The dissolution of iron in concentrated alkali

This paper presents a review of the redox and electrocatalytic properties of transition metal oxide electrodes, paying particular attention to the oxygen evolution reaction. Metal oxide materials may be prepared using a variety of methods, resulting in a diverse range of redox and electrocatalytic properties. Here we describe the most common synthetic routes and the important factors relevant to their preparation. The redox and electrocatalytic properties of the resulting oxide layers are ascribed to the presence of extended networks of hydrated surface bound oxymetal complexes termed surfaquo groups. This interpretation presents a possible unifying concept in water oxidation catalysis -bridging the fields of heterogeneous electrocatalysis and homogeneous molecular catalysis. In contextOver the past 50 years considerable research efforts have been devoted to the realisation of efficient, economical and renewable energy sources. Metal oxide materials have played a large part in this drive with demonstrated applications at both the research and commercial level. Their use in areas such as batteries, fuel cells and water electrolysis has resulted in the development of materials with a diverse range of structural and chemical properties. In all cases, understanding the fundamental electrochemistry of the material can be invaluable for rational design and optimisation. This review focuses on the redox, charge transport and electrocatalytic properties of transition metal oxide electrodes as they pertain to the electrolytic splitting of water. Particular emphasis is placed on the nature of the active surface which is interpreted in terms of hydrated interlinked oxymetal complexes termed surfaquo groups. In this way, the review seeks to bridge the gap between heterogeneous electrocatalysis and homogeneous molecular catalysis for water oxidation, areas of considerable modern interest and activity.

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“…Furthermore, it has been noted that active dissolution to form soluble oxy iron species may occur according to, 200,201 FeO + OH À -HFeO 2…”

Section: Interfacial Redox Chemistry Of Iron Based Electrodes In Alkamentioning

confidence: 99%

Redox and electrochemical water splitting catalytic properties of hydrated metal oxide modified electrodes

Doyle

Godwin

Brandon

et al. 2013

Phys. Chem. Chem. Phys.

521

565

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“…Many investigations were carried out using highly alkaline solutions [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] or using buffer solutions as carbonate/bicarbonate [19][20][21][22][23][24][25][26] or borate buffer [27][28][29][30][31][32] when a constant and not very high pH is desirable. Many products have been identified as resulting from the anodic polarization of iron at different potentials, by different surface analysis techniques [6][7][8][9][10][11][12][13]22,26,[33][34][35][36][37][38][39][40]…”

Section: Introductionmentioning

confidence: 99%

“…Many products have been identified as resulting from the anodic polarization of iron at different potentials, by different surface analysis techniques [6][7][8][9][10][11][12][13]22,26,[33][34][35][36][37][38][39][40][41][42][43][44][45] . Several electrochemical techniques have also been used to investigate the kinetics of the formation of these products and among them cyclic voltammetry is one of the most used [2][3][4][5][6][7][8][14][15][16][17][18][19][20][21][22] . The surface analysis techniques that perform in-situ analysis have the great advantage of avoiding decomposition and/or dehydration of products formed which is inevitable with ex-situ analysis due to the high vacuum conditions and to the heating promoted by electron bombardment 1,14,28,[33][34][35][36]…”

Section: Introductionmentioning

confidence: 99%

Electrochemical Behaviour of Iron in NaOH 0.01 mol/L Solutions Containing Variable Amounts of Silicate

Amaral¹,

Müller²

1999

J. Braz. Chem. Soc.

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Ciclos voltamétricos repetitivos do ferro em soluções de NaOH contendo concentrações variáveis de silicato entre 10 ppm e 1500 ppm, mostram comportamentos diferentes da primeira varredura quando comparada com as subsequentes, em todas as soluções testadas. Esta diferença indica uma modificação do processo de formação do filme com a ciclagem. Foi observada uma transição do perfil i/E entre 10 ppm e 100 ppm de silicato o que permite formular considerações sobre a incorporação de silicato ao filme.Repetitive voltammetric cycling of iron in NaOH solutions containing variable silicate concentrations between 10 ppm and 1500 ppm, shows different behaviour for the first scan when compared to the following ones in all studied solutions. This difference indicates a modification on the film formation process. A transition in the i/E profile between 10 ppm and 100 ppm of silicate was observed allowing considerations about silicate incorporation to be formulated.

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“…Several key studies have been made of the chemical reactions which accompany the first step discharge of an iron electrode in KOH electrolyte (1,2). It has also been established that the Fe(OH)2 product of the first piateau discharge is formed by a dissolutionprecipitation mechanism (2,3).…”

mentioning

confidence: 99%

“…It has also been established that the Fe(OH)2 product of the first piateau discharge is formed by a dissolutionprecipitation mechanism (2,3). However, in terms of the physical structure of an iron electrode as it affects the discharge capacity on the first plateau, little has been written.…”

mentioning

confidence: 99%

The Importance of Physical Structure to the Capacity of Porous Iron Electrodes

Bryant

1979

J. Electrochem. Soc.

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The discharge capacity of a porous iron electrode is controlled by either the extent of interparticle neck growth achieved during sintering or the amount of surface area retained following sintering. The mode of capacity control is related to the density of the electrode.Several key studies have been made of the chemical reactions which accompany the first step discharge of an iron electrode in KOH electrolyte (1, 2). It has also been established that the Fe(OH)2 product of the first piateau discharge is formed by a dissolutionprecipitation mechanism (2, 3). However, in terms of the physical structure of an iron electrode as it affects the discharge capacity on the first plateau, little has been written. Hancock and Strasser (4) have demonstrated that the use of various iron powders to increase electrode surface area provided a corresponding increase in discharge capacity.In the present work capacity is examined as a function of electrode density and the results compared to a porosity (density) model proposed by Selanger (5). Finally, the physical features of an iron electrode which determine its capacity are examined and discussed.Procedure Sponge iron powder was prepared by the hydrogen reduction of Fe208. Two lots of powder were used in the study. They were designated as lots A and B and had respective BET surface areas of 4.4 m2/g and 7.3 m2/g. Green electrodes having nominal dimensions of 0.31 cm (thick) by 3.2 cm by 3.2 cm and a nominal density of 17.2% TDFe (percent of the theoretical density of iron) were prepared by pressing powder between pairs of perforated nickel current collectors. Sintering in flowing hydrogen for various times at temperatures between 650 ~ and 900~ provided electrodes having densities ranging from 18.1 to 25.8% TDFe. A current collector tab was then spot welded to one face of each electrode.The electrodes were automatically tested at 44~ against nickel sheet electrodes in 25 weight percent (w/o) KOH containing 15 g/liter LiOH. Test conditions included a 100 mA/cm 2 charge current density and a 50 mA/cm 2 discharge current density to a cutoff voltage of 0.750V (vs. a Hg/HgO reference electrode). A large excess of electrolyte, relative to the weight of iron, was employed to minimize the need for water makeup to the electrolyte. Discharge capacities for electrodes prepared from each powder were determined.Experimental Results Because of its relative ease of measurement, the density of a pressed and sintered body has often been adopted as a measure of its physical structure. To test the usefulness of this measure to correlate the capacity data of the present work, the capacities of electrodes prepared by numerous combinations of sintering time and temperature were determined as a function of electrode density. These results, for lot A and lot B electrodes respectively, are given in Fig. 1 and 2.According to the porosity model proposed by Selanger, a maximum achievable discharge capacity * Electrocl~emical Society Active Member.

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The dissolution of iron in concentrated alkali

Cited by 99 publications

References 13 publications

Redox and electrochemical water splitting catalytic properties of hydrated metal oxide modified electrodes

Redox and electrochemical water splitting catalytic properties of hydrated metal oxide modified electrodes

Electrochemical Behaviour of Iron in NaOH 0.01 mol/L Solutions Containing Variable Amounts of Silicate

The Importance of Physical Structure to the Capacity of Porous Iron Electrodes

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