It is an electrochemical
device which convert
hydrogen and oxygen into
water producing electricity
and heat in the process.
It is much like a battery that
can be recharged while you
are drawing power from it.
It provides a DC voltage that
can be used to power
motors, lights and any
number of electrical
Fuel cells differ from conventional cells in the respect that
active material (fuel & oxygen) are not contained within the cell
but are supplied from outside.
Pure or fairly pure hydrogen gas would be preferred fuel for
Alternatively impure hydrogen obtained from hydrocarbon fuels,
such as natural gas , methane, LPG & liquid petroleum
products can be used in fuel cell as a fuel.
Efforts are going on to develop cells that can use carbon
monoxide as the fuel; if they are successful, it should be
possible to utilize coal as the primary energy source.
Main uses of fuel cells are in power production, automobile
vehicles and in special military use.
6. The Invention of the Fuel Cell
Sir William Grove invented the first fuel cell in 1839. Grove
knew that water could be split into hydrogen and oxygen by
sending an electric current through it (a process called
electrolysis). He hypothesized that by reversing the procedure
you could produce electricity and water.
He created a primitive fuel cell and called it a gas voltaic
battery. After experimenting with his new invention, Grove
proved his hypothesis. Fifty years later, scientists Ludwig Mond
and Charles Langer coined the term fuel cell while attempting
to build a practical model to produce electricity
7. What is a fuel cell?
A fuel cell is an electrochemical energy conversion device.
A fuel cell converts the chemicals hydrogen and oxygen into
water, and in the process it produces electricity.
A fuel cell is a device that generates electricity by a
chemical reaction. Every fuel cell has two electrodes, one
positive and one negative, called cathode and anode
respectively. The reactions that produce electricity take place at
8. Why we need fuel cell?
Due to energy crisis all over the world.
Due to the issue of global warming.
Due to the unavailability of different renewable sources at each
and every place due to geographic condition.
Fuel cell provides an alternate efficient non polluting power
source that produces no noise and has no moving parts.
It is expected that by 2050 the global energy demand is going
to rise by 2 to 3 times.
This calls for optimization of generation of energy through well-
known sources, preferably renewable energy for commercial
9. Classification Of Fuel Cells:
Classification of fuel cells is very difficult as several operational variable
Based on the temperature range in which they operate: low
temperature(25-100 C), medium temperature (100-500) , high
temperature(500-1000) & very high temperature(above 1000)
According to the type of electrolyte : aqueous, non aqueous, molten
According to the physical state of the fuel: Gas(hydrogen, lower
hydrocarbons ), Liquid(alcohols, hydrazine, higher hydrocarbons),
Primary fuel cell: Reactants are passed through the cell only once &
the products of the reaction being discarded. (H 2 – O 2 fuel cell )
Secondary fuel cell: Reactants are passed through the cell many
times because they are regenerated by different methods.( Nitric oxide
– chlorine fuel cell)
10. Types of fuel cell
As per the fuel used the fuel calls are classified as follows.
11. Design Principle & Operation of Fuel
Chemistry of fuel cell
2H2 4H + 4e
O2 + 4H + 4e 2H2O
2H2 + O2 2H2O
12. Hydrogen Oxygen Cell:
40% KOH solution as electrolyte (Ion exchange membrane).
The membrane is non permeable to the reactant gases, hydrogen and
oxygen, which thus prevents them from coming into contact.
The membrane is however , permeable to hydrogen ions which are the
current carriers in the electrolyte.
The desired properties of an ideal ion exchange membrane electrolyte
High ionic conductivity.
Zero electronic conductivity
Low permeability of fuel and oxidant
Low degree of electro-osmosis.
High resistance to dehydration.
High resistance to its oxidation or hydrolysis and,
Considerable amount of research has been carried out in a search for
the ideal membrane.
Interpolymers of polyflurocarbon and poltstyerene sulfonic acids have
been found to be quite satisfactory.
In order that electrolyte resistance be low as possible, a thin sheet of
this material (0.076 cm thickness) is used as the electrolyte.
An advantageous feature of this electrolyte is that it retains only a
limited quantity of water and rejects excess water produced in fuel cell.
This cell operates at about 40-60 ̊C. The thermodynamic reversible
potentials for the reaction is 1.23 volts at 25˚C.
14. Fossil Fuel Cells:
The most interesting fuel cells for the near future are modified
hydrogen- oxygen cells, in which a gaseous or liquid hydrocarbon is
the source of hydrogen.
Coal may be serve as the primary energy source for fuel cells. Cells
based on fossil fuels have three main components.
The fuel processor which converts the fossil fuel into a hydrogen rich
The power section consisting of the actual fuel cell (or combination of
The inverter for changing the direct current generated by the fuel cell
into alternating current to be transmitted to user.
In phosphoric cell utilizes a concentrated aqueous solution of
phosphoric acid as the electrolyte.
The primary fuel is light hydrocarbon, such natural gas or nephtha.
The operating temperature is 150 to 200˚ C and the discharge voltage
is 0.7 to 0.8 volt.
Each cell unit is only a few millimeters thick so that a large number can
be stacked in a package of reasonable size to produce the desired
voltage and power.
17. Molten Carbonate Cells:
These high temperature fuel cells offer the prospect for use with
variety of fossil fuels, including coal.
A special feature of these cells is that during operation they can
oxidize CO to CO2 as well as hydrogen to water.
Hence gaseous mixture of H2 and CO, which are relatively
inexpensive to manufacture, can be used in the cell, the presence of
CO2 would have only a minor effect.
The electrolyte in the high temperature fuel cells under development is
a molten mixture of alkali metal (lithium, sodium, potassium)
carbonates at a temperature of 600-700 ˚C.
This is retained in an inert porous matrix sandwiched between two
porous nickel electrodes.
The mixture of H2 and CO is supplied to negative electrodes and
oxygen to the positive electrodes.
The discharge e.m.f of the cell is above 0.8 volt.
An important aspect of the molten carbonate fuel cell is that the
discharged gases, consisting of the steam and CO2 products and
nitrogen from the air, are at a temperature exceeding 540˚ C.
The hot gases could be used to provide industrial process heat, to
operate a gas turbine or to produce steam in a waste heat boiler to
drive a steam turbine which produce electric power.
20. Solid Oxide Electrolyte Cells:
Certain solid, ceramic oxides are able to connect electricity at high
temperatures and can serve as electrolyte for fuel cells.
A possible electrolyte is zirconium dioxide containing a small amount
of another oxide to stabilize the crystal structure; this material is able
to conduct oxygen ions at high temperature.
The electrode material might be porous nickel and the operating
temperature in the range 600-1000˚ C .
Electrochemical catalyst would not be required.
Other energy sources or fuels, that can be conveniently stored and
transported in liquid form such as methanol, ammonia and hydrazine
have been proposed for fuel cell.
21. Methanol as a fuel:
Methanol can be catalytically reformed with steam at about 200˚C to
yield a mixture of hydrogen (75 volume percent) and carbon dioxide.
This gas can be supplied to the negative electrode of a fuel cell with air
at the positive electrode.
The cell with aqueous phosphoric acid solution as the electrolyte,
might be similar to those already described.
22. Ammonia (NH3) as a fuel:
In this the ammonia gas obtained from the stored liquid is decomposed
catalytically into hydrogen and nitrogen.
Part of the hydrogen is burned in air to provide the heat required for
Other hydrogen is supplied to the negative electrode of the hydrogen
cell in which potassium hydroxide is used as electrolyte.
The nitrogen produced due to decomposition is an inert gas and plays
no roll in the cell.
The advantage of ammonia as fuel is that it can be stored in the
The disadvantage include higher vapour pressure and cell
operate satisfactory at low temperature.
23. Hydrazine(N2H4) as a fuel:
A compact fuel cell for mobile application possibly for vehicle
propulsion utilizes the liquid hydrazine as a fuel and hydrogen
peroxide or air as the energy source.
Hydrazine is injected as required into the aqueous potassium
hydroxide potassium hydroxide electrolyte to provide the active
material at the negative electrode.
The oxygen is either supplied by decomposition or from air.
The electrode is made up of nickel (negative) or silver (positive) as the
The overall cell reaction is the oxidation of hydrazine to water and
nitrogen, but the discharged e.m.f is similar to that of the hydrogen
Basic drawback of hydrogen oxygen cell is that hydrogen and oxygen
are gases, so there is storage difficulty.
Liquid hydrazine is highly reactive/ toxic a well as costly.
Power output is more (1.56V)as compared to hydrogen oxygen
In Aluminum oxygen cell , the aluminum forms the negative
electrode and the oxygen is the positive electrode.
The electrolyte is an aqueous solution of sodium hydroxide.
25. Regenerative Systems:
A regenerative fuel cell is one in
which the fuel cell product
(water) is recovered into the
reactants (hydrogen and
oxygen) by one of the several
possible methods – thermal,
electrical and radio chemical.
There are two stages in a
regenerative fuel cell:
Conversion of fuel cell
reactants into products while
producing electrical energy, and
Reconversion of fuel cell
products into reactants.
26. Conversion efficiency of Fuel Cell:
The electrical energy generated by fuel cell depends on what is called
the “free” energy rather than on heat energy of the overall cell reaction.
The free energy of formation of 1 mole (18 grams) of liquid water from
hydrogen and oxygen gases at atmospheric pressure is 56.67 Kcal or
237 KJ at 25˚C while the heat energy of the reaction under the same
conditions is 68.26 Kcal (286 KJ)
Thus theoretical efficiency of the conversion of the heat energy into
mechanical energy in a hydrogen oxygen fuel cell is
(56.67/68.26)*100 = 83 %
Efficiencies as high as 70% have been observed, but the practical
cells using pure fuel have conversion efficiency of 50-60%.
The efficiency is lower when we use air as the source of oxygen and
when hydrogen is derived from hydrocarbon sources.
However this value is higher than the efficiency that is obtain by using
these sources in the conventional plants.
The discharged voltages observed in actual cells are always below the
theoretical value, the difference increasing with increasing strength of
the current drawn from the cell.
For the hydrogen oxygen cell at 25˚C with the gases at atmospheric
pressure , the ideal e.m.f is 1.23 Volts & for the moderate currents at
which fuel cells normally operate the e.m.f is 0.7 to 0.8 volts.
This deviation from the theoretical e.m.f accounts for the conversion
efficiency of a fuel cell being below the ideal maximum value.
The departure of a fuel cell from ideal behavior arises from several
factors one is the Inherent slowness of the electrode reactions.
This is dominant at low current drains.
It can be reduced by an effective electrochemical catalyst and by
increasing the operating temperature.
At larger currents there is an additional contribution from the electrical
resistance of the electrolyte.
A low resistance (i.e. high conductivity) electrolyte is therefore
In ideal hydrogen oxygen cell, (100-83) = 17 % of the chemical
reaction energy would be liberated as heat & this proportion increases
in an actual cell.
In order to avoid this temperature rise, heat is removed from the fuel
cell during operation.
In some cell design it is proposed to utilize the heat to provide space
heating of a building and to supply hot water.
The heat released in high temperature cells might be used for
industrial purposes (i.e. process heat) or to generate steam.
29. Polarization in Fuel Cells:
The difference between the
theoretical voltage and the
actual voltage is known as
the polarization. This is also
called as overvoltage.
The effect of polarization is to
reduce the efficiency of the cell
from the theoretical maximum.
Significant drop in voltage and
hence energy loss takes place
as the current density is
There are mainly three types of polarization:
Activation Polarization.(Chemical polarization)
Resistance or ohmic Polarization and
31. Activation Polarization:
This is related to the activation energy barrier for the electron transfer
process at the electrode.
In fuel cells electrons are liberated and reaction is chemisorption
At low current densities significant number of electrons are not
emitted, which results in such a potential loss.
This process requires that certain minimum activation energy supplied
so that sufficient number of electrons are emitted, this energy is
supplied by the output of the cell.
This loss is known as activation or chemical polarization.
This polarization may be reduced by using better electrode
catalysts, increasing surface area, and by raising operating
32. Resistance Polarization:
The voltage drop in linearly related to the current flow according to the
The internal resistance is composed of the electrode resistance, the
bulk electrolyte resistance and interface contact resistance between
electrode and electrolyte.
The loss due to resistance polarization is significant when current
density is quite large.
The reduction in the internal resistance is the main design criteria for
low resistance polarization losses.
The electrolyte resistance can be decreased usually by using
more concentrated electrolyte by closer spacing of electrodes
and by increased temperature.
Loss due to resistance polarization can be reduced by:
Selecting proper shape of the electrode to have minimum contact
between electrode and electrolyte.
Reducing the gap between electrodes.
By using concentrated electrolyte.
34. Concentrated Polarization:
This type of polarization tends to limit the current drawn.
It is generally divided into two categories
Electrolyte side polarization: This is due to the slow diffusion in the
electrolyte causing a change in concentration at the electrodes.
This effect can be minimized by increasing the electrolyte
concentration or by stirring or circulating the electrolyte.
Gas side polarization: This is caused from slow diffusion of reactants
through the porous electrode to the reaction site or of slow diffusion of
products away from the reaction site.
The loss in voltage due to gas side polarization is reduced by using
electrodes of smaller pore size and by increasing temperature.
We have observed that all the three loses in a fuel cell are
decreased by increasing temperature , due to this a given cell is
usually operated in practice at the higher end of its temperature
38. Advantages & Disadvantages:
Fuel cell system are environmentally.
High conversion efficiency .
Extremely low emission.
Noise less operations so readily accepted in residential areas.
Has no moving parts.
Availability to use at any location. So less transmission & distribution
No requirements of cooling tower as conventional plants.
Less space require as compared to conventional plants.
The main disadvantages of fuel cells are their high initial costs
and low service life.
The application of the fuel cell may be discussed in the following areas.
Central Power Station.
40. Some useful points regarding
The e.m.f. or voltage of a fuel cell depends to some extend on the
discharge current strength. The average voltage per cell is 0.75 volt.
By joining a number of cells in series and parallel can provide any
reasonable voltage and current.
Types of current that are generated by fuel cell.
If the fuel cells of reasonably low cost and long life can be produced , a
major use might be by electrical utilities for load leveling
A long term possibility is a central station power plant in which coal is
gasified and the gas is used to generate electricity directly by means of
Such an installation is expected to have a higher efficiency for fuel
utilization than a conventional steam- electrical plant.
Portable generating sets seem to be a favorable field for fuel cells.
Here already fuel cells appear to be competitive as compared with
conventional sources. Low temperature fuel cells have a favorable
position for operating times of 3000 to 4000 hours per year, using
methanol as a fuel.
As we know that demand for power is variable. when the demand is
less than the rated output, the excess would be used to generate
hydrogen by electrolysis of water.
At the times when the load is greater than the rated power, the
hydrogen would be used in fuel cells to satisfy the additional demands.
By using fuel cell at the site of power, the transmission and distribution
cost would be reduced.
For new load centers different fuel might be utilized more economically
in fuel cells located near the new load centers.
Some fuel cells have been proposed for remote or rural areas or
unattended location , for mobile and emergency power sources, and
for vehicle propulsion.
The aluminum- air cell is of special interest for electrical vehicle
propulsion because of the high specific energy that is possible. The
weight of these batteries are same as conventional batteries.
More than this methanol –air and hydrogen – oxygen cell are also
used for vehicle propulsion.
Many of the fuel cells currently under development are for special
application where convenience is of importance, cost is secondary.
For these application hydrogen is the superior fuel from the view point
of the reactivity and availability of invariant electrolyte, although it is
It seems likely that hydrogen- oxygen and hydrogen carbon- oxygen cells
will be used to an increasing extent in special military & space application.
Fuel cells powered cars will
start to replace gas and diesel
engine cars in about 2055.
Fuel cell powered buses are
already running in several
This promising application will
one day even power our
45. Telecommunications - With the use of computers, the Internet, and
communication networks steadily increasing, there comes a need for
more reliable power than is available on the current electrical grid, and
fuel cells have proven to be up to 99.999% (five nines) reliable. Fuel
cells can replace batteries to provide power for 1kW to 5kW telecom
sites without noise or emissions, and are durable, providing power in
sites that are either hard to access or are subject to inclement
weather. Such systems would be used to provide primary or backup
power for telecom switch nodes, cell towers, and other electronic
systems that would benefit from on-site, direct DC power supply.
Initial cost of installation is higher.
Comparative cost of energy storage of fuel cells is around twice that of
conventional sources of energy.
Energy produced by one fuel cell is around 0.7 volts.
51. Recent development:
LLC, Latham, NY has successfully developed 50 KW power
Fuel cell of capacity 1.5KW is powering houses in Australia.
GAIL is actively involved in establishing fuel infrastructure for
fuel cell vehicles in India.
CECRI, Karaikudi has developed and tested MCFC stack.
The above discussion prove the existence of huge market for fuel
The commercial power units are technically feasible .
Research and development should be aimed at reducing cost and
Future cities can be planned on fuel cell systems for their power and