Oxygen overpotential
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This document discusses oxygen overvoltage and overpotential. It explains that oxygen overvoltage is the difference between the theoretical oxygen reduction potential of +1.23 V and the experimentally observed electrode potential. It occurs because oxygen reduction involves multiple steps - the oxidation of water to oxygen gas and protons, and then the reverse reduction of oxygen and protons back to water. These multi-step reactions contribute to an overpotential above the theoretical potential. The document also includes the electrochemical series and diagrams showing how concentration gradients and distance from the electrode surface can contribute to overvoltage.
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Oxygen overpotential
- 1. Oxygen overvoltage Dr. Mithil Fal Desai Shree Mallikarjun and Shri Chetan Manju Desai College Canacona Goa
- 2. Understanding hydrogen overpotential Electrode H+ (aq) e- ½H2(g) Step 1. Reduction of H+ ions to form H atoms H+ (aq) + e– → H Step 2. Adsorption of H atoms on the cathode surface. Step 3. Combination of adsorbed atoms to give hydrogen molecules 2H H2(g)
- 3. The overvoltage is the difference between the theoretical cell voltage and the actual voltage that is necessary to cause electrolysis. Overvoltage/Overpotential Oxygen Overvoltage The overvoltage is the difference between the theoretical oxygen reduction potential (+1.23 V) experimentally observed electrode potential.
- 4. H2 O(l) ½ O2 (g) + 2H+ (aq) + 2e- ½ O2 (g) + 2H+ (aq) + 2e- H2O(l) Oxidation and reduction oxygen Oxidation Reduction
- 5. Electrochemical series (E°) ½ F2(g) + e- F- (aq) (MnO4)- (aq) + 8H+ (aq) + 5e- (g) Mn2+ (aq) + 4H2O(l) ½ Cl2(g) + e- Cl- (aq) ½ O2 (g) + 2H+ (aq) + 2e- H2 O(l) Fe3+ (aq) + e- Fe2+ (aq) H+ (aq) + e- ½ H2(s) Zn2+ (aq) + 2e- Zn(s) Li+ (aq) + e- (g) Li(s) (E° in V) +2.87 +1.51 +1.36 +1.23 +0.77 0 -0.76 -3.04 Redox couple
- 6. An Overpotential ELECTRODE Concentration Distance from electrode surface