Hydrogen Fuel Cell Principles of Engineering © 2012 Project Lead The Way, Inc.

Trends in the Use of Fuel It is interesting to note that as fuel use has developed through time, the percentage of hydrogen content in the fuels has increased. It seems a natural progression that the fuel of the future will be hydrogen. The two principal reactions in the burning of a hydrocarbon fuel are the formation of water and the formation of carbon dioxide. As hydrogen content in a fuel increases, the formation of water becomes more significant, resulting in proportionally lower emissions of carbon dioxide.

Internal combustion engine 19th century: Steam engine 20th century: Internal combustion engine 21st century: Fuel cells A varied range of organizations, from energy companies to automobile manufacturers, are working to develop fuel cells and the accompanying infrastructure. A trend in the production of power is clearly visible: The 19th century was the century of the steam engine, The 20th century was the century of the internal combustion engine, The 21st century will be the century of the fuel cell.

The History of Fuel Cells The first fuel cell was developed in 1839 by Sir William Grove, a British scientist and lawyer. The principle was discovered by accident. He was performing an electrolysis experiment. When he disconnected the battery from the electrolyser and connected the two electrodes together he noticed that a current flowed in the opposite direction, consuming the gases of hydrogen and oxygen. He called this device a ‘gas battery’. His gas battery consisted of platinum electrodes placed in test tubes of hydrogen and oxygen, immersed in a bath of dilute sulphuric acid. It generated a voltage of about one volt. However Grove’s fuel cell was not practical, due to problems of corrosion and instability of the materials. As a result there was little research and development into fuel cells for many years to follow. Electrolyser Grove’s Gas Battery (first fuel cell, 1839) (after Larminie and Dicks, 2000)

Significant development work on fuel cells began again in the 1930s, by Francis Bacon, a chemical engineer at Cambridge University. In the 1950s Bacon successfully produced the first practical fuel cell, an alkaline fuel cell. It used an alkaline electrolyte instead of dilute sulphuric acid. The electrodes were constructed of porous sintered nickel powder so that the gases could diffuse through the electrodes to be in contact with the aqueous electrolyte on the other side. This greatly increased the contact area contact between the electrodes, the gases, and the electrolyte, thus increasing the power density of the fuel cell. In addition, the use of nickel was much less expensive than that of platinum. An assistant can be seen in this photograph mounting a plate onto the side of Bacon’s fuel cell stack.   Alkaline fuel cell reactions: Anode reaction: 2 H2 + 4 OH-  4 H2O + 4 e- Cathode reaction: O2 + 4 e- + 2 H2O  4 OH- Overall reaction: 2 H2 + O2  2 H2O Photo courtesy of University of Cambridge Bacon’s laboratory in 1955

NASA Space Shuttle fuel cell The Bacon fuel cell was modified by NASA in the 1960s as a method to supply on-board drinking water as well as electricity for the astronauts aboard the Apollo space missions. An alkaline fuel cell is still used today in the present day Space Shuttle Orbiter. The Space Shuttle Orbiter fuel cell has been produced since the 1970s by International Fuel Cell, USA. It produces 12 kW electricity, weighs 202 lb (98 kg), and occupies a space of 4.6ft3 (154 litres). Photo courtesy of NASA Alkaline fuel cells offer the advantages of high voltage output per cell (each cell in the Space Shuttle has an operating voltage of about 0.875 volts) and that non-precious materials can be used as electrodes. The primary disadvantage of alkaline fuel cells for terrestrial applications is that of carbon dioxide poisoning the electrolyte. Carbon dioxide, present in both the atmosphere as well as in ‘reformate’ (the hydrogen-rich gas produced from the reformation of hydrocarbon fuels) reacts with the hydroxide ion in the electrolyte to form a carbonate, thus reducing the hydroxide ion concentration in the electrolyte. This reduction in hydroxide ion concentration inhibits the ability of the fuel cell to generate current. Because of the complexity of isolating carbon dioxide from the alkaline electrolyte for terrestrial applications, most fuel cell developers today have focused their attention on developing new types of fuel cells using electrolytes other than that of alkaline. Carbon dioxide reacting with potassium hydroxide electrolyte forming a carbonate:   2 KOH + CO2 → K2CO3 + H2O   Photo courtesy of NASA NASA Space Shuttle fuel cell

Applications for Fuel Cells Transportation vehicles In the mid-1980s Ballard Power, based in Vancouver, BC, and working on a contract from the Canadian Department of National Defense, made significant breakthroughs in fuel cells. Working with Johnson Matthey in the UK, they developed PEM fuel cells which had a significant increase in power density. From these breakthroughs it was recognized that fuel cells could be made small, powerful, and inexpensive enough to replace conventional power technologies. The California Low Emission Vehicle Program, a program of the California Air Resources Board (CARB) has been a large incentive for automakers to develop fuel cell automobiles. This program requires that beginning in 2003, ten percent of passenger cars delivered for sale in California must be Zero Emission Vehicles, called ZEVs. Automobiles powered by fuel cells meet these requirements. To date seven of the world’s ten leading auto manufacturers plan to introduce fuel cell automobiles beginning in the 2003–2005 timeframe. The NECAR 5 shown here is a prototype automobile by DaimlerChrysler. This automobile is fueled with liquid methanol and has a top speed of over 90 miles per hour (150 km/h). In forthcoming years there are plans for buses, trucks, and trains all powered with fuel cell engines. Thirty buses will be commercially introduced in ten European cities beginning in 2002. Photo courtesy of DaimlerChrysler NECAR 5

250 kW distributed cogeneration power plant Applications for Fuel Cells Distributed power stations Electrical energy demands throughout the world are continuing to increase. In Canada the electrical energy demand is growing at an annual rate of approximately 2.6%. In America the electrical energy demand is growing at an annual rate of about 2.4% (IEA 1997). In developing countries, electrical demand is growing at an annual rate of almost 6% (Khatib, 1998). How can these demands be met responsibly and safely? There are many problems associated with the building of new power plants, both financial and environmental. Fuel cell distributed power stations provide a solution. Fuel cell distributed power plants can provide high quality, reliable power. Depending on the type of fuel used fuel cell power plants produce little or no emissions. Shown here is a prototype fuel cell distributed power plant, recently developed by Ballard Power. This particular unit was commissioned for the BC Hydro grid. It provides 250 kilowatts of electricity and about the same amount of heat, fuelled from natural gas. This is enough power to provide heat and electricity to a community of about 50 homes for example, or to a hospital or to a remote location school. Ballard plans to introduce its first commercial fuel cell distributed power plant as a backup power supply in 2003. Photo courtesy of Ballard Power Systems 250 kW distributed cogeneration power plant

7 kW home cogeneration power plant Applications for Fuel Cells Home power Fuel cell power plants are also being developed by several manufacturers to provide electricity and heat to a single-family home. Fueled by either natural gas or propane these fuel cell power plants will be able to power a home independent of the grid. Plug Power, based in Latham New York has developed a new fuel cell power plant that supplies 7 kilowatts of electricity and heat, using either natural gas or propane as the fuel. That is enough power to supply the electrical demand of a modern energy efficient home. Initially these fuel cell power plants will be grid parallel. Eventually they will be grid independent. Plug Power plans to commercially introduce this home power plant, distributed through General Electric, in 2002. Photo courtesy of Plug Power 7 kW home cogeneration power plant

50 W portable fuel cell with metal hydride storage Applications for Fuel Cells Portable power Several manufacturers are currently developing portable fuel cell power supplies. These power supplies can provide anything from a few watts up to several kilowatts of electricity. Portable fuel cell power supplies will be an alternative to conventional batteries for many applications. Applications include laptops, mobile phones, remote road signs, and lighting. Portable fuel cell power supplies have several advantages over conventional batteries. The primary advantage is that of energy density. Fuel cells can provide a higher energy density by both volume and weight. Thus fuel cell portable power packs can be lighter and can supply power for a longer period of time than that of conventional batteries. In addition the storage losses for hydrogen fuel cells are practically nonexistent. Whereas conventional batteries slowly discharge their power over time, fuel cells powered by hydrogen can maintain their charge almost indefinitely. The third advantage is that the storage capacity of rechargeable batteries decreases as a function of the number of cycles of charge and discharge, such that they will eventually have to be replaced. Fuel cells will maintain their power output almost indefinitely. This particular fuel cell is a prototype 40 watt PEM fuel cell by Heliocentris, powering a remote blinking lamp. The fuel cell is contained in the upper part of the unit. The lower part of the unit contains a metal hydride storage cylinder, containing the hydrogen. Motorola Labs and the Los Alamos National Laboratory are co-developing portable fuel cell technology using direct methanol fuel cells. Company officials say these fuel cells, including a canister of methanol, will supply ten times the energy of a rechargeable battery of equivalent size. Thus mobile phones, for example, will apparently be able to remain on standby for a period of over a month. When the methanol in the canister is consumed, a new canister can easily be inserted. With the advent of this process, recharging batteries will no longer be necessary. Motorola expects these fuel cells to be commercially available in three to five years. 50 W portable fuel cell with metal hydride storage

The Science of Fuel Cells Alkaline (AFC) Polymer Electrolyte Membrane (PEMFC) Phosphoric Acid (PAFC) Polymer Electrolyte Membrane (PEMFC) Types of Fuel Cells Molten Carbonate (MCFC) Fuel cells are classified by the type of electrolyte they use (Table 1). The different electrolytes operate at different temperatures. Low-temperature fuel cells include the alkaline fuel cell (AFC), the proton exchange membrane fuel cell (PEMFC), and the phosphoric-acid fuel cell (PAFC). All of these fuel cells use hydrogen as a fuel. This hydrogen can be extracted from natural gas, biogas, methanol, or propane by the process of reformation. The hydrogen can also be created through the electrolysis of water. High-temperature fuel cells include the molten carbonate fuel cell (MCFC) and the solid oxide fuel cell (SOFC). These fuel cells offer the advantage that they can use either natural gas or untreated coal gas as a fuel directly without the use of a reformer through a process called "Direct Internal Reforming". The sixth type of fuel cell is the direct methanol fuel cell (DMFC). It is also a low temperature fuel cell, but it can use methanol as a fuel directly without the need of reforming. The primary limitation to the direct methanol fuel cell is that the rate of reaction on the anode is very slow. This results in a very low operating voltage output. For certain applications (e.g., portable power), the direct methanol fuel cell may be ideal. Direct Methanol (DMFC) Direct Methanol (DMFC) Solid Oxide (SOFC) Solid Oxide (SOFC)

PEM Fuel Cell Electrochemical Reactions Anode: H2 2H+ + 2e- (oxidation) Cathode: 1/2 O2 + 2e- + 2H+ H2O (l) (reduction) Overall Reaction: H2 + 1/2 02 H2O (l) ΔH = - 285.8 kJ/mole A fuel cell is a device that through an electrochemical process converts hydrogen and oxygen directly into water. In this process energy is released in the form of electricity and heat. The chemical process is electrolysis in reverse. In the PEM fuel cell, hydrogen molecules are oxidized at the anode to positively charged hydrogen ions, protons, releasing electrons to the cathode via an external electric load. The protons diffuse through an ion-conducting membrane to the cathode. At the cathode, oxygen combines with the electrons and the protons to form water. The overall reaction is hydrogen plus oxygen producing water. The enthalpy of this exothermic reaction is –285.8 kilojoules per mole

A Simple PEM Fuel Cell Hydrogen + Oxygen  Electricity + Water Water In this diagram we can see the various components of a simple fuel cell. A single cell consists of two gas field flow plates, one for hydrogen and one for oxygen, separated by a membrane electrode assembly, abbreviated MEA. The field flow plates contain channels to ensure that the gases are in contact with as much of the MEA as possible. As can be seen in the diagram, hydrogen molecules enter on the anode side of the cell, while oxygen enters on the cathode side. In a reduction reaction, the hydrogen molecule releases its electrons, which flow from the anode electrode through the external electric load to the cathode electrode. It is this flow of electrons which we observe as electricity. The hydrogen protons flow through the ion-conducting membrane to the cathode. At the cathode they combine with the oxygen molecules and the free electrons to form water. The fuel cell has electrochemically converted hydrogen and oxygen gases into electricity and water. Water

Membrane Electrode Assembly (MEA) i s Oxidation 4 e - T r a n s p o r t Platinum- catalyst H 2 2 H 2 4 H + R e s i s t a n c e N a f i o n O 2 H O 2 Reduction H + Platinum- catalyst Anode Cathode K 4 4 e e - - Polymer electrolyte (i.e. Nafion) O O 2 2 N a f i o n The MEA consists of two porous carbon-cloth electrodes bonded to each side of a polymer electrolyte membrane. This material, the electrolyte, allows the conduction of hydrogen protons from one side of the membrane through to the other. At the same time it prevents oxygen molecules from flowing in the reverse direction. On the electrodes are nano-sized particles of platinum. The platinum acts as a catalyst for the redox reaction to take place. Initially the hydrogen molecules are chemically adsorbed onto the platinum surface, forming hydrogen-platinum bonds. Platinum is unique in that it has the ideal bonding strength to both break the hydrogen molecule bond, to form the hydrogen-platinum bonds, while being able to release the hydrogen, allowing the redox reaction to proceed. A fuel cell therefore supplies a current, much the same way as a battery. However, unlike a battery, a fuel cell can provide electrical power indefinitely as long as hydrogen and oxygen are supplied. Carbon cloth Carbon cloth 4 4 H H + + 2 2 H H O O 2 2 N N a a f f i i o o n n 2

Polytetrafluoroethylene (PTFE) chains Polymer Electrolyte Membrane Polytetrafluoroethylene (PTFE) chains Water collects around the clusters of hydrophylic sulphonate side chains Sulphonic Acid The membrane of a fuel cell is between 50 and 175 microns thick; that’s about the thickness of 2 to 7 sheets of paper. It is produced in sheets which can be cut to the required size. The electrolyte membrane consists of Polytetrafluoroethylene (PTFE) chains, commonly called Teflon. On the Teflon chains are side chains ending with sulphonic acid, HSO3. A close-up view of the membrane material shows spaghetti-like long chain molecules with clusters of sulphonate side chains. An interesting feature of this material is that whereas the long chain molecules are hydrophobic (repel water), the sulphonate side chains are highly hydrophylic (attract water). The hydrophylic regions absorb large quantities of water. Within these hydrated regions the H+ ions of the sulphonic acid are able to move, creating the ability for this material to transfer H+ ions from one side of the membrane to the other. For this reason the hydrated regions must be as large as possible. 50-175 microns (2-7 sheets of paper) (after Larminie and Dicks, 2000)

Thermodynamics of PEM Fuel Cells Change in enthalpy (ΔH) = - 285,800 J/mole Gibb’s free energy (ΔG) = ΔH - TΔS ΔG at 25° C: = - 285,800 J - (298K)(-163.2J/K) = - 237,200 J Ideal cell voltage (Δ E) = - ΔG/(nF) ΔE at 25º C = - [-237,200 J/((2)(96,487 J/V))] = 1.23 V ΔG at operating temperature (80º C): = - 285,800 J - (353K)(163.2 J/K) = - 228,200 J ΔE at 80º C = - [-228,200 J/((2)(96,487 J/V))] = 1.18 V Working through the calculations we see that the ideal cell voltage at room temperature is 1.23 volts. However as the fuel cell heats up to an operating temperature of about 80º C, the ideal cell voltage drops to 1.18 volts. More factors are involved in practical fuel cells, which reduce the cell voltage considerably.

activation losses + internal currents Characteristic Curve Power Curve activation losses + internal currents 1.2 MPP 2.5 1 ohmic losses x concentration losses 2 0.8 V 0.6 P 1.5 0.4 1 0.2 0.5 1 2 3 4 1 2 3 4 5 I I Factors Affecting Curve: activation losses fuel crossover and internal currents ohmic losses mass transport or concentration losses Max Power Point (MPP): We can see here the characteristic curve of the fuel cell. The characteristic curve of a fuel cell is the relationship between the current density and the cell voltage. Notice a sharp fall from the ideal cell voltage immediately following open circuit. This is followed by a somewhat linear decline in cell voltage. This is followed by a rapid drop off in cell voltage. The primary factors affecting the curve are listed below. Each of these losses contributes to the decline in cell voltage. Activation losses are a result of the slow speed of the reactions taking place. Fuel crossover and internal currents is a result of fuel which crosses through the membrane, not contributing to the chemical redox reaction, thus not contributing to the production of electricity. Ohmic losses are a direct relationship to the combined resistance of the various components within the fuel cell circuit. This includes the material of the electrodes, the membrane, and the various interconnections. Mass transport, often called concentration losses, is a result of a reduction of the concentration of hydrogen and oxygen on the electrode surface. This is due to the failure to transport the required gases to the electrode surfaces. By careful design in all of the components involving science, engineering, and the technical trades, these losses can be minimized resulting in fuel cells that are efficient and deliver high power density. The second graph is the ‘power curve’. This is a plot of the relationship between the current density and the power output of the cell. The maximum power point of a fuel cell can be determined either by plotting it on graph paper, as shown here, or by determining the equation of the curve and differentiating that equation.

Liters to store 1 kg hydrogen Hydrogen Storage 56 L 14 L 9.9 L It is interesting to compare the various methods available to date for the storage of hydrogen. We see that to store one kilogram of hydrogen in compressed gas cylinders requires 56 liters, as liquid hydrogen, not including the necessary equipment requires 14 liters. Hydrogen stored in a magnesium metal hydride container requires 9.9 liters. Compressed gas (200 bar) Liquid hydrogen MgH2 metal hydride Liters to store 1 kg hydrogen

Hydrogen: Energy Forever Fuel tank Reformer H2 Hydrogen bottles Algae Solar panel Electrolyser Reformers convert a hydrogen rich fuel such as natural gas, methanol, or even gasoline into pure hydrogen plus the emission of carbon dioxide. They work via a catalytic process combining the fuel with water vapor at a high temperature. The result is fuel cell automobiles are able to carry liquid fuels and fuel cell stationary power plants can use natural gas or propane. For the immediate future, as long as fossil fuels are available, the use of reformers is the most cost-efficient method of producing hydrogen. Hydrogen can be produced sustainably from a solar hydrogen system, that is, a system using a device that transforms the radiant energy of sunlight into electricity (such as a wind turbine, solar panel, or hydro-electric turbine) for use by an electrolyser. When the sun shines, the wind blows, or the water flows, the electrolyser can produce hydrogen. Solar hydrogen systems are truly sustainable, for as long as there is sunlight, there can be hydrogen. There is also research and development taking place in the production of hydrogen from biological methods. For example Dr. Melis at University of California has discovered a green algae (Chlamydomonas reinhardtii) that electrolyzes water producing hydrogen gas when sulphur is depleted from the water source. Biological mechanisms may one day provide the world with an additional source of hydrogen.

Renewable Energy Sources As long as the sun shines, the wind blows, or the rivers flow, there can be clean, safe and sustainable electrical power, where and when required, with a solar hydrogen energy system As long as the sun shines, the wind blows, or the rivers flow, there can be clean, safe, and sustainable electrical power, where and when required, with a solar hydrogen energy system

The Benefits of Fuel Cells Clean Modular Quiet Benefits of Fuel Cells Safe Sustainable Fuel cells are efficient. As fuel cells convert hydrogen and oxygen directly into electricity and water, there is no combustion in the process. As a result the efficiency is high, between 50 and 60%, about double that of an internal combustion engine. Fuel cells are clean. If hydrogen is the fuel, there are no pollutant emissions from a fuel cell, only the production of pure water. In contrast to an internal combustion engine, a fuel cell produces no emissions of sulfur dioxide which can lead to acid rain, oxides of nitrogen which produces smog, or particulates grit and dust. If methanol or natural gas is the fuel, there is an emission of carbon dioxide. However as the efficiency of a fuel cell is higher than that of an internal combustion engine, the emission of carbon dioxide is proportionally lower. Fuel cells are quiet. A fuel cell itself has no moving parts; however, a fuel cell system may have a few moving parts, including pumps and fans. As a result a fuel cell produces electrical power virtually silently. Many hotels and resorts in quiet locations, for example, would like to replace diesel engine generators with fuel cells, for both main power supply or for backup power in the event of power outages. Fuel cells are modular. That is, fuel cell stacks of varying sizes can be theoretically combined together to meet a required power demand. Fuel cells are environmentally safe. They produce no hazardous waste products, only the production of water. Fuel cells provide the opportunity to produce a sustainable source of electrical power. If fuel cells get their hydrogen from renewable energy sources, such as solar, wind, hydro, or biological methods, they can provide a sustainable source of electrical power. Efficient

Heliocentris: Science education through fuel cells 22 Our Fragile Planet. We have the responsibility to mind the planet so that the extraordinary natural beauty of the Earth is preserved for generations to come. Heliocentris: Science education through fuel cells 22 Photo courtesy of NASA

Presentation courtesy of Heliocentris