Adjustment Procedures (Mat-CAPs) for removal of maturational status performance influences.

Altered Functional Connectivity of the Basal Nucleus of Meynert in Subjective Cognitive Impairment, Early Mild Cognitive Impairment, and Late Mild Cognitive Impairment.

Background: The spectrum of early Alzheimer's disease (AD) is thought to include subjective cognitive impairment, early mild cognitive impairment (eMCI), and late mild cognitive impairment (lMCI). Choline dysfunction affects the early progression of AD, in which the basal nucleus of Meynert (BNM) is primarily responsible for cortical cholinergic innervation. The aims of this study were to determine the abnormal patterns of BNM-functional connectivity (BNM-FC) in the preclinical AD spectrum (SCD, eMCI, and lMCI) and further explore the relationships between these alterations and neuropsychological measures.Methods: Resting-state functional magnetic resonance imaging (rs-fMRI) was used to investigate FC based on a seed mask (BNM mask) in 28 healthy controls (HC), 30 SCD, 24 eMCI, and 25 lMCI patients. Furthermore, the relationship between altered FC and neurocognitive performance was examined by a correlation analysis. The receiver operating characteristic (ROC) curve of abnormal BNM-FC was used to specifically determine the classification ability to differentiate the early AD disease spectrum relative to HC (SCD and HC, eMCI and HC, lMCI and HC) and pairs of groups in the AD disease spectrum (eMCI and SCD, lMCI and SCD, eMCI and lMCI).Results: Compared with HC, SCD patients showed increased FC in the bilateral SMA and decreased FC in the bilateral cerebellum and middle frontal gyrus (MFG), eMCI patients showed significantly decreased FC in the bilateral precuneus, and lMCI individuals showed decreased FC in the right lingual gyrus. Compared with the SCD group, the eMCI group showed decreased FC in the right superior frontal gyrus (SFG), while the lMCI group showed decreased FC in the left middle temporal gyrus (MTG). Compared with the eMCI group, the lMCI group showed decreased FC in the right hippocampus. Interestingly, abnormal FC was associated with certain cognitive domains and functions including episodic memory, executive function, information processing speed, and visuospatial function in the disease groups. BNM-FC of SFG in distinguishing eMCI from SCD; BNM-FC of MTG in distinguishing lMCI from SCD; BNM-FC of the MTG, hippocampus, and cerebellum in distinguishing SCD from HC; and BNM-FC of the hippocampus and MFG in distinguishing eMCI from lMCI have high sensitivity and specificity.Conclusions: The abnormal BNM-FC patterns can characterize the early disease spectrum of AD (SCD, eMCI, and lMCI) and are closely related to the cognitive domains. These new and reliable findings will provide a new perspective in identifying the early disease spectrum of AD and further strengthen the role of cholinergic theory in AD.

Three-dimensional model for stacks of tubular high temperature proton exchange membrane fuel cells incorporating a thin layer approach for the membrane electrode assembly

A three-dimensional, non-isothermal, steady state model for stacks of tubular high temperature proton exchange membrane fuel cells (HT PEM FCs) is developed. It is based on a thin layer approach for the membrane-electrode assembly while retaining Butler-Volmer kinetics, concentration and Ohmic losses on both electrodes. It solves for flow, temperature and concentration fields as well as locally resolved current densities for multiple cells. Single cell results for the polarization curve compare well with experimental data for single tubular HT PEM FCs. The model allows for efficient simulations of stacks of multiple tubular HT PEM FCs with a shared air channel in which the interactions between local FC performance and flow, temperature and concentration fields pose a major design challenge. The effects of flow field design, flow rate and cell distance in a stack of 7 tubular cells are investigated and basic approaches for the design of such stacks are derived.

Anode Monitoring By Electrochemical Impedance Spectroscopy in Polymer Electrolyte Membrane Fuel Cells

Although widely used to study the operation of Polymer Exchange Membrane Fuel Cells (PEMFC), Electrochemical Impedance Spectroscopy (EIS) remains a complex tool: experimental data are somewhat delicate to interpret because of the wide range of physical phenomena occurring in Membrane Electrode Assemblies (MEA) and in the flow field plates. Therefore, impedance models are often based on oversimplified equations or conversely, include too many correlated parameters. A typical example of the complexity of the phenomena governing fuel cell electrical behavior are the oscillations of oxygen concentration resulting from the measuring signal, that propagate along the gas channels and makes more difficult the interpretation of the low frequency loop [1, 2, 3]. In addition, most of the impedance models assume Fickian oxygen diffusion although, at least in fuel cells fed with air, Stefan-Maxwell equations should be used as in most stationary models [4, 5]. In this regard, oxygen diffusion and thus the low frequency impedance are strongly dependent on the overall convective flux and as a result, on water management [6].However, due to the characteristic times of oxygen diffusion, these limitations do not apply to the high frequency region of the impedance spectra. The high frequency impedance of a PEMFC remains mostly governed by the cathode [7] but at least in some cases, considering the anode in the Electrical Equivalent Circuit (EEC) is necessary to improve the quality of the fit of the model to the experimental data (Figure). Since the anode has an impact on fuel cell impedance, this means that it becomes possible to monitor its ageing while performing Accelerated Stress Tests (AST). Since most of FC lifetime issues presumably originate from the cathode [8, 9] anode degradation has been rarely studied in the literature. Nevertheless, Schwämmlein et al. showed recently that it may be significant in the case of repeated start-up and shut-down - because of potential cycling - and have a measurable impact on FC performance [10].In this work, we performed AST combining potential and humidity cycles to be as representative as possible of the stressful conditions encountered by the FC in real operating conditions. Commercially available MEA with an initial voltage of the order of 0.7 V at 0.5 A/cm² showed a drop in performance comprised between 400 and 900 µV/h, and a significant degradation of the anode operation was observed by EIS (Figure), confirmed by an increase of its local potentials, and linked to Pt ElectroChemical Surface Area (ECSA) losses. Post-mortem physico-chemical analysis of MEA will be carried out to bridge the decrease of performance with the degradation mechanisms occurring at the anode catalytic layer. Note that these tests were carried out using a 30 cm² segmented cell with 5 straight parallel gas channels [11] (30×1 cm² active area) and that its overall performances may be lower than with regular cells.

PGM-Free Electrode Development and Optimization Using H2 Limiting Current

PEMFCs with platinum group metal (PGM) catalysts can meet performance targets, but the main obstacle for widespread commercialization is the high cost. Alternatively, precious group metal-free (PGM-free) catalyst can meet cost targets and have the potential to reach DOE performance goals. However, successful PGM-free PEMFC development must include device-level studies and microstructure optimization, especially for minimizing the concentration overpotential in the thick PGM-free electrode layers. To date, limited work has been done to decouple the gas phase transport losses from those associated with stability1, active-site density2 and ion transport at the MEA level. Elucidating the voltage loss contributions or resistances stemming from gas transport and proton conduction at the MEA level along with subsequent correlation to MEA performance will help identify phenomena currently limiting the inception of PGM-free electrode performance and identify paths to improved electrode optimization. Baker et al. and Beuscher first suggested the use of limiting current for mass transport characterization in 2006.3,4 The technique has been developed over the past decade for operando measurement, deconvolution, and quantification of the discrete contributions to the concentration overpotential, often expressed as a mass transport resistance, arising from constituent materials and cell components.5,6 However, this method can be difficult to apply to PGM-free based electrodes, where ohmic contributions may dominate over transport phenomena. In this condition, hydrogen could be used as the molecular probe for mass transport resistance instead of oxygen. Spingler et al. first attempted the use of hydrogen as a probe molecule for PGM based electrodes.7 In this work, we integrated a platinum black (PtB) sensor layer into the MEA., enabling in situ determination of mass transport resistance throughout the entire PGM-free catalyst layer. These experiments were performed using a 5 cm2 differential cell, operated at differential conditions in all experiments such that the reactant concentration gradient down the channel was negligible. The total transport resistance ( ) is written in Equation 1 and was measured for various PGM-free electrodes with different ionomer loadings. Rtotal = nFCH2, channel / id Here, we will present 1) a limiting current measurement approach to characterize in situ mass transport resistances in fuel cell materials through bulk catalyst layer at an MEA device level; 2) PGM-free catalyst performance with different ionomer loading in the cathode; 3) how to balance mass transport and ionomer loading to achieve the best FC performance. The results from this experimental approach not only offer the guidance of transport properties and the role of ionomer loading played in the PGM-free electrodes but also increase our understanding of achieving an optimized performance for a PGM-free catalyst at an MEA level. Improved device-level understanding of mass transport limitations in the catalyst coated layer can help accelerate deployment of low cost, PGM-free PEMFCs and be useful to guide ongoing research and development in both catalyst synthesis and membrane electrode assembly fabrication.

High performance electrocatalysts supported on graphene based hybrids for polymer electrolyte membrane fuel cells

In this study, new electrocatalysts for PEM fuel cells, based on Pt nanoparticles supported on hybrid carbon support networks comprising reduced graphene oxide (rGO) and carbon black (CB) at varying ratios, were designed and prepared by means of a rapid and efficient microwave-assisted synthesis method. Resultant catalysts were characterized ex-situ for their structure, morphology, electrocatalytic activity. In addition, membrane-electrode assemblies (MEAs) fabricated using resultant electrocatalysts and evaluated in-situ for their fuel cell performance and impedance characteristics. TEM studies showed that Pt nanoparticles were homogeneously decorated on rGO and rGO-CB hybrids while they had bigger size and partially agglomerated distribution on CB. The electrocatalyst, supported on GO-CB hybrid containing 75% GO (HE75), possessed very encouraging results in terms of Pt particle size and dispersion, catalytic activity towards HOR and ORR, and fuel cell performance. The maximum power density of 1090 mW cm−2 was achieved with MEA (Pt loading of 0.4 mg cm−2) based on electrocatalyst, HE75. Therefore, the resultant hybrid demonstrated higher Pt utilization with enhanced FC performance output. Our results, revealing excellent attributes of hybrid supported electrocatalysts, can be ascribed to the role of CB preventing rGO sheets from restacking, effectively modifying the array of graphene and providing more available active catalyst sites in the electrocatalyst material.

Evaluation of Parameters Accelerating the Aging of PEMFCs Operating under Reformate Containing Carbon Monoxide

Development of efficient accelerated stress test protocols for polymer electrolyte membrane fuel cells (PEMFCs) is an extremely important topic closely related to FC lifetime prediction and a decrease of the FC test costs. This work is dedicated to precise investigation of the impact of various accelerating factors on a FC performance over 1000 h scale. Five identical membrane electrode assemblies with Pt-based catalysts on the cathode and PtRu-based catalyst on the anode were studied using load cycling protocols. The impact of accelerating aging stressors and their combinations, such as carbon monoxide in fuel, frequency and amplitude of current cycling and regular electrochemical diagnostics via polarization curves and cyclic voltammograms measurements was thoroughly investigated. In addition, electrochemical cell behavior under fixed and varied fuel compositions is addressed. Total and irreversible cell performance losses are quantified for different aging tests. It is shown that the importance of aging factors can change depending on a test duration. This study combines large amount of experimental electrochemical data giving quantitative ranking for the importance of factors accelerating cell aging in operation conditions close to real ones for stationary fuel cells.

Advanced nanocomposite membranes for fuel cell applications: a comprehensive review

Combination of inorganic fillers into organic polymer membranes (organic–inorganic hybrid membranes) has drawn a significant deal of attention over the last few decades. This is because of the incorporated influence of the organic and inorganic phases towards proton conductivity and membrane stability, in addition to cost decline, improved water retention property, and also suppressing fuel crossover by increasing the transport pathway tortuousness. The preparation methods of the composite membranes and the intrinsic characteristics of the used particles as filler, such as size, type, surface acidity, shape, and their interactions with the polymer matrix can significantly affect the properties of the resultant matrix. The membranes currently used in proton exchange membrane fuel cells (PEMFCs) are perfluorinated polymers containing sulfonic acid, such as Nafion®. Although these membranes possess superior properties, such as high proton conductivity and acceptable chemical, mechanical, and thermal stability, they suffer from several disadvantages such as water management, CO poisoning, and fuel crossover. Organic-inorganic nanocomposite PEMs offer excellent potentials for overcoming these shortcomings in order to achieve improved FC performance. Various inorganic fillers for the fabrication of composite membranes have been comprehensively reviewed in the present article. Moreover, the properties of polymer composites containing different nanoparticles have been thoroughly discussed.

Can PEM Fuel Cells Experience Appreciable Degradation at Short Circuit?

AbstractOperation of PEM fuel cells at very low voltages can occur in the case of direct hybridization with supercapacitors, depending on their charge level: in such cases, the cell acts as reliable current sources that can be used with low voltage devices. In spite of the growing importance of this electrical mode aging phenomena for such conditions are still unknown. A single 100 cm2 cell was operated for more than 2,000 hours at short circuit. The current delivered by the cell provided with an MEA after suitable maturation, was shown to be approx. 98% of that corresponding to the injected hydrogen flow rate. The state‐of‐health of the cell was followed by impedance measurements and determination of the electrochemical surface area of the cathode and the fuel crossover. Significant, regular decay rate of the cell voltage after the low‐voltage run was observed to range from 30 to 100 µV h−1 depending on the current density. The features of the cell were little‐to‐moderately affected by the particular regime: 43% of ECSA was lost which affects only little the FC performance, and hydrogen crossover remains unchanged. Only the diffusion resistance was increased up to fourfold at high current density.

(Invited) A Highly Durable Polymer Electrolyte Fuel Cell Catalyst Based on Double-Polymer-Coated Carbon Nanotubes

We report the design and fabrication of a highly durable fuel cell electrocatalyst based on double-polymer-coated carbon nanotubes for use in polymer electrolyte membrane fuel cells. The prepared FC catalyst is composed of Pt-deposited polybenzimidazole-coated carbon nanotubes, which are further coated with Nafion. We fabricated MEA using the catalyst and examined the FC performance. By using this electrocatalyst, a high FC performance with a power density of 375 mW/cm2 (at 70˚C, 50% relative humidity using air (cathode)/H2(anode)) was obtained, and a remarkable durability of 500,000 accelerated potential cycles was recorded with only a 5%-loss of the initial FC potential and 20%-loss of the maximum power density, which were far superior properties compared to those of the MEAs prepared using carbon black in place of the carbon nanotubes. The present study indicates that the prepared highly durable fuel cell electrocatalyst is a promising material for the next generation of PEMFCs.