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2H 2 O → O 2 + 4H + + 4e − Oxidation (generation of dioxygen) 4H + + 4e − → 2H 2 Reduction (generation of dihydrogen) 2H 2 O → 2H 2 + O 2 Total Reaction Of the two half reactions, the oxidation step is the most demanding because it requires the coupling of 4 electron and proton transfers and the formation of an oxygen-oxygen bond.
The 4e − pathway reaction is the cathode reaction in fuel cell especially in proton-exchange membrane fuel cells, alkaline fuel cell and solid oxide fuel cell. While the 2e − pathway reaction is often the side reaction of 4e- pathway or can be used in synthesis of H 2 O 2.
O 2 + 4H + + 4e − → 2H 2 O +0.82 In classical electrochemistry, E° for O 2 = +1.23 V with respect to the standard hydrogen electrode (SHE). At pH = 7, E red = 1.23 – 0.059 V × 7 = +0.82 V: P680 + + e − → P680 ~ +1.0 Half-reaction independent of pH as no H + is involved in the reaction
Photolytic oxygen evolution during photosynthesis occurs via the light-dependent oxidation of water to molecular oxygen and can be written as the following simplified chemical reaction: 2H 2 O → 4e − + 4H + + O 2
2h 2 o 4e − + 4h + + o 2 The protons are released into the thylakoid lumen , thus contributing to the generation of a proton gradient across the thylakoid membrane. This proton gradient is the driving force for adenosine triphosphate (ATP) synthesis via photophosphorylation and the coupling of the absorption of light energy and the oxidation ...
4 + H + + e −: ⇌ HMnO − 4: 0.9 1 Po Po 4+ + 2 e −: ⇌ Po 2+ 0.9 2 [8] Hg 2 Hg 2+ + 2 e −: ⇌ Hg 2+ 2: 0.91 2 [13] Pd Pd 2+ + 2 e −: ⇌ Pd(s) 0.915 2 [15] Au [AuCl 4] − + 3 e −: ⇌ Au(s) + 4 Cl −: 0.93 3 N: NO − 3 + 3 H + + 2 e −: ⇌: HNO 2 (aq) 0.94: 2 [6]: 789 Mn MnO 2 (s) + 4 H + + e −: ⇌ Mn 3+ + 2 H 2 O: 0.95 1 ...
Cathode: reduction of oxygen: O 2 + 4H + + 4e − → 2 H 2 O Global redox reaction: 2 Fe + O 2 + 4 H + → 2 Fe 2+ + 2 H 2 O. Acidic conditions favor the redox reaction according to Le Chatelier principle because the H + ions added to the reagents side displace the reaction equilibrium to the right and also increase the solubility of the ...
Bipolar electrochemistry scheme. In electrochemistry, standard electrode potential, or , is a measure of the reducing power of any element or compound.The IUPAC "Gold Book" defines it as; "the value of the standard emf (electromotive force) of a cell in which molecular hydrogen under standard pressure is oxidized to solvated protons at the left-hand electrode".