Solar radiation and related terms, measurement of solar radiation, solar energy collectors-flate plate collector, air collector, concentrating collectors, application and advantages of various collectors, solar energy storage system (thermal, chemical, mechanical), solar pond, application of solar energy

1. DEPARTMENT OF CHEMICALENGINEERING
CHAPTER-3
“FUEL CELL”
PROF. DEVARSHI P. TADVI
ASSISTANT PROFESSOR
CHEMICAL ENGINEERING
DEPARTMENT
S S AGRAWAL INSTITUTE OF
ENGINEERING & TECHNOLOGY,
NAVSARI
1

2. CONTENTS
• History
• Hydrogen Energy
• Fuel Cell
• Importance Of Fuel Cell Technology
• Working Of Fuel Cell
• Types Of Fuel Cell
• Importance Of Hydrogen
• Hydrogen Production
• Applications
• Benefits
2

3. HISTORY
1838: discovered by German scientist
Christian Friedrich Schoenbein
1839: Demonstrated by Welsh scientistSir
William Robert Grove
3

4. Hydrogen Energy
Hydrogen is the simplest and the most
plentiful element in the universe.
It's always combined with other
elements.
Hydrogen is high in energy, yet an engine
that burns pure hydrogen produces almost
no pollution.
NASA has used liquid hydrogen since the
1970s to propel the space shuttle and other
rockets into orbit.
4

5. Hydrogen Production
The biggest challenge regarding hydrogen production is
the cost
There are three general categories of Hydrogen
production
 Thermal Processes
 Electrolyte Processes
Photolytic Processes
5

6. IMPORTANCE OF HYDROGEN
Fuel Cells require highly purified hydrogen
as a fuel
Researchers are developing a wide range of
technologies to produce hydrogen economically from
a variety of resources in environmentally friendly
ways
6

7. 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 movingparts.
 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 exploitation.
7

8. Classification Of Fuel Cells:
Classification of fuel cells is very difficult as several operational variable exists.
 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 or solid.
 According to the physical state of the fuel: Gas(hydrogen, lower hydrocarbons ),
Liquid(alcohols, hydrazine, higher hydrocarbons), Solid(Metals)
 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)
8

9. Types of fuel cell
As per the fuel used the fuel calls are classified as follows.
 Hydrogen
 Fossil Fuel
 Hydrocarbon fuel.
 Alcohol fuel.
 Hydrazine fuel.
9

10. Introduction
 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 appliances.
10

11.  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 fuel cell.
 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.
11

12. WHAT IS A FUELCELL?
A Fuel Cell is an electrochemical device that combines
hydrogen and oxygen to produce electricity, with water and
heat as its by-product.
Fuel cells are electrochemical cells consisting of two
electrodes and an electrolyte which convert the chemical
energy of chemical reaction between fuel and oxidant directly
into electrical energy.
overall reaction: oxidation of a fuel by
 oxygen
2H2(g) + O2(g) 2H2O(l)
(Hydrogen) Fuel + oxygen  water
12

13. WHY IS FUEL CELLTECHNOLOGY
IMPORTANT?
Since conversion of the fuel to energy takes place via
an electrochemical process, not combustion.
It is a clean, quiet and highly efficient process- two
to three times more efficient than fuel burning.
13

14. How does a Fuel Cell work?
It operates similarly to a battery, but it does not run down nor
does it require recharging
As long as fuel is supplied, a Fuel Cell will produce both energy
and heat
14

15. A Fuel Cell consists of two catalyst coated electrodes
surrounding an electrolyte
One electrode is an anode and the other is a cathode
The process begins when Hydrogen molecules enter
the anode
The catalyst coating separates hydrogen’s negatively
charged electrons from the positively charged protons
15

16.  The electrolyte allows the protons to pass through to
the cathode, but not the electrons
 Instead the electrons are directed through an
external circuit which creates electrical current
While the electrons pass through the external circuit,
oxygen molecules pass through the cathode
There the oxygen and the protons combine with the
electrons after they have passed through the external
circuit
16

17. When the oxygen and the protons combine with the
electrons it produces water and heat
17

18. Types of fuel cell
As per the fuel used the fuel calls are classified as follows.
 Hydrogen
 Fossil Fuel
 Hydrocarbon fuel.
 Alcohol fuel.
 Hydrazine fuel.
18

19. Fuel Cell type Electrolyte Anode gas Cathode gas Temp
oC
Efficiency
%
Proton Ex
Membrane (PEM)
Solid polymer
membrane
Hydrogen Pure or Atm
Oxygen
75 35 - 60
Alkaline
(AFC)
Potassium
Hydroxide
Hydrogen Pure Oxygen < 80 50 - 70
Direct Methanol
( DMFC)
Solid polymer
membrane
Methanol solln
in Water
Atm Oxygen 75 35 - 40
Phosphoric Acid
(PAFC)
Phosphorus Hydrogen Atm Oxygen 210 35 - 50
Molten Carbonate
(MCFC)
Alkali Carbonate Hydrogen /
Methane
Atm Oxygen 650 40 - 55
Solid Oxide
( SOFC)
Ceramic Oxides Hydrogen /
Methane
Atm Oxygen 800 -
1000
45 - 60
19

20. 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 are:
 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,
 Mechanical stability
20

21.  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.
21

22. 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.
22

23.  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
gas.
 The power section consisting of the actual fuel cell (or combination of
cells), and
 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.
23

24. MOLTEN CARBONATE FUEL CELL
 Molten alkaline carbonate like sodium
bicarbonate is used as the electrolyte.
 They can produce high powers up to
100 Mega Watts. Thus they can be
used as high power generators.
 They can also be operated at high
temperatures up to 650 degree
Celsius.
 They are not so expensive in
production and hence can be used for
commercial uses. It has an
efficiency of almost 55%.
24

25. Proton Exchange Membrane
(PEM)
25

26. This is the leading cell type for passenger car application
Uses a polymer membrane as the electrolyte
Operates at a relatively low temperature, about 175
degrees
Sensitive to fuel impurities
26

27. Phosphoric Acid
This is the most commercially
developed fuel cell
 It generates electricity at more than
40% efficiency
Uses liquid phosphoric acid as the
electrolyte and operates at about 450
degrees F
One main advantage is that it can use
impure hydrogen as fuel
27

28. Solid Oxide
 Uses a hard, non-porous ceramic
compound as the electrolyte
Can reach 60% power generating
efficiency
 Operates at extremely high
temperatures 1800 degrees
Used mainly for large, high
powered applications such as
industrial generating stations,
mainly because it requires such
high temperatures
28

29. Alkaline
 Used mainly by military and space programs
Can reach 70% power generating efficiency, but considered to
costly for transportation applications
 Used on the Apollo spacecraft to provide electricityand
drinking water
Uses a solution of potassium hydroxide in water as the
electrolyte and operates at 75 -160 degrees
Can use a variety of non-precious metals as catalyst at the
anode and cathode
29

30. 30

31. Regenerative Fuel Cells
 Currently researched by NASA
This type of fuel cell involves a closed loop form of
power generation
Uses solar energy to separate water into hydrogen and
oxygen
 Hydrogen and oxygen are fed into the fuel cell
generating electricity, heat and water
The water by product is then recirculated back to the
solar-powered electrolyser beginning the process again
31

32. Regenerative Fuel Cells
32

33. Polarization in Fuel Cells:
• The diffrence 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
increased.
33

34.  There are mainly three types of polarization:
 Activation Polarization.(Chemical polarization)
 Resistance or ohmic Polarization and
 Concentration Polarization.
34

35. 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
reaction.
 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 temperature.
35

36. Resistance Polarization
 The voltage drop in linearly related to the current flow according to the ohm’s
law.
 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.
36

37.  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.
37

38. 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 range.
38

39. Fuel Cell Technology Be Used
 Transportation
 Stationary Power Stations
 Telecommunications
 Micro Power
39

40. 40

41. Benefits Of Fuel Cell Technology
Physical Security
 Reliability
 Efficiency
 Environmental Benefits
 Battery Replacement/Alternative
 MilitaryApplications
41

42. 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 losses.
 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.
42

43. Disadvantages
 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.
 High initial cost.
 Life times of the cells are not accurately known.
 Large weight and volume of gas fuel storage system.
 High cost of pure hydrogen.
 Hydrogen can be stored in lesser volume by liquefaction but
liquefaction itself require 30% of the stored energy.
 Lack of infrastructure for distributing hydrogen.
43

44. Application
The application of the fuel cell may be discussed in the following
areas.
 Domestic Power
 Central Power Station
 Automotive Vehicles
 Special Application
44

45. Some useful points regarding application:
 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
fuel cells.
 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. 45

46.  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.
46

47.  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
relatively costly.
 It seems likely that hydrogen- oxygen and hydrogen carbon- oxygen
cells will be used to an increasing extent in special military & space
application.
47

48. Applications
 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 cities.
 This promising application will one day even
power our houses.
 Fuel cells also make sense for portable power
like laptop computers and cellular phones.
48

49.  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.
Nokia mobile with fuel cell battery
49

50. Wheel chair powered by fuel cell
Toshiba mp3 with a fuel cell
50

51. Hydrogen - Today
Production Storage
Use
Steam Reforming
of Petroleum
Cryogenic Liquid
Space Programme
51

52. Hydrogen - Tomorrow
Production
Storage
Use
Bio-mass &
Electrolysis
Innovative Tank
Designs
Fuel for FUELCELLS
52

53. Hydrogen Production For Future
Photo-
electrochemical
Algal Production
Solar powered
Electrolysis
53

54. 54