Fundamentals of Hydrogen Production and Utilization in Fuel Cell Systems

By Seyed Ehsan Hosseini

Fundamentals of Hydrogen Production and Utilization in Fuel Cell Systems provides a comprehensive overview of the complex and interdisciplinary issues surrounding the use of hydrogen fuel cells in the global transportation system. With a particular emphasis on the commercialization and implementation of hydrogen fuel cells, the book deals with production, utilization, storage and safety, and addresses the application of fuel cells in the road, rail, maritime and aviation sectors. For each sector, the book discusses the fundamentals of fuel cells, the current technical, environmental, safety, and economic performance, the main barriers to implementation and how to address themThis book is an invaluable reference for researchers, graduate students and industry engineers across the fuel cells and transportation sector, but is also ideal for policymakers involved in the energy transition.

• Offers the first account of hydrogen fuel cell systems that considers every sector: road, rail, maritime and aviation
• Focuses on the practical utilization and implementation of hydrogen fuel cells in transportation systems
• Summarizes the latest research and developments in hydrogen fuel cell powered transportation

• Language: English
• Publisher: Elsevier Science
• Release date: Jul 26, 2023
• ISBN: 9780323884228

Seyed Ehsan Hosseini

Dr. Seyed Ehsan Hosseini PhD is an Asst. Professor in the Department of Mechanical Engineering at Arkansas Tech University (ATU). He established Combustion and Sustainable Energy Laboratory (ComSEL) at ATU working on several projects such as Hydrogen production and utilization, Fuel cell, Flameless combustion, small-scale combustion, Trap Vortex Combustion (TVC) and application of Phase Change Material (PCM) in the refrigeration and electronic systems. Before joining Arkansas Tech University, Dr. Hosseini was a postdoctoral researcher fellow in Combustion and Solar Energy Laboratory with the Department of Mechanical Engineering at San Diego State University

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Front Cover for Fundamentals of Hydrogen Production and Utilization in Fuel Cell Systems - 1st edition - by Seyed Ehsan Hosseini

Fundamentals of Hydrogen Production and Utilization in Fuel Cell Systems

Seyed Ehsan Hosseini

Department of Mechanical Engineering, Arkansas Tech University, Russellville, AR, United States

Table of Contents

Cover image

Title page

Copyright

Dedication

Preface

Acknowledgments

Chapter 1. Hydrogen, a green energy carrier

Abstract

Abbreviation

1.1 Global energy demand and environmental issues

1.2 Hydrogen, a green energy carrier

1.3 Public acceptance of hydrogen as the fuel of the future

1.4 Summary

1.5 Review questions

References

Chapter 2. Hydrogen fuel production methods

Abstract

2.1 Introduction

2.2 Hydrocarbon reforming

2.3 Hydrogen from hydrocarbon pyrolysis

2.4 Summary

References

Chapter 3. Hydrogen production methods based on the primary energy sources

Abstract

Abbreviations

3.1 Introduction

3.2 Hydrogen colors

3.3 Pink hydrogen (nuclear hydrogen)

3.4 Biomass to hydrogen (green hydrogen)

3.5 Coal to hydrogen (black/brown hydrogen)

3.6 Solar to hydrogen (yellow hydrogen)

3.7 Wind to hydrogen

3.8 Geothermal-based hydrogen production

3.9 Hydropower-to-hydrogen (green hydrogen)

3.10 Tidal power to hydrogen

3.11 Summary

Review questions

References

Chapter 4. Electrochemical hydrogen production

Abstract

4.1 Introduction

4.2 Fundamentals of electrochemical processes

4.3 Thermodynamics of the electrochemical process

4.4 Electrolysis technologies

4.5 Principles of alkaline water electrolyzers

4.6 Solid oxide steam electrolyzer

4.7 Energy and exergy efficiency of an electrolyzer

4.8 Summary

References

Chapter 5. Hydrogen storage and delivery challenges

Abstract

5.1 Introduction

5.2 Hydrogen storage principles

5.3 Hydrogen delivery principles

5.4 Hydrogen systems risk and reliability issues

5.5 Summary

Review questions

References

Chapter 6. Fundamentals of hydrogen fuel cell systems

Abstract

6.1 Introduction (hydrogen fuel cell background)

6.2 Environmental and safety concerns associated with fuel cell system applications

6.3 Fuel cell function

6.4 Key parameters of fuel cell systems

6.5 Fuel cell stack design

6.6 Challenges in hydrogen fuel cell technologies and their advantages

6.7 Hydrogen fuel cell open circuit voltage

6.8 Hydrogen fuel cell efficiency

6.9 Summary

6.10 Questions

6.11 Review questions

References

Chapter 7. Hydrogen utilization in transportation systems

Abstract

Abbreviations

Nomenclature

7.1 Introduction

7.2 Hydrogen fuel cell structure and technical challenges in vehicles

7.3 Hydrogen-fueled trains/locomotives

7.4 Hydrogen fuel cell–powered systems in aviation

7.5 Hydrogen fuel cell for maritime applications

7.6 Summary

Review questions

References

Chapter 8. Hydrogen economy and transition to hydrogen energy

Abstract

8.1 Introduction

8.2 Geopolitical implications of hydrogen trade

8.3 Hydrogen roadmaps and strategies

8.4 Summary

Review questions

References

Index

Copyright

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Notices

Knowledge and best practice in this field are constantly changing. As new research and experience broaden our understanding, changes in research methods, professional practices, or medical treatment may become necessary.

Practitioners and researchers must always rely on their own experience and knowledge in evaluating and using any information, methods, compounds, or experiments described herein. In using such information or methods they should be mindful of their own safety and the safety of others, including parties for whom they have a professional responsibility.

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Dedication

Seyed Ehsan Hosseini

To my beloved mother, wife, and son, Sam. Your support and encouragement have been instrumental in helping me to achieve my goals. This book is dedicated to you as a tribute to your unwavering love, guidance, and inspiration.

I would also like to dedicate this book to my late father, who taught me to be an independent and determined person. I am forever grateful for the love and wisdom you shared with me during your time with us.

Preface

Seyed Ehsan Hosseini

Hydrogen has long been recognized as a promising clean energy carrier due to its high energy density and clean combustion products. Fuel cell systems are one of the most promising technologies for utilizing hydrogen as a sustainable energy source. In recent years, there has been a growing interest in hydrogen production and utilization in fuel cell systems as the need for clean energy sources continues to increase.

This book is aimed at providing a comprehensive overview of the fundamentals of hydrogen production and utilization in fuel cell systems. It covers the basics of hydrogen production, including steam methane reforming, electrolysis, and biomass gasification, as well as the different types of fuel cells, such as proton-exchange membrane fuel cells and solid oxide fuel cells.

The book also explores the challenges and opportunities in the production, storage, and distribution of hydrogen, as well as the economic and environmental benefits of utilizing hydrogen as an energy carrier. It is designed to be a valuable resource for students, researchers, and professionals who are interested in the field of hydrogen energy and fuel cell systems.

The author has made a significant effort to provide a balanced and objective view of the various aspects of hydrogen production and utilization in fuel cell systems. He has drawn upon his experience and knowledge to create a comprehensive and up-to-date resource that will be of great value to anyone interested in this exciting field.

The author hopes that this book will serve as a useful reference for those who are interested in learning more about the fundamentals of hydrogen production and utilization in fuel cell systems. He also hopes that it will inspire new ideas and innovations in the field as we work together to create a cleaner and more sustainable energy future.

Acknowledgments

I would like to express my deepest gratitude to the higher administration of Arkansas Tech University (ATU) for their support and encouragement throughout the research and writing of this book. Their commitment to fostering innovation and advancing knowledge has been instrumental in making this project a reality.

I would also like to extend my sincere thanks to my colleagues and students at the Department of Mechanical Engineering at ATU. Their insights, feedback, and support have been invaluable in helping me to refine my ideas and produce work that is both informative and accessible.

Finally, I would like to express my gratitude to my family and loved ones for their support and encouragement throughout this endeavor. Their love and encouragement have been a constant source of motivation, and I am forever grateful for their presence in my life.

Chapter 1

Hydrogen, a green energy carrier

Abstract

In this chapter, the significant challenges in global energy demand and environmental issues were analyzed. The effects of greenhouse gases (GHGs) on the environment, global warming, and climate change and using renewable and sustainable energy (such as wind, solar, geothermal, tidal power, and hydropower) as a solution for GHGs emission reduction were reviewed. The opportunities offered by hydrogen fuel as a green energy carrier were developed, and various methods of green hydrogen production were explained. Hydrogen properties (physical and chemical) and the safety issues during hydrogen production, storage, delivery, and utilization were scrutinized. The role of hydrogen in the policymakers' attitude about the energy mix in the world was explained, and it was highlighted that hydrogen fuel will play a crucial role in the energy mix of the world by the year 2050. A summary of the hydrogen supply chain and research about public acceptance of hydrogen as the fuel of the future was given.

Keywords

Hydrogen production; greenhouse gases; renewable energy; sustainability; the fuel of the future

Abbreviation

CH2 Compressed hydrogen

FC Fuel cell

GHG Greenhouse gas

HHV Higher heating value

ICE Internal combustion engine

LH2 Liquid hydrogen

LHV Lower heating value

MIE Minimum ignition energy

NDC Nationally determined contributions

NFPA National Fire Protection Association

NG Natural gas

OECD Organization for Economic Cooperation and Development

PEMFC Polymer exchange membrane fuel cell

PV Photovoltaic

UV Ultraviolet

1.1 Global energy demand and environmental issues

In recent decades energy as one of the pillars of industrialization has emerged as a controversial issue globally. Using the predominant fossil fuels energy source has increased greenhouse gas (GHG) emissions and global warming. Expediting global environmental dilemmas needs an international consensus to balance energy security, economic growth, and environmental protection. In this context, energy, economy, and environmental policies have been integrated into several countries to address national and global issues. Several countries have understood that energy and environmental issues are two sides of the economy coin. Sustainable growth is expected by incorporating environmental standpoints in deploying energy technologies and vice versa. The energy demand comes from various sources, including nonrenewables, such as oil, natural gas (NG), coal, uranium, and renewables, such as solar, wind, geothermal, tidal, and hydropower (Fig. 1.1) [1].

Figure 1.1 Global growth energy consumption by source 1990–2040.

Solar power is energy from the sun that is converted to electrical power or thermal energy. Solar is the most abundant renewable energy available for clean power generation. Solar technologies can harness this energy for various applications, including water distillation systems, providing light, generating electricity or a comfortable interior environment, and heating water for domestic, commercial, or industrial use. Solar energy can be harnessed by photovoltaic (PV) systems, concentrated solar systems, and solar heating and cooling techniques. The PV systems could surge ahead of NG and coal and become the largest source of installed global power capacity in the next two decades, significantly reducing toxic gas production in the environment.

The electrical power is also generated via air flows that occur naturally in the earth’s atmosphere. The so-called wind power is generated using modern wind turbines to capture kinetic energy from the wind and generate electricity. Unlike conventional energy sources, wind power significantly decreases carbon emissions, saves billions of gallons of crude oil annually, and cuts pollution that makes smog and triggers various diseases.

Geothermal energy is another clean source of energy that comes from the subsurface of the earth. To generate electrical power from geothermal energy, wells are dug a mile deep into underground reservoirs to access the steam and hot water, which can then be employed to drive steam turbines connected to electricity generators. Modern closed-loop geothermal power plants generate electricity consistently, emitting no GHGs, running 24 hours per day, seven days per week, regardless of weather conditions.

It is estimated that world energy consumption will increase by 48% in 2040 compared to 2012, in which most of this growth is due to the countries not listed in the Organization for Economic Cooperation and Development (OECD), including China and India. OECD is an international organization with 36 members that attempts to build better conditions for better lives. The OECD aims to regulate policies that foster equality, prosperity, opportunity, and well-being for all people. The environmental rules to decrease CO2 emissions and ensure sustainable development in the power generation sectors coincides with a looming new investment cycle in energy generation in most OECD countries. The OECD has regulated a firm framework for monitoring progress toward green development, including a set of indicators. The essential indicators related to the energy sectors are the items that measure CO2 emission or intensity of energy generation and consumption, energy efficiency, clean energy production research and development, as well as measures of energy-related subsidies and taxes [2].

Renewables and nuclear power, respectively, by an average 2.6% and 2.3% growth per year through 2040, are the fastest-growing energy sources over this period. Although renewables are projected to grow faster than fossil fuels, nonrenewables still account for more than 75% of world energy consumption by 2040. Among the nonrenewables, NG, which has lower carbon intensity than petroleum and coal, has the fastest growth in this period with approximately 1.9% annual growth. In this outlook, the liquid fossil fuels share of world marketed energy consumption is anticipated to mitigate from 33% in 2012 to 30% in 2040, although it will remain the largest energy source. During this period, coal is the slowest-growing energy source increasing by 0.6% annually through 2040. China, the United States, and India are the most coal consumers, which together are considered for more than 70% of global coal consumption. Since 2010, approximately one-third of the total US coal power plants (102 GW) have been terminated, and it is projected that 17 GW more will be retired by 2025. Thanks to the support of states’ policies and federal tax credits, renewables could completely retire coal-fired power generation by 2030 in the post-COVID-19 era [3]. On the other hand, it is expected that global crude oil and NG reservoirs will run out in less than 60 years, and it seems renewables will be the most important source of energy in the next century.

Carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and fluorinated gases (F-gases) are the most abundant GHGs in the atmosphere (Fig. 1.2) [1].

Figure 1.2 Global GHG emissions by gas.

CO2 is an essential gas within the context of GHG emissions. CO2 is the most abundant gas in the atmosphere and has high calorific power. Approximately 30 billion tons of CO2 are emitted annually due to human activities, essentially by fossil fuel and wood burning. Although the preventive role of CO2 for the earth from space-frozen balls is inevitable, the rising rate of droughts, storms and floods, and global warming are the substantial consequences of high rates of CO2 production. The GHGs can trap the heat radiation from the earth’s surface in the atmosphere, and global warming is the direct consequence of the GHGs (Fig. 1.3).

Figure 1.3 Schematic of GHG effect.

The period that a kilogram of gas remains in the atmosphere before removing it by a chemical reaction is the atmospheric lifetime of that gas. The lifetimes of CH4 and CO2 are approximately 12 and 200 years, respectively [4]. The anthropogenic CO2 emission has risen sharply during the last 50 years, and because of that, the global temperature has recently increased by 0.3°C–0.6°C. Therefore, sea levels have risen 10–20 cm during the last century due to the melting of the glaciers and polar ice caps.

The CO2 levels, which were 200 parts per million (ppm) during the ice ages, raised to 280 ppm during the warm interglacial periods, and due to anthropogenic activities, its level surpassed 400 ppm in 2013 (Fig. 1.4) [5]. This significant increase in CO2 level indicates a special constant relationship with fossil-fuel consumption in which it is premised that approximately 60% of fossil-fuel emissions stay in the air.

Figure 1.4 CO2 levels in the world.

Two primary anthropogenic sources of GHG emissions are oil and gas-fired power plants and road transportation, including road, rail, sea, and air transport. The other significant contributor to GHG emissions is fossil fuel combustion in manufacturing industries. Moreover, the energy-used sectors, such as the iron and steel manufacturers or chemical factories, and households in the form of fuel combustion for domestic heating are the primary sources of GHG emissions (Fig. 1.5) [1].

Figure 1.5 Global GHG emissions by economic sector.

If fossil fuel consumption continues at the current rate, the CO2 level will exceed 1500 ppm over the next few centuries. In that circumstance, the atmosphere would not rebound even tens of thousands of years into the future. Energy and environmental policies play a crucial role in the future of the climate and planet.

Besides water, food, and health, the United Nations mentioned global warming as one of the crucial challenges the world faces [6]. In 2015 representatives of almost 200 countries gathered in Paris to discuss this essential issue and find a solution to global warming. Based on the Paris Agreement, decarbonization of the energy systems is vital to limit global temperature rises to within 2°C of preindustrial levels and to pursue efforts to limit the increase to 1.5°C. To limit global warming to 1.5°C, the net-zero CO2 emissions target must be achieved by the year 2050, which requires decarbonization of fossil fuel and electricity, energy demand reduction, and greater electrification and complementary levels of CO2 removal activities. Although the political situation and the insufficient nationally determined contributions (NDCs) reports achieve ambitious landmark agreements blurry [7], shifting from fossil fuel-based energy generation to renewables is still the best way to reduce GHGs and control global warming. To make such a transition and meet the Paris Agreement, global investment in renewables and related technologies, such as battery storage and networks, must rise above current commitment levels [8]. In this context, the great potential of hydrogen to play a crucial role in meeting energy storage and balancing demands has emerged hydrogen economy through several decarbonization policies to decrease fossil fuel reliance.

Renewables comprise a heterogeneous class of technologies for thermal or mechanical energy production, electrical power generation, or producing fuels as an energy carrier to fulfill multiple energy service needs. Some renewable energy technologies are technically mature and being developed at a notable scale, and some are in an earlier phase of maturity and commercial development. Energy conversion of some renewables is done at the point of use in urban or rural environments (decentralized). Some renewables should convert to appropriate energy at a center and distribute by an extensive energy network (centralized). As a widely used renewable energy, biomass can be produced from various feedstocks, such as agricultural, forest, livestock residues, crops, organic waste materials and sewage systems, and municipal solid waste. The biomass feedstock can be directly used to generate electrical power or heat or can be converted to hydrogen or other gaseous, solid, and liquid fuels. The range of biomass and related technologies is broad with various technical maturity. For instance, lignocellulose-based transport fuels and biomass gasification integrated into a combined cycle power generation system are two technologies at a precommercial phase. However, hydrogen production from algae and other biological conversion systems is still at the research and development (R&D) stage. It is possible to convert biomass to a useful power in a centralized system (e.g., landfill gas to electrical energy) or employ it traditionally decentralized, such as the current widespread application of biomass in developing countries.

1.2 Hydrogen, a green energy carrier

The world is searching for sources of energy to substitute fossil fuels. With the rapid development in technology, the availability of alternative energy sources, such as solar and wind energy, geothermal, tidal power, nuclear, and hydropower, has increased. The main criteria for an ideal fuel are cleanliness, inexhaustibility, convince, and independence from foreign control. Hydrogen fuel has indicated all these characteristics and is promoted worldwide as an environmentally friendly replacement for fossil fuels in the industrial and transportation sectors. Hydrogen fuel is considered the most promising energy carrier for generalized use in the future as it is a renewable and sustainable fuel, low-polluting, energy-efficient, and versatile. Hydrogen is a high-quality fuel which can be employed with high efficiency and near-zero or zero emissions at the point of use.

In The Mysterious Island, a novel written by Jules Verne in 1874, the author saw hydrogen as the fuel of the future in which hydrogen was produced by water dissociation via electrolysis and would replace coal, the primary energy source at that time.

For decades hydrogen has been employed in industrial applications, such as a coolant in power plant generators, petroleum refining, aerospace applications, pharmaceuticals, welding, annealing and heat-treating metals, glass purification, fertilizer production, semiconductor manufacturing, and for hydrogenation of unsaturated fatty acids in vegetable oil.

Hydrogen is mixed with inert gases to achieve a reducing atmosphere needed for many processes in the metallurgical industry, such as heat treating steel and welding. It is used in sintering and copper brazing, annealing stainless steel alloys, and magnetic steel alloys. Hydrogen also can be produced by ammonia dissociation at about 982°C with the aid of a catalyst - which results in a mix of 25% mononuclear nitrogen (N rather than N2) and 75% hydrogen. The mix is a protective atmosphere for applications such as bright or brazing annealing.

In refineries, hydrogen is used to remove crude oil sulfur. Hydrogen is catalytically combined with different intermediate processing streams and is applied with catalytic cracking operations to convert unsaturated and heavy compounds to lighter and more stable ones. Hydrogen is also used in the pharmaceutical industry to manufacture vitamins and other pharmaceutical products. In glass and ceramics industries, hydrogen is required to prevent oxidation of the large tin bath. In the food and beverages production, hydrogen is used to hydrogenate unsaturated fatty acids in animal and vegetable oils, making solid fats for margarine and other food products. In the electronic industry, in the manufacture of semiconducting layers in integrated circuits, hydrogen is applied as a carrier gas for such active trace elements as arsine and phosphine. Nearly all of the produced hydrogen in the United States is employed by the industry for treating metals, refining petroleum, producing fertilizer, and processing foods.

For the past 100 years, hydrogen has been employed as a common fuel in several applications due to its high energy-to-weight ratio. The balloon named hydrogen gas aerostat was one of the first hydrogen-fueled systems made by Jacques Charles and Nicolas Robert in the eighteenth century in Paris, which operated for about 45 minutes at a distance of about 21 km. The first automobile powered by an internal combustion engine (ICE) was invented by Francoise Isaac de Rivaz from Switzerland in January 1807, in which hydrogen was employed as the fuel. In 1954 the first experimental studies of liquid hydrogen (LH2) for propulsion were commenced in the United States. After that, in the 1960s, hydrogen was applied in airships, launching systems, and nuclear submarines. In the 1970s, the interest in alternative energy and technologies intensified because of increased fossil fuel prices and environmental issues. Solar energy concepts were deployed, with hydrogen as the primary energy carrier. At the beginning of the 21st century, the discussions on hydrogen fuel intensified to make the hydrogen fuel dream come true [9].

The deployment of fuel cell (FC) systems opened a new window to hydrogen fuel success in the transportation sector. Currently, hydrogen-powered engines based on polymer exchange membrane fuel cell have been used worldwide. The main pros of the FC systems are high efficiency in well-to-wheel assessment, energy-efficient drive train, and silent mode of operation. As a fuel, hydrogen yields significantly higher energy per unit weight than other fuels, such as kerosene, diesel, petrol, and methanol. Therefore several new markets have emerged for automobiles, buses, other transportation vehicles, and industrial trucks. To support these vehicles, several indoor and outdoor hydrogen refueling stations have been built. An FC is a device that uses oxygen from the air and hydrogen in an electrochemical reaction to generate electricity to power an electric motor and propel a vehicle. The FCs emit only water and heat without producing any air pollutants or GHGs, and their efficiency is twice that of IC engines. Besides mobile applications, hydrogen FC could be employed in stationary systems, such as power generation for telecommunications in remote locations, uninterruptible power supply for data centers and hospitals, and backup power generation for regional emergency shelters.

Hydrogen is not a source of energy, and it is considered a versatile energy carrier. In other words, hydrogen, as the most common element globally, is not available in nature in its pure form. It should be produced through a chemical, thermal, or electrical process or a combination of these processes (Fig. 1.6) [10].

Figure 1.6 Processes for hydrogen production.

Hydrogen can be generated from almost all energy resources, and today, the most produced hydrogen is used in chemical and oil refining processes. This hydrogen demand is supplied by fossil fuels, in which 6% of global NG and 2% of coal consumption are dedicated to hydrogen production, being responsible for 830 MtCO2 of CO2 emissions per annum. Currently the primary source of hydrogen production is the NG (around 70 million tons). Fig. 1.7 shows the global demand and sources of hydrogen production [11].

Figure 1.7 Global demand and sources of hydrogen production.

Although the electrolysis process currently produces a small portion of hydrogen demand, this technology has been significantly noticed by the development of renewable energy. The production of hydrogen from surplus electricity could be an option to enhance the flexibility of renewable energy systems.

Hydrogen is considered the fuel of the future to be used in transportation systems and industrial processes to improve air quality in cities and facilitate energy security. In fact, hydrogen fuel capabilities to become a part of modern industry were found over 200 years ago when the first ICEs were powered by hydrogen, and it was anticipated that pretty soon, hydrogen would play a significant role in clean transportation, buildings, and power generation.

As an attractive energy carrier, hydrogen can be generated from fossil fuels, alternative fuels, and electricity and water. Electrolysis’s required electrical power may eventually come from renewables, such as wind, solar, geothermal, or tidal power. Hence, hydrogen could be considered a crucial link between renewables’ physical energy to chemical energy carriers. Most renewables are subjected to weather circumstances and, therefore, to the variability of electrical power generation. Consequently, a gap between power generation from renewables and its consumption exists, which could be exacerbated in the future. As a result, it is imperative to store unused electrical power to employ it in high electrical demand moments or use it in another form of energy. The direct storage of renewable electricity using chemical batteries has widely been applied to reserve electrical power. However, their limited capacity and lifetime and their high cost have confined their applications. Power-to-gas is an indirect method of storing renewable electricity, attracting attention using highly efficient electrolyzers to produce hydrogen fuel [12]. The stored hydrogen can be converted to electrical power using a gas turbine or FC system or utilized in ICEs. In addition to hydrogen production and its utilization, which have attracted the most significant attention in recent years, the hydrogen economy (Fig. 1.8) is another substantial aspect of the hydrogen era, which includes packing, transporting, storing, and transferring the generated hydrogen from production to final use.

Figure 1.8 Principles of the hydrogen economy.

Hydrogen could compete with conventional fuels if it is clarified how much energy is required during hydrogen production, compression, liquefaction, storage, and transportation. So many concerns should be addressed before hydrogen can serve as a worldwide energy medium. The maturity of hydrogen utilization technologies, their cost, and safety are essential issues in the hydrogen economy. Hydrogen fuel utopia can become true if the consumed energy to make and deliver hydrogen and its utilization technologies for useful power generation become affordable.

1.2.1 Hydrogen properties

1.2.1.1 Hydrogen physical properties

The most common isotope of hydrogen includes only one electron and one proton. At the standard conditions (T=298 K, P=1 bar), hydrogen exists in a gaseous form. As the lightest element, hydrogen is a colorless, odorless, tasteless, nonpoisonous, and no-toxic gas that is lighter than air (at standard conditions, the density of hydrogen is 0.08988 grams per liter) and diffuses faster than any other gas. Hydrogen is not a corrosive gas. However, it can embrittle¹ some metals (i.e., cause substantial deterioration of the metal’s mechanical properties).

Hydrogen could be condensed to liquid at −253°C and solid at −259°C. The electrical conductivity of the solid metallic hydrogen is greater than any other solid element. The heat capacity of hydrogen gas is one of the highest among gaseous (14.4 kJ/kg K). The hydrogen solubility in metals is extremely high, and the adsorption of hydrogen in steel may pose embrittlement that may lead to the failure of equipment.

Hydrogen is 14 times lighter than air and approximately 57 times lighter than gasoline (Fig. 1.9), which means it will be immediately dispersed in an outside environment, which can be considered a safety advantage of hydrogen fuel in an open environment [13].

Figure 1.9 Relative some fuels vapor density.

Propane and NG are also odorless; however, a sulfur-containing odorant is added to them in the industry to make them detectable to the people. Since there are no known odorants that adequately light to travel with hydrogen fuel at the same dispersion rate, odorants are not used with hydrogen. Moreover, the current odorants can contaminate FC systems which are essential equipment for converting the chemical energy of hydrogen to electrical power.

As the simplest element in the universe, hydrogen represents 75 wt.% or 90 vol.% of all matter.

Among conventional fuels, hydrogen has the highest energy content, which is approximately about three times gasoline’s energy content; however, the energy density per volume of hydrogen is quite low at standard conditions. In other words, hydrogen has a high energy content by weight but not by volume, which causes some challenges for its storage. The volumetric energy density of hydrogen can be increased by its storage at high pressures or low temperatures as a liquid. Table 1.1 summarizes the physical properties of hydrogen [14,15].

Table 1.1

1.2.1.2 Hydrogen chemical properties

Hydrogen is relatively nonreactive at ordinary temperatures unless it is activated in some manner. The chemical reactivity of hydrogen atoms at higher temperatures is very high; hence hydrogen is not found chemically free in nature as it is mostly bound to either carbon or oxygen atoms. Therefore energy expenditure is required to produce hydrogen from natural compounds, and because of that hydrogen is considered an energy carrier.

To dissociate hydrogen molecules very high temperature is required. For instance, even at 5000 K, approximately 5% of hydrogen remains undissociated.

Even at room temperature, atomic hydrogen is a powerful reducing element. For instance, it reacts with the chlorides and oxides of metals, such as copper and silver, and makes free metals. Some salts, such as potassium, sodium, and nitrates, are reduced to the metallic state by hydrogen. Hydrogen could react with metal and nonmetal elements to yield hydrides, such as H2S or NH3. Atomic hydrogen reacts with organic compounds to yield a complex mixture of products; for instance, atomic hydrogen reaction with ethylene produces C2H6 and C4H10. Reacting with oxygen, atomic hydrogen produces peroxide (H2O2).

Hydrogen intensely reacts with halogens (e.g., chlorine and fluorine), oxidizers, such as nitrous oxide, and unsaturated hydrocarbons (e.g., acetylene) with exothermic heat. The product of hydrogen reaction with oxygen either in an electrolyzer or in a combustion process is water vapor. At room temperature, the reaction of hydrogen and oxygen is immeasurably slow; however, an electric spark or a catalyst, such as platinum, can significantly accelerate the reaction.

The hydrogen’s lower heating value (LHV) is 120 MJ/kg, corresponding to 33.3 kWh/kg, and the higher heating value (HHV) of hydrogen is 142 MJ/kg, corresponding to 39.4 kWh/kg. HHV is the heat of hydrogen combustion, assuming that all the water in the products has condensed to liquid, while LHV results from hydrogen combustion when none of the water is considered to condense. The difference between the HHV and LHV is 44.01 kJ/mol due to the molar enthalpy of water vaporization. Compared to gasoline, with an ignition temperature of about 501 K, the ignition temperature of hydrogen is high (approximately 858 K), and the energy-to-weight ratio of hydrogen is about three times more than kerosene, diesel, and gasoline. Ignition of hydrogen is performed easily with a wide range of mixtures of air in comparison to any other fuel. The flammability range of hydrogen is between 4 and 75 vol.% in air and 4–95 vol.% in pure oxygen, and the ability of its detonation is between 11 and 59 vol.% in the air [16]. The optimum combustion condition for hydrogen is a 29% hydrogen-to-air volume ratio in which the needed energy to ignite the mixture is much lower than the required energy for other common fuels.

Table 1.2 summarizes the energy density and flammability of hydrogen compared to the other fuels [17]. Table 1.3 indicates hydrogen’s selected chemical, thermo-physical, and combustion properties compared to the other popular fuels [15].

Table 1.2

Table 1.3

NTP, Normal temperature and pressure.

1.2.2 Hydrogen safety

Safety is one of the substantial issues in the public use of hydrogen as it does not have a good reputation due to some unfortunate accidents during history. The main hazard of hydrogen fuel is its leakage which increases the possibility of making fire during hydrogen production, storage, transmission, and utilization (as in-home use or vehicle fuel).

Since hydrogen is known as the fuel of the future, its widespread utilization will bring incidents in production, storage, transportation, and utilization steps [18]. The large-scale hydrogen utilization will undoubtedly get many people in touch with hydrogen technologies; however, hydrogen engineering standards are not everywhere compared to the high level of present-day petrochemical complexes. Hydrogen as an energy carrier is required not only in industrial sectors but also in densely populated regions, and consequently, people may become hurt in the incidents. On the other hand, a large-scale incident with fatalities can throw the hydrogen fuel scenario backward for years.

To adequately control the risks, a reliable risk analysis is required to improve operational safety by designing and installing preventive and protective measures which are suitable, economical, and embodied by standards and codes. Moreover, it could help land-use planning, licensing of installations, and emergency planning, the latter with respect to self-rescue and impressive development of emergency response units [19].

Safety engineers, designers, technical staff at refueling stations and maintenance workshops, and first responders should be professionally trained to deal with high-pressure hydrogen systems (up to 100 MPa) and liquid hydrogen (temperatures down to –253°C) in confined and open spaces.

Associated risks and hazards for hydrogen-powered vehicles should be determined and interpreted professionally with complete comprehension of consequences by all stakeholders, from system designers to regulators to users [20].

In general, hydrogen fuel risks are characterized by chemical, physical, and physiological hazards.

• Chemical hazard: The air–hydrogen mixture is extremely explosive and can burn or explode quickly. Flammability limits depend on temperature and pressure diluents, ignition energy, and the size and configuration of equipment. A shock wave can detonate hydrogen gaseous or LH2 or its solid phase with oxygen [21]. The required ignition energy is minuscule (0.02 m J); therefore, the heating and electrical equipment and open flames should be safely isolated in the systems containing hydrogen.

• Physical (embrittlement and component failures): Embrittlement degrades metals’ mechanical properties used to store hydrogen, which fails the tank and causes hydrogen leakage. Some parameters, such as the purity of the employed metal and its surface condition, the exposure time to hydrogen and ambient pressure, and temperature, affect this failure. The maximum hydrogen embrittlement (HE) is at temperatures between 200 and 300 K, controlled by oxide coating, removing stress concentrations additives to hydrogen and alloy selection. At low temperatures, a transition from ductile-to-brittle plus elastic and plastic alter occurs because of the crystalline structure’s phase alteration. The thermal contraction coefficients should be considered to prevent hydrogen leakage due to dimension alteration at cryogenic temperature. At LH2 temperature (about 20 K), metals contraction is less than 1% compared to the