The significance of electrochemical impedance spectra recorded during active oxygen evolution for oxide covered Ni, Co and Fe electrodes in alkaline solution

Abstract

Please cite this article as: M.E.G. Lyons, M.P. Brandon, The significance of electrochemical impedance spectra recorded during active oxygen evolution for oxide covered Ni, Co and Fe electrodes in alkaline solution, Journal of Electroanalytical Chemistry (2009Chemistry ( ), doi: 10.1016Chemistry ( /j.jelechem.2009 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. ACCEPTED MANUSCRIPTTitle: The significance of electrochemical impedance spectra recorded during active oxygen evolution for oxide covered Ni, Co and Fe electrodes in alkaline solution. Abstract: Although the mechanism for the oxygen evolution reaction (OER) is likely to be similar for oxidised electrodes of the adjacent transition metals Ni, Co and Fe, the electrochemical impedance spectra, recorded for each of these anodes during oxygen evolution in 1.0 M NaOH, are significantly different in appearance. This impedance data is analysed using an approach similar to that of Cahan and Chen [1] in an earlier important article on this topic. A controversial proposal by these workers that OER "Tafel slopes" (measured by either ac or dc techniques) for many electrode systems are not in fact characteristic of the kinetics of the reaction, but instead of the potential dependent conductivity of the oxide, is dismissed on the basis of our data. In the case of Co however, it is found that the kinetics of the OER are masked by a dominant low frequency pseudo-capacitance, arising most likely from a nonhomogeneous surface charge distribution associated with the oxidation of Co(III) to Co(IV) oxy-hydroxide species. A consistent interpretation of the data is provided, which envisages that Fe exhibits the most general impedance response with the spectra for the other anodes taking the form of limiting cases. Consideration is also given to the most appropriate choice of equivalent circuit model (with a firm physical basis) to aid our understanding of the complex interface at which oxygen evolution proceeds.

A comparative study of the oxygen evolution reaction on oxidised nickel, cobalt and iron electrodes in base

“…The preparation of the working electrodes from pure polycrystalline samples (>99.9%, metals basis) of the relevant metal has been described elsewhere [38,40], along with details of the sourcing of these metals. It is worth commenting that the Ni and Fe electrodes were prepared from foils (exposed apparent surface area = 0.16 cm 2 ), while the Co anode was prepared from a wire (exposed apparent cross sectional area = $0.0314 cm 2 ).…”

“…Even though we have performed impedance spectroscopy measurements on the electrodes considered here, significant frequency dispersion was noted in each case for the double layer capacitance [40], thereby casting significant doubt over roughness factors calculated by the capacitance ratio approach.…”

Anodic Oxygen Evolution on Iron, Cobalt and Nickel Silicides in Alkaline Electrolyte

“…3); прямая располагается в том же частотном диапазоне, что и при потенциалах пас-сивного состояния электрода [13]. По данным работ [9,10,14] в области пе-репассивации в растворах NaOH на поверхности Fe-электрода отмечается интенсивное выделение кислорода. Авторами [9] для этой области были получены тафелевские константы ~ (0,040-0,050) В и порядок реакции по OH --ионам ~ 1,0 (при Е = =const).…”

“…на железе в щелочном электролите характеризуется константой Тафеля, равной (0,040-0,045) В, и порядком реакции ~ 1,0. Спектры импеданса Fe-электрода при E выделе-ния кислорода состоят из трех перекрывающихся емкостных полуокружностей: ВЧ-полуокружность отвечает пассивной пленке (предполагается, что выделение кислорода протекает не на металле, а на покрывающем его оксиде), полуокружность при средних частотах -переносу заряда через межфазную границу оксидная пленка/электролит в поле двойного электрического слоя, НЧ-полу-окружность -адсорбции интермедиата на поверх-ности электрода [9,10,14].…”

“…4б также была использована авторами [9,10,14] для моделирования процессов на границе оксид/электролит системы Fe-элект-род|оксид|электролит в области потенциалов вы-деления кислорода. На спектрах импеданса FeSi-электрода в области высоких частот не было об-наружено дополнительной временной константы, которая характеризовала бы релаксацию процес-сов в оксидной пленке.…”