Log Q = 2.74 -2.78 Ec, 0.55 > Ec > 0 (4) where Q is the amount of copper deposited in microcoulombs (/uC). The total quantity of copper deposited at 0 V, Q*, is 540 ± 25 pC/cm2 for a reduced or an oxidized electrode. Q* represents the total copper involved in the surface controlled reductions and oxidations, Ri -
Films of antimony-doped tin oxide on glass, after treatment with 10 M NaOH, show Nernstian pH response from pH 2 to 10. The treated electrodes, after exposure to sulfur vapor, show Nernstian response to pS over the range of 6.0 to 15.2, depending upon the total sulfide concentration and pH. At a constant pS, the pH dependence is 59 mV below pH 6.5 and 30 mV from pH 6.5 to 10.65 in accordance with theory.
The electrochemistry and spectroelectrochemistry of manganese tetrakis(N‐methyl‐4‐pyridyl)porphine (Mn‐TMPyP) in aqueous media have been studied. For MnIIITMPyP two water molecules ligate to the metal center and the formation constant(β2) is 0.11 in acetonitrile solution. The pKa1 and pKa2 for MnIIIIMPyP(H20)2 are 10.9 and 12.3, respectively in aqueous media. There is only one pKa at 11.7 for MnIIIMPyP(H2O)2. The pKa of the oxo‐manganese(IV) porphyrin, O = MnIVTMPyP(H2O), is 11.3. MnIITMPyP demetallates rapidly to free base in acidic aqueous solution. MnIITMPyP also undergoes electrocatalysis for oxygen reduction. In acidic conditions, demetallation and catalysis rates are competitive. The transmetallation of MnTMPyP by Zn2+ can be achieved in the presence of thiols. The UV‐Visible spectra in the reaction process suggest that the formation of some reactive intermediate is essential for the transmetallation.
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