Das verhalten der magnesiumelektrode in alkalischen elektrolyten

Abstract

The behaviour of magnesium electrodes in aqueous alkaline electrolytes was studied. Generally, reproducible current density/overvoltage curves cannot be obtained with such a system, since changes of structural parameters of the electrode take place in the course of time. The transition from the passive state to the active one is particularly important here, but it can also happen that the structural parameters of the passive layers themselves alter. By employing different methods of measurement an attempt was made to obtain a picture of the behaviour of the electrode. Normally, the electrode is covered by an electron-conducting polyatomic passive layer. All phenomena can be interpreted by applying the Vetter passive-layer model, if one takes into consideration an additional redox reaction but still regards the electrochemical potential of electrons over the passive layer as quasiconstant. To explain the negative difference effect for the active dissolution, a new pitting model is put forward, which explains the specific features observed without assuming ions of low valency. The difficulties encountered when these electrodes are used in practice are due to the passive—active behaviour. On the other hand, it is only because of the passivation that the good corrosion resistance of electrodes in the aqueous electrolyte is possible. A specific feature is that the atmospheric oxygen can hardly exert a detrimental effect on the passivated electrode, which fact is not without significance for the use in air cells. Unfortunately, it has proved true that in systems with activating anions a reduction of the very unwelcome H 2 development during the active phase will be hardly possible.