Presented by:
UB. No: -
FEBRUARY 4, 2019
An Overview
Principles of Fuel Cells
Definition of A Fuel Cell
Difference Between Battery and A Fuel Cell
Various types of Fuel Cells
Application, Advantages and Disadvantages Comparison of Fuel
Cell Technologies
Principles of Fuel Cells
1.1Definition of Fuel Cells
We can note that; -
Fuel cell: An electrochemical device, which converts chemical energy to electrical energy without
combustion and has its fuel & / or oxidant supplied externally.
Fuel cell is an electrochemical devise, which converts chemical energy of the fuel to electricity by combining
gaseous hydrogen with air in the absence of combustion. The basic principles of operation of the fuel cell is
similar to that of the electrolyser in that the fuel cell between them.
Fuel Cell is a device that generates electricity by a chemical reaction. Every fuel cell has two electrodes called,
respectively, the anode and cathode.
Fuel cell can be seen as an energy storage device as energy can be input to create hydrogen and oxygen which
can remain in the cell until its used at latter time. In this sense, they work much like a battery. On the other
hand, uses an external supply of chemical energy and can run indefinitely. The sources of technology if generally
referred to as FUEL and this gives the FUEL CELL its name although there is no combustion involved. Hydrogen
fuel cell is actively being researched and develop.
Every fuel cell also has an electrolyte, which carries electrically charged particles from one electrode to the
other, and a catalyst, which speeds the reactions at the electrodes.
Hydrogen is the basic fuel, but fuel cells also require oxygen. One great appeal of fuel cells is that they generate
electricity with very little pollution–much of the hydrogen and oxygen used in generating electricity ultimately
combine to form a harmless byproduct, namely water.
How does 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,
such as powering an electric motor or illuminating a light bulb or a city. Because of the way electricity behaves,
this current returns to the fuel cell, completing an electrical circuit. The chemical reactions that produce this
current are the key to how a fuel cell works.
There are several kinds of fuel cells, and each operates a bit differently. But in general terms, hydrogen atoms
enter a fuel cell at the anode where a chemical reaction strips them of their electrons. The hydrogen atoms are
now "ionized," and carry a positive electrical charge. The negatively charged electrons provide the current
through wires to do work. If alternating current (AC) is needed, the DC output of the fuel cell must be routed
through a conversion device called an inverter.
A Fuel cell is like a battery but with constant fuel and oxidant supply
Two main electrochemical reactions occur
in the fuel cell. One at the anode (anodic
reaction) and one at the cathode.
At the anode, the reaction releases
hydrogen ions and electrons whose
transport is crucial to energy production.
2H+ + 2eThe hydrogen ion on its way to the cathode
passes through the polymer membrane
while the only possible way for the
electrons is through an outer circuit. The
hydrogen ions together with the electrons
of the outer electric circuit and the oxygen which has diffused through the porous cathode reacts to water.
2H+ + ½ O2 + 2e-
The water resulting from this reaction is extracted from the system by the excess air flow. The reaction is:
H + ½ O2
This process occurs in all types of fuel cells.
Difference Between Battery and A Fuel Cell
 Batteries have a limited range, take substantial time to re-charge and cool before reuse, and are prone
to voltage drops as power discharges.
 Unlike batteries, fuel cells can be rapidly refueled, eliminating the time and cost associated with
swapping batteries.
 The voltage delivered by the fuel cell is constant as long as hydrogen fuel is supplied.
 Early Markets: Fuel Cells for Material Handling Equipment — This fact sheet provides an overview of fuel
cells as an alternative to batteries and combustion engines for material handling equipment. It features
a lifecycle-cost-analysis comparison table.
 Compared with batteries, fuel cells offer longer continuous runtime and greater durability in harsh
outdoor environments. And with fewer moving parts, they require less maintenance than generators or
batteries. They can also be monitored remotely, reducing maintenance time. Compared with
generators, fuel cells are quieter and have no emissions.
 On a lifecycle basis, fuel cells can offer significant cost savings over both battery-generator systems and
battery-only systems when shorter runtime capabilities of up to 72 hours are sufficient (fuel cell system
costs for longer runtimes can be higher than incumbent technologies due to the cost of hydrogen
storage tank rentals).
Alkali fuel cells operate on compressed hydrogen and oxygen. They generally use a
solution of potassium hydroxide (chemically, KOH) in water as their electrolyte.
Efficiency is about 70 %, and operating temperature is 150 to 200 degrees C, (about 300
to 400 degrees F). Cell output ranges from 300 watts (W) to 5 kilowatts (kW). Alkali cells
were used in Apollo spacecraft to provide both electricity and drinking water.
Fig.2 Alkali cell.
Molten Carbonate fuel cells (MCFC): use high-temperature compounds of salt (like sodium or magnesium)
carbonates (chemically, CO3) as the electrolyte. Efficiency ranges from 60 to 80%, and operating temperature is
about 650 degrees C. Units with output up to 2 megawatts (MW) have been constructed, and designs exist for
units up to 100 MW. The high temperature limits damage from carbon monoxide "poisoning" of the cell and
waste heat can be recycled to make additional electricity. Their nickel electrode-catalysts are inexpensive
compared to the platinum used in other cells. But the high temperature also limits the materials and safe uses of
MCFCs–they would probably be too hot for home use. Also, carbonate ions from the electrolyte are used up in
the reactions, making it necessary to inject carbon dioxide to compensate.
Fig.3 Molten carbonate cell
Phosphoric Acid fuel cells (PAFC): use phosphoric acid as the electrolyte. Efficiency ranges from 40 to 80%, and
operating temperature is between 150 to 200 degrees C. Existing phosphoric acid cells have outputs up to 200
kW, and 11 MW units have been tested. PAFCs tolerate a carbon monoxide concentration of about 1.5%, which
broadens the choice of fuels they can use. If gasoline is used, the sulfur must be removed. Platinum electrodecatalysts are needed, and internal parts must be able to withstand the corrosive acid.
Fig.4 how both phosphoric acid and PEM fuel cells operate
Proton Exchange Membrane (PEM) fuel cells: work with a polymer electrolyte in the form of a thin, permeable
sheet. Efficiency is about 40 to 50%, and operating temperature is about 80 degrees C . Cell outputs generally
range from 50 to 250 kW.
Solid Oxide fuel cells (SOFC) use a hard, ceramic compound of metal (like calcium or zirconium) oxides
(chemically, O2) as electrolyte. Efficiency is about 60 percent, and operating temperatures are about 1,000
degrees C (about 1,800 degrees F). Cells output is up to 100 kW. At such high temperatures a reformer is not
required to extract hydrogen from the fuel, and waste heat can be recycled to make additional electricity.
However, the high temperature limits applications of SOFC units and they tend to be rather large. While solid
electrolytes cannot leak, they can crack.
Fig.5. solid oxide cell.
Fuel cells. Many applications require more voltage than one single fuel cell delivers.
Fuel cells technology program
Fuel Cell Type
Proton exchange
-Backup power
-Solid electrolyte reduces corrosion
-Expensive catalyst
Membrane (PEMFC)
-portable power
and electrolyte management problem
-sensitive to fuel impurity
-Distributed generation
-Low Temperature
-Quick start-up
-Low temperature heat
-cathode reaction faster in alkaline
-sensitive to Co2 in fuel and air
electrolyte leads to high performance
-Electrolyte management
-Special vehicles
Alkali (AFC)
-Low cost components
Phosphoric acid (PAFC)
Molten Carbonate(MCFC)
Solid-oxide (SOFC)
-Distributed generation
-Higher temperature enables CHP
-Long startup time
-Increased tolerance to fuel impurities
-low current and power
- Distributed generation
-High Efficiency
-High temperature corrosion
-Electric utility
-Fuel flexibility
breakdown of cell components
-Can use a variety of catalysts
-long startup time
-Suitable for CHP
-low power density
-Auxiliary power
-High Efficiency
-High temperature corrosion
- Distributed generation
-Fuel flexibility
breakdown of cell components
-Electric utility
-Can use a variety of catalysts
- High temperature operation
–solid electrolyte
require long startup time and
-suitable for CHP and CHHP
Fuel Cell Technologies focus on several key applications:
Specialty vehicles
Emergency backup power
Prime power for critical loads
Summary and Conclusions
Fuel cells for portable, backup, automotive, or stationary power applications have been demonstrated, and
there are some fuel cells commercially available in these categories. DMFCs and PEMFCs are commonly used for
portable applications. Backup power often uses PEMFC fuel cells with compressed hydrogen storage.
Automobile applications can the PEMFC and DMFC fuel cell types. Fuel cell buses use PAFCs, PEMFCs, DMFCs,
and ZAFCs. Utility vehicles, scooters, and bicycles primarily use PEMFCs. Stationary power applications use
SOFCs, MCFCs, AFCs, and PEMFCs. The fuel cell design such as power output, heat balance, efficiency, size,
weight, and fuel supply may be slightly different for each application, and must be customized to suit the
required load.
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