Electrochemical oscillations and bistability during anodic dissolution of vanadium electrode in acidic media—part I. Experiment

Abstract

Dynamic instabilities, current oscillations and bistability observed during anodic dissolution of both stationary and rotating disk vanadium electrode in acidic phosphoric media, were reported using both dc and ac techniques. The effect of various experimental conditions, concentration of H 3 PO 4 , temperature, disk rotation rate, and external resistance, was analyzed. Systematic studies allowed the construction of bifurcation diagrams, showing the regions of oscillations and bistability, including the complex behaviors like coexistence of both dynamic regimes. Analogous comparative measurements and analyses were performed for other media-sulfuric, nitric, perchloric, and trifluoroacetic acids-also indicating complex dynamic behaviors. These complexities arise not only due to the difficulties with the precise identification of the composition of the passive layer in every acid but are also due to relatively fast dissolution of V electrode, even in the presence of passive layer, which causes permanent drift of the system's characteristics. Due to these experimental difficulties, theoretical modeling seems to be an appropriate method to analyze the essential nonlinear dynamic properties of the studied system.

Electrochemical oscillations and bistability during anodic dissolution of vanadium electrode in acidic media—part II. The model

“…The validity of general construction of our model was confirmed by the fact that, in our numerical calculations, we were able to reproduce both oscillatory and bistable courses of the vanadium electrooxidation for physically reliable parameters and conditions similar to those existing in our experiments [1]. A representative comparison of experimental and simulated oscillatory courses is collected in Fig.…”

“…In a previous paper [1], we described the oscillations and bistability reported during the anodic oxidation of vanadium in various aqueous acidic media: H 3 PO 4 , H 2 SO 4 , HNO 3 , HClO 4 , and CF 3 COOH. The complexity of these systems is caused, among others, by the relatively fast electrodissolution process, being a source of temporal drift of its characteristics.…”

“…This makes systematic experimental studies of this process rather difficult. Nevertheless, the dynamic instabilities accompanying the vanadium electrodissolution in various acidic media have not been intensively studied so far, except for primary reports for the occurrence of the oscillations [2], followed by our recent experimental studies [1]. In the case of such complicated systems, theoretical modeling, focused on the properties essential for the onset of dynamic instabilities, is a convenient tool for understanding of the core oscillatory mechanism and its quantitative analysis.…”

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Abstract Following our experimental results on the oscillatory and bistable vanadium electrooxidation in phosphoric acid medium (Gorzkowski et al, 2011), we constructed a theoretical model of the V/H 3 PO 4 passivation/dissolution system which allowed us to reproduce the basic dynamic instabilities observed. In this model, the formation of the negative resistance (N-NDR) region was ascribed to the potential-dependent formation/destruction of the inhibitive V 2 O 5 layer on the electrode surface.

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Electrochemical oscillation of vanadium ions in anolyte

“…In the H2SO4 solution, however, the V2O5 is dissolved due to the presence of large amount of H + what can be described by equation (5). From all results and discussion mentioned above, the electrochemical oscillation could be explained in terms of the competition between the growth and the chemical dissolution of V2O5 film [18,19].…”