Oxygen overpotential

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 - ½H 2(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  H 2(g)

3. The overvoltage is the difference between the theoretical cell voltage and the actual voltage that is necessary to cause electrolysis. O vervoltage/Overpotential Oxygen O vervoltage The overvoltage is the difference between the theoretical oxygen reduction potential (+1.23 V) experimentally observed electrode potential .

4. H 2 O (l)  ½ O 2 (g) + 2 H + (aq) + 2e - ½ O 2 (g) + 2 H + (aq) + 2e -  H 2 O (l) Oxidation and reduction  oxygen Oxidation Reduction

5. Electrochemical series ( E° ) ½ F 2(g) + e -  F - (aq) (MnO 4 ) - (aq) + 8H + (aq) + 5e - (g)  Mn 2+ (aq) + 4H 2 O (l) ½ Cl 2(g) + e -  Cl - (aq) ½ O 2 (g) + 2 H + (aq) + 2e -  H 2 O (l) Fe 3+ (aq) + e -  Fe 2+ (aq) H + (aq) + e -  ½ H 2(s) Zn 2+ (aq) + 2e -  Zn (s) Li + (aq) + e - (g)  Li (s) ( E° in V ) +2.87 +1.51 +1.36 +1.23 +0.77 -0.76 -3.04 Redox couple

6. An Overpotential ELECTRODE Concentration Reactant Product Distance from electrode surface

7. O vervoltage/Overpotential Electrode e - H 2 O (l) H + (aq) ½ O 2(g) H + (aq) e -