Photoelectrochemical Characterization of the Anodic Film on Zinc in  KOH  Solution

Scholl, Peter F.; Shan, Xiu; Bonham, D. Bivings; Prentice, Geoffrey

doi:10.1149/1.2085743

Cited by 26 publications

(9 citation statements)

References 23 publications

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“…Second, the assignment is consistent with the expected reduction potentials of these species,35 i.e. and or Zn(OH) + 2e -Zn + 4 OH-E° = -1.285 V [1] Zn(OH)2 + 2e -÷ Zn + 2 OH-E° = -1.246 V [2] ZnO + 1120 + 2e Zn + 2 OH-E° = -1.248 V [3] albeit the difference in their potentials is small. We believe the the prepassive species is hydroxide-doped zinc oxide, ZnO,_x(OH)2a,.…”

Section: Resultssupporting

confidence: 76%

Spectroelectrochemical Studies on Dissolution and Passivation of Zinc Electrodes in Alkaline Solutions

Cai

Park

1996

J. Electrochem. Soc.

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Electrochemical oxidation of zinc electrodes has been studied in 1.0 M KOH solutions employing cyclic voltammetnc and in situ spectroelectrochemical techniques. The results indicate that three different processes, i.e., dissolution, prepassivation, and passivation, take place in different potential regions. Two optically different solution species absorbing at 250 and 290 nm, which are assigned to Zn(OH) and Zn(OH), respectively, are produced initially during anodic oxidation of zinc at different potentials to different extents with different respective ratios. These species undergo a series of consecutive chemical reactions to eventually lead to passive films on the surface. The film compositions were identified to be ZnO1(OH)2, OW-doped ZnO, and Zn-doped ZnO depending on the potential regime and aging. Details of the electrochemistry and chemistry taking place during electrolysis in these three regions are discussed based on the cyclic voltammetric and spectroelectrochemical data.

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Section: Resultssupporting

confidence: 76%

Spectroelectrochemical Studies on Dissolution and Passivation of Zinc Electrodes in Alkaline Solutions

Cai

Park

1996

J. Electrochem. Soc.

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“…Aurian-Blajeni and Tomkiewicz proposed that these passive lms are composite layers of the electrolyte and the oxide lm, 43 oen found to retain properties typical of an amorphous semiconductor lm. 44 The passivation processes at highly alkaline pH were summarised by Dirkse. 45 The Zn(OH) 2 lm on the surface of ZnO lm dissolves as Zn(OH) 3 À or Zn(OH) 4 2À and, once the electrolyte layer covering the electrode becomes supersaturated, re-deposits again as amorphous Zn(OH) 2 .…”

Section: Long-term Stabilitymentioning

confidence: 99%

Photoelectrochemical water oxidation by screen printed ZnO nanoparticle films: effect of pH on catalytic activity and stability

et al. 2014

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Nanostructured ZnO films are promising photoanode materials in photoelectrochemical water splitting. While such ZnO photoanodes have achieved high activity and good light conversion efficiency in the UV spectral region, their application in water splitting devices has been hampered by the susceptibility of ZnO towards photocorrosion in aqueous electrolytes. We report a systematic investigation aimed at optimising the electrolyte solution to improve the long-term stability of ZnO photoanodes. A stability diagram, based on the band edge positions of ZnO and the pH-dependent photodegradation potentials of ZnO (relative to the decomposition of water), indicates that the optimum pH operating conditions for ZnO photoanodes lie between pH 9-12.5. To verify this prediction experimentally, the activity and long-term stability of uniform screen-printed nano-ZnO films was tested in a wide range of buffered and non-buffered electrolytes (pH 6-13.5). The ZnO films were more active in buffered, than in non-buffered electrolytes, and the highest activities were observed close to the pKa of the phosphate and borate buffers used. Under zero applied potential, these screen-printed films achieved the highest reported photocurrents to date (0.42 mA cm(-2) at pH 6 and 0.67 mA cm(-2) at pH 10.5) for any pristine or modified ZnO-based water oxidation catalyst. The films were subjected to 12 h of controlled potential electrolysis, in selected electrolytes, under AM 1.5G simulated sunlight. The results are in good agreement with calculations based on thermodynamic data for ZnO. Films tested at pH 6 and 7 (representing typically used operating conditions) degraded rapidly, whereas they exhibited the highest stability when tested in a pH 10.5 borate buffer. In this case, 75% of the initial photoactivity was preserved after 12 hours, indicating that the lifetime of the electrode could be increased by over an order of magnitude compared to standard testing conditions.

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“…6 is the fact that through potentiostatic measurements, only the potentiostatic growth charge density (q3) is determined. This is related with the q1 by the equation = q0 + [8] where q0 is the initial charge density of the film, prior to potentiostatic growth.…”

Section: Theorymentioning

confidence: 99%

Potentiostatic Growth of ZnO on Zn: Application of an Ohmic Model

D’Alkaine

Boucherit

1997

J. Electrochem. Soc.

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A quantitative theory is developed for better understanding of the potentiostatic growth of passivating films on metals following a previously proposed general treatment for voltammetric and galvanostatic transients. The theory is based, in this case, on an ohmic model for the current/overpotential relation inside the film and a Tafel relation for current/overpotential at the metal/film interface. The equations are applied to the potentiostatic growth of the passivating film on Zn in 0.3 M H3B03 plus 0.15 M Na2B4O7 solution. It is shown that the initial charge, after electrode polishing and before potentiostatic growth, can be disregarded. It is then observed that, during potentiostatic growth, the film ionic specific resistivity decays, passes through a minimum value, and then increases, giving rise to an aged film. The time for the occurrence of this last increase is proposed to be called "aging time." As a result, there is the appearance in the potentiostatic experiments of a maximum charge for film formation, which depends on the growth potential. This maximum charge presents, with the increase of the growth potential, a maximum followed by subsequent increase. As a consequence, it is proposed that the results can be interpreted through the existence of two kinds of films present, each appearing in two different potential regions. Finally, a general explanation is proposed for the evolution of the ionic specific resistivity in terms of the existence of defect injection at the metal/film (interstitial cations) and film/solution (cation vacancies) interfaces, the migration of the defects and their recombination inside the film.

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Photoelectrochemical Characterization of the Anodic Film on Zinc in KOH Solution

Cited by 26 publications

References 23 publications

Spectroelectrochemical Studies on Dissolution and Passivation of Zinc Electrodes in Alkaline Solutions

Spectroelectrochemical Studies on Dissolution and Passivation of Zinc Electrodes in Alkaline Solutions

Photoelectrochemical water oxidation by screen printed ZnO nanoparticle films: effect of pH on catalytic activity and stability

Potentiostatic Growth of ZnO on Zn: Application of an Ohmic Model

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