Fuel Cell Science & Technology – ME 6580 Khalil Raza – Wright State University 1 Fuel Cell Sciences and Technology – ME 6580 Fuel Cell Electric Vehicles Graduate Project – Report Khalil Raza
Nov 08, 2014
Fuel Cell Science & Technology – ME 6580
Khalil Raza – Wright State University
1
Fuel Cell Sciences and Technology – ME 6580
Fuel Cell Electric Vehicles
Graduate Project – Report
Khalil Raza
Fuel Cell Science & Technology – ME 6580
Khalil Raza – Wright State University
2
Contents Introduction Operation of Fuel Cells Chemistry of Fuel Cells Types of Fuel Cells:
Polymer Electrolyte Membrane Fuel Cells (PEMFC)
Direct Methanol Fuel Cells (DMFC)
Phosphoric Acid Fuel Cells (PAFC)
Molten Carbonate Fuel Cells (MCFC)
Basic Components of Fuel Cell Vehicles:
The Motor
Transmission of Fuel Cell Vehicles
AC Motor Controller
Regenerative Braking
Ultracapacitors
Hydrogen Production
Hydrogen Storage for Fuel Cell Vehicles
Metal Bounded Hydrogen Storage
Storing Hydrogen as Liquid
Hydrogen Storage in Carbon Nanotubes
Conclusion
References
Fuel Cell Science & Technology – ME 6580
Khalil Raza – Wright State University
3
1. Introduction:
Fuel Cell is one of the emerging technologies with an immense potential to fill the energy
gap created by oil shortages. It is the direct energy conversion process in which the
chemical energy of fuel primarily hydrogen is converted to electrical energy. Fuel Cell
takes oxygen from air and uses hydrogen as a fuel to generate electricity using an
electrolysis process. In addition to this, it generates water and heat as by-products.
According to energy experts, there is a great future for fuel cells and we may see fuel
cells generating electrical power. It is much cleaner and environmental friendly power
generation than many other conventional power processes. Fuel Cells are majorly used
for three types of application that includes the transportation, stationary and portable
power.
Fuel Cells for large stationary power are bigger in size and have high working
temperatures. They can produce power equivalent to current conventional power plants
and can be used as load center for high electricity demands. The fuel cells for portable
devices are reasonably extremely small that are used to power up small devices like cell
phones, laptops, computers etc. Fuel cells for transportation can be small to medium
sizes. They are installed under the hood of the vehicles along with other auxiliary devices
that make up the whole fuel cell system. In my this research paper I will be focusing on
the fuel cells that are used for the transportation system. Almost, in most cases the fuel
cells used for the transportation are the Polymer Electrolyte Membrane or Proton
Exchange Membrane fuel cells (PEMFC).
Hydrogen is the commonly used fuel in the fuel cells. Besides, the hydrocarbons such as
natural gas and methanol are also used as fuel. Fuel Cells seems similar to batteries as
they both work on electrochemical process but the major difference is that in Fuel Cells
the energy is produced while in the batteries the energy is stored in the chemical form.
Fuel cells continue to produce electricity as long as the fuel is fed into the device.
The idea of using Fuel Cell to produce electricity was put forwarded by a German
Physicist Christian Fridrech Schönbein in 18381. Later NASA space programs made use
Fuel Cell Science & Technology – ME 6580
Khalil Raza – Wright State University
4
of fuel cells commercially to produce power for space vehicles. Afterwards, the fuel cells
have been put in use to produce power for almost all kind of electricity consuming
applications that includes residential, industrial and commercial. Due to the shortage of
oil and its increasing prices, almost all the automotive companies are investing in fuel
cell technology. Automotive sector takes a huge amount of oil resources that is expanding
exponentially every year. Therefore, companies are looking for more sustainable process
of transportation that could cater the future needs while also keeping the environmental
problems in view as an important factor.
Thus the fuel cell can be the most promising technology that could solve the
transportation problems of the globe while also contributing positively to the
environment. Since the fuel cell goes through the electrolysis process and it takes oxygen
from air and hydrogen as fuel so it emits only water from exhaust tailpipe. Moreover, the
conventional car use internal combustion engines, their efficiency are 20 percent to
produce power and rest of the 80 percent of energy is lost and dumped into our
environment as heat or thermal energy. Since, the engine uses heat from combustion of
fuel to build up pressure and transforms that pressure to mechanical work through piston
and crankshaft mechanism. The 80 percent of the heat is lost due to less efficient thermal
efficiency. During this process heat is dumped into an atmosphere, which poses a great
threat to our environment. This act as catalyst to radically change the standard parameters
of nature resulting in climate change and global warming. As human beings on this planet
it is highly preemptive to protect the surroundings and live sustainably while moving
forward to future. Whereas, the fuel cells use electric motors that are fairly efficient up to
80 – 90 percent. In recent years there has been major breakthrough in this technology
however, the future of this fuel cell technology still depends on many factors. Amongst
those factors the production of hydrogen at economical level is the prominent one.
Along-with that the infrastructure development, on-board fuel tank and on board fuel cell
will determine the real future of this technology.
There are different types of fuel cells being used in industry for commercial and
residential purposes depending upon the type of the application. The most important
Fuel Cell Science & Technology – ME 6580
Khalil Raza – Wright State University
5
factor determining which of the fuel cell systems to be used for particular application
depends on the temperature range. Fuel cells have the temperature range starting from 90
Celsius to 700 Celsius. Polymer Electrolyte membrane fuel cells (PEMFC) have the
temperature range from 80 – 90 Celsius this makes it applicable to use it in fuel cell
vehicles. It is easier to manage the heat in PEM Fuel cells. The fuel cells have typical
configuration that have one electrolyte, two electrodes – cathode and anode. Commonly,
fuel cells are also classified according to the electrolytes as well.
With close analysis of the above figure, it can easily be predicted that the future of fuel
cell is really bright. Since the year 2000, there has been a great progress made in this field
and it is believed that this will continue to grow in future and the growth rate will be
exponential. Therefore, it is high time for everyone involved in technological
development sector to support this green technology and make our future more
sustainable.
Figure 1: This chart shows the development in fuel particularly in the areas of Hydrogen production and its storage before 2000 till 2012. Source: https://www1.eere.energy.gov/hydrogenandfuelcells/images/fct_graph_accelerating_commercialization.gif
Fuel Cell Science & Technology – ME 6580
Khalil Raza – Wright State University
6
2. Operation of Fuel Cells: A fuel cell system works on the basis of electrochemical process that needs fuel, oxidant
or air and coolant to maintain the working temperature of the fuel cell systems. Besides,
it requires the proper pressure, flow rate of oxygen and fuel to regulate the systems
according to standard operating conditions of the fuel cells systems. Therefore, along-
with the fuel cell stacks, the fuel delivery system, air system and humidification system is
also installed to get the optimum level of energy from the fuel cells. As the fuel cells
generate the power the must be inverted to required form of source which would be used
to power a particular device. For example, the fuel cells generate power in direct current
and that has to be converted to AC power through a DC to AC inversion system.
Figure 2: Chemistry of Proton Exchange Membrane Fuel Cell Source: http://www.hydrogen-‐fuelcells.com/2012/08/hydrogen-‐fuel-‐cell-‐and-‐its-‐amazing.html
Fuel Cell Science & Technology – ME 6580
Khalil Raza – Wright State University
7
3. Chemistry of Fuel Cell Systems: As already stated in the introduction section that a fuel cell consists of an electrolyte and
cathode and anodes as two of its electrodes. The anode supplies electrons and cathode
receives the electrons. The cathode and anode are separated by an electrolyte. The
electrolyte conducts ions between cathode and anode in order to complete the cycle of the
circuit. When hydrogen is supplied as a fuel to the anode, it is oxidized generating the
hydrogen ions and electrons. Whereas, at the cathode the oxygen is fed where the
hydrogen ions from the anode absorb the electrons and produce water by reacting with
oxygen2.
4. Types of Fuel Cells: Fuel cells are classified according to their Electrolytes. Different electrolytes have
different working conditions thus are used for different application. Following are the
basic commonly fuel cells for the power generation:
1. Polymer Electrolyte Membrane Fuel Cells (PEMFC):
In PEMFCs the working temperature is considerably lower than other types of fuel cells
less than 90 degrees Celsius3. Therefore, more applicable for the vehicular application. A
membrane is used to separate the electrodes, which is used as catalyst for the proton
conduction. Primarily this type of fuel cells is used for portable application, back up
power and automotive vehicles.
2. Direct Methanol Fuel Cells (DMFC):
Direct methanol fuel cell comes under the category of the proton exchange membrane
fuel cells. They use methanol as the fuel. The major benefit of using this kind of fuel cell
is the methanol as a fuel, which is very easy to transport and its energy density is very
high. Methanol is non-volatile in liquid state. The downside of DMFC is that their
efficiency is quite low4. When the circumstances demands for higher power density over
higher efficiency DMFCs are well preferred.
3. Phosphoric Acid Fuel Cells (PAFC):
Phosphoric Acid Fuel Cell as the name suggests, they use liquid phosphoric acid as the
electrolyte. The anode and cathode are carbon paper coated with platinum catalyst5.
Fuel Cell Science & Technology – ME 6580
Khalil Raza – Wright State University
8
Positive charge ions flow through electrolyte from anode to cathode. Finally the electrons
produced are passed through an external circuit powering up the device with direct
electric current.
4. Molten Carbonate Fuel Cells (MCFC):
Molten Carbonate Fuel Cells use mixture of hydrogen and carbon monoxide produced
from water and fuel. Molten potassium lithium carbonate is used as electrolyte, which
carries out the process of producing electricity at the temperature of about 650 degree
Celsius6.
Figure 3: This shows the different fuel cell's fuel, electrolyte, and temperature range. Source: http://www.fuelcells.org/fuel-‐cells-‐and-‐hydrogen/types/
Fuel Cell Science & Technology – ME 6580
Khalil Raza – Wright State University
9
5. Basic Components of Fuel Cell Vehicles 1. The Motor:
Fuel Cell vehicles use an electric motor instead of internal combustion engines to get
mechanical power. Electric motors have many advantages over conventional internal
combustion engines in terms of high torque and they can achieve wide revolutions per
minute (RPM). Fuel cell vehicles can be powered through both the AC motors and DC
motors. A DC motor is quite simple in its operation and less expensive than Alternating
Current (AC) motors. It is very easy to control and regulate the DC motors.
Notwithstanding, DC motors are hard to find in bigger sizes to power up the vehicles and
they require more maintenance as well. The heavier downside of DC motors is that these
are not efficient when used as generators. Since, the basic goal is to achieve maximum
efficiency in fuel cell vehicles. The DC motors cannot generate power through
regenerative braking. Thus reducing down the overall efficiency of the system of the
vehicle. Whereas, the AC motor can perform this task very well. That is the reason the
AC motors are generally preferred over DC motors to be used in the fuel cell vehicles.
However, the AC motors are difficult to control and they require AC controller separately
to regulate the power. But, AC motors are easily available in much bigger size and can
produce enough power to propel a vehicle.
2. Transmission of Fuel Cell Vehicles:
Transmission of Fuel Cell vehicles is much simpler than the transmission of conventional
vehicles. Engines create torque at relatively lower rates, which requires the transmission
to obtain the required level of torque to transmit to the wheels through driveshaft and
differential. However, in the electric vehicles the motor already produces torque at flat
and high rates therefore, simpler transmission is needed to transmit the power to the
wheels. Without a complex transmission, the mechanical losses generated in transmission
can be avoided and efficiency can largely be improved. Although, it does not need
heavier and complex transmission like in conventional vehicles but it still needs a fixed
gear system to give the optimum level of power when required during climbing or at
higher working conditions.
3. AC Motor Controller:
AC motor requires a controller, which regulates and actuates the motor according to the
Fuel Cell Science & Technology – ME 6580
Khalil Raza – Wright State University
10
power demand of the vehicles. It also serves as actuator for the pedal control and sends
information to the motor to produce require torque and power when a driver pushes the
acceleration pedal. AC motor controller is also responsible for generating power from
regenerative braking. When vehicle is applied brake to stop the heat generated in the
wheel is transformed to DC power that is processed through AC Motor Controller.
4. Regenerative Braking:
Regenerative braking is the process of braking a vehicle to complete without the loss of
energy applied during the braking system. When the barking is applied to a vehicle the
kinetic energy of vehicle is transformed to another form and stored to be used for later
use. When a conventional vehicle applies brakes all the energy is transmitted to the heat
and thermally dissipated. Since the motor can produce power and simultaneously can be
used to generate power. As soon as the brake is applied the controller sends signals to the
ultra capacitor that automatically connects to the generator (motor) to insert load on
generator. The motor is connected to the wheels and when the ultra capacitor put load on
the generator it start-generating power from braking as the wheels are still spinning.
5. Ultracapacitors:
Ultracapacitors are used in fuel cell vehicles in addition to the batteries to store electrical
power. When the power is produced from the regenerative braking it is generated in
matter of few seconds and that power has to be immediately stored in some form.
Batteries cannot store that power so fast; therefore, the ultracapacitors is the new
technology, which has the answer to this problem. Ultracapacitors can store the fast-
generated electric power produced in extremely short time7. There are few advantages of
ultracapacitors, which can challenge the batteries. First, the rate of storing the electrical
energy is very high and secondly, the power density of the ultracapacitors is high too.
This adds into the more power storage in a smaller sized storage as compared to the
conventional batteries. Moreover, the ultracapacitors have higher life cycle and carries
less weight8. This less weight can also improve in efficiency of the vehicle as motor has
to do less amount of work to propel the lighter vehicle. In fuel cell vehicles, when
regenerative power is produced the AC controller regulates the ultracapacitors to open the
connection and connects with the motor. At this particular point the motor works as a
generator in which, the generator is loaded that starts generating power and that power is
Fuel Cell Science & Technology – ME 6580
Khalil Raza – Wright State University
11
transmitted and stored in ultracapacitors.
Figure 4: Basic operation of Fuel Cell Vehicles. Process Flow and Basic Devices used in the Fuel Cell Source: Sam Glidden, Jared Delahanty – Graduate Project, Hydrogen Fuel Cell Vehicles – The Future of Transportation
As shown in this above figure, an overall working of the devices used in the fuel cell
vehicles is presented. The green storage tanks in which, the hydrogen is stored or fed into
it from the any source. Oxygen is taken from the air by the help of the air pump;
afterwards, the air is filtered through filters to block any kind of additional particles.
Fuel Cell Science & Technology – ME 6580
Khalil Raza – Wright State University
12
Oxygen from air and hydrogen from the storage tank is allowed for the chemical reaction
in the fuel cell stacks. Electricity is generated in the fuel cells and transmitted to AC
controller and ultracapacitors simultaneously. Since the power produced by the Fuel Cell
is in DC. Therefore, it is converted to the AC and passed to the AC motor which, further
supplies power to the wheels through fixed gear drive. Also, there is another line going
back to ultracapacitors through the AC controller. This line transmits power back to
Ultracapacitors when generated during the regenerative braking.
6. Hydrogen Production: Most of the hydrogen is produced from the hydrocarbons or fossil fuel. Hydrocarbons are
composed of H2 hydrogen and Carbon, during the process of producing the hydrogen the
hydrocarbons are decomposed into hydrogen and carbons. Hydrogen is stored for the
usage for power generation and carbon is released into our environment.
The released carbon in atmosphere later combines with oxygen to form carbon dioxide.
Though this process of generating the hydrogen is cheaper but the it is not clean process
at all. At this point in time, more focused attention is being given to the clean production
Figure 5: Process of Generating Hydrogen Gas by the Electrolysis of the Water Source:http://www.instructables.com/files/orig/F4A/54HN/F5R8MQ53/F4A54HNF5R8MQ53.gif
Fuel Cell Science & Technology – ME 6580
Khalil Raza – Wright State University
13
of hydrogen despite being its costlier process. The cleanest process of getting hydrogen is
by the electrolysis of the water.
7. Hydrogen Storage for Fuel Cell Vehicles: Hydrogen is extremely light gas; thus, it has to compressed at really high pressures and
stored in extremely high strength tanks. So, that in case of collision or accident the tanks
must not be ruptured. Hydrogen does not need spark to get ignited, the only thing it needs
get ignited is the oxygen from the atmosphere and it will blow off the tank. So far,
hydrogen is stored in the following three ways.
• Metal Bounded Hydrogen
• Liquid Hydrogen
• Carbon Nanotubes
1. Metal Bounded Hydrogen Storage:
The high-pressurized hydrogen gas or liquid hydrogen is not safe in case of collision. In
metal bounded hydrogen, the hydrogen is heated and merged with the metal. This makes
it safer to be used for vehicular application as it does not blows off the tanks even if the
tanks get ruptured during collision. The only downside of using this technology for the
storage of hydrogen is the cost of the process9. The process is relatively costlier and while
heating the hydrogen to bound with the metal, the overall efficiency of the fuel cell
vehicle reduces down considerably. Therefore, if the cost is major factor than metal
bounded hydrogen is not preferable to use as storage.
2. Storing Hydrogen as Liquid:
To store hydrogen as liquid, it has to be cooled down to 20 K10 above absolute
temperature so that it should not evaporate in the atmosphere. It takes huge amount of
energy to get this temperature range. Therefore, in this process the cost and efficiency is
affected.
3. Hydrogen storage in Carbon Nanotubes:
Hydrogen can be stored in Nano-scaled carbon. There have been several claims that
hydrogen can be stored in carbon nanotubes obtaining 50wt% hydrogen11. Still this
process is in early stage of development. It would take time to get matured and can be
used practically in the fuel cell vehicles.
Fuel Cell Science & Technology – ME 6580
Khalil Raza – Wright State University
14
8. Conclusion: Fuel Cell Technology for Automotive Application can bring a positive change towards
transportation industry by solving the environmental problems and at the same time
providing safe and sustainable medium of transport. Since, the process involved direct
conversion of chemical energy to electrical energy, it has considerably higher efficiency
than the convention vehicles. Moreover, the simplicity of transmission system can add
more efficiency to the system. Another positive side of fuel cells is that the motor
efficiency is much higher the internal combustion engine (ICE). The ICE have the lower
efficiency as much as 20 – 25 percent whereas, the motor efficiency can as much 90 %.
Hydrogen is clean, plenty in nature and renewable source of fuel. Currently the only
problem is optimizing the technology and get and store the hydrogen in a cheap and safer
mode. With the advancement of technology, there is a great hope that there would be
major breakthrough in the future in getting the hydrogen and easily be used for storage
and power up the vehicles.
Fuel Cell Science & Technology – ME 6580
Khalil Raza – Wright State University
15
9. Reference 1 Fuel Cell -‐ http://en.wikipedia.org/wiki/Fuel_cell 2 Fuel cell – From Chemical Energy to Electrical Energy -‐ http://www.britannica.com/EBchecked/topic/221374/fuel-‐cell 3 Types of Fuel Cells -‐ http://www.fchea.org/index.php?id=44 4 Direct Methanol Fuel Cells Systems -‐ DMFC http://www.fuelcellmarkets.com/fuel_cell_markets/direct_methanol_fuel_cells_dmfc/4,1,1,2504.html 5 Phosphoric Acid Fuel Cell Technology http://www.fossil.energy.gov/programs/powersystems/fuelcells/fuelscells_phosacid.html 6 Types of Fuel Cells -‐ http://www.britannica.com/EBchecked/topic/221374/fuel-‐cell 7 2004, Sam Gliden and Jared Delahanty, Hydrogen Fuel-‐Cell Vehicles, The Future of Transportation. 8 John M. Milter, Natural Science – Ultracapaciotrs challenge the battery http://www.ec-‐central.org/kfi/files/Ultracap-‐%20World%20&%20I%20-‐%20June%202004.pdf 9 2007 Billur Sakintuna, Farida Lamari-‐Darkrim, Michael Hirscher, “Metal hydride materials for solid hydrogen storage: A review.” International Journal of Hydrogen Energy. 10 Takuji Hanada and Kunihiro Takahashi Liquid Hydrogen Storage, Energy Carries and Conversion Systems Vol – II, Liquid Hydrogen. 11 Hydrogen Storage – Carbon Nanotubes http://en.wikipedia.org/wiki/Hydrogen_storage#Carbon_nanotubes