Oszillographische Überspannungsmessungen. I

Abstract

Durch oszillographische Registrierung des Spannungs‐Zeit‐Verlaufs bei kurzzeitigen Stromimpulsen ist eine Messung des Polarisationswiderstandes und der Stromspannungskurve der schnellen Elektrodenvorgänge ohne Beeinflussung durch die langsamer anklingende Diffusionspolarisation möglich. Ferner kann in gleicher Weise das Anklingen der Diffusionspolarisation untersucht werden. Meßanordnung und theoretische Grundlagen des Meßverfahrens werden beschrieben.Als Untersuchungsbeispiel wird die Kinetik der Metallelektrolyse an festen Cadmiumelektroden behandelt. Als polarisationsbestimmend erweist sich hier die Ionenentladung. Die Austauschstromdichte wird nach zwei Methoden, der Durchtrittsfaktor nach drei unabhängigen Methoden bestimmt. Die Übereinstimmung ist befriedigend. Das Anklingen der Diffusionspolarisation liefert Aufschlüsse über die Oberflächenrauhigkeit der Elektrode.Die Tatsache, daß bei Cadmium die Ionenentladung polarisationsbestimmend ist, wird zum Schluß an Hand der Kristallisationstheorie diskutiert.

Aluminum Deposition and Dissolution in [EMIm]Cl-Based Ionic Liquids–Kinetics of Charge–Transfer and the Rate–Determining Step

“…In a more refined approach one would have to consider that the value for the charge-transfer resistance decreases with increasing overpotential. 39 However, for the following discussion this estimation seems to be sufficient.…”

“…Depending on the height of the amplitude of the controlled current or controlled potential step, the resulting transients provide valuable information about the diffusion coefficient of the electrochemically active species, 31,32 the nucleation behavior [33][34][35][36][37][38] and charge-transfer reaction. 39 Density functional theory (DFT) calculations were performed to assess if the suggested mechanisms are thermodynamically reasonable.…”

Reactivity of Scratched Cadmium Electrodes in Alkaline Solutions

“…The kinetic data cannot distinguish these three mechanisms. Reactions [5] and [6] are solid-state processes in which the film is formed directly from the metal surface without prior dissolution. Reaction [4] is a dissolution-precipitation process if the CdOH + ion desorbs from the metal surface before undergoing precipitation by either of the following reactions…”

“…The work was, however, criticized by Heusler and Gaiser (8) for the limited potential range over which it was studied. By extending the potential range to more positive values, Heusler and Gaiser showed that the anodic behavior deviates from the 60 mV Tafel law given by Lorenz (4)(5)(6) and gave a Tafel slope of 108 mV where the anodic current density i is between ~60 and 500 mA-cm -s, The idea that both mechanisms operate in different potential ranges was supported by Hampson et al, (9,10).…”

“…Even in acidic sulfate and perchlorate solutions in which the metal does not equilibrate with any of it~ oxides (3), there is no agreement regarding its mechanism of dissolution (4-10). Lorenz (4)(5)(6) originally showed that the reaction Cd ~ Cd 2+ -t-2e proceeds in a single step with both electrons being transferred simultaneously; this process has been cited (7) as typifying a two-electron transfer reaction. The work was, however, criticized by Heusler and Gaiser (8) for the limited potential range over which it was studied.…”