Mechanism of Potential Oscillation during Electrolysis of Water in Acidic Solutions

Self Cite

The reduction of nitrate ions on Cu and Ag electrodes shows three kinds of oscillations in the potential region of the hydrogen evolution reaction (HER). The oscillations, which appear both under potential-controlled and current-controlled conditions, are sequentially named oscillations I, II, and III as the rate of the HER increases. Oscillation I appears when the electrolyte is acidic, while the other oscillations appear irrespective of the electrolyte pH. To reveal how N-shaped negative differential resistances (N-NDRs) are associated with the HER, a high-speed camera, electrochemical impedance analyzer, and high-gravity electrode are used, which leads to the following conclusions: oscillations I and III are hidden N-NDR (HN-NDR) types, with the former caused by a reaction intermediate of the HER, while the latter is attributed to the inherent nature of bubbles. This paper discusses how these N-NDR characteristics are induced and hidden by the occurrence of the HER. On the other hand, oscillation II is explained by the diffusion limitation of nitrate ions, enhanced convection due to the hydrogen bubble evolution, and change in the pH at the electrode surface.

Section: Discussionmentioning

confidence: 84%

mentioning

confidence: 99%

A Systematic Study on Three Kinds of Oscillations during Simultaneous Occurrence of Nitrate Reduction and Hydrogen Evolution Reaction on Cu and Ag Electrodes

Kuge

Oshikiri

Harada

et al. 2022

Self Cite

“…Specifically, these are strictly (or truly) potentiostatic, 29,32 S-shaped NDR, 33 capacitance-mediated positive differential resistance, 34,35 electrochemical reactions, and diffusion--convection types. [36][37][38] Note that these mechanisms are not responsible for the corrosion potential oscillation because an N-NDR characteristic is essential for the oscillation as shown below.…”

mentioning

confidence: 99%

Corrosion Potential Oscillation of Iron Electrodes in Nitric Acid

Sato,

Kuge,

Nakanishi

et al. 2023

Self Cite

Although iron dissolves in diluted nitric acid solutions, it does not dissolve in concentrated solutions because of surface passivation. When a small amount of water is added to a concentrated solution, the dissolution and passivation of iron occur alternately, and the amount of gaseous products generated by nitric acid reduction varies in an oscillatory manner. During the corrosion process, the corrosion potential of iron oscillates spontaneously. In this study, we investigated the factors that cause oscillations in corrosion potential through electrochemical measurements using a three-electrode system and numerical simulations. The study revealed that an N-shaped negative differential resistance characteristic of iron oxidation plays a vital role in the oscillation of the corrosion potential and, simultaneously, the reduction of nitric acid results in oscillation. We considered metal corrosion has essential factors resulting in oscillatory instability. Thus, the corrosion potentials of various metals are expected to oscillate spontaneously under the appropriate conditions.

“…Other than these typical oscillators, there are several distinct types, namely, strictly potentiostatic, S-shaped NDR (S-NDR), 20 coupled N-NDR (CN-NDR), 18,19 capacitance-mediated positive differential resistance (C-PDR), 21,22 and electrochemical reactions and diffusion-convection (ERDC) [23][24][25] types. When determining the type of oscillation, electrochemical impedance spectroscopy (EIS) measurements are highly useful because EIS can show whether and how an NDR is involved in the system of interest.…”

mentioning

confidence: 99%

“…Interestingly, not only the HPRR but also the HER shows oscillations because of the increase in pH s . 25,31,32 The suppression of reactions is partially due to an increase in the solution pH. For example, the pH of 0.1 M H 2 SO 4 solution slightly increases by adding Na 2 SO 4 or K 2 SO 4 , resulting in the suppression of the HER (i.e., a decrease in the HER current).…”

mentioning

confidence: 99%

Electrochemical Oscillations (Named Oscillations H and K) during H₂O₂ Reduction on Pt Electrodes Induced by a Local pH Increase at the Electrode Surface

Okada

Mizuochi

Sakurada

et al. 2021

Self Cite

The reduction of H2O2 on Pt electrodes in H2SO4 solution shows various electrochemical oscillations, named sequentially from A to J, as reported previously. The present work demonstrates that this electrochemical system also shows a new type of oscillation, called oscillation K, when an alkali metal sulfate is added to the H2SO4 solution containing H2O2. In the presence of alkali metal ions, the local pH at the electrode surface (pHs) becomes basic during H2O2 reduction, and, consequently, reduction and oxidation reactions of HO2 −, which is formed by dissociation of H2O2, take place at the electrode. Detailed studies reveal that oscillation K is caused by an N-shaped negative differential resistance (N-NDR) that is induced by the autocatalytic reduction of HO2 − and that the oscillation can be classified as a “hidden” N-NDR (HN-NDR) type. In this sense, oscillation K is similar to oscillation H which is induced by the autocatalytic reduction of H2O2 and is an HN-NDR oscillator. Besides, a numerical simulation was conducted to understand how HO2 − reduction and oxidation cause oscillation K. To estimate the change in pHs, our simulation employs a newly developed model in which the dissociation of water and that of H2O2 at the electrode are considered.