Electrochemical impedance spectroscopy (EIS) is a versatile technique that can characterize electrochemical systems, but nonlinear EIS (NLEIS) can yield more information. In this work, the NLEIS response of Ti dissolution in 25 mM HF is reported. The NLEIS was acquired using lock-in amplifier as well as FFT analyzer. The data from lock-in amplifiers had better signal to noise ratio compared to the data from FFT analyzer but the runtime was significantly longer for lock-in measurements. The magnitude and phase of the current response at fundamental and higher harmonics are reported. A four step mechanism with two adsorbed intermediates was proposed to explain the observed results. The experimental results were compared with the reaction mechanism model predictions. © The Electrochemical Society.

Srinivasan Ramanathan

Department Of Chemical Engineering

Rajesh Pachimatla

Amplifiers (electronic)

dissolution

Fast Fourier transforms

LIGHT AMPLIFIERS

Locks (fasteners)

Signal to noise ratio

Spectroscopic analysis

titanium

ADSORBED INTERMEDIATES

CURRENT RESPONSE

Electrochemical impedance

Electrochemical systems

FFT ANALYZERS

Higher harmonics

Lock-in amplifier

reaction mechanism

Electrochemical impedance spectroscopy

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ECS Transactions

The effect of instabilities on the nonlinear electrochemical impedance spectroscopic (NLEIS) response of a simple electron transfer reaction in a kinetic and diffusion-controlled regime was studied using classical Fe2+/Fe3+ redox couple on a gold electrode. Numerical simulations were employed to calculate the NLEIS response, and the predictions were compared with experimentally acquired NLEIS data. Instabilities were introduced by continuously changing the dc potential or the active species concentrations. At high frequencies, the effect of potential instabilities manifested more clearly in higher harmonic signals than at the fundamental frequency. In case of changes in species concentrations which did not break the symmetry, the higher harmonics were not particularly more sensitive than the fundamental. An analysis of the results shows that multiple factors contribute to the higher harmonics. The sensitivity of second harmonics to the instabilities arises from the nonlinear component of the rate constant as well as the interaction between the rate constant oscillations and concentration oscillations at the applied frequency. The results show that NLEIS can be used to quickly identify instabilities which alter the symmetry. © The Author(s) 2019.

Journal of the Electrochemical Society

Analysis of instabilities in electrochemical systems using nonlinear electrochemical impedance spectroscopy

Nonlinear electrochemical impedance spectroscopic analysis of Ti dissolution in HF

Anodic dissolution of Ti metal in varying concentrations of hydrofluoric acid (10-1000 mM HF) was investigated using potentiodynamic polarization and electrochemical impedance spectroscopy. Polarization curves obtained at all concentrations of HF solution showed that current initially rises with potential, and decreases at higher potentials. Complex plane plot of the impedance spectra of Ti dissolution in 25 and 50 mM HF solutions exhibited three capacitive loops in the active region and a capacitive behavior with negative resistance in the passive region. The surface was characterized using X-ray photoelectron spectroscopy. A four step mechanism with chemical and electrochemical dissolution steps was employed to model Ti dissolution. The analysis shows that the simulated results match the polarization trends satisfactorily in all the solutions investigated. The model predicts that HF2- and remaining HF are the species that influence chemical and electrochemical dissolution steps respectively. The estimates of surface coverage values of the adsorbed species showed that with increasing over potential, the metal surface was progressively covered with oxide film, while an increase in nominal HF concentration leads to a decrease in fractional surface coverage. © The Author(s) 2017. Published by ECS. All rights reserved.

Effect of HF concentration on anodic dissolution of titanium

Nonlinear Electrochemical Impedance Spectroscopy (NLEIS) is a method of characterizing an electrochemical systems by applying a large amplitude sinusoidal perturbation signal. This article presents a comprehensive review of existing literature on NLEIS analysis development and applications. Two types of NLEIS reports available in the literature, viz. one in which only the fundamental impedance is studied and the other in which both the fundamental and higher harmonic responses are analyzed, are reviewed. Early reports on the development of NLEIS methodology are compiled. Recent advances in the application of NLEIS, in particular in the area of fuel cells, are summarized. In addition, applications of related techniques such as total harmonic distortion and Volterra kernel are included in the purview of this article. There is a large scope for applying NLEIS to understand electrochemical processes. The roadblocks that need to be overcome to enable wider application of NLEIS are identified, and directions for further research are suggested. © The Author(s) 2017. Published by ECS. All rights reserved.

Review - Nonlinear electrochemical impedance spectroscopy

We investigated the anodic dissolution of polycrystalline titanium rotating disc electrode in 0.1 M hydrofluoric acid in active and passive regions using potentiodynamic polarization and electrochemical impedance spectroscopy. In the active region, complex plane plots of the impedance spectra exhibited three capacitive loops indicting the presence of at least two adsorbed intermediates. In the passive region, they exhibited a negative resistance and a low frequency inductive loop. The high frequency loops exhibit constant phase element behavior indicating that a heterogeneous 2D film with partial surface coverage is present in the active and passive regions. The impedance data was fit to a reaction model and a four step mechanism with two adsorbed intermediate species is proposed to explain the observed trends in the active and passive regions. The change in the surface coverage of the adsorbed intermediate species, with the overpotential is estimated. This model describes the dissolution of Ti via two parallel paths, viz. a chemical step and an electrochemical step. The onset of passivation ensues when the rate of TiO<inf>2</inf> film formation is more than that of its dissolution. Transpassive dissolution becomes dominant when the electrochemical dissolution from the bare surface becomes negligible. © The Author(s) 2015. Published by ECS.

Fulltext

A kinetic model for the anodic dissolution of Ti in HF in the active and passive regions

Journal of Applied Electrochemistry

Nonlinear frequency response analysis for the diagnosis of carbon monoxide poisoning in PEM fuel cell anodes

Journal	ECS Transactions
Publisher	Electrochemical Society Inc.
ISSN	19386737
Open Access	No