The effect of cobalt on the kinetics of oxygen evolution at a lead oxide anode in sulphuric acid.

The overpotential (n)-log current density (log i) curves for the evolution of oxygen at a lead dioxide anode in 2N H2SO4 both in the absence and presence of cobaltous sulphate in solution have been used to determine the electrode kinetic constants α ; i0 for a series of temperatures and also ΔH0*:. At 25 �C in the absence of cobalt α=O.59, i0= 10-11, and ΔH0*= 15 kcal mole-1 When 13 mg/l cobaltous sulphate is added α= 1.0, i0= 10-15, and ΔH0*:=29 kcal mole-1. Possible mechanisms for the reaction are discussed on the basis of these values and the rate determining steps suggested (where M represents the PbO2 surface) are M +H2O =MOH +H+ +e in the absence of cobalt and 2CoOH++ = 2Co++ +H2O + O in its presence.

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Effect of various cations on the initial rate of formation of peroxodisulphates

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc19802272 ◽

1980 ◽

Vol 45 (8) ◽

pp. 2272-2282 ◽

Cited By ~ 4

Author(s):

Jan Balej ◽

Martin Kadeřávek

Keyword(s):

Sulphuric Acid ◽

Oxygen Evolution ◽

Anodic Polarization ◽

Initial Rate ◽

Degree Of Conversion ◽

Polarization Curves ◽

Mixed Solutions ◽

Low Degree ◽

Partial Polarization

Preparation of peroxodisulphates by electrolysis of mixed solutions of sulphuric acid and various sulphates was studied at low degree of conversion; the partial polarization curves of peroxodisulphate formation and of oxygen evolution obtained from the overall anodic polarization curves and current yields of the principal anodic processes were examined. The mechanism of the effect of various cations on the rate of anodic formation of peroxodisulfates is discussed.

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Photosystem II: Thermodynamics and Kinetics of Electron Transport from QA- to QB(QB- ) and Deleterious Effects of Copper(II)

Zeitschrift für Naturforschung C ◽

10.1515/znc-1993-3-419 ◽

1993 ◽

Vol 48 (3-4) ◽

pp. 234-240 ◽

Cited By ~ 32

Author(s):

G. Renger ◽

H. M. Gleiter ◽

E. Haag ◽

F. Reifarth

Keyword(s):

Oxygen Evolution ◽

Manganese Content ◽

Fluorescence Emission ◽

Laser Flash ◽

Fluorescence Induction ◽

Oxygen Evolving Complex ◽

Ps Ii ◽

Thermodynamics And Kinetics ◽

Redox Active ◽

Kinetics Of

Studies on thermodynamics and kinetics of electron transfer from QA- to QB(QB-) were performed by monitoring laser flash induced changes of the relative fluorescence emission as a function of temperature (220 K < T < 310 K) in isolated thylakoids and PS II membrane fragments.In addition, effects of bivalent metal ions on PS II were investigated by measuring conventional fluorescence induction curves, oxygen evolution, manganese content and atrazine binding mostly in PS II membrane fragments. It was found: a) the normalized level of the fluorescence remaining 10 s after the actinic flash (Ft/F0) steeply increases at temperatures below -10 to - 20 °C, b) the fast phase of the transient fluorescence change becomes markedly retarded with decreasing temperatures, c) among different cations (Cu2+, Zn2+, Cd2+, Ni2+, Co2+) only Cu2+ exhibits marked effects in the concentration range below 100 μᴍ and d) Cu2+ decreases the normalized variable fluorescence, inhibits oxygen evolution and diminishes the affinity to atrazine binding without affecting the number of binding sites. The content of about four manganeses per functionally competent oxygen evolving complex is not changed by [Cu2+] < 70 μᴍ.Based on these findings it is concluded: i) a temperature dependent equilibrium between an inactive (I) and active (A) state of QA- reoxidation by QB(QB- ) is characterized by standard enthalpies ΔH° of 95 kJ mol-1 and 60 kJ mol-1 and standard entropies ΔS° of 370 kJ K-1 mol-1 and 240 kJ K-1 mol-1 in isolated thylakoids and PS II membrane fragments, respectively, ii) the activation energies of QA- reoxidation by plastoquinone bound to the QB site are about 30 kJ mol-1 (thylakoids) and 40 kJ mol-1 (PS II membrane fragments) in 220 K < T < 300 K, and iii) Cu2+ causes at least a two-fold effect on PS II by modifying the atrazine binding affinity at lower concentrations ( ~ 5 μᴍ) and interference with the redox active tyrosine Yz at slightly higher concentration ( ~ 10 μᴍ) leading to blockage of oxygen evolution.

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