14- Redox II Flashcards
Name of negative electrode?
Anode
Name of positive electrode?
Cathode
Whats the Cathode in a Lead-Acid battery made of?
Lead (IV) Oxide
Whats the Anode in Lead-Acid battery made of?
Lead metal.
What is the electrolyte in Lead-Acid batteries?
Conc. Sulphuric Acid (~6 molddm-3)
Reaction at the Anode in Lead acid battery?
Lead is oxidised in presence of sulphate ions. Lead sulphate forms.
Reaction at the Cathode in lead acid battery?
Lead (IV) Oxide is reduced by Sulphate ions under acidic conditions. Lead Sulphate and Water forms.
Overall equation of discharging lead acid battery.
Pb + PbO2 +2SO4 2- +4H+ –> 2PbSo4 +2H2O
What issue occurs if the cell is discharged too far?
Inert Lead Sulphate precipitate builds up on electrodes, making capacity of cell decrease and making it trickier to reverse the reaction.
Whats anode made of in Lithium ion battery?
Carbon graphite.
What is cathode made of in lithium ion battery?
A variety of materials, usually a variety of transition metal oxides with lithium ions incorporated into the structure.
Regularly cobalt and manganese oxides.
Electrolyte in Lithium ion battery?
A lithium ion conducting polymer or gel.
Pros of lithium ion batteries?
They can be cycled over a thousand times with little loss of capacity.
Reaction at anode of lithium ion battery?
Lithium ion moves out of graphite structure.
LiC6 –> C6 +Li+ + e-
Reaction at cathode of lithium ion battery?
Lithium ions are intercalated into the transition metal oxide.
Li+ + MO2 +e- –> LiMO2
M is a transition metal
Overall equation of lithium ion battery?
LiC6 + MO2 –> C6 + LiMO2
What generates the cell voltage in a lithium ion battery?
The difference in instability of Li+ ions in Graphite (unstable) and the oxide (more stable).
What problems occur with lithium ion batteries?
Phase change (?)
Li+ trapped in both structures; loss of capacity
Volume changes as Li+ ions move causing loss of contact between the electrode and electrolyte; loss of capacity
What causes fuel cells to be more efficient than energy turbines?
Fuel cells convert energy directly from chemical into electrical.
What occurs at anode?
Oxidation
What occurs at cathode?
Reduction
Reaction at anode of fuel cell under acidic conditions?
H2 gas is oxidised:
H2 –> 2H+ + 2e-
Reaction at cathode of fuel cell under acidic conditions?
O2 is reduced with H+:
1/2 O2 + H2 –> H2O
Overall equation for fuel cell?
1/2 O2 + H2 –> H2O
Reaction at anode of fuel cell under basic conditions?
H2 is oxidised in presence of OH-:
H2 + 2OH- –> 2H20 +2e-
Reaction at cathode of fuel cell under basic conditions?
O2 is reduced with H20:
1/2 O2 +H2O +2e- –> 2OH-
Reaction at anode of methanol oxygen fuel cell?
Methanol is oxidised in water:
CH3OH +H2O –> CO2 + 6H+ + 6e-
Reaction at cathode of Methanol oxygen fuel cell?
O2 is reduced with H+ :
1/2 O2 +6H+ + 6e- –> 3H2O
Overall reaction in a methanol oxygen fuel cell?
CH3OH +~3/2 O2 –> CO2 + 2H20
