Commercial applications of electrochemical cells

Question 1

What are the reactions in the lithium cell on charging?

Answer 1

• postivie electrode:
  
  • Li⁺ + CoO₂ + e^- → Li[CoO₂]^-
• -ve electrode:
  
  • Li⁺ + e^- → Li
• reversed on discharging

Question 2

What are the advantages of the lithium ion battery?

Answer 2

• light
  
  • least dense metal
• electrolyte is a solid polymer
  
  • rather than liquid or paste
  • cannot leak
    
    • even when bent
• charge can be topped up w/o memory effect
  
  • some only effectively recharged when they’ve been fully discharged

Question 3

How does charging of a lithium ion battery work?

Answer 3

• positive electrode is lithium cobalt oxide, -ve is carbon
• arranged in layers with a sandwich of solid electrolyte in between
• on charging
  
  • electrons forced through external circuit from positive to negative electrode
  • lithium ions move through electrolyte towards the positive electrode to maintain balance of charge

Question 4

What are the electrode reactions and ovarall reaction of an alkaline hydrogen-oxygen fuel cell?

Answer 4

• -ve
  
  • 2H₂(g) + 4OH^-(aq) → 4H₂O(l) + 4e-
• +ve
  
  • O₂(g) + 2H₂O (l) + 4e^- → 4OH^-(aq)
• ovarall
  
  • 2H₂(g) + O₂(g) → 2H₂O(l)

Question 5

Describe the structure of the alkaline hydrogen-oxygen fuel cells?

Answer 5

• the cell has two electrodes of a porous platinum-based material
• separated by a semi-permeable membrane and the electrolyte is sodium hydroxide solution

Question 6

How do the reactions take place in the alkaline hydrogen-oxygen fuel cell?

Answer 6

• hydrogen enters at the -ve electrode
  
  • causes the first reaction
    
    • 2H₂(g) + 4OH^-(aq) → 4H₂O(l) + 4e^-
• this releases e-
  
  • flow through circuit to the other electrode
• oxygen enters and the second reaction takes place
  
  • O₂(g) + 2H₂O (l) + 4e^- → 4OH^-(aq)
• this accepts e- from the other electrode and releases OH- ions which travel through a semi-permeable to that electrode

Question 7

Why is the alkaline hydrogen-oxygen cell important?

Answer 7

• same reaction as burning hydrogen and oxygen
  
  • takes place at lower temp
  • no production of NOx
• generate electricity on spacecraft
  
  • only product is pure water, used by astronauts
  • produces no CO2

Question 8

What is the problem with the alkaline hydrogen-oxygen cells?

Answer 8

• hydrogen made from crude oil
  
  • cheaper than electrolysis of water
    
    • also electricity used for this made by burning fossil fuels
• hydrogen vehicles need infrastructure
  
  • also problems w storing and transporting a highly flammible gas