Volume 4 fuel cells and hydrogen technology 4 01 – preface and context to hydrogen and fuel cells

Volume 4 fuel cells and hydrogen technology 4 01 – preface and context to hydrogen and fuel cells Volume 4 fuel cells and hydrogen technology 4 01 – preface and context to hydrogen and fuel cells Volume 4 fuel cells and hydrogen technology 4 01 – preface and context to hydrogen and fuel cells Volume 4 fuel cells and hydrogen technology 4 01 – preface and context to hydrogen and fuel cells Volume 4 fuel cells and hydrogen technology 4 01 – preface and context to hydrogen and fuel cells

4.01 Preface and Context to Hydrogen and Fuel Cells

AJ Cruden, University of Strathclyde, Glasgow, UK

© 2012 Elsevier Ltd

4.01.2.2 Chapter 4.02: Current Perspective on Hydrogen and Fuel Cells

4.01.2.4 Chapter 4.04: Hydrogen Safety Engineering: The State-of-the-Art and Future Progress

4.01.2.6 Chapter 4.06: Hydrogen Storage: Liquid and Chemical

4.01.2.7 Chapter 4.07: Alkaline Fuel Cells: Theory and Application

4.01.2.8 Chapter 4.08: PEM Fuel Cells: Applications

4.01.2.9 Chapter 4.09: Molten Carbonate Fuel Cells: Theory and Application

4.01.2.10 Chapter 4.10: Solid Oxide Fuel Cells: Theory and Materials

4.01.2.11 Chapter 4.11: Biological and Microbial Fuel Cells

4.01.2.12 Chapter 4.12: Hydrogen and Fuel Cells in Transport

4.01.2.13 Chapter 4.13: H2 and Fuel Cells as Controlled Renewables: FC Power Electronics

4.01.2.14 Chapter 4.14: Future Perspective on Hydrogen and Fuel Cells

4.01.3.1 Flow Cells or Regenerative Fuel Cells

4.01.3.3 Hydrogen Demonstration Units – State of the Art

References

4.01.1 Introduction

Hydrogen is the most abundant material in the Universe, forming over 75% of known matter; however, it does not commonly exist

on Earth in its natural form, due to its highly reactive nature, but within other compounds, most notably water and hydrocarbons The discovery of hydrogen gas is credited to the famous English philosopher Henry Cavendish (although he was actually born in Nice, France!) who, in 1766, wrote a seminal paper entitled ‘Experiments on Factitious Airs’ [1] (Figure 1) after experiments dissolving different metals (such as zinc) in acidic solutions

These experiments produced a gas, the ‘factitious air’ that “takes fire, and goes off with an explosion” (see a further exert from the Cavendish paper of 1766 shown in Figure 2), which is now a common high-school test for hydrogen gas – set fire to it and it goes ‘pop’! Cavendish went on to determine that this gas was significantly lighter than air and, although credited with isolating this new inflammable gas, it was another Frenchman, Antoine Lavoisier, who named this gas as hydrogen in 1783 Indeed, the name

‘hydrogen’ itself is from the Greek words ‘hydros’ (meaning ‘water’) and ‘generos’ (meaning ‘to make’ or ‘to create’); hence, the name hydrogen means ‘to make water’ or ‘water former’

The story of hydrogen took a further step forward around this time when the Englishman, William Nicholson, correctly identified it following his early experiments on electrolysis Figure 3 shows an extract of Nicholson’s famous paper of 1800 [2]

where he correctly determines that water is composed of hydrogen and oxygen

Of course, the discovery and naming of hydrogen at this time is all the more challenging due to its properties which, at standard temperature and pressure (STP), render it odorless, colorless, tasteless, nontoxic yet highly flammable (within its flammability limits of 4–74% in air) It is a highly reactive substance (hence, it does not naturally occur but is found bonded within many other compounds) and is the lightest element in the periodic table

Hydrogen at STP is in the form of a molecular gas It was not until 1898 that the Scotsman, Sir James Dewar, liquefied hydrogen for the first time (see Figure 4 showing a repeat of this first experiment in 1899), achieving temperatures of 20 K or –253 °C Even at such extreme low temperatures, hydrogen formed a colorless liquid

Dewar continued his pursuit of ever colder temperatures and was the first to produce solid hydrogen, at temperatures below 14 K (–259 °C) in 1899

Comprehensive Renewable Energy, Volume 4 doi:10.1016/B978-0-08-087872-0.00401-7 1

Figure 1 Cavendish’s paper on ‘factitious air’ from 1766 From http://www.theworldsgreatbooks.com/images/Science/cavtext.jpg

The manufacture of coal gas in the United Kingdom decreased rapidly following the discovery and extraction of natural gas, principally methane, from the North Sea, which could be both extracted and used in a much environmentally clean fashion, with less remediation required, than coal gas production [4]

The use of coal gas was widespread and very visible in many towns and cities, principally due to the large gas holders (or gasometers as they became known as) that stored the coal gas These tanks (an example is shown in Figure 5) were a common site and are only now being replaced by high pressure storage in modern, underground, plastic high pressure natural gas pipelines

So hydrogen gas has been in use, albeit in a mixed dilute form within a coal gas mix, for well over a century Hydrogen has also many industrial and speciality uses: as a product in semiconductor processing, petroleum refining, ammonia production for fertilizer production, heat treatment of metals, as a coolant in large electrical generators in power stations, and as a rocket fuel for space missions! However, this volume will concentrate on the technologies that aim to use pure hydrogen as a fuel

Hydrogen is not a source of ‘primary energy’, as hydrogen requires to be produced/released or manufactured as a pure gas, and also requires further treatment to liberate energy when being converted to useful work It is also not a form of renewable energy,

3 Preface and Context to Hydrogen and Fuel Cells

id=TggAAAAAMAAJ&printsec=frontcover&source=gbs_ge_summary_r&cad=0#v=onepage&q&f=false

rather it should be viewed as an ‘energy vector’, in a similar fashion to electricity which does not naturally occur, and requires to be produced (generated) from primary energy sources/fuels, and is then reconverted to useful work in our electric lights, heaters, machinery, computers, and so on However, hydrogen is a unique type of energy vector in that it can be stored, in large volumes, unlike electricity, and this unique feature will enable its use to support development and implementation of the other forms of renewable energy reported in this Comprehensive Renewable Energy series

Figure 5 Coal gas storage tank (gasometer) http://www.igg.org.uk/gansg/12-linind/gasworks.htm

This capacity for hydrogen to be used as both an energy store and a fuel is particularly relevant to the transport sector, a sector dominated by fossil fuels and hence carbon emission concerns, and a sector that forms of renewable energy like wind or solar (unless biofuels) is not frequently linked to The use of hydrogen as an intermediate energy store and fuel will allow wind energy and other forms of renewables to power water electrolysis plants, to produce hydrogen gas for use in vehicles, thereby creating a

‘double benefit’: increase the usage of renewable energy and replace vehicle fossil fuel consumption with a zero emission alternative

A significant contributory factor in the pursuit of hydrogen use as a fuel has been the parallel development of fuel cells, a DC electrical source that can be thought of as a ‘continuously operating battery’ The fuel cell was first discovered by William Grove in

1839 [5], and was reported as a postscript in a paper focussing on developments on ‘voltaic series’, at the time an area of feverish scientific development in the new field of electricity, following Alessandro Volta’s creation of the zinc/copper pile battery Grove’s postscript to his paper is shown in Figure 6, and marks the time when Grove, in a subsequent publication in 1842 [6], presented further details of this initial fuel cell and included an image of the experimental arrangement, an image which has become redolent with the history of fuel cells A full copy of this paper is shown in Figure 7, first to illustrate the image of Grove’s fuel cell and second

to highlight the spirit of research at this time (Note the comments on p 418 regarding the detection of electric potential by means

of an electric shock felt across five persons joining hands!)

A principal difference between a ‘battery’ and a ‘fuel cell’ is that a battery contains (or holds internally) the ‘fuel’ or chemical compounds with which to generate electricity within the casing of the battery: by contrast, the ‘fuel’ for a fuel cell is both held and supplied externally, and hence can be continuously supplied or replenished if desired

4.01.2 An Overview of This Volume

This volume, entitled ‘Hydrogen and Fuel Cell Technology’, part of the overall Comprehensive Renewable Energy Major Reference Work, covers a range of technologies spanning the hydrogen and fuel cell sector This particular chapter presents the context to this

5 Preface and Context to Hydrogen and Fuel Cells

sector and an overview of hydrogen and fuel cell technology The remaining chapters of this volume will now be briefly introduced,

in the order they are presented within the volume:

4.01.2.1 Chapter 4.01: Introduction

The history and background to the production and use of hydrogen as a fuel within fuel cells is presented in this chapter, in addition

to providing an introduction to the fundamental thermodynamics of how fuel cells operate This is as a precursor to the further, more technically detailed, chapters that follow and includes an overview and context to the hydrogen and fuel cell sector It also

Figure 7 Grove’s ‘Gaseous Voltaic Battery’ – the first reported hydrogen fuel cell

presents information on examples of existing hydrogen production technology, namely, large-scale alkaline electrolysis, and of one current transportable proton exchange membrane (PEM)-based hydrogen production system for vehicle refuelling Finally, some detail of a regenerative fuel cell, a novel type of fuel cell that is gaining traction as a potential energy storage technology, is presented

to illustrate that some fuel cell technologies do not require hydrogen gas to operate

7 Preface and Context to Hydrogen and Fuel Cells

4.01.2.2 Chapter 4.02: Current Perspective on Hydrogen and Fuel Cells

This chapter presents a historical perspective and the current state of the utilization of hydrogen as a fuel, and of fuel cells as a power source Given the impetus to develop and use hydrogen and fuel cells within the space exploration sector, this chapter gives a particular perspective of these early developments and an overview of current uses

4.01.2.3 Chapter 4.03: Hydrogen Economics and Policy

Developing hydrogen gas as a new form of energy vector requires significant technical development, as later chapters within this volume will discuss; however, it will also require significant financial investment Additionally, to break into the classic ‘chicken and egg’ cycle that tends to inhibit new technology uptake (e.g., users will not purchase hydrogen vehicles until there is an established network of hydrogen refuelling stations, while energy companies will not develop or invest in a network of hydrogen refuelling stations until there is a significant population of hydrogen vehicles to utilize this investment), the nature and use of government policy instruments to stimulate this development is presented and discussed

4.01.2.4 Chapter 4.04: Hydrogen Safety Engineering: The State-of-the-Art and Future Progress

A key issue surrounding the utilization of hydrogen as a fuel centers on the safe use of this highly reactive, flammable gas The subject of hydrogen safety is simultaneously both technical and emotive, with considerable ongoing technical work studying hydrogen flammability and safety equipment, while also addressing public perceptions and concerns through publicity campaigns and demonstration programs This chapter presents technical information surrounding the physical properties of hydrogen and its characteristic behavior during leakage, combustion, and explosion It also details current international standards in this area surrounding the safe use of hydrogen as a fuel

4.01.2.5 Chapter 4.05: Hydrogen Storage: Compressed Gas

A critical element in the development of a potential ‘hydrogen economy’ is the ability to store and transport hydrogen gas as a fuel The storage of hydrogen has, and remains most commonly, been in the form of a compressed gas Historically, this has typically been at ‘industrial’ gas pressures of around 200 bar, a typical pressure for a steel cylinder of hydrogen for laboratory or factory use; however, in recent times, the use of high pressure (up to 700 bar) storage of hydrogen within composite pressure vessels has been promoted particularly for vehicular use This chapter explores the issues and technologies involved in storing hydrogen gas at such pressures, and discusses the safe handling and use of hydrogen within such systems

4.01.2.6 Chapter 4.06: Hydrogen Storage: Liquid and Chemical

Hydrogen storage in the form of compressed gas has a number of limitations and this chapter studies other possible forms of storing hydrogen as a fuel, namely, as a liquid at very low temperatures or within chemical media capable of absorption or reversible material reactions Some details of these alternative forms of storage are presented, and the issues surrounding reversibility, the dynamics and speed of storage/release, cost, storage density and cyclability are discussed within this context

4.01.2.7 Chapter 4.07: Alkaline Fuel Cells: Theory and Application

There are several different types of fuel cell that can be broadly characterized by the type of electrolyte used within the cell In the late 1950s, the main electrolyte of interest was potassium hydroxide, an alkaline solution, and hence, it was this particular fuel cell technology that reinvigorated research and commercial interest following on from successful use in early space flights This chapter presents both further technical detail of alkaline fuel cell (AFC) technology and further historical information on past and current developments

4.01.2.8 Chapter 4.08: PEM Fuel Cells: Applications

For transport applications of fuel cells, an obvious disadvantage to the use of AFCs was the requirement to contain and protect (in the event of collision/accident) a highly caustic liquid electrolyte A solution to this issue arose from the study of ion-conducting solid membranes, which obviated the need for a liquid electrolyte, thereby removing accompanying spill/leakage issues This work led to the development of positive ion-conducting membranes (e.g., proton conduction), as opposed to negative hydroxyl ion conduction within AFC, and spawned the PEM fuel cell sector This genre of fuel cell is now the most widely researched and most promising for utilization within the transport sector, and this chapter explores the material developments, capabilities, and demonstration of this technology

4.01.2.9 Chapter 4.09: Molten Carbonate Fuel Cells: Theory and Application

As the chapter name suggests, this fuel cell technology is characterized by operation using a molten carbonate salt as the cell electrolyte This requires temperatures of several hundred degrees Celsius to produce the molten electrolyte and achieve appropriate

ion mobility, thereby enabling fuel cell operation, and this technology has developed to accommodate the resulting technical challenges This chapter presents details of the development of molten carbonate fuel cells, in particular the significant installed commercial capacity of these fuel cells, and discusses the future potential for this technology

4.01.2.10 Chapter 4.10: Solid Oxide Fuel Cells: Theory and Materials

Of the range of electrolytes available for use within fuel cells, the highest temperature electrolyte currently used is a negative ion-conducting ceramic within the solid oxide fuel cell (SOFC) class Typically, operating temperatures of between 550 and 1000 °C are needed to produce the conditions necessary for appropriate ionic conduction in these materials; however, such high-temperature fuel cell technology is attractive in many process industries where high-grade waste heat may be employed to readily create the operating temperatures or direct use of fossil fuel combustion products that are available This chapter explains how an SOFC operates, discusses the material requirements and developments, and presents information on the current state of the art in this sector

4.01.2.11 Chapter 4.11: Biological and Microbial Fuel Cells

Microbial and biological fuel cells are relatively new forms of fuel cell that typically use either hydrocarbons as a fuel, or utilize electrogenic bacteria to convert chemical energy to electrical energy rather than a more typical electrocatalyst These forms of fuel cell are gaining prominence in developing niche markets, such as wastewater treatment where electrical energy can be derived while simultaneously processing and cleaning the waste stream, and are potentially able to address the growing legislative requirements to clean hitherto neglected process streams This chapter explores the theory and materials (including enzymes and bacteria) employed

to create these unique fuel cells and presents details of their resulting performance characteristics

4.01.2.12 Chapter 4.12: Hydrogen and Fuel Cells in Transport

Of the many application areas for fuel cells, the sector that may provide the greatest advance in terms of commercial breakthrough and success is within the transport field Fuel cell utilization within electric vehicles, ships or as on-board electrical generators for load refrigeration or cab power, is increasing rapidly and offers efficiency and carbon emissions benefits compared to conventional fossil fuel options The transport sector offers both a huge market and a direct interface to the public (compared to the stationary power market for fuel cells which tends to ‘isolate’ the consumer from the technology, whereas, for example, transport fuel cells are accessible under the hood of a car); hence, fuel cells can gain rapid consumer acceptance and market traction within this key end-use sector This chapter presents details of fuel cell technology relevant to the transport sector and illustrates several examples of typical use 4.01.2.13 Chapter 4.13: H2 and Fuel Cells as Controlled Renewables: FC Power Electronics

Neither hydrogen nor fuel cells are formally defined as ‘renewable sources’ of power within current legislation [7]; however, they are commonly viewed as an integral element of any future clean energy mix Uniquely, within the context of renewable energy sources where many of these sources are stochastic (i.e., variable) and uncontrolled in terms of their energy delivery, hydrogen and fuel cell technology offers the user direct control of the power delivered at any instant The ability to control the power and energy delivery from a fuel cell, and to control the storage and utilization of hydrogen as a fuel, conveys significant benefits to the utilization of hydrogen and fuel cell technologies This chapter explores the use of power electronics as a mechanism to control the output electrical power from a fuel cell, and examines the type and nature of the power electronic interface between the electrochemical cell and the electrical load

4.01.2.14 Chapter 4.14: Future Perspective on Hydrogen and Fuel Cells

The final chapter of this volume presents a perspective of how hydrogen and fuel cell technology may develop in the future, and how hydrogen use as a fuel may pervade more aspects of our lives This concept, of a future hydrogen-based economy, is a view that many researchers and analysts believe it is inevitable as the world’s fossil fuel resources are depleted and environmental pressures compound the shift toward a cleaner energy supply

4.01.3 Hydrogen and Fuel Cell Technology – Supplementary Material

It has not been possible within this volume to adequately cover ‘all’ aspects of hydrogen and fuel cell technology, and this brief section aims

to introduce the reader to areas considered by the author as important with appropriate references to allow further reading as required

4.01.3.1 Flow Cells or Regenerative Fuel Cells

The first technology of interest is the flow cell or flow battery, where the energy capacity of the system is stored external to the cell generally in the form of oppositely charged liquid electrolytes These electrolytes are reacted within a fuel cell, in the form of two half

9 Preface and Context to Hydrogen and Fuel Cells

cell reactions (see Section 4.01.4.1) separated by an ion-selective membrane (i.e., a membrane that allows only specific ions to pass through it but prevents the liquid electrolytes from mixing directly) that convert the chemical energy in the electrolytes fuels to electrical energy This technology is viewed as different from a ‘conventional’ hydrogen and oxygen (or air) fuel cell This technology can be encountered under a number of different names, for example, regenerative fuel cell or redox flow fuel cell

This technology is exemplified by the technology such as the sodium polysulfide bromide-based system developed by a UK company called Regenesys, from the late 1990s to the early 2000s Regenesys aimed at commissioning a demonstration plant rated

at 120 MWh, 12 MW at a site near Little Barford, Cambridgeshire, UK, to evaluate regenerative fuel cell technology as a large-scale form of electrical energy storage The test site was almost completed, as per Figure 8, but ultimately never fully commissioned, as explained in Reference [8]

technology produces DC electrical power, and hence, a power electronic inverter was required to convert this to AC electrical power suitable for delivery into the electricity grid For the Little Barford test site, the inverter was developed by ABB and was rated at 18.25 MVA [9] although the fuel cells were rated to deliver only up to 12 MW

The Regenesys technology employed two electrolytes: sodium bromide (NaBr) and sodium polysulfide (NaS2) These two liquid electrolytes were circulated through the regenerative fuel cell as per the diagram shown in Figure 10, where the half-cell redox reactions occurred, generating electrical energy if pumped in one direction, and capable of reversal to store electrical energy if the electrolytes were pumped through the cell in the opposite sense (with electrical energy input to the cell in this instance)

“Regenesys Utility Scale Energy Storage – Project Summary”, DTI, Contract Number: K/EL/00246/00/00, URN Number: 04/0148, 2004

EL/00246/00/00, URN Number: 04/0148, 2004

Currently, the most common method of producing hydrogen gas on a large scale is through the process of steam methane reformation, where methane gas (CH4) is reacted with steam (H2O) to, ultimately, produce carbon dioxide (CO2) and hydrogen (H2) However, within the context of this volume, focussing on renewable energy, the preferred method of producing hydrogen is via electrolysis of water (see Section 4.01.1) where electrical energy, preferably from clean sources such as wind or solar power, is used to split water into its constituent gases, namely, hydrogen and oxygen

This process, and accompanying electrolyser technology, has been extensively developed by companies such as Norsk Hydro

then combine the hydrogen with nitrogen extracted from the air, to form ammonium, a key component of fertilizer

The technology surrounding large-scale electrolysers, even today, is based on alkaline technology employing potassium hydro­xide as an electrolyte, and such units are available in capacities up to 2 MW rating, as shown in Figure 11 Figure 11 shows the electrical connections on the left-hand side of this image to supply DC electrical power to the fuel cells, with the white lye (potassium hydroxide) tanks shown toward the rear right-hand side of the image

Transformer Rectifier

Gas holder Compressor Electrolyser separator separator

Feed water to electrolyser Lye tank

Preface and Context to Hydrogen and Fuel Cells 11

Capacity

Energy Power consumption at 4000 amp DC (kWhNm−3 H2) 4.1
0.1 Power consumption at 5150 amp DC (kWhNm−3 H2) 4.3
0.1 Purity

Pressure

Maximum H2 outlet pressure after compressor 440 bar g Operation

Source: NEL Hydrogen Ltd

The technical specification of such a large-scale alkaline electrolyser is shown in Table 1, which defines the energy requirement for hydrogen production (e.g., 4.1 kWh Nm−3 of H2) and the feed water flow rate required (e.g., 0.9 l Nm−3 of H2) It also defines the typical purity of hydrogen produced and the typical use of subsequent cleanup processes to improve the hydrogen gas purity to five

‘9s’ purity, that is, 99.999% which is typically required for fuel use for fuel cells

The flow diagram for this technology is shown in Figure 12, including the electrical supply, electrolyte, and gas separation and handling systems

image also shows the manifold ducts on the top and bottom of the electrode which are used to capture the gases and circulate the liquid electrolyte, respectively

cathode electrodes (see Section 4.01.4.1) yet prevents gas and liquid crossover Figure 15 gives a closeup view of the gas manifold ducts, illustrating (from an edge view) that the oxygen and hydrogen gases are produced and collected from opposite sides of the membrane and fed to separate gas ducts

alkaline electrolysers of a type similar to those in Figure 11

4.01.3.3 Hydrogen Demonstration Units – State of the Art

There are a number of hydrogen production and utilization demonstration units in trial around the world, based on a variety of different fuel cell technologies One such system, which has attracted a lot of attention within the United Kingdom, is the ITM Power

Figure 13 Electrode of alkaline electrolyser (NEL Hydrogen Ltd.)

Oxygen

Hydrogen

Preface and Context to Hydrogen and Fuel Cells 13

compression and high pressure storage of hydrogen gas, and finally dispensing of this fuel gas to on-vehicle storage for use within a hydrogen internal combustion engine (HICE) on a van

Some of the technology used within the HOST unit is illustrated in the following series of images For example, Figure 17 shows the water processing plant requiring to clean up a typical potable water supply for use within high purity PEM electrolysers

gas compression and storage This stage helps prevent corrosion issues within the compressor and storage vessels

The purified hydrogen gas is subsequently stored in a tiered system of pressure vessels from ‘low’ pressure (up to 250 bar) to

‘medium’ pressure (up to 350 bar, shown in Figure 19) tanks, and finally up to 450 bar in the ‘high’ pressure tanks (the top four tanks shown in Figure 20) The compressor used is shown in Figure 21

The high pressure hydrogen stored is subsequently dispensed via a high pressure nozzle connector, as shown in Figure 22, which directly mates to a vehicle-mounted receptacle, shown in Figure 23 A vehicle refueller control system (i.e., a dispensing refueller system) is shown in Figure 24, and is used to control and monitor the quantity of hydrogen fuel gas dispensed to the vehicle

petrol station forecourt Hence, Figure 24 shows the type of technology that is being developed for use within a future hydrogen economy for dispensing vehicle fuel