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FUELCELLS KNOCKHARDY PUBLISHING 2008 SPECIFICATIONS.

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Presentation on theme: "FUELCELLS KNOCKHARDY PUBLISHING 2008 SPECIFICATIONS."— Presentation transcript:

1 FUELCELLS KNOCKHARDY PUBLISHING 2008 SPECIFICATIONS

2 INTRODUCTION This Powerpoint show is one of several produced to help students understand selected topics at AS and A2 level Chemistry. It is based on the requirements of the AQA and OCR specifications but is suitable for other examination boards. Individual students may use the material at home for revision purposes or it may be used for classroom teaching with an interactive white board. Accompanying notes on this, and the full range of AS and A2 topics, are available from the KNOCKHARDY SCIENCE WEBSITE at... Navigation is achieved by... either clicking on the grey arrows at the foot of each page orusing the left and right arrow keys on the keyboard KNOCKHARDY PUBLISHING FUEL CELLS

3 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 FUEL CELLS

4 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 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        ANODEANODEANODEANODE CATHTODECATHTODECATHTODECATHTODE MEMBRANEMEMBRANEMEMBRANEMEMBRANE  CLICK ON A NUMBER FOR AN EXPLANATION OF WHAT IS TAKING PLACE

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

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

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

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

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

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

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

15  WATER IS PRODUCED PROTON EXCHANGE MEMBRANE FUEL CELL        ANODEANODEANODEANODE CATHTODECATHTODECATHTODECATHTODE MEMBRANEMEMBRANEMEMBRANEMEMBRANE  2H 2 (g) + O 2 (g) —> 2H 2 O(l) CLICK ON A NUMBER FOR AN EXPLANATION OF WHAT IS TAKING PLACE

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

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

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

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

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

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

23 CELL REACTIONS - SUMMARY Anode (-) 2H 2 (g) —> 4H + (aq) + 4e¯ E° = 0.00V OXIDATION Cathode (+) O 2 (g) + 4H + (aq) + 4e¯ —> 2H 2 O(l) E° = +1.23V REDUCTION overall reaction 2H 2 (g) + O 2 (g) —> 2H 2 O(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 4 + H 2 O —> CO + 3H 2 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 4 + H 2 O —> CO + 3H 2 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 4 + H 2 O —> CO + 3H 2 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 pressureor adsorbed on the surface of a solidor 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 4 + H 2 O —> CO + 3H 2 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 pressureor adsorbed on the surface of a solidor absorbed within a solid

30 FUEL CELL VEHICLES (FCV’S) - ADVANTAGES produce less pollution from exhaust gases (no NOx, CO, unburnt hydrocarbons) produce less CO 2 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 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 THE END FUELCELLS


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