Kinetic studies on the short time deposition and dissolution of copper in solutions of cupric sulphate, chloride, perchlorate, acetate and aminosulphonate, and their corresponding acids, were carried out by means of a galvanostatic transient method at 30°C, using electrodes prepared by melting in helium (A-type) or by electrodeposition @-type).Tafel relations were observed on B-type electrodes (&a 120 and b a ~ 40 mv). Overpotentialtime transients indicated deviations from a simple double-layer charging model, and these were greatest on A-type electrodes. 3 In i0/3 In a c u z + ~0 -5 ; anion effects increased with increasing size of the ions.Two rate-determining steps are assumed under specific conditions : surfaw diffusion when the surface has a relatively low number of surface dislocations, and charge transfer, Cu2++e-+Cu+, respectively. The number of growth sites is calculated. A-type electrode$ have a lesser dislocation density than B-type. The transfer reaction suggested is consistent with the large rise time of overpotential on B-type electrodes, because electricity is needed to equilibrate the " fast ,' step Cu++e+Cu. The concentration dependence of io is interpreted in terms of an increasing rate-controlling influence of the Cu++e+Cu step at the highest concentrations. The asymmetric i against 7 relation observed on A-type electrodes depends on an approach to saturation (with adions) of the electrode surface. Differences of io for the transfer reaction on A and B electrodes are due to secondary causes, e.g., surfaces of A electrodes spend less time ia contact with solution. Anion effects u e consistent with a simple blocking of sites by specifically adsorbed anions.Deposition and dissolution at the Cu/aq. CuSO4, H2S04 interface was studied by Mattsson and Bockris.* The galvanostatic transient studies reported here are concerned with the dependence of the velocity of the metal-solution exchange reaction on metal ion concentration and anions present in solution. EXPERIMENTAL APPARATUSThe cell used was similar to that reported elsewhere.l.2 Air was removed by purzed helium.3 The traps with active charcoal used in gas purification were heated frequently. The cell was thermostatted at 30f03"C. ELECTRODESThese were prepared and used as reported 1 9 4 (spectroscopically pure). The electrodes attained reversible potential in a short time after they were immersed in the solution and their glass sheaths broken. A glass tube covered the wire connecting the spherical electrode to the holder. The reference electrode was a copper Wire.

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Cobalt(ii)-tetraphenylporphyrin (CoVpp)-fixed glassy carbon (GC) electrodes were prepared using 4-aminopyridine (pyNH2) in the form of Colltpp-pyNH-CO/GC, which were active for electroreduction of C 0 2 to CO at potentials 100 mV more positive than water-soluble Coil porphyrins, and the overall turnover number of Coiltpp for CO production exceeded 105.Metalloporphyrins have been reported to be active as catalysts in the electroreduction of C 0 2 in aqueous' and nonaqueous2 media. In aqueous media, water-soluble CoIItetraphenylporphyrin sulphonate and CoTTrneso-tetracarboxyphenylporphyrin have been reported to be catalytically active for the electroreduction of C 0 2 . Pyridine (py) is reported to coordinate at the axial position of planar CoII(sa1en) (H2salen = bissalicylideneethylenediamine) and stabilizes C 0 2 in the opposite coordination site.3 In the present work, we attempted to obtain a CoIItpp-py (tpp = tetraphenylporphyrin) complex-fixed electrode by applying the water-insoluble CoIItpp on glassy carbon (GC) substrate plates modified initially with 4-aminopyridine (pyNH2). 4-Aminopyridine is expected not only to immobilize CoIItpp on the G C electrode, but also to provide the CoIItpp-fixed GC electrode with new properties.CoIItpp-pyNH-CO/GC (I) was prepared as follows Glassy carbon (GC) plates (Tokai GC-30, 27 mm x 5 mm, 1 mm thick) were subjected to anodic oxidation in 0.5 mol dm-3 H2S04, and refluxed in SOC12 for 24 h, for chlorination as COCl/GC. The electrodes were then immersed in 4-aminopyridine-saturated benzene solution for 24 h at room temperature to produce pyNH-CO/GC (11). Finally, the electrodes were refluxed in a 0.6 mmol dm-3 CoIItpp solution in benzene for 24 h to produce I.The fixation of 4-aminopyridine was confirmed by the diffuse reflectance FT IR spectrum of 11, which showed a peak at 1665 cm-1 due to C=O stretching of the -CO-NH-amide group together with pyridine ring C=C and C=N stretching peaks at 1610 and 1537 cm-1, respectively. These results showed that 4-aminopyridine was fixed in the form of pyNH-CO/GC. Fig. l(a) shows the diffuse reflectance UV-VIS spectrum of I, together with spectra of ( b ) CoIItpp and (c) CoIItpp-py in CH2C12 for comparison. Spectra ( a ) and (c) show the Soret band at 440 nm, whereas that of ( b ) is at 420 nm. These spectra indicated that Co**tpp was fixed as the pyridine complex, CoIItpp-py, and the electron density of the central ColI ions of I was increased by the pyridine 1igand.s Fig. 2 shows cyclic voltammograms (CV) of I in standard phosphate buffer solution at pH 6.86 saturated with He or C02. No CoIItpp/CoItpp redox peak was observed, but this is probably due to the small amount of CoIItpp distributed on the electrode which has a high roughness factor (3 x 103). The surface concentration of CoIItpp of (10-12 mol cm-2; apparent surface area) was evaluated by ESCA. A pronounced increase of the cathodic current was observed at potentials more negative than -0.95 V [vs. saturated calomel electrode (SCE)] in C02-saturated solution, this increase st...