α-FeOOH (goethite) and γ-FeOOH (lepidocrocite) were found to be the main corrosion products of the steel cathode in the sodium chlorate process; the identification of the phases formed under reducing potentials, along with the study of the electrodes during the reoxidation, is fundamental to understanding their role in this process. In this work, FeOOH-based electrodes were investigated through in situ and in operando X-ray absorption spectroscopy (XAS), combined to electrochemical measurements (e.g., voltammetry and chronoamperometry). At sufficiently negative potentials (below −0.4 V vs RHE ca.) and under hydrogen evolution conditions an unknown iron(II)-containing phase is formed. A comprehensive analysis of the whole XAS spectrum allowed proposing a structure bearing a relation with that of green rust (space group P3̅1m). This phase occurs independently of the nature of the starting electrode (α- or γ-FeOOH). During electrochemical reoxidation, however, the original phase is restored, meaning that the reduced phase brings some memory of the structure of the starting material. Spontaneous reoxidation in air suppresses the memory effect, producing a mixture of α and γ phases

α- and γ-FeOOH: Stability, Reversibility, and Nature of the Active Phase under Hydrogen Evolution / M. Fracchia, A. Visibile, E. Ahlberg, A. Vertova, A. Minguzzi, P. Ghigna, S. Rondinini. - In: ACS APPLIED ENERGY MATERIALS. - ISSN 2574-0962. - 1:4(2018), pp. 1716-1725. [10.1021/acsaem.8b00209]

α- and γ-FeOOH: Stability, Reversibility, and Nature of the Active Phase under Hydrogen Evolution

Alberto Visibile;Alberto Vertova;Alessandro Minguzzi;Sandra Rondinini
2018

Abstract

α-FeOOH (goethite) and γ-FeOOH (lepidocrocite) were found to be the main corrosion products of the steel cathode in the sodium chlorate process; the identification of the phases formed under reducing potentials, along with the study of the electrodes during the reoxidation, is fundamental to understanding their role in this process. In this work, FeOOH-based electrodes were investigated through in situ and in operando X-ray absorption spectroscopy (XAS), combined to electrochemical measurements (e.g., voltammetry and chronoamperometry). At sufficiently negative potentials (below −0.4 V vs RHE ca.) and under hydrogen evolution conditions an unknown iron(II)-containing phase is formed. A comprehensive analysis of the whole XAS spectrum allowed proposing a structure bearing a relation with that of green rust (space group P3̅1m). This phase occurs independently of the nature of the starting electrode (α- or γ-FeOOH). During electrochemical reoxidation, however, the original phase is restored, meaning that the reduced phase brings some memory of the structure of the starting material. Spontaneous reoxidation in air suppresses the memory effect, producing a mixture of α and γ phases
FeOOH; FEXRAV; goethite; hydrogen; lepidocrocite; stability; XAS
Settore CHIM/02 - Chimica Fisica
Settore CHIM/01 - Chimica Analitica
Settore CHIM/03 - Chimica Generale e Inorganica
Settore CHIM/04 - Chimica Industriale
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/2434/595168
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