Performance assessment of proton exchange membrane fuel cell (PEMFC) stack by means of semi-empirical model

Thesis (Master)--Izmir Institute of Technology, Energy Engineering, Izmir, 2011Includes bibliographical references (leaves: 72-75)Text in English; Abstract: Turkish and Englishxiii, 77 leavesThe charge transfer coefficient estimated around 0.4In this study, the performance of a 10 kW peak power proton exchange membrane fuel cell stack under different operating conditions was investigated experimentally by its i-V polarization curve. The stack has been fed with pure hydrogen and air and PEM fuel cell stack has active area 200 cm2 and is composed of 75 single cells. The stack was tested for different reactant inlet temperatures as from 50 °C to 65 °C with 5 °C intervals keeping constant other conditions and for different relative humidities as 75%, 85% and 95% again keeping constant other operation conditions. Then the analytical nonlinear model adapted to describe the polarization curve has been discussed. Model parameters have been simultaneously estimated by fitting data into model by using LABFIT nonlinear regression program. These parameters are the cathode exchange current density, charge transfer coefficient and polymer electrolyte membrane internal resistance. The polarization curve of the fuel cell stack showed the stack performance improved from 50 °C to 65 °C temperature with the decrease of voltage losses. However the decrease of relative humidity from 95% to 75% did not show any explicit effect onto stack performance. Data fitting was obtained with reasonable model parameters in accordance with literature and with high coefficient of determination (R2) values. The effect of temperature on model parameters was also investigated. The cathode exchange current density value increased from 2.247X10-6 A/cm2 at T=50 °C to 5.643X10-6 A/cm2 at T=65 °C. The charge transfer coefficient estimated around 0.4 coherently with literature. The membrane internal resistance value followed the slightly decreasing tendency with increasing temperature as the value around 0.1 cm2

Identification of critical parameters for PEMFC stack performance characterization and control strategies for reliable and comparable stack benchmarking

This paper is focused on the identification of critical parameters and on the development of reliable methodologies to achieve comparable benchmark results. Possibilities for control sensor positioning and for parameter variation in sensitivity tests are discussed and recommended options for the control strategy are summarized. This ensures result comparability as well as stable test conditions. E.g., the stack temperature fluctuation is minimized to about 1 °C. The experiments demonstrate that reactants pressures differ up to 12 kPa if pressure control positions are varied, resulting in an average cell voltage deviation of 21 mV. Test parameters simulating different stack applications are summarized. The stack demonstrated comparable average cell voltage of 0.63 V for stationary and portable conditions. For automotive conditions, the voltage increased to 0.69 V, mainly caused by higher reactants pressures. A benchmarking concept is introduced using “steady-state” polarization curves. The occurring 20 mV hysteresis effect between the ascending and descending polarization curve can be corrected calculating the mean value of both voltages. This minimizes the influence of preceding load levels, current set points, and dwell times

Analysis of Hydrogen Fuel Cell Powerplant Architectures for Future Transport Applications

[ES] A la luz de la crisis medioambiental y del creciente interés en el uso del H2 para avanzar hacia la Economía del Hidrógeno, esta tesis tiene como objetivo analizar y optimizar nuevas arquitecturas de sistemas propulsivos de FCV para aplicaciones en turismos y vehículos pesados en términos de rendimiento, durabilidad e impacto medioambiental. Para ello, se ha desarrollado una plataforma de modelado de FCV multifísica y flexible que integra un modelo de pila de combustible validado junto con los componentes del BoP, los componentes mecánicos y eléctricos del vehículo y el sistema propulsivo, un modelo de degradación de FC semi-empírico informado por tendencias físicas diseñado para ser utilizado en condiciones de conducción y un optimizador de EMS en tiempo real que ofrece el mejor rendimiento dado un diseño de sistema propulsivo y un ciclo de conducción, de tal forma que todas las arquitecturas propuestas para una aplicación determinada sean comparables en términos justos. La discusión de los resultados puede dividirse en tres partes diferentes. La primera está orientada a la optimización del rendimiento del FCS. Los resultados de esta parte ayudaron a identificar la estrategia de gestión del aire que, dado un conjunto de restricciones impuestas en los componentes del BoP, maximizaba la potencia neta del FCS (eficiencia) para cada valor de densidad de corriente. El balance energético resultante, que comprende la potencia producida por la pila de combustible, las perdidas electroquímicas y el consumo de los componentes del BoP, fue analizado y utilizado para determinar y diseñar la estrategia de control de los actuadores del BoP para condiciones de conducción. La segunda parte se centra en la evaluación y optimización, cuando es posible, de la arquitectura FCREx para aplicaciones de turismos y la configuración multi-FCS para aplicaciones de vehículos de transporte pesado. Desde el punto de vista del rendimiento, la arquitectura FCREx ofrecía un consumo mínimo de H2 con una elevada potencia de la pila de combustible y una gran capacidad de la batería, pero este diseño podría ser prohibitivo en términos de costes. Podía ofrecer hasta un 16.8-25% menos de consumo de H2 y un 6.8% menos de consumo de energía. La limitación en la dinámica de esta arquitectura aumento la durabilidad de la FC en un 110% con una penalización en el consumo de H2 del 4.7%. La arquitectura multi-FCS para aplicaciones pesadas podría funcionar con una dinámica aún menor, con un aumento de la durabilidad de la pila del 471% con una penalización en el consumo de H2 del 3.8%, ya que el perfil de conducción de los vehículos pesados suele ser menos dinámico. El control y el dimensionamiento diferencial solo podrían aportar beneficios en términos de impacto ambiental o de coste, pero no de rendimiento. La última parte considera los resultados obtenidos en términos de rendimiento y durabilidad para analizar el impacto medioambiental de cada arquitectura. La estrategia de producción de H2 afecta significativamente a las emisiones del ciclo de vida en ambas aplicaciones sobre cualquier otra elección de diseño. El diseño óptimo para la arquitectura FCREx que minimiza las emisiones tiene una alta potencia de la pila de combustible y una capacidad moderada de la batería. En el caso de la aplicación para vehículos pesados, se identificó la dinámica de control óptima para cada diseño y estrategia de producción de H2, y se determinó que la estrategia de diseño de dimensionado diferencial solo proporcionaba beneficios si se consideraba una tecnología de pila de combustible diferente para las distintas pilas integradas en el sistema propulsivo.[CA] A la llum de la crisi mediambiental i del creixent interés en l'ús de l'H2 per a avançar cap a l'Economia de l'Hidrogen, aquesta tesi té com a objectiu analitzar i optimitzar noves arquitectures de sistemes propulsius de FCV per a aplicacions en turismes i vehicles pesants en termes de rendiment, durabilitat i impacte mediambiental. Per a això, s'ha desenvolupat una plataforma de modelatge de FCV multifísica i flexible que integra un model de pila de combustible validat juntament amb els components del BoP, els components mecànics i elèctrics del vehicle i el sistema propulsiu, un model de degradació de pila de combustible semi-empíric informat per tendències físiques dissenyat per a ser utilitzat en condicions de conducció i un optimitzador d'EMS en temps real que ofereix el millor rendiment donat un disseny de sistema propulsiu i un cicle de conducció, de tal forma que totes les arquitectures proposades per a una aplicació determinada siguen comparables en termes justos. La discussió dels resultats pot dividir-se en tres parts diferents. La primera està orientada a l'optimització del rendiment del FCS. Els resultats d'aquesta part van ajudar a identificar l'estratègia de gestió de l'aire que, donat un conjunt de restriccions imposades en els components del BoP, maximitzava la potència neta del FCS (eficiència) per a cada valor de densitat de corrent. El balanç energètic resultant, que comprén la potència produïda per la pila de combustible, les pèrdues electroquímiques i el consum dels components del BoP, va ser analitzat i utilitzat per a determinar i dissenyar l'estratègia de control dels actuadors del BoP per a condicions de conducció. La segona part se centra en l'avaluació i optimització, quan ¿es possible, de l'arquitectura FCREx per a aplicacions de turismes i la configuració multi-FCS per a aplicacions de vehicles de transport pesat. Des del punt de vista del rendiment, l'arquitectura FCREx oferia un consum mínim d'H2 amb una elevada potència de la pila de combustible i una gran capacitat de la bateria, però aquest disseny podría ser prohibitiu en termes de costos. Podia oferir fins a un 16.8-25% menys de consum d'H2 i un 6.8% menys de consum d'energia. La limitació en la dinàmica d'aquesta arquitectura va augmentar la durabilitat de la pila en un 110% amb una penalització en el consum d'H2 del 4.7%. L'arquitectura multi-FCS per a aplicacions pesades podria funcionar amb una dinàmica encara menor, amb un augment de la durabilitat de la pila del 471% i una penalització en el consum d'H2 del 3.8%, ja que el perfil de conducció dels vehicles pesants sol ser menys dinàmic. El control i el dimensionament diferencial només podrien aportar beneficis en termes d'impacte ambiental o de cost, però no de rendiment. L'última part considera els resultats obtinguts en termes de rendiment i durabilitat per a analitzar l'impacte mediambiental de cada arquitectura. L'estratègia de producció d'H2 afecta significativament a les emissions del cicle de vida en totes dues aplicacions sobre qualsevol altra elecció de disseny. El disseny òptim per a l'arquitectura FCREx que minimitza les emissions té una alta potència de la pila de combustible i una capacitat moderada de la bateria. En el cas de l'aplicació per a vehicles pesants, es va identificar la dinàmica de control `optima per a cada disseny i estratègia de producció d'H2, i es va determinar que l'estratègia de disseny de dimensionament diferencial només proporcionava beneficis si es considerava una tecnologia de pila de combustible diferent per a les diferents piles integrades en el sistema propulsiu.[EN] In light of the environmental crisis and the growing interest in the use of H2 to advance toward the Hydrogen Economy, this thesis aims at analyzing and optimizing novel FCV powerplant architectures for passenger car and heavy-duty vehicle applications in terms of performance, durability, and environmental impact. For that purpose, a multi-physics flexible FCV modeling platform was developed integrating a validated FC stack model together with the BoP components, the mechanical and electrical components of the vehicle and powertrain, a semi-empirical physics-informed FC degradation model designed to be used in driving conditions and a real-time EMS optimizer that offers the best performance given a powerplant design and driving cycle so that all the proposed architectures for a given application are comparable. The discussion of the results can be divided into 3 different parts. The first one is oriented towards the FCS performance optimization. The results in this part helped to identify the air management strategy that, given a set of constraints imposed in the BoP components, maximized the FCS net power output (efficiency) for each value of current density. The resulting energy balance comprising the FC stack power produced, the electrochemical losses, and the consumption of the BoP components was analyzed and used to determine and design the control strategy of the BoP actuators for driving cycle conditions. The second part is focused on the evaluation and optimization, when possible, of the FCREx architecture for passenger car applications and the multi-FCS configuration for heavy-duty vehicle applications. Performance-wise the FCREx architecture offered minimum H2 consumption with high FC stack power and high battery capacity, but this design could be prohibitive in terms of costs. It could offer up to 16.8-25% lower H2 consumption and 6.8% lower energy consumption. Limiting the dynamics of this architecture increased the FC durability by 110% with a penalty in H2 consumption of 4.7%. The multi-FCS architecture for heavy-duty applications could operate with even lower dynamics, with an increase in the FC durability of 471% with a penalty in H2 consumption of 3.8%, since the driving profile of heavy-duty vehicles is usually more steady. Differential control and sizing could only provide benefits in terms of environmental impact or cost, not performance. The last part considers the results obtained in terms of performance and durability to analyze the environmental impact of each architecture. The H2 production pathway affected significantly the life cycle emissions of both applications over any other design choice. The optimum design for FCREx architecture that minimized emissions had high FC stack power and moderate battery capacity. In the case of heavy-duty application, the optimum control dynamics for each design and H2 production pathway were identified, and the differential sizing design strategy was determined to only provide benefits if different FC stack technology was considered for the various stacks in the powerplant.López Juárez, M. (2022). Analysis of Hydrogen Fuel Cell Powerplant Architectures for Future Transport Applications [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/18921

One-dimensional platinum-based hybrid nanostructures for high performance electrodes in proton exchange membrane fuel cells

To reduce the required high loading of Pt to catalyse the sluggish oxygen reduction reaction (ORR) at cathodes in proton exchange membrane fuel cells (PEMFC), much development has been made on increasing the efficiency of the catalyst material. However, there is big challenge to fully translate catalytic enhancements into higher performance catalyst electrodes in PEMFCs. Pt nanowire (NW) array gas diffusion electrodes (GDEs) matches the promise of higher PEMFC performances. Alloying of Pt with a non-noble metal such as Ni, and using alternative carbonaceous supports such as carbon nanotubes (CNTs) are known methods of increasing ORR catalytic activity. This study applies both methods to improve the performance of the Pt NW array system and to better understand the mechanisms that influence real performance of PEMFC catalyst materials. Herein, a facile method for the preparation of PtNi NWs supported on carbon is developed by an impregnation and annealing approach. The optimal PtNi NW/C catalyst is achieved at an annealing temperature of 150°C with a duration of 24 hrs, showing 1.78-fold mass activity enhancement with respect to the pure Pt NWs. However, very poor power performance is observed for the PtNi NW/C GDE in PEMFCs. This is ascribed to the increased mass transport resistance resulting from ionomer contamination within the catalyst layer caused by severe Ni dissolution from the PtNi NWs. An acid leaching step is therefore introduced in the fabrication of PtNi NW array GDEs and an optimised GDE gave a 1.07-fold of power density with respect to the Pt NW array GDE. Finally, nitrogen-doped CNT arrays are fabricated directly onto the GDL surface by plasma enhanced chemical vapour deposition (PECVD) and active screen plasma treatment (ASP). These act as the catalyst support for Pt NW arrays where much enhanced power performance as compared to Pt NW array and Pt/C GDEs is attributed to an increase in macropores with a diameter range of 315-360 nm, concluding that mass transport properties are the key to translating effective ORR catalysts into high performance PEMFC electrodes

Development and Characterization of Low Pt-Loaded Membrane Electrode Assemblies with Focus on Performance and Durability

For many applications of polymer electrolyte membrane fuel cell (PEMFC), the loading attributed to platinum as catalyst is still too high for this technology to penetrate into the mass market. However, this high loading of platinum is still necessary to achieve the performance and service life targets. Therefore, reducing the loading of precious group metals is a major challenge to low temperature PEM fuel cell community. The performance of the membrane electrode assembly (MEA) with low Pt loading depends on the optimization of numerous parameters like catalyst activity, proton conductivity of ionomer, ionomer to catalyst ratio, diffusion media, operating conditions, and last but not the least the microstructure of the electrode, which is determined by the coating method. An efficient electrode with low platinum loading and durable performance requires a thin but porous catalyst layer, in which the catalyst particles and ionomer are homogenously distributed with a large surface area. The fundamental goal of this dissertation is to understand the relationships between structural properties and performance, and to derive strategies for a goal oriented development. In the first part of the study, PEMFC electrodes were fabricated with the same Pt loading by means of diverse coating techniques. Current-voltage curves, electrochemical analysis, and physical characterizations are evaluated to interpret the influence of microstructure caused by the coating methods on performance and durability. In order to obtain different catalytic layer structures, the electrodes were produced using six different coating techniques with the same Pt loading. The selected coating techniques are wet spraying, screen printing, inkjet printing, dry spraying, doctor-blade and drop casting. Similar drying conditions were maintained after all the wet coating processes. The physical and electrochemical characterizations of the individual catalyst layers (CL) were investigated under identical operating conditions. The results show that wet spraying and screen printing showed the highest performance due to the low proton resistance. The lowest efficiencies were observed in doctor-blade and drop-cast techniques, which are associated with particularly low protonic conductivity. Microstructure investigation by focus-ion-beam scanning electron microscope analysis were used to determine transport properties such as porosity, permeability, diffusivity and inverse tortuosity by image analysis in GeoDict. A comparison of peak power density and effective transport parameters shows that an increase in permeability, diffusivity and porosity correlates strongly with increasing power. A dimensionless classification of the transport properties of the MEA with a point system and their summation can describe the observed performance very well. Consequently, the measured and analyzed transport parameters seem to be sufficient for predicting the performance of a membrane electrode assembly (MEA). This can help to optimize coating techniques and thus increase MEA performance together with service life. Furthermore, the dry coating technology developed at DLR was improved in order to produce MEAs nearly 50 % more efficient than before. Additionally, the effect of ionomer with diverse side chain length as well as the significance of membrane thickness is also studied for long and short term application upon load cycling test. This research further provides a deep insight into the importance of ionomer and its microstructure both in the electrode and the membrane in PEM fuel cell, which influences the performance and also the long term stability. After 600 hours of load cycle operation with the cells, roughly 120 mV of drastic degradation was observed owing to the higher gas crossover through thinner membrane, while the performance can be increased approximately 16 % due to the shorter side chain of ionomer. Another important result of this work is the investigation of the influence of the drying process of MEA production on the electrode microstructure, i.e. the open porosity, the ionomer distribution and the size of the reactive interface. An unconventional drying method known as freeze drying, shows three-fold improvement in the porosity and promising ionomer distribution in CL. Consequently, this can reduce the transport limitations and improve the peak power density about 34 % compared to the conventional drying technique. Furthermore, a transient 2D physical continuum model was applied and simulations were performed to numerically investigate the influence of different drying methods on PEM fuel cell performance. Both experimental and simulation data emphasize the fact that the sublimation of the catalyst layer improves the architecture by optimizing porosity, permeability and tortuosity. These above-mentioned properties of the microstructure of the catalytic layer significantly improve water management and diffusion properties, which has an impact on performance and reduced mass transport limitation. This work is able to identify important process engineering relationships between the microstructure of CL and its performance. In addition, promising manufacturing processes, drying methods and operating conditions were found, which should allow a targeted improvement of CL performance in the next step

Fuel Cell Renewable Hybrid Power Systems

Climate change is becoming visible today, and so this book—through including innovative solutions and experimental research as well as state-of-the-art studies in challenging areas related to sustainable energy development based on hybrid energy systems that combine renewable energy systems with fuel cells—represents a useful resource for researchers in these fields. In this context, hydrogen fuel cell technology is one of the alternative solutions for the development of future clean energy systems. As this book presents the latest solutions, readers working in research areas related to the above are invited to read it

Alternative Fuels for Transportation

With existing petroleum oil and natural gas reserves enough for only several more decades, there is an imminent need for alternative energy sources. This critical situation has incited greater improvements in automotive technology and the increased use of nonconventional fuels. Alternative Fuels for Transportation covers the potential, production methods, properties, vehicle tests, merits, and drawbacks of alternative fuels. The esteemed editor highlights the importance of moving toward alternative fuels and the problems and environmental impact of depending on petroleum products. Each self-contained chapter focuses on a particular fuel source, including vegetable oils, biodiesel, methanol, ethanol, dimethyl ether, liquefied petroleum gas, natural gas, hydrogen, electric, fuel cells, and fuel from nonfood crops. For most of these fuels, production methods, storage, transportation and distribution, physiochemical properties, system modification, engine tests, economics, applications, safety aspects, material compatibility, and future scope are discussed. Although we now know that increases in greenhouse gases will contribute to global climate change, the transportation sector and decentralized power generation continue to heavily rely on petroleum products, particularly gasoline and diesel. Exploring how to counteract the world’s energy insecurity and environmental pollution, this book provides a comprehensive understanding of nonconventional fuel sources and technology

Alternative Fuels for Transportation

Exploring how to counteract the world's energy insecurity and environmental pollution, this volume covers the production methods, properties, storage, engine tests, system modification, transportation and distribution, economics, safety aspects, applications, and material compatibility of alternative fuels. The esteemed editor highlights the importance of moving toward alternative fuels and the problems and environmental impact of depending on petroleum products. Each self-contained chapter focuses on a particular fuel source, including vegetable oils, biodiesel, methanol, ethanol, dimethyl ether, liquefied petroleum gas, natural gas, hydrogen, electric, fuel cells, and fuel from nonfood crops