Option C Secondary Cell, Hydrogen Microbial Fuel Cell and Thermodynamic Efficiency
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This document provides a tutorial on secondary cells, hydrogen fuel cells, and microbial fuel cells. It discusses the basic principles and reactions of lithium-ion batteries, lead-acid batteries, nickel-cadmium batteries, alkaline fuel cells, direct methanol fuel cells, and microbial fuel cells. It also covers topics such as thermodynamic efficiency, the factors that determine voltage, and how lithium-ion batteries overcome issues with lithium reacting with the electrolyte.
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Option C Secondary Cell, Hydrogen Microbial Fuel Cell and Thermodynamic Efficiency
- 1. http://lawrencekok.blogspot.com Prepared by Lawrence Kok Tutorial on Secondary Cells, Hydrogen and Microbial Fuel Cell, Thermodynamic Efficiency.
- 2. Lithium ion Types voltaic cell NH4CI and ZnCI2 Alkaline cellDry cell Nickel cadmium cell Primary cell (Non rechargeable) MnO2 and KOH Secondary cell (Rechargeable) Lead acid battery Fuel cell H2 fuel cell- alkaline electrolyte H2 fuel cell- acidic electrolyte Direct Methanol fuel cell Microbial fuel cell (MFC) H2H2 O2 O2 H2O CH3OH O2 CO2 H2O C6H12O6 O2 - No pollution - Fuel is constantly supply - Convert fuel H2 /organic fuel to electricity Longer life time Rechargeable Diff rechargeable vs fuel cell Rechargeable battery are reversible fuel cell irreversible – need supply fuel Similarity rechargeable vs fuel cell Both convert chemical to electrical – redox rxn (spontaneous) vs
- 3. Battery/Fuel cell Advantage Disadvantage Lead acid High amt charge High energy density Cheap Heavy Lead/H2SO4 pollution Nickel cadmium Longer lifetime Quick recharge time Low resistance Cadmium toxic Expensive Memory effect Lithium ion Low density High voltage – 3.7V Longer lifetime High recharge cycle Non toxic Expensive Explosive expose to heat Fuel Cell More efficient High energy density No pollution Low density H2 explosive Diff to store/transport gas Expensive Low storage density Microbial Fuel Cell Safe and renewable Treatment waste Low energy Battery/Fuel cell Energy density /MJdm-1 Specific energy /MJkg-1 H2 fuel cell 2 120 Methanol fuel cell 16 20 Liquid natural gas 21 50 Liquid propane 27 46 Gasoline 32 46 H2 highest specific energy ( ratio energy to mass) 1 mol H2 – 2g 1 mol methanol – 32g 1 mol propane - 44 g 1 mol octane/gasoline – 114g Comparison in terms of energy density/specific energy Advantage/disadvantage of battery/fuel cell H2 lowest energy density (ratio energy to vol) 1 mol H2 – 24000 cm3 1 mol methanol – 40.4 cm3 1 mol propane - 76 cm3 1 mol octane/gasoline – 162 cm3 Comparison in terms of energy density/specific energy Zinc carbon alkaline nickel/cad Li/Fe Li/Mn nickel/MH Li/ion Li/polymer fuel cell Zinc air
- 4. Types voltaic cell Discharging Pb + PbO2 + 2H2SO4 2PbSO→ 4 + 2H2O Lead acid battery (-ve) (Anode) - Oxidation Pb + SO4 2- PbSO→ 4 + 2e− + ve (Cathode)- Reduction PbO2 + 4H+ + SO4 2- + 2e− PbSO→ 4 + 2H2O (-ve) (Cathode)- Reduction PbSO4 + 2e Pb + SO→ 4 2− + ve (Anode)- Oxidation PbSO4 + 2H2O PbO→ 2 + 4H+ + SO4 2- 2e− Charging Electrolyte H2SO4 Nickel cadmium battery Discharging (-ve) (Anode) - Oxidation Cd + 2OH- Cd(OH)→ 2 + 2e− + ve (Cathode)- Reduction 2NiO(OH) + 2H2O+ 2e− 2Ni(OH)→ 2 + 2OH- Charging nickel (III) oxide hydroxide (-ve) (Cathode) - Reduction Cd(OH)2 + 2e− Cd + 2OH→ - + ve (Anode)- Oxidation 2Ni(OH)2 + 2OH- 2NiO(OH)+ 2H→ 2O+ 2e− net eqn 2NiO(OH)+ Cd + 2H2O+ 2Ni(OH)→ 2 + Cd(OH)2 net eqn NiO(OH) Cd Electrolyte KOH Lithium ion battery (-ve) (Anode) - Oxidation Li Li→ + + e− + ve (Cathode)- Reduction Li+ + MnO2 + e− LiMnO→ 2 Discharging Lithium in Graphite layer – prevent lithium for oxidizing to oxide (reactive) LiMnO2 Li -+ Charging (-ve) (Cathode) - Reduction Li+ + e− Li→ + ve (Anode)- Oxidation LiMnO2 Li→ + + MnO2 + e− Li + MnO2 LiMnO→ 2 net eqn Discharging/Charging possible - insoluble PbSO4/PbO reversible Discharging/Charging possible - insoluble Cd(OH)2/Ni(OH)2 reversible Lithium in MnO2 lattice – prevent lithium for oxidizing to oxide (reactive)
- 5. 2H2 + O2 2H→ 2O H2 fuel cell- alkaline electrolyte (-ve) (Anode) - Oxidation 2H2 + 4OH- 4H→ 2O + 4e− + ve (Cathode)- Reduction 2H2O + O2 + 4e− 4OH→ - net eqn net eqn CH3OH + 1.5O2 CO→ 2 + 2H2O net eqn Fuel cell Electrolyte KOH O2H2 H2 fuel cell- acidic electrolyte (-ve) (Anode) - Oxidation 2H2 4H→ + + 4e− + ve (Cathode)- Reduction 4H+ + O2 + 4e− 4H→ 2O 2H2 + O2 2H→ 2O O2H2 PEM – made of Teflon allow H+ ion to flow Proton Exchange Membrane Electron flow in external circuit Direct Methanol fuel cell H2O H2O (-ve) (Anode) - Oxidation CH3OH + H2O CO→ 2 + 6H+ + 6e− + ve (Cathode)- Reduction 6H+ + 1.5O2 + 6e− 3H→ 2O O2 H2OCO2 CH3OH Proton Exchange Membrane PEM – made of Teflon allow H+ ion to flow Carbon oxidized to CO2 - C (-2) to C (+4) Catalyst – platinum used anode/cathode Catalyst – platinum used anode/cathode Catalyst – platinum used anode/cathode
- 6. CH3COOH Microbial fuel cell (MFC) (-ve) (Anode) - Oxidation C6H12O6 + 6H2O 6CO→ 2 + 24H+ + 24e− + ve (Cathode)- Reduction 24H+ + 6O2 + 24e− 12H→ 2O net eqn net eqn net eqn Fuel cell O2CO2 CH3COOH + 2O2 2CO→ 2 + 2H2O CH3COOH Electron flow in external circuit C6H12O6 O2CO2 Proton Exchange Membrane PEM – made of Teflon allow H+ ion to flow C6H12O6 + 6O2 6CO→ 2 + 6H2O Microbial/bacteria in anode, anaerobic oxidized organic/fatty acid/ alcohol to CO2/H2O Elec and H+ produced when oxidized (-ve) (Anode) - Oxidation CH3COOH + 2H2O 2CO→ 2 + 8H+ + 8e− + ve (Cathode)- Reduction 8H+ + 2O2 + 8e− 4H→ 2O Microbial fuel cell (MFC) – Ethanoic acid O2CO2 Electron flow in external circuit Bacteria GEOBACTER in anode, anaerobic oxidized ethanoic acid to CO2/H2O Elec and H+ produced when oxidized Microbial fuel cell (MFC) – Ethanoic acid (-ve) (Anode) - Oxidation CH3COOH + 2H2O 2CO→ 2 + 8H+ + 8e− + ve (Cathode)- Reduction 8H+ + 2O2 + 8e− 4H→ 2O CH3COOH + 2O2 2CO→ 2 + 2H2O Bioremediation to break down oil spill/organic waste
- 7. H2 fuel cell- acidic electrolyte 2H2 + O2 2H→ 2O net eqn Fuel cell (-ve) (Anode) - Oxidation 2H2 4H→ + + 4e− + ve (Cathode)- Reduction 4H+ + O2 + 4e− 4H→ 2O O2 H2 PEM – made of Teflon allow H+ ion to flow Proton Exchange Membrane H2O Catalyst – platinum used anode/cathode Thermodynamic Efficiency fuel cell %100 .. .. . ×= energyinputtotal energyoutputuseful efficiencyMax %100. × ∆− ∆− = sys sys H G efficiencyMax Ratio of Gibbs Free energy to Enthalpy change of rxn 2H2 (g) + O2 (g) 2H→ 2O (l) ∆Hf = -285.8kJ mol-1 ∆Gf = -237.1 kJ mol-1 %83%100 8.285 1.237 . %100. =×= × ∆− ∆− = efficiencyMax H G efficiencyMax sys sys 2H2 (g) + O2 (g) 2H→ 2O (g) ∆Hf = -241.8kJ mol-1 ∆Gf = -228.6 kJ mol-1 %95%100 8.241 6.228 . %100. =×= × ∆− ∆− = efficiencyMax H G efficiencyMax sys sys STHG ∆−∆=∆ Liquid water – Entropy lower (order) ∆S sys = ∆S(product – reactant) is higher ∆G = ∆H - T∆S ∆G = less negative Efficiency = Less Gas produced–Entropy gas high (disorder) ∆S sys = ∆S(product – reactant) is lower ∆G = ∆H - T∆S ∆G = more negative Efficiency = More STHG ∆−∆=∆ H2 fuel cell- acidic electrolyte Click here making H2 fuel cell
- 8. H2 fuel cell- acidic electrolyte 2H2 + O2 2H→ 2O net eqn Fuel cell (-ve) (Anode) - Oxidation 2H2 4H→ + + 4e− + ve (Cathode)- Reduction 4H+ + O2 + 4e− 4H→ 2O O2 H2 PEM – made of Teflon allow H+ ion to flow Proton Exchange Membrane H2O Catalyst – platinum used anode/cathode Thermodynamic Efficiency CH3OH+ 1.5O2 CO→ 2 + 2H2O ∆Hf = -726 kJ mol-1 ∆Gf = - 685 kJ mol-1 %94%100 726 685 . %100. =×= × ∆− ∆− = efficiencyMax H G efficiencyMax sys sys Sucrose, C12H22O11 used as substrate in MFC i. Where do the bacteria live in fuel cell ii. Oxi number carbon in –ve electrode iii. Oxi number oxygen in + ve electrode iv. Overall redox rxn Direct Methanol fuel cell CH3OH CO2 O2 H2O C12H22O11 + 12O2 12CO→ 2 + 11H2O Oxi C = 0 Oxi C = +4Oxi O = 0 Oxi C = 0 to +4 (oxidized) 48 electron lost (-ve) electrode C12H22O11 + 13H2O 12CO→ 2 + 48H+ + 48e– Oxi O = -2 Oxi O = 0 to -2 (reduced) 48 electron gain (+ve ) electrode 48H+ + 12O2 + 48e– 24H→ 2O Microbial fuel cell (MFC) Bacteria in anode (-ve) –oxidation of substrate - + C12H22O11 + 12O2 12CO→ 2 + 11H2O
- 9. Eθ value DO NOT depend surface area of metal electrode. E cell = Energy per unit charge. (Joule)/C E cell- 10v = 10J energy released by 1C of charge = 100J energy released by 10C of charge Eθ – intensive property– independent of amt – Ratio energy/charge Increasing surface area metal will NOT increase E cell Total Energy increase ↑ Total Charge increase ↑ Current increase ↑ BUT E cell remain SAME E cell = (Energy/charge) t Q I tIQ = ×= Q up ↑ – I up ↑ i. Nature of material, further apart oxidising / reducing in std electrode potential, more voltage produce ii. Quantity material, surface area and total number of elec moving iii. Large thick plates increase surface area- quantity of material (work/energy) increase, current/charges increase BUT NO VOLTAGE CHANGE Placing in series increase voltage i. State factors that determine voltage of battery ii. Outline what determine , total energy/work/current a battery can do iii. Explain the effect of large surface area, battery have on voltage and work Surface area increase ↑ E/Voltage remain SAME Reactive lithium form oxide layer on metal which decrease the contact with electrolyte How lithium ion battery overcome this problem Mixing lithium with graphite at anode. and lithium with MnO2 lattice at cathode, prevent oxidation of lithium metal LiMnO2 Li - graphite Oxi Li = +1, deduce oxi number of Mn in mixed oxide LiMnO2, and show Mn has been reduced Li +(polymer) + MnO2 + e- LiMnO→ 2 Oxi Mn = +4 Oxi Li = +1 Oxi O = -2 Oxi Mn in LiMnO2 +1 + Mn + 2(-2) = 0 Oxi Mn = +3 Oxi Mn = +4 to +3 ( reduced )
- 10. Acknowledgements Thanks to source of pictures and video used in this presentation Thanks to Creative Commons for excellent contribution on licenses http://creativecommons.org/licenses/ http://spmchemistry.onlinetuition.com.my/2013/10/electrolytic-cell.html http://www.chemguide.co.uk/physical/redoxeqia/introduction.html http://educationia.tk/reduction-potential-table http://2012books.lardbucket.org/books/principles-of-general-chemistry-v1.0/s23- electrochemistry.html Prepared by Lawrence Kok Check out more video tutorials from my site and hope you enjoy this tutorial http://lawrencekok.blogspot.com