Electrochemistry of active chromium, part III: Effects of temperature

It was shown that the temperature in the range 20 ? 65 ?C has considerable effects on the electrochemical anodic dissolution of chromium in the active potential range as well as on the electrochemical hydrogen evolution reactions on bare and oxide covered chromium surfaces. Also, the chemical dissolution of chromium is strongly affected. The apparent energy of activation for anodic dissolution is 63.1 kJ mol-1, for hydrogen evolution on a bare Cr surface 19.5 kJ mol-1, for the same reaction on an oxide covered surface 44.0 kJ mol-1 and for the chemical ("anomalous") dissolution 66.9 kJ mol-1. The temperature dependences of the total corrosion rate, and the electrochemical corrosion rate alone, are presented in polynomial forms with the appropriate constants obtained by the best fit of the experimental data. For the hydrogen evolution reaction on both bare and oxide covered chromium, the Volmer-Heyrovsky reaction mechanism with the second step as rate determining was proposed.

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Dissolution of chromium in sulfuric acid

Journal of the Serbian Chemical Society ◽

10.2298/jsc0211777d ◽

2002 ◽

Vol 67 (11) ◽

pp. 777-782 ◽

Cited By ~ 8

Author(s):

Dragutin Drazic ◽

Jovan Popic

Keyword(s):

Corrosion Rate ◽

Room Temperature ◽

Corrosion Potential ◽

Analytical Data ◽

Electrochemical Corrosion ◽

Spectrophotometric Analysis ◽

Weight Loss Method ◽

Loss Method ◽

Anomalous Dissolution

By combining electrochemical corrosion rate measurements and spectrophotometric analysis of the electrolyte it was shown that at room temperature chromium dissolves in deaerated 0.1M Na2SO4 + H2SO4 (pH1) solution as Cr(II) and Cr(III) ions in he ratio Cr(II):Cr(III)?7:1. This process was stable over 4h without any detectable change. The total corrosion rate of chromium calculated from the analytical data is about 12 times higher, than that determined electrochemically by cathodic Tafel line extrapolation to the corrosion potential. This finding was confirmed by applying the weight-loss method for the determination of the corrosion rate. This enormous difference between these experimentally determined corrosion rates can be explained by the rather fast, "anomalous" dissolution process proposed by Kolotyrkin and coworkers (chemical reaction of Cr with H2O molecules) occurring simultaneously with the electrochemical corrosion process.

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Investigations on the Redox Characteristics and Hydrogen Evolution Efficiencies of Pd and Mo Deposited Pd Electrodes in Alkaline Electrolyte

Bangladesh Journal of Scientific and Industrial Research ◽

10.3329/bjsir.v43i1.861 ◽

1970 ◽

Vol 43 (1) ◽

pp. 103-116 ◽

Cited By ~ 2

Author(s):

M Ashraful Islam Molla ◽

Mithun Sarker ◽

AKM Fazle Kibria

Keyword(s):

Hydrogen Evolution ◽

Hydrogen Adsorption ◽

Stable Condition ◽

Alkaline Electrolyte ◽

Potential Range ◽

Cyclic Voltammograms ◽

Absorption Region ◽

Potential Value ◽

Density Values ◽

Hydrogen Evolution Reactions

Redox behaviors and hydrogen evolution efficiencies of Pd and Mo deposited Pd electrodes have been investigated in 30wt.% KOH electrolyte by cyclic voltammetry. Cyclic voltammograms of Pd electrode in between the potential range - 1.05 V to + 0.75 V showed two couples of redox peaks for the transformations of Pd(0) ←→ Pd(OH)2 and Pd(OH)2 ←→ PdOOH, an anodic peak for the desorption of diffusional hydrogen (dH) and hydrogen and oxygen evolutions at the terminal potential regions. Hydrogen evolution efficiency found decreased with time and then reached to a stable condition after 35 minutes. In presence of deposited Mo, the electrode stable condition appeared after 10 minutes only. Pd found predominates over deposited Mo. Both the Pd(0) ←Pd(OH)2 and Mo(0) ← Mo(OH)2 transformations appeared at the same potential value. Mo stopped the movement of hydrogen adsorption and absorption region of Pd electrode towards negative potential direction. It increased the hydrogen evolution efficiency of Pd electrode remarkably. At the potentials - 1.1 V, - 1.2 V, - 1.25 V and - 1.3 V, currents for Pd + Mo system found 1.44, 1.25, 1.20, 1.23 times higher than those of Pd electrode. Mo also showed hydrogen migratory role to the fraction of Pd surface covered by it. Hydrogen evolution reactions (HER) over Pd and Pd + Mo surfaces seemed followed similar mechanisms. Tafel plots for the HER for both the systems showed two Tafel regions. Exchange current density values (io) for the low and high overpotential regions of Pd + Mo system showed 2.85 times and 1.29 times higher values than those of Pd electrode. Key words: Pd, Pd-Mo, Hydrogen evolution efficiency, Hydrogen evolution reactions (HER) DOI: 10.3329.bjsir.v43i1.861 Bangladesh J. Sci. Ind. Res. 43(1), 103-116, 2008

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Electrochemistry of Active Chromium: Part 1—Anomalous Corrosion and Products of Chromium Dissolution in Deaerated Sulfuric Acid

CORROSION ◽

10.5006/1.3287734 ◽

2004 ◽

Vol 60 (3) ◽

pp. 297-303 ◽

Cited By ~ 9

Author(s):

D. M. Dražić ◽

J. P. Popić

Keyword(s):

Sulfuric Acid ◽

Corrosion Rate ◽

Electrochemical Corrosion ◽

Metal Corrosion ◽

Chemical Dissolution ◽

Rate Measurement ◽

Electrochemical Processes ◽

Corrosion Rate Measurement ◽

Anomalous Dissolution

Abstract Chromium corroding in deaerated aqueous solution of sulfuric acid (H2SO4; pH 1 to 3) produces Cr(II) and Cr(III) ions simultaneously in the ratio 7:1, as well as H2. The corrosion potentials of electrochemically activated chromium are determined by the electrochemical processes as expected according to the Wagner-Traud model. However, the real rates of chromium corrosion determined by collecting evolved hydrogen, spectrophotometric determination of the accumulated Cr ions in the solution, or by weight-loss measurements are higher than the electrochemical dissolution rate by up to 12 times for pH 1.0. The effect is smaller for higher pH. This was due to the simultaneous “anomalous” (or chemical) dissolution process of the direct chemical reaction of Cr with H2O molecules, as proposed some time ago by Kolotyrkin and coworkers. Since “anomalous” dissolution cannot be detected by electrochemical means, it has been pointed out that in the presence of “anomalous” dissolution processes during metal corrosion, electrochemical corrosion rate measurements should be taken only as approximate, while the level of approximation should be determined by some other direct corrosion rate measurement method.

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Effect of Ethylene Diamine Tetra Acetic Acid (EDTA) on the Surface Reaction Behavior and the Hydrogen Evolution Efficiency of Ni-30at.%Cu Electrode in Alkaline Medium

Bangladesh Journal of Scientific and Industrial Research ◽

10.3329/bjsir.v43i2.955 ◽

1970 ◽

Vol 43 (2) ◽

pp. 145-158

Author(s):

AKM Fazle Kibria

Keyword(s):

Acetic Acid ◽

Hydrogen Evolution ◽

Surface Reaction ◽

Ethylene Diamine ◽

Potential Range ◽

Cyclic Voltammogram ◽

Oxidation Reduction ◽

Hydrogen Evolution Reactions ◽

Kinetics Of ◽

Voltammetric Technique

The surface reaction characteristics, hydrogen evolution efficiency and hydrogen evolution reaction kinetics of Ni-30at.%Cu electrode have been investigated in 30wt.%KOH electrolyte in presence and absence of ethylene diamine tetra acetic acid (EDTA) at room temperature by cyclic voltammetric technique. Cyclic voltammogram of the electrode showed three couples of oxidation-reduction peaks in between the potential range - 1.1 to + 0.4 V. The peak couples were originated from the electrochemical transformations of Ni(0) ←→ Ni(OH)2, Cu(0) ←→ Cu(I) and Cu(I) ←→ Cu(OH)2. An interference of the adsorped hydrogen over Cu(0) surface on the transformation of Ni(OH) 2 → Ni(0) was found. It was realized that added EDTA forms Cu-EDTA complex over the electrode surface. With increasing the amount of EDTA, the thickness of Cu(OH) 2 layer gradually decreased. Addition of 0.04g, 0.08g and 0.12g EDTAincreased the hydrogen evolution efficiency of the electrode more than 6%, 12% and 17%. Tafel plots for both the systems showed two well-defined Tafel regions. 0.12g EDTA increased the exchange current density (i0) values 1.3 times for both the Tafel regions. The observed i0 value for the high overpotential (η) region is 1.8 and 2.9 times higher than those of Ni and Cu electrodes. The Tafel slope (b) values for both the low and high η regions are smaller than those observed for without EDTA system and also for the Ni electrode. From the achieved information, it can be concluded that addition of EDTA remarkably increased the hydrogen evolution efficiency of the Ni-30at.%Cu electrode. It seems that hydrogen evolution reactions (HER) followed like mechanisms in absence and presence of EDTA. Key words: Ni-30at.%Cu electrode, EDTA, Electrochemical transformation, Surface reactions, Hydrogen evolution, Hydrogen evolution reactions (HER)DOI: 10.3329/bjsir.v43i2.955 Bangladesh J. Sci. Ind. Res. 43(2), 145-158, 2008

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