1.Introduction 2.Properties of Fuel cell 3.Fuel Cell Classification 4.Various types pf Fuel Cell description 5. Advantages and Disadvantages

1. Chapter 03:Fuel Cell
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“Fuel cell”
 Fuel cell:
A Fuel Cell is a device that converts the Chemical energy from a fuel into electricity through a
chemical reaction with oxygen or another Oxidizing agent. Fuel cells are different from batteries
in that they require a continuous source of fuel and oxygen/air to sustain the chemical reaction.
There are many types of fuel cells, but they all consist of an anode a cathode and an electrolyte
that allows charges to move between the two sides of the fuel cell. Fuel cells are used for
primary and backup power for commercial, industrial and residential buildings and in remote or
inaccessible areas. They are also used to power fuel-cell vehicles, including forklifts,
automobiles, buses, boats, motorcycles and submarines.
 How do Fuel cells work?
The purpose of a fuel cell is to produce an electrical current that can be directed outside the cell
to do work.
Single fuel cell consists of three parts:
1. Anode (that is a negative electrode that provides electrons)
2. An electrolyte in the center.
3. Cathode (a positive electrode that accepts electrons)
-The hydrogen is supplied to the fuel cell anode catalyst on the anode help separate the hydrogen
atoms into protons, hydrogen ions and electrons.
-The electrolyte in the center allows only the proton to pass through the electrolyte to the cathode
side of the fuel cell.
-These electrons from the hydrogen can’t pass through the electrolyte and hence pass through a
circuit joined between anode and cathode & hence in turn generate electricity that passes through
that circuit.

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-As oxygen flows into fuel cell cathode, another catalyst causes oxygen protons and electrons to
combine to produce pure water & heat.
Fig: working principle of a fuel cell.
 Types of fuel cell
1.Proton Exchange Membrane Fuel Cells (PEMFC)
2. Direct Methanol Fuel Cells (DMFC)
3. Phosphoric Acid Fuel Cells (PAFC)
4. Alkaline Fuel Cells (AFC)
5. Solid Oxide Fuel Cells (SOFC)
6. Molten Carbonate Fuel cells (MCFC)

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 Bischoff cell
 Construction:
Fuel (here carbon) acts as anode. Wire gauze makes electrical connection with fuel bed. Oxygen
electrode (set up by circulating oxygen continuously through bed of granular magnetite) acts as
cathode. Sodium carbonate acts as electrolyte.
Fig: Construction of Bischoff cell
 Working/mechanism of Bischoff cell:
Anode: The carbon ions (C4+
) generated at anode react with carbonate ions present in electrolyte
to form carbon dioxide.
C-4e C4+
2CO3
2-
+ C4+
3CO2
2CO3
2-
+C C4+
+3CO2
Cathode: At the cathode oxygen ionizes at the magnetite surface to form oxygen ions.
O2+ 4e 2O2
2-
4Na+
+ 2O2-
2Na2O
4Na+
+ O2+ 4e 2Na2O

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Since the clay support for the electrolyte is thin and porous, sodium oxide and carbon dioxide
readily come into contact and in doing so react to regenerate the ionized electrolyte.
Na2O + CO2 2Na+
+ CO3
2-
Overall cell reaction: C+ O2---------- CO2
 Hydrogen/Oxygen fuel cell
The overall chemical reaction in a hydrogen fuel electrochemical cell involves the oxidation of
hydrogen by oxygen to produce only water. Hydrogen fuel cells offer an alternative to
rechargeable cells and batteries.
-We can get hydrogen from reforming process such as coal reforming, natural gas reforming,
Fischer tropsch synthesis.
- Very small quantity of voltage is produced from fuel cell.
-Extreme pure H2 are used for hydrogen fuel cell.
 Hydrogen fuel cells are mainly two types
1. Davtyan fuel cell
Cell voltage: 0.75V, If very few amount of CO are present in davtyan fuel cell then it occur a
problem. Efficiency: 60%
2. Bacon fuel cell
Cell voltage: 0.79V, Temp: 2000
c, Pressure: 400lb/inch2
. Efficiency: 60%.
 Bacon fuel cell
The alkaline fuel cell (AFC), also known as the Bacon fuel cell) after its British inventor, Francis
Thomas Bacon, is one of the most developed fuel cell technologies. Alkaline fuel cells consume
hydrogen and pure oxygen producing potable water, heat, and electricity. They are among the
most efficient fuel cells, having the potential to reach 70%.Alkaline fuel cell also known as
hydrogen fuel cell or hydrogen-oxygen fuel cell.
This is one of the oldest designs for fuel cells; the United States space program has used them
since the 1960s.
• The AFC is very susceptible to contamination, so it requires pure hydrogen and oxygen. It is
also very expensive, so this type of fuel cell is unlikely to be commercialized.
• They are among the most efficient fuel cells, having the potential to reach 70%.The electrolyte
used is aqueous potassium hydroxide (KOH). The electrolyte acts as a medium for conduction of

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ions in between the electrodes. Porous (and catalyzed) graphite electrodes .Semi-permeable,
Teflon coated carbon material. Heavily catalyzed.
Construction:
Aqueous potassium hydroxide (KOH) is used as an electrolyte in an alkaline fuel cell. Ni coated
porous graphite is used as anode .Ni and nickel oxide coated graphite materials act as a cathode.
Nickel and nickel oxide is act as a catalyst at the electrode.
Working
The chemistry behind the AFC is:-
The fuel cell produces power through a redox reaction between hydrogen and oxygen. At the
anode, hydrogen is oxidized, producing water and releasing two electrons. The electrons flow
through an external circuit and return to the cathode, reducing oxygen producing hydroxide ions.
The net reaction consumes one oxygen atom and two hydrogen atoms in the production of each
water molecule. Electricity and heat are formed as by-products of this reaction.
Reaction:
Anodic: 2H2+ 4OH-
- 4e ----- 4H2O
Cathodic: O2 + 2H2O +4e ------ 4OH-
-----------------------------------------------
Overall: 2H2+ O2---------- 2H2O

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Applications of AFC (alkaline fuel cell):
The alkaline fuels cells are the most used as they are the most efficient and are cheap to
manufacture.
• The first alkaline fuel cells were used by NASA in the Apollo missions to provide power as
well as provide with potable water for the astronauts.
• The alkaline fuel cell is commercially incubated into a 22 seated hydrogen ship ,power assisted
by an electric motor that gets its electricity from a fuel cell.
 Proton Exchange Membrane Fuel Cells (PEMFC)
Proton exchange membrane fuel cells, also known as polymer electrolyte membrane (PEM) fuel
cells (PEMFC), are a type of fuel cell being developed for transport applications as well as for
stationary fuel cell application and portable fuel cell application.
Cell Reaction:
Anodic: 2H2 -4e----------- 4H+
Cathodic: O2+ 4H+
+4e -------- 2H2O

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 Redox fuel cell:
-Fe2+/
Fe3+
cell
Na2CO3+
magnetite+ titanium
trioxide + soda glass
Fe2O3+ Fe3O4
AirCO2+ H2
50%+ 50% Cathode
Anode

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Mechanism:
Anode: 4Fe2+
-4e -------------- 4Fe3+
Regeneration: Fe3+
+2H2O+e --------------- Fe2+
2H2O+ C- 4e --------------------- 4H+
+ CO2
Cathodic reaction: 4Fe3+
+ 4e --------- 4Fe2+
4Fe2+
+4H+
+ O2 ------------ 2H2O + 4Fe3+
4H+
+ O2 + 4e --------------------- 2H2O
Advantages of fuel cell
 Fuel cells have a higher efficiency than diesel or gas engines.
 Most fuel cells operate silently, compared to internal combustion engines. They are therefore
ideally suited for use within buildings such as hospitals.
 Fuel cells can eliminate pollution caused by burning fossil fuels; for hydrogen fuelled fuel
cells, the only by-product at point of use is water.
 If the hydrogen comes from the electrolysis of water driven by renewable energy, then using
fuel cells eliminates greenhouse gases over the whole cycle.
 Fuel cells do not need conventional fuels such as oil or gas and can therefore reduce
economic dependence on oil producing countries, creating greater energy security for the
user nation.
 Since hydrogen can be produced anywhere where there is water and a source of power,
generation of fuel can be distributed and does not have to be grid-dependent.
 Low temperature fuel cells (PEMFC, DMFC) have low heat transmission which makes them
ideal for military applications.
 Higher temperature fuel cells produce high-grade process heat along with electricity and are
well suited to cogeneration applications (such as combined heat and power for residential
use).
 Operating times are much longer than with batteries, since doubling the operating time needs
only doubling the amount of fuel and not the doubling of the capacity of the unit itself.
 Unlike batteries, fuel cells have no "memory effect" when they are getting refuelled.
 The maintenance of fuel cells is simple since there are few moving parts in the system.
Disadvantages of Fuel Cells
 High costs compared to other energy systems technology.
 Operation requires a consistent fuel supply.
 The technology is not yet fully developed and few products are available.
 Some fuel cells use expensive materials.