Direct Liquid Fuel Cells: Fundamentals, Advances and Future

Direct Liquid Fuel Cells is a comprehensive overview of the fundamentals and specificities of the use of methanol, ethanol, glycerol, formic acid and formate, dimethyl ether, borohydride, hydrazine and other promising liquid fuels in fuel cells. Each chapter covers a different liquid fuel-based fuel cell such as: Anode catalysts of direct methanol fuel cells (DMFCs), future system designs and future trends for direct ethanol fuel cells (DEFCs), development of catalysts for direct glycerol fuel cells (DGFCs), the mechanisms of the reactions taking place at the anode and cathode electrodes, and the reported anode catalysts for direct formic acid fuel cell (DFAFC) and direct formate fuel cell (DFFC), characteristics of direct dimethyl ether fuel cell (DDMEFC), including its electrochemical and operating systems and design, the developments in direct borohydride fuel cells, the development of catalysts for direct hydrazine fuel cells (DHFCs), and also the uncommonly used liquids that have a potential for fuel cell applications including 2-propanol, ethylene glycol, ascorbic acid and ascorbate studied in the literature as well as utilization of some blended fuels. In each part, the most recent literature is reviewed and the state of the art is presented. It also includes examples of practical problems with solutions and a summarized comparison of performance, advantages, and limitations of each type of fuel cell discussed. Direct Liquid Fuel Cells is not a typical textbook but rather designed as a reference book of which any level of students (undergraduate or graduate), instructors, field specialists, industry and general audience, who benefit from current and complete understanding of the many aspects involved in the development and operation of these types of fuel cells, could make use of any chapter when necessary.

• Presents information on different types of direct liquid fuel cells.
• Explores information under each section, for specific fuel-based fuel cells in more detail in terms of the materials used.
• Covers three main sections: direct alcohol, organic fuel-based and inorganic fuel-based fuel cells

• Language: English
• Publisher: Academic Press
• Release date: Sep 10, 2020
• ISBN: 9780128187364

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Turkey

Preface

Ramiz Gültekin Akay, Kocaeli University, Kocaeli, Turkey

Ayşe Bayrakçeken Yurtcan, Atatürk University, Erzurum, Turkey

Energy has always been the most important need for a modern society. With both increasing population of the world and increased use of electricity, both the demand and consumption have increased exponentially in recent decades. Parallel to this increase, it was realized that the conventional technologies used for producing electrical energy caused two major problems: First is the undeniable global warming that affects each of us in our daily lives wherever we are living as a consequence of the high carbon emissions released into the atmosphere; second is that the conventional petroleum-based energy infrastructure caused wars and instabilities particularly in the regions of these resources. Therefore, it had been realized that a new energy approach was needed urgently. This new approach or understanding needed technologies that can produce or convert energy from renewable sources as possible as it is and it should include a distributed nature instead of centralized power. Among the energy conversion technologies, fuel cells seemed to be promising due to their outstanding properties. In spite of these promising features commercial products could not have entered into the picture as expected because of the technical and economical problems. But when the history and development of today’s internal combustion engines and the fact that this maturity of the technology reached to this level in a century is considered, this is not surprising. Fuel cell development and technology is a very tedious task which needs an interdisciplinary approach and also depends on cutting-edge materials. So sometimes in the past, the fuel cell communities themselves also hesitated about the fuel cell future. However, today a fuel cell industry is realized. Direct liquid fuel cells (DLFCs) also attracted special attention due to the ease of storage and distribution of the fuels compared to that of hydrogen-fueled fuel cells. DLFCs are very well suited and have a great potential for distributed energy production and particularly for mobile applications.

In the 1990s, there were very few number of books on the field, in the last 2 decades the number of publications have increased rapidly. Today there are a number of very good books on fuel cells particularly on hydrogen-fueled polymer electrolyte membrane fuel cells (PEMFCs) and related subtopics as well as some covering direct alcohol fuel cells (DAFCs); however, there was a lack of a book reviewing the technology of DLFCs with other potential fuels also, which are becoming very promising and which could be considered as a new subclass of fuel cells. Therefore, this book is an extra effort to offer additional knowledge on related concepts particularly for DLFC types, filling the gap of a book for describing less pronounced DLFC types and also aiming to contribute to the nomenclature and classification since as new types of fuel cells enter into the picture, this issue is becoming important.

This book is designed to shed light on researchers working on DLFCs. The book covers three main sections: direct alcohol, organic fuel-based and inorganic fuel-based fuel cells. Under each section, specific fuel-based fuel cells were described in more detail in chapters after general introduction chapters of the sections.

Chapter 1 summarizes the general information about the fuel cells including the historical development of fuel cell technology and the current state of these systems, basic components of fuel cells (on the specialty of PEMFC), operating principles and the basis of DLFCs in which the fuel (alcohols, acids, glycols, etc.) is in the liquid phase. Section 1 (Chapters 2–5) is devoted to direct alcohol fuel. Chapter 2 gives a brief introduction to DAFCs. Chapter 3 summarizes the anode catalysts of direct methanol fuel cells (DMFCs) and also provides information about other factors for the commercialization of DMFCs. In Chapter 4, future system designs and future trends for direct ethanol fuel cells (DEFCs) to achieve commercial and engineering success is given. Chapter 5 is focused on the development of catalysts for direct glycerol fuel cells (DGFCs) in addition to the effects of other factors. Section 2 includes the organic-based fuel cells other than the alcohols as given in Chapters 6–8. Chapter 6 gives a brief introduction to the organic fuel-based fuel cells. In Chapter 7, mechanisms of the reactions taking place at the anode and cathode electrodes, and the reported anode catalysts for direct formic acid fuel cell (DFAFC) and direct formate fuel cell (DFFC) in recent years are presented. Chapter 8 discusses in-depth the characteristics of direct dimethyl ether fuel cell (DDMEFC), including its electrochemical and operating systems and design, the potential of DME for commercialization is also explored. The third section (Chapters 9–11) is devoted to inorganic fuel-based fuel cells. A brief introduction is given in Chapter 9. Chapter 10 summarizes the developments in direct borohydride and ammonia borane fuel cells particularly. In Chapter 11, recent advances in the development of catalysts for direct hydrazine fuel cells (DHFCs), the challenges and perspectives from the point of health and environmental perspectives especially in this field are also discussed. Chapter 12 summarizes the uncommonly used liquids that have a potential for fuel cell applications including 2-propanol, ethylene glycol, ascorbic acid and ascorbate studied in the literature as well as utilization of some blended fuels.

As it could be understood from the definition of the content of the book described above, this book is not a typical textbook but rather designed as a reference book which any level of students (undergraduate or graduate), instructors, field specialists, industry and general audience could make use of any chapter when necessary.

First, the editorial board acknowledges Prof. Dr. İnci Eroğlu, emeritus professor in Middle East Technical University, Ankara, Turkey, for opening the doors of the fuel cells to us; Prof. Dr. Nejat Veziroğlu for his pioneering studies and efforts in hydrogen and fuel cell studies all over the world and support to the studies on the field which is believed to make their importance realizable today. They also thank the contributing authors for their efforts during the publication process. Michelle Fisher, Chiara Giglio, Indhumati Mani, Peter Adamson and Nirmala Arumugam from Elsevier deserve special thanks for their efforts and assistance which helped the book to complete on time. We would also like to thank Cenk Çelik, our dear friend, who designed the pleasing front cover of this book for his valuable effort.

Ramiz Gültekin Akay thank Elsevier ex-editor Raquel Zanol for her efforts in growing the idea of this book which was born during a conservation on the topic in the 22nd World Hydrogen Energy Conference (WHEC) held in Rio De Jenerio in 2018. I would also thank my PhD student Tuncay Kadıoğlu for his contribution and to my family and friends for their support.

Ayşe Bayrakçeken Yurtcan acknowledges her past and current graduate students: Fulya Memioğlu, M. Selim Çögenli, Elif Daş, Ayşenur Öztürk, Hande Ungan, Emine Öner, Niyazi Özçelik, Meryem Samancı, Merve Hurşit, Mohamed Ali Mohamud and Sonnur Kurtuluş for their valuable contributions to fuel cell studies. I would especially like to thank my dear mother, father, sister and brothers for their support in every stage of my life and my friends. I also thank my beloved husband Mustafa Tolga Yurtcan and my beloved daughters Hale and Defne for adding meaning to my life.

Chapter 1: Introduction to fuel cells

Ayşenur Öztürka; Ramiz Gültekin Akayb; Serdar Erkanc; Ayşe Bayrakçeken Yurtcana,d,⁎    a Faculty of Engineering, Department of Chemical Engineering, Atatürk University, Erzurum, Turkey

b Faculty of Engineering, Chemical Engineering Department, Kocaeli University, Kocaeli, Turkey

c Atombir Energy Technologies Laboratory Chemistry Informatics Software Automation Contact Electric Electronic Limited Company, Middle East Technical University Technocity, Ankara, Turkey

d Nanoscience and Nanoengineering Research and Application Center, Atatürk University, Erzurum, Turkey

* Corresponding author

Abstract

Fuel cells (FCs) have been mentioned as an alternative energy technology in which the chemical energy of the fuel is directly converted into electrical energy. Fuel cell technology is progressing gradually with intense researches in the fields of material engineering, nanotechnology, transport phenomena, electrocatalysts engineering, etc., and it is now possible to use these systems in many stationary and portable applications. This chapter consists of four subsections. In the first part, a brief introduction to the history of fuel cells was given. Subsequently, the information on the development of fuel cell technology and the current state of these systems in recent years will be provided in the second part. The third part was dedicated to basic components of fuel cells (on the specialty of PEMFC). The last part was concerned about the basis of direct liquid fuel cells (DLFCs) in which the fuel (alcohols, acids, glycols) is in liquid form.

Keywords

Fuel cell history and technology; PEM fuel cell components; Membrane electrode assembly; Gas diffusion layer; Direct liquid fuel cells

Chapter outline

1.1A brief history of the development of fuel cell (FC) technology

1.2Fundamentals of FC technology

1.2.1Basic operating principles of a fuel cell

1.2.2Kinetics and losses

1.3Basic components (on the specialty of PEMFC)

1.3.1Gas diffusion layer (GDL)

1.3.2Catalyst layer

1.3.3Polymer electrolyte membrane

1.3.4Bipolar plate

1.3.5Gasket

1.3.6Current collector

1.3.7End plate

1.4Introduction to direct liquid fuel cells (DLFCS)

1.5Conclusions

References

1.1: A brief history of the development of fuel cell (FC) technology

Initial studies on fuel cell systems coincide with the end of the 18th century and the beginning of the 19th century. Although the importance given to fuel cells has increased in recent years, it has a history of approximately 150 years. Although the German chemist Christian Friedrich Schönbein and the Welsh chemical physicist Sir William Robert Grove both have a reputation for being the first researchers on the fuel cell, Sir William Robert Grove is mostly considered to be the inventor of the first fuel cell. But even before, the concept of a fuel cell was also attributed to Humphry Davy in the early 19th century (1802) for his observations and studies [1, 2]. Sir William Robert Grove created the Grove Cell and discovered that it could generate current flow from the electrochemical reaction between the oxygen and hydrogen gases by using platinum electrodes immersed in dilute sulfuric acid solution [1, 3]. Then by further developing the system, he connected the cells in series. In this integrated system, which he called the gas battery (1842), he observed a higher potential drop between the electrodes and discovered that more current was drawn through the cells connected in series [1, 2, 4]. This arrangement forms the basis of the fuel cell systems used today. The representative demonstration of the gas battery was given in Fig. 1.1[4].

Fig. 1.1 Basic demonstration of gas battery system [4].

Although the first fuel cell developed by Sir William Robert Grove was a major step forward for the introduction of this technology, much more had to be understood in order to implement fuel cells into practical applications. Grove stated the significance of the electrochemical active area in which three phases such as gas, electrolyte and electrode interact with each other. Friedrich Wilhelm Ostwald (1893), who is known as the founder of physical chemistry and a Nobel Prize Winner (1909), contributed a lot to the fuel cell field by theoretical explanations regarding the fuel cell operation principles. He explained the difference between the internal combustion engines and fuel cells in terms of energy efficiency. The first one has a lower capability comparatively to the second one regarding the energy conversion because of the Carnot Cycle limitations. In a fuel cell, direct conversion of the fuel chemical energy into electrical energy is possible with high energy efficiency and low pollutant emission [1, 5].

In line with Grove’s statement about the significance of an electrochemically active area between gas, electrode and electrolyte, the British chemist Ludwig Mond and Charles Langer (1889) modified the Grove Cell and designed the electrodes in a porous and three-dimensional structure. They used coal as fuel in their design instead of pure hydrogen, thus controverting Grove’s claim which was about the necessity of using pure hydrogen gas in the cell in order to obtain current. They achieved 20 A/m² at 0.73 V with their fuel cell. Ostwald, Mond and Langer foresaw the potential of the hydrogen fuel cell as the 20th century energy source [1, 2]. Walther Hermann Nernst is a scientist who won the chemical and physical Nobel prizes in 1920. He contributed to literature the well-known Nernst Equation which is related to the calculation of thermodynamic potential between two electrodes in a fuel cell. He stated a theorem dealing with osmotic potential between the electrodes of a battery. He also had an important contribution to the field by first using zirconium as a solid electrolyte [1].

The first practical application of the fuel cell was attempted by William W. Jacques in 1896. He succeeded in obtaining a 1.5-kW high power fuel cell with a stack contained 100 tubular units. Emil Baur (1921) used the first molten carbonate fuel cell system and further on he employed solid oxide electrolytes under the condition of high temperature [1]. In 1932, a British engineer Sir Francis Thomas Bacon ignited the wick for the adaptation of the fuel cell to daily life applications. Finally in 1959, he was able to produce a 5-kW fuel cell stack (40 cells) with 60% energy efficiency with the support of the Marshall Aerospace company [1, 5]. Firstly, he carried out studies on alkaline fuel cells. The fuel cell with nickel electrodes that can work at high pressure (200 atm) was constructed by him. Pratt & Whitney Company patented the works in order to develop and use proper fuel cells to meet the needs of the Apollo spacecraft [1]. During 1956–59, a 6-kW fuel cell stack (40 cells) for forklifts and weldings is also among the works of Bacon [6].

Since 1950, the development of proton exchange membrane (PEM) fuel cells has accelerated with the establishment of companies such as Aerojet Company, General Electric (GE), National Carbon Company, the Patterson-Moos Division of the Universal Winding Company and Pittsburgh Consolidation Coal [7]. In 1950, the introduction of a polytetrafluoroethylene (PTFE) polymer, called Teflon, into fuel cells eliminated the difficulty of using liquid electrolytes in the fuel cells for daily applications and enabled the current state of the fuel cells to emerge [1]. Willard T. Grubb and Leonard Niedrach, who were the researchers of the GE Company, were also founders of today’s PEM fuel cell form. In 1955, Willard T. Grubb focused on the development of an ion exchange membrane which was made of polystyrene sulfate and suitable for working under the conditions of room temperature and atmospheric pressure; on the other hand, after 3 years, Leonard Niedrach succeeded in loading instead of installing platinum on the membrane. The criteria that Grubb considered when developing membranes were: permeability to solely one type of ion, negligible electrical conductivity, mechanical strength, area and thickness variability [1, 8].

The US National Aeronautics and Space Administration (NASA) announced the manned space program (Mercury & Gemini). It was aimed at flying the manned capsule to space powered via the battery in the scope of the Mercury program in the period 1958–63. In the second phase of the main program, which is Gemini (1962–66), the aim was to ensure that the manned capsule sent to space stayed in space for a longer period. This case required a better system than the existing batteries at the time, which would work in an isolated environment. At this point, NASA has given the GE Company an important role in developing fuel cells that they could use in their Gemini program. Gemini was modified to allow the spacecraft to remain for 2 weeks, and the third program, which is the Apollo Lunar-Landing Mission (1963–72), was created [7].

In 1959, Allis Chalmers acquired 15 kW power with a fuel cell system consisting of hydrogen-oxygen-fed bipolar porous electrodes coated with platinum and potassium hydroxide embedded in asbestos (as electrolyte) and adapted it to the tractor [1, 6]. Acid electrolyte fuel cells began to gain importance in the early 1960s. G. H. J. Broers and J. A. A. Ketelaar revealed the molten carbonate fuel cell that has the ability of working at high temperature up to 650°C and the different electrolyte structure which is made up of a mixture of lithium carbonate, sodium and/or potassium, impregnated on a magnesia sintered porous disk. In 1961, G.V. Elmore and H.A. Tanner introduced their new design, which came to be known then as the phosphoric acid fuel cell, and differentiated the electrolyte of this fuel cell by using the mixture of 35% phosphoric acid and 65% of silicon dust stuck to the Teflon. It was stated that the new fuel cell could be operable at 90 mA/cm² and 0.25 V for 6 months. In 1962, J. Weissbart and R. Ruka worked on the fuel cell which was operated at 1000°C and held conducting ceramic oxide impregnated zirconia as a solid electrolyte [1]. General Motors built a van powered by a 160-kW alkaline fuel cell developed by Union Carbide in 1967 [6]. Nafion membrane, which is still used as the indispensable electrolyte in PEM fuel cells, was produced by EI DuPont de Nemours and Company (DuPont) in 1968 and it is an excellent membrane in terms of chemical and mechanical durability for PEM fuel cells [7]. In 1970, studies on fuel cell technology mainly concentrated on increasing the electrode area and reducing the cost of catalyst [1]. Additionally, from this date on, alkaline fuel cells were launched by Siemens in order to be used in submarines [6].

In the 1980s, PTFE bonded gas diffusion electrodes were used in the EloFlux cell produced by Varta (Germany). During these years, intensive studies such as developing carbon-supported platinum catalysts, humidification of the gases, elevating differential pressure at the oxygen side, increasing the operating temperature, etc. were carried out to improve PEM fuel cell performance [6]. By the year 1990, methanol fuel cell was developed by the Jet Propulsion Laboratory of NASA in cooperation with the University of Southern California [1]. Perry Energy Systems and Ballard Power Systems respectively demonstrated the fuel cell powered passenger cars and buses in 1993 [5]. The world-renowned automobile companies (Honda, Hyundai, Peugeot, Toyota, Mitsubishi, Ford, etc.) have carried out intensive efforts to adapt fuel cell technology to vehicles, and for this purpose they had introduced many prototypes powering with hydrogen fuel cells in certain periods of time. After all these efforts, the production of FCX Clarity began in June 2008 as the first fuel cell vehicle manufactured in series for selling by leasing in the United States. Some of the examples of fuel cell vehicles in those years (2007 and 2008) are presented in Fig. 1.2.

Fig. 1.2 Fuel cell vehicles (2007 and 2008) [1].

Today, while the fuel cell market for passenger vehicles is growing, although not at the expected rate because of the economical considerations, fuel cell developments and projects for heavy duty vehicles are gaining more importance. On the side of passenger vehicles, Toyota Mirai and Hyundai NEXO are among the ones drawing attention. According to the annually released fuel cell industry review report of 2019 [9], the 10,000th Mirai left Toyota’s production line in September 2019. Toyota is increasing its production capacity to 30,000 in 2020 in line with the previous announcements. Toyota and Hyundai seem to be leading the FC vehicle market today, Honda being the third and following them. Daimler, the only other manufacturer with a commercial FCEV for today, also has very few vehicles on the road. In Europe, manufacturers seem to focus on delivering battery vehicles to avoid costly fines when CO2 emissions regulations tighten in 2021. Direct battery cars and fuel cell cars are competing in technology (not in the market for now), but many experts predict that in the long-term technological and theoretical advantages of fuel cells will be dominating the transportation sector. BMW also showed the iHydrogen NEXT concept car at the 2019 Frankfurt Motor Show. BMW is also planning a small series of FC-powered X5s by 2022, but does not expect commercialization until 2025. All these market views today show us that the industry of fuel cells is still in the baby steps period, although we are already talking about a billions of dollars industry. Although many scientists have been working in the field of fuel cell technology up to this time, it can be said that two important contributions to the development of today’s fuel cell technology have been made by Ostwald and Bacon respectively detailing the operation of fuel cells in theory and enabling the design of fuel cell systems in order to be used in everyday life applications in practice [1].

Developing technologies in which hydrogen is used as a fuel and meeting the energy demand with these technologies have gained increasing interest and the studies in this field have mediated the emergence of a concept called Hydrogen Economy. This phrase was used for the first time in the paper by Appleby in 1972. Cornell University organized a meeting on this concept in 1973. The first important name that comes to mind when hydrogen is mentioned is T. Nejat Veziroğlu. He has pioneered many hydrogen-related organizations in different countries of the world and arranged the first major meeting (World Hydrogen Energy Conference-WHEC) with 900 participants in Miami. The 22nd WHEC was hosted in Rio de Janeiro-Brazil in 2018 with 757 participants from 51 countries. Professor Veziroğlu is one of the scientists who played a major role in the worldwide appreciation of hydrogen energy. The establishment of the International Journal of Hydrogen Energy in 1974, now one of the leading journals in the field of hydrogen, is just one example of his far-sight in the field of hydrogen technologies [10].

1.2: Fundamentals of FC technology

Fuel cells come to the forefront in the alternative energy sector because, first of all, they promise and provide high energy conversion efficiency without damaging the environment. In fuel cells, energy loss is less than that of internal combustion engines because the chemical energy of the fuel is directly converted to electrical energy in these systems which contain no moving parts that may cause friction losses. Some fuel cell types with different specifications are available in the current fuel cell technology. These are demonstrated in Table 1.1. In addition to those given in Table 1.1, microbial and enzymatic fuel cells have been also developed as new kinds of fuel cells [2, 11]. Fuel cells are generally classified according to the type of electrolyte used in the system. Additionally, each of them has a different operating temperature, power output, energy efficiency and capacity to meet the requirements of any application that needs energy [12].

Table 1.1

The use of fuel cells as a power supplier also brings many other advantages besides the higher energy efficiency in comparison to the conventional internal combustion engine. The products released by electrochemical reactions are mostly environmentally friendly as they do not lead greenhouse gas emissions. If pure hydrogen is used, water is the only product. The products may change according to the fuel used. They work quietly since there are no moving mechanical parts, which is particularly preferred in defense and security-related applications. This property also makes the fuel cells easier to operate and the durability issues related to friction are no longer a problem to consider. The modularity of fuel cell systems allows us to achieve high power density without compromising energy efficiency even with small-sized systems. The dynamic load response characteristic is sensitive to any change on the system. Fuel cells can work in various power ranges (mW-MW) which vary according to the purpose of the application. Pure hydrogen gas in fuel cells, hydrogen produced by the reforming process from sources such as methanol, methane, propane, natural gas, hydrocarbons and also hydrogen coming from alcohols such as in liquid fuel cells could be used; therefore, this provides a great flexibility of utilization to these systems [12].

1.2.1: Basic operating principles of a fuel cell

A fuel cell is basically a voltaic or galvanic electrochemical cell which converts the chemical energy into electrical energy directly electrochemically. So this is a typical redox reaction in which oxidation occurs at the anode and reduction occurs at the cathode by basic definition. A polymer electrolyte membrane separates the anode and cathode parts and allows only the ions (protons specifically for H2 acidic type fuel cells) from the anode to the cathode for the completion of the circuit. Electrons produced at the anode as a result of the oxidation of fuel flows from the anode to the cathode by electrically conductive parts. They take their part in the reduction of the oxidant (O2 mostly) by combining with the protons arriving at the cathode. These half reactions and the overall reaction are given below. The simplified schematic of the single cell for an H2 PEMFC (Polymer Electrolyte Membrane Fuel Cell) is also shown in Fig. 1.3.

   (1.1)

   (1.2)

   (1.3)

Fig. 1.3 A simplified single PEM fuel cell schematic [13].

The potentials given for the reactions are standard reduction potentials (vs SHE) and cell potential is calculated by the equation: E⁰cell = E⁰cathode − E⁰anode = 1.229 − 0 = 1.229 V. Therefore, the standard potential at 25°C and atmospheric conditions is approximately 1.23 V for an H2/O2 PEMFC, similar to the conventional batteries, since fuel cells are also galvanic cells in which the electrochemical reaction occurs spontaneously, anode is a negative (−) pole, cathode is a positive (+) pole. One may imagine this sign convention since the negative charges (electrons) are produced at the anode spontaneously