1. KNOCKHARDY PUBLISHING
FUEL
CELLS
2008 SPECIFICATIONS
KNOCKHARDY PUBLISHING

2. KNOCKHARDY PUBLISHING
FUEL CELLS
INTRODUCTION
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3. FUEL CELLS CONTENTS Introduction
The Proton Exchange Membrane Fuel Cell (PEMFC)
PEMFC Cell – theory and electrode reactions
Why use fuel cells?
Sources of hydrogen
Fuel cell vehicles
Fuel cells - Advantages
Fuel cells – Disdavantages
The future of fuel cells
Other types of fuel cell

4. FUEL CELLS INTRODUCTION
Fuel cells generate electricity from an electrochemical reaction in which oxygen (from air) and a fuel (e.g. hydrogen) combine to form water.
The electricity produced can be used to power cars, buses, laptops and mobile phones. The by-product, heat, can also be used.

5. FUEL CELLS INTRODUCTION
Fuel cells generate electricity from an electrochemical reaction in which oxygen (from air) and a fuel (e.g. hydrogen) combine to form water.
The electricity produced can be used to power cars, buses, laptops and mobile phones. The by-product, heat, can also be used.
STRUCTURE
• cells consist of two electrodes, a negative anode and a positive cathode
• electrodes are separated by a solid or liquid electrolyte
• electrically charged particles move between the two electrodes
• catalysts (e.g. Pt) are often used to speed up reactions at the electrodes
• electricity is generated when oxygen and hydrogen combine

6. The Proton Exchange Membrane Fuel Cell - PEMFC
A TYPICAL FUEL CELL
The Proton Exchange Membrane Fuel Cell - PEMFC
Operation
• hydrogen (the fuel) is oxidised to H+ ions (protons) at the anode
• protons move through the electrolyte
• electrons pass through the external circuit
• oxygen is reduced at the cathode
• water is produced
• a platinum catalyst accelerates the reactions at the electrodes

7.         PROTON EXCHANGE MEMBRANE FUEL CELL MEMBRANE CATHT ODE
ANODE    
CLICK ON A NUMBER FOR AN EXPLANATION OF WHAT IS TAKING PLACE

8.         PROTON EXCHANGE MEMBRANE FUEL CELL
CATHT ODE 
ANODE    
 HYDROGEN GAS ENTERS THE CELL
CLICK ON A NUMBER FOR AN EXPLANATION OF WHAT IS TAKING PLACE

9.         PROTON EXCHANGE MEMBRANE FUEL CELL
CATHT ODE 
ANODE    
 HYDROGEN IS OXIDISED TO H+ AT THE ANODE
2H2(g) —> 4H+(aq) + 4e¯
CLICK ON A NUMBER FOR AN EXPLANATION OF WHAT IS TAKING PLACE

10.         PROTON EXCHANGE MEMBRANE FUEL CELL
CATHT ODE 
ANODE    
 ELECTRONS TRAVEL VIA THE EXTERNAL CIRCUIT
CLICK ON A NUMBER FOR AN EXPLANATION OF WHAT IS TAKING PLACE

11.         PROTON EXCHANGE MEMBRANE FUEL CELL
CATHT ODE 
ANODE    
 H+ IONS TRAVEL THROUGH THE ELECTROLYTE AND MEMBRANE
CLICK ON A NUMBER FOR AN EXPLANATION OF WHAT IS TAKING PLACE

12.         PROTON EXCHANGE MEMBRANE FUEL CELL
CATHT ODE 
ANODE    
 OXYGEN GAS ENTERS THE CELL
CLICK ON A NUMBER FOR AN EXPLANATION OF WHAT IS TAKING PLACE

13.         PROTON EXCHANGE MEMBRANE FUEL CELL
CATHT ODE 
ANODE    
 OXYGEN IS REDUCED AT THE CATHODE
O2(g) + 4H+(aq) + 4e¯ —> 2H2O(l)
CLICK ON A NUMBER FOR AN EXPLANATION OF WHAT IS TAKING PLACE

14.         PROTON EXCHANGE MEMBRANE FUEL CELL
CATHT ODE 
ANODE    
 A CATALYST SPEEDS UP THE REACTION BETWEEN OXYGEN AND H+
CLICK ON A NUMBER FOR AN EXPLANATION OF WHAT IS TAKING PLACE

15.         PROTON EXCHANGE MEMBRANE FUEL CELL  WATER IS PRODUCED
CATHT ODE 
ANODE    
 WATER IS PRODUCED
2H2(g) + O2(g) —> 2H2O(l)
CLICK ON A NUMBER FOR AN EXPLANATION OF WHAT IS TAKING PLACE

16. THEORY The relevant half reactions are…
O2(g) + 4H+(aq) + 4e¯ 2H2O(l) E° = +1.23V
2H+(aq) + 2e¯ H2(g) E° = 0.00V

17. THEORY The relevant half reactions are…
O2(g) + 4H+(aq) + 4e¯ 2H2O(l) E° = +1.23V
2H+(aq) + 2e¯ H2(g) E° = 0.00V
The equation with the MORE POSITIVE E° value reverses the one with the less positive E° value.
O2(g) + 4H+(aq) + 4e¯ 2H2O(l)
H2(g) 2H+(aq) + 2e¯

18. THEORY The relevant half reactions are…
O2(g) + 4H+(aq) + 4e¯ 2H2O(l) E° = +1.23V
2H+(aq) + 2e¯ H2(g) E° = 0.00V
The equation with the MORE POSITIVE E° value reverses the one with the less positive E° value.
O2(g) + 4H+(aq) + 4e¯ 2H2O(l)
H2(g) 2H+(aq) + 2e¯
Double the second equation to balance the electrons then combine both to give the overall reaction…

19. THEORY The relevant half reactions are…
O2(g) + 4H+(aq) + 4e¯ 2H2O(l) E° = +1.23V
2H+(aq) + 2e¯ H2(g) E° = 0.00V
The equation with the MORE POSITIVE E° value reverses the one with the less positive E° value.
O2(g) + 4H+(aq) + 4e¯ 2H2O(l)
H2(g) 2H+(aq) + 2e¯
Double the second equation to balance the electrons then combine both to give the overall reaction…
2H2(g) + O2(g) —> 2H2O(l) E° = +1.23V

20. THEORY The relevant half reactions are…
O2(g) + 4H+(aq) + 4e¯ 2H2O(l) E° = +1.23V
2H+(aq) + 2e¯ H2(g) E° = 0.00V
The equation with the MORE POSITIVE E° value reverses the one with the less positive E° value.
O2(g) + 4H+(aq) + 4e¯ 2H2O(l)
H2(g) 2H+(aq) + 2e¯
Double the second equation to balance the electrons then combine both to give the overall reaction…
2H2(g) + O2(g) —> 2H2O(l) E° = +1.23V
ELECTRODE REACTIONS
Anode (-) H2(g) —> 4H+(aq) + 4e¯ OXIDATION
Cathode (+) O2(g) + 4H+(aq) + 4e¯ —> 2H2O(l) REDUCTION

21. THEORY The relevant half reactions are…
O2(g) + 4H+(aq) + 4e¯ 2H2O(l) E° = +1.23V
2H+(aq) + 2e¯ H2(g) E° = 0.00V
The equation with the MORE POSITIVE E° value reverses the one with the less positive E° value.
O2(g) + 4H+(aq) + 4e¯ 2H2O(l)
H2(g) 2H+(aq) + 2e¯
Double the second equation to balance the electrons then combine both to give the overall reaction…
2H2(g) + O2(g) —> 2H2O(l) E° = +1.23V
ELECTRODE REACTIONS
Anode (-) H2(g) —> 4H+(aq) + 4e¯ OXIDATION
Cathode (+) O2(g) + 4H+(aq) + 4e¯ —> 2H2O(l) REDUCTION

22. CELL REACTIONS - SUMMARY
Anode (-) H2(g) —> 4H+(aq) + 4e¯ E° = 0.00V OXIDATION
Cathode (+) O2(g) + 4H+(aq) + 4e¯ —> 2H2O(l) E° = +1.23V REDUCTION
overall reaction H2(g) + O2(g) —> 2H2O(l) E° = +1.23V

23. CELL REACTIONS - SUMMARY
Anode (-) H2(g) —> 4H+(aq) + 4e¯ E° = 0.00V OXIDATION
Cathode (+) O2(g) + 4H+(aq) + 4e¯ —> 2H2O(l) E° = +1.23V REDUCTION
overall reaction H2(g) + O2(g) —> 2H2O(l) E° = +1.23V
Electrolyte • Carries charged particles from one electrode to the other
• It must allow only the appropriate ions to pass between the electrodes
• If other substances travel through the electrolyte,
they can disrupt the chemical reaction.

24. FUEL CELLS – Why use them?
• our society is dependent upon fossil fuels such as coal, oil and gas
• fossil fuels are a non-renewable energy resource
• fuel prices are rising and resources dwindling
• food, transport and electricity costs are affected by fuel prices
• the atmosphere is becoming more and more polluted
• carbon dioxide contributes to climate change and the greenhouse effect

25. FUEL CELLS – Why use them?
• our society is dependent upon fossil fuels such as coal, oil and gas
• fossil fuels are a non-renewable energy resource
• fuel prices are rising and resources dwindling
• food, transport and electricity costs are affected by fuel prices
• the atmosphere is becoming more and more polluted
• carbon dioxide contributes to climate change and the greenhouse effect
Limitations
• storage of hydrogen - safety considerations
• transportation of hydrogen - low density so expensive to deliver
• feasibility of liquefied hydrogen under pressure - safety considerations
• limited life of adsorber / absorber - economic considerations
• limited life cycle of cell - economic considerations
• high production costs - economic considerations
• use toxic chemicals in cell production - environmental considerations

26. FUEL CELLS – Manufacture of hydrogen
METHODS
• ideally from non-polluting and renewable resources; (solar, wind, hydro)
• from hydrocarbon fuels by reforming
• from natural gas (methane) or ethanol CH H2O —> CO H2
• electrolysis of water

27. FUEL CELLS – Manufacture of hydrogen
METHODS
• ideally from non-polluting and renewable resources; (solar, wind, hydro)
• from hydrocarbon fuels by reforming
• from natural gas (methane) or ethanol CH H2O —> CO H2
• electrolysis of water
REFORMING
Most of today’s hydrogen is generated by steam reforming. Unfortunately it uses non-sustainable, natural resources.
Fuel is mixed with steam in the presence of a metal catalyst to produce hydrogen and carbon monoxide.
This method is cost effective and efficient with conversion rates of 70-80%.

28. FUEL CELLS – Manufacture of hydrogen
METHODS
• ideally from non-polluting and renewable resources; (solar, wind, hydro)
• from hydrocarbon fuels by reforming
• from natural gas (methane) or ethanol CH H2O —> CO H2
• electrolysis of water
REFORMING
Most of today’s hydrogen is generated by steam reforming. Unfortunately it uses non-sustainable, natural resources.
Fuel is mixed with steam in the presence of a metal catalyst to produce hydrogen and carbon monoxide.
This method is cost effective and efficient with conversion rates of 70-80%.
STORAGE OF HYDROGEN
• liquid stored under pressure or
• adsorbed on the surface of a solid or
• absorbed within a solid

29. FUEL CELLS – Manufacture of hydrogen
METHODS
• ideally from non-polluting and renewable resources; (solar, wind, hydro)
• from hydrocarbon fuels by reforming
• from natural gas (methane) or ethanol CH H2O —> CO H2
• electrolysis of water
REFORMING
Most of today’s hydrogen is generated by steam reforming. Unfortunately it uses non-sustainable, natural resources.
Fuel is mixed with steam in the presence of a metal catalyst to produce hydrogen and carbon monoxide.
This method is cost effective and efficient with conversion rates of 70-80%.
STORAGE OF HYDROGEN
• liquid stored under pressure or
• adsorbed on the surface of a solid or
• absorbed within a solid

30. FUEL CELL VEHICLES (FCV’S) - ADVANTAGES
• produce less pollution from exhaust gases
(no NOx, CO, unburnt hydrocarbons)
• produce less CO2
• are more efficient

31. FUEL CELLS - Advantages
• eliminates pollution caused by burning fossil fuels; the only by-product
is water
• eliminates greenhouse gases if the hydrogen used comes from
electrolysis of water
• eliminates economic dependence on politically unstable countries for
fossil fuel
• have a higher efficiency than diesel or gas engines
• most operate silently compared to internal combustion engines
• some have low heat transmission - ideal for military applications
• operating times are much longer than with batteries
• maintenance is simple since there are few moving parts in the system

32. FUEL CELLS - Disadvantages
• production, transportation, distribution and storage of hydrogen is
difficult
• reforming is technically challenging and not environmentally friendly
• refuelling and starting times of fuel cell vehicles (FCV’s) are longer
• driving range of cars is shorter than in a traditional vehicles
• fuel cells are generally slightly bigger than comparable batteries or
engines
• currently expensive to produce, since most units are hand-made
• some use expensive materials
• the technology is not yet fully developed and few products are available

33. Limited supplies of fossil fuels may cause
FUEL CELLS - The future
Limited supplies of fossil fuels may cause
us to move to a ‘hydrogen economy’.
However
• greater acceptance by the public and politicians is necessary
• handling and maintenance of hydrogen systems must be safe
• improvements to hydrogen manufacturing must be made

34. FUEL CELLS – Other types
Fuel cells are classified according to the nature of the electrolyte.
Alkaline Fuel Cells (AFC)
• uses an alkaline electrolyte such as potassium hydroxide
• used by NASA in space shuttles
Direct Methanol Fuel Cells (DMFC)
• uses a polymer membrane as an electrolyte
• a catalyst on the anode draws hydrogen from liquid methanol
• eliminates need for a fuel reformer, so pure methanol can be used as fuel
Molten Carbonate Fuel Cells (MCFC)
• uses a molten carbonate salt as the electrolyte.
• has the potential to be fuelled with coal-derived fuel gases, methane / natural gas
Phosphoric Acid Fuel Cells (PAFC)
• anode and a cathode made of a finely dispersed platinum catalyst on carbon
• has a silicon carbide structure that holds the phosphoric acid electrolyte
• used to power many commercial premises and large vehicles, such as buses

35. FUEL CELLS – Other types
Fuel cells are classified according to the nature of the electrolyte.
Proton Exchange Membrane Fuel Cells (PEMFC)
• uses a polymeric membrane as the electrolyte, with platinum electrodes
• operate at relatively low temperatures.
• can vary their output to meet shifting power demands.
• best for cars, for buildings and smaller applications
Solid Oxide Fuel Cells (SOFC)
• use solid ceramic electrolytes; eg zirconium oxide stabilised with yttrium oxide
• work at high temperatures
• can reach efficiencies of around 60 per cent
• are expected to be used for generating electricity and heat in industry
• have potential for providing auxiliary power in vehicles
Regenerative Fuel Cells (RFC)
• produce electricity from hydrogen and oxygen
• can be reversed to produce hydrogen and oxygen; effectively storing energy

36. ©2010 JONATHAN HOPTON & KNOCKHARDY PUBLISHING
FUEL
CELLS
THE END
©2010 JONATHAN HOPTON & KNOCKHARDY PUBLISHING