Working Principle of Fuel Cell and Oxygen Reduction Reaction

1. Presented By
Shanta Majumder
ID: 21714002; Reg No: 21714002
Session: 2016-17
Department of Chemistry
Comilla University
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2. Presentation On
Working Principle & Application of Fuel Cell,
Oxygen Reduction Reaction of Fuel Cell,
Electrocatalysts for Oxygen Reduction Reaction
and Mechanism of Oxygen Reduction Reaction
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3. Working Principle of Fuel Cell
Applications of Fuel Cell
Oxygen Reduction Reaction (ORR)
Mechanism of ORR
Electrocatalysts for ORR
My Today’s Presentation Outline
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4. Working Principle of Fuel Cell
Construction
• Anode & Cathode: Materials which have
high electric conductivity and zero proton
conductivity in the form of porous catalyst
• Catalyst: Platinum
• Electrolyte: High proton conductivity and
zero electron conductivity
Figure
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5. Working Principle of Fuel Cell
• Hydrogen or hydrogen –rich fuel, is fed to the anode where a catalyst separates
hydrogen’s negatively charged electrons from positively charged ions.
• At a cathode, oxygen combines with electrons and in some cases, with species
such as protons or water, resulting in water or hydroxide ions, respectively.
• The electrons from the anode side of the cell cannot pass through the membrane to
the positively charged cathode; they must travel around it via an electrical circuit
to reach the other side of the cell.
• This movement of electrons is an electrical current.
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6. Reactions
At cathode: 2𝐻2 → 4 𝐻+ + 4𝑒−
At anode: O2 + 4H+ + 4e−→ 2H2O
Overall reaction: O2 + 2H2→ 2𝐻2 𝑂
Working Principle of Fuel Cell
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7. Applications of Fuel Cell
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8. • Occurs at cathode
• Produces hydrogen peroxide, super oxide, water or hydroxyl ion based
on electrode materials and the nature of electrolytes
• Kinetics is generally slow
• SEP depends on pathway of reaction
Oxygen Reduction Reaction (ORR)
Standard electrode potentials of the selected ORR
in aqueous electrolytes at 25 °
C
Electrochemical reactions Eo
/ Vvs. SHE
O2 + 4H+
+ 4e−
→ 2H2O 1.229
O2 + 2H+
+ 2e−
→H2O2 0.695
O2 + 2H2O + 4e−
→ 4OH−
0.401
O2 + H+
+ e−
→ HO2 −0.053
O2 + H2O + 2e−
→ + OH− −0.065
O2 + 2H2O + 2e−
→ H2O2 + 2OH−
−0.133
O2 + e−
→ 𝑂2
−
−0.284
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9. Mechanism Oxygen Reduction Reaction
Electrolyte ORR Reaction
Acidic Aqueous Solution O2 + 4H+ +4e- →H2O
O2 + 2H+ +2e- → H2O2
H2O2 + 2H+ +2e- → 2H2O
Alkaline Aqueous
Solution
O2 + H2O +4e- → 4OH-
O2+ H2O + 2e- →HO2
- + OH-
HO2
- + H2O +2e- → 3OH-
Non-aqueous Aprotic
Solvents
O2 + e- → O2
-
O2
- + e- → O2
2-
Mechanism
• 4-electron reduction pathway(O2 to 𝐻2 𝑂)
• 2-electron reduction pathway (O2 to 𝐻2 𝑂2)
• 1-electron reduction pathway (O2 to 𝑂2
−
)
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10. Electrocatalyst
for ORR
Graphite & Carbon
Graphite & Glassy
Carbon
Carbon Nanotubes
Heteroatom Doped
Carbon
Pre-Treated
Carbon Surface
Quinone &
Derivatives
AO Process
Quinone
Metal Catalysts
Platinum
Mixed Pt Surface
Pt AlloysMacrocyclic
Transition Metal
Complexes
Other Catalysts
Transition Metal
Chalcogenides
Transition Metal
Carbide
Electrocatalysts for Oxygen Reduction Reaction
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11. Glassy Carbon Graphite
O2(ads) +e-
→O2
-
(ads) (1)
2O2
-
(ads) +H2O→O2 +HO2
-
+OH-
(2)
ORR on Graphite and Glassy Carbon
Oxygen Reduction Reaction on Graphite & Carbon
𝑂2 → 𝑂2(𝑎𝑑𝑠 ) (1)
O2(ads) + e-
→ [O2(ads)]-
(2)
[O2(ads)]-
→ O2(ads)
-
(3)
O2(ads)
-
+ H2O → HO2(ads) + OH-
(4)
HO2(ads) + e-
→ HO2
-
(ads) (5)
HO2
-
(ads) → HO2
-
(6)
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12. ORR on Carbon Nanotubes ORR on Heteroatom Doped Carbons
• Various heteroatoms, such as N, S, P,
B, and I, have been introduced into
pure carbon materials
• Enhance conductivity and tune the
electron distribution
Oxygen Reduction Reaction on Graphite & Carbon
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13. ORR on Pre-treated Carbon Surface
• More surface functional groups
• Fresh carbon edges, micro particles
• Increase the surface area of carbon
Oxygen Reduction Reaction on Graphite & Carbon
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14. AO Process ORR Catalysed by Quinone
Q+e-
→Qx-
(1)
Qx-
+O2 → O2
x-
+Q (2)
O2
x-
+H2O+e-
→HO2
-
(3)
or
2O2
x-
+H2O→HO2 +O2 +OH-
(4)
Oxygen Reduction Reaction Catalysed by Quinone &Derivatives
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15. Oxygen Reduction Reaction on Metal Catalysts
ORR on Platinum
Dissociative Mechanism:
Associative Mechanism:
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16. Mixed Pt Surface & Rest Potential on Pt
• On Pt and at high potential:
Pt + ½ O2 → PtO Eo = 0.88V
• Here two reactions occur:
Platinum Oxidation
Oxygen Reduction
ORR on Pt Alloys
Due to alloying of Platinum:
• Increase the Pt d- band vacancy
• Change in Pt- Pt interatomic
distance
• Lattice contraction
Oxygen Reduction Reaction on Metal Catalysts
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17. • Reduction proceeds through 2- electron or 4- electron transfer pathway
Mechanism
Oxygen Reduction Reaction on Macrocyclic Transition Metal Complexes
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18. ORR Catalysed by Transition Metal Chalcogenides
• 2 or 4 electron pathway
• Due to semiconducting properties of chalcogenides & occurs
through the interaction of oxygen with transition metal d-
state
• O2 interacts with a transition metal atom of a cluster through a
bridge type bonding to two adjacent metal atoms in the same
cluster.
• The electron transfers between the cluster and the O2 could
result in a metal distance increase, which possibly facilitates
the breaking of the O-O bond and an upward shift of the
electronic level due to the loss of electrons.
• Tungsten Carbide
• The main catalytic activity of carbide is not in the oxygen reduction
reaction, but rather in other reactions such as H2 oxidation.
• WC, TaC, TiC, and TiN showed catalytic activity towards ORR in
acid solutions but these materials are not stable in alkaline solution.
• Even in acid solutions, WC does not show long-term stability in the
presence of O2. Addition of Ta to WC significantly improves its
catalytic activity and stability.
• The best activity can be observed with a W2C-Pt/C catalyst.
Oxygen Reduction Catalysed by Other Catalysts
ORR Catalysed by Transition Metal Carbides
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19. Thank You…….
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