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Learning Activity 2
Lecture : Fuel Cells
Introduction
Teacher introduces the basic concept of fuel cells using the Power Point presentation.
Learning Objectives
Students will be able to

acquire the brief history of fuel cells, including the types of batteries and fuel
cells.

understand what is a fuel cell and how fuel cell works as well as compare the
differences between fuel cells and power energy.


recognise the different applications of fuel cells.
appreciate the impact of fuel cells on the environment and the economy.
Time

40 minutes
Materials and Resources

A Powerpoint presentation file
Instructions to Teacher
After the lecture, students would be involved in a question-and-answer activity
monitored by the teacher. Students could review the information found through this
activity.
The suggested questions are :

List non-renewable energy and renewable energy sources.
 Name different forms of energy.
 What is a fuel cell ?
 How does a fuel cell operate ?
Two Types of Energy Supplies
Energy utilization is the major driving force of modern economic development. We
can classify our energy supplies into two categories:
1.
Fossil Fuel (化石燃料) – Energy stored in the form of fossilized remains of
ancient living organisms. Coal (煤), natural gas (天然氣), oil (石油) and tar
sands (焦油沙) are examples of this type of fuel. This type of energy source is
also called non-renewable energy source (非再生能源).
2.
Renewable Energy Source (可再生能源)– Energy from sources that do not
deplete resources on earth. Hydroelectric power（水力發電）, solar power（太
陽能）, wind power（風力發電）, wave and tidal power（潮汐發電）and
geothermal power（地熱能源）are gaining popularity in the modern economy
that requires sustainable development（可持續發展）.
Renewable Energy Sources
Hydroelectric Power（水力發電） – Conversion of potential（位能）and kinetics
energy（動能）of flowing water into electrical energy. Hydroelectric power
plants are suitable for mountainous areas with fast flowing streams. The Three
Gorges Dam（三峽大壩）will be the largest hydroelectric power generation
facility when it is completed.
Solar Power（太陽能） – Radiation from our Sun is the ultimate source of energy on
earth. Solar energy can be collected as heat energy for cooking and home
heating, or solar concentrator can be used to generate steam for generation of
electricity using turbine（渦輪）. Solar panels are also employed throughout the
world to convert solar radiation into electricity directly.
Wind Power（風力發電）– Wind Mills have been in use for a few centuries. Wind
turbines are suitable for remote flat areas with constant high wind.
Wave and Tidal Power（潮汐發電）– are suitable for coastal area with high wind and
sea wave. United Kingdom had tested a few designs but none is currently
economical.
Geothermal Power（地熱能源）– In areas where there are lots of volcanic activities,
underground water is heated to form steam with high pressure. This steam can
be harnessed to drive turbines and generate electricity. Iceland, Italy and United
States have limited success with this method of electricity generation.
Different Forms of Energy
1.
Heat Energy（熱能）
2.
Mechanical Energy（機械能）
3.
Electrical Energy（電能）
4.
Solar Energy（太陽能）
5.
Chemical Energy（化學能）
6.
Nuclear Energy（核能）
Energy can be converted from one form to another form. Laws of Thermodynamics
（熱動力學定律） restricted the conversion efficiency. The theoretical energy
conversion efficiency limited is set out by the Carnot efficiency:
Efficiencycarnot =
TH  Tc
TH
Where TH is the intrinsic temperature of the energy source
Tc is the intrinsic temperature of the energy sink
Ordinary Oil-fired electrical power generating plant （火力發電廠）has an efficiency
of around 20-30%.
Fuel Cell（燃料電池）has the highest theoretical efficiency that approaches 90%.
Fuel Cells Basic
A fuel cell is a device that generates electricity without combustion. In a fuel cell,
chemical energy is converted directly into electrical energy.
Fuel cell is similar to battery. There are two electrodes in a fuel cell. These electrodes
are separated by an electrolyte. Fuel is supplied to the anode and oxidant is supplied
to the cathode. As long as fuel and oxidant are supplied to the fuel cell, the fuel cell
will continue to operate.
The most common fuel for fuel cell is hydrogen. The oxidant is usually oxygen in air.
The common types of fuel cell:
Type
Alkaline (AFC)
Operating Temperature
Applications
50C -250C
U.S. Space Program
Polymer Electrolyte (PEFC) 50C -100C
Battery replacement,
Transportation
Phosphoric Acid (PAFC)
200C
Airports, School, Hospitals
Direct Alcohol (DAFC)
50C -100C
Battery replacement
Molten Carbonate (MCFC) 600C
Cogeneration
Solid Oxide (SOFC)
Cogeneration
500C -1000C
Different types of fuel cells have different reactions at the electrodes.
Alkaline Fuel Cell (AFC)
At the anode:
2 H2(g) + 4OH-(aq)  4H2O(l) + 4eAt the cathode:
O2(g) + 2H2O(l) + 4e-  4OH-(aq)
Polymer Electrolyte (PEFC), also called Proton Exchange Membrane Fuel Cell
(PEMFC)
At the anode:
2H2(g)  4H+ + 4eAt the cathode:
4H+ + 4e- + O2  2H2O
Typical Fuel Cell Operation