Influence of low temp. and electrical field strength on oxygen evolution (photo)catalysis with n-ruthenium disulfide electrodes

Colell, H.; Tributsch, H.

doi:10.1021/j100133a024

Cited by 16 publications

(10 citation statements)

References 5 publications

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“…From comparative electrochemical studies between RuO 2 and RuS 2 Tributsch et al concluded that a thin Ru-oxide layer is formed under oxidative electrochemical conditions onto crystal surfaces of the RuS 2 , which is supposed to be responsible for the catalytic activity towards water oxidation. [8][9][10] This is also verified by XPS and electroreflectance measurements. 10,11 By this surface oxidation the semiconducting property of the RuS 2 as absorber is combined on an atomic level with the Ru-oxide's outstanding catalytic activity for water oxidation.…”

Section: Introductionsupporting

confidence: 71%

Ruthenium sulphide thin layers as catalysts for the electrooxidation of water

Bogdanoff

Zachäus

Brunken

et al. 2013

Phys. Chem. Chem. Phys.

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Crystalline RuS(2) layers were prepared on titanium sheets by reactive magnetron sputtering using a metallic ruthenium target and a H(2)S-Ar mixture as process gas. The ability of these layers for the electrooxidation of water (OER) was investigated by differential electrochemical mass spectrometry (DEMS) in 0.5 M H(2)SO(4) electrolyte. It was observed that the activity for water oxidation is increased with increasing temperature of the titanium substrate during the sputter deposition process whereas a competitive corrosion process is diminished. The reason for this effect seems to be a better crystallinity of these layers at higher substrate temperatures as it is proved by XRD analysis. In contrast to RuS(2) single crystals no photo effect could be observed on the sputtered layers under illumination with a tungsten lamp. Time resolved microwave conductivity analysis indicates the presence of mobile charge carriers after illumination but apparently these cannot participate in the electrooxidation of water.

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Section: Introductionsupporting

confidence: 71%

Ruthenium sulphide thin layers as catalysts for the electrooxidation of water

Bogdanoff

Zachäus

Brunken

et al. 2013

Phys. Chem. Chem. Phys.

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“…RuS, samples were produced from bismuth melts and washed in 30% HNO,. Degenerate samples were obtained by adding 1% As to the melt.l 4 The samples were mounted on electrode holders as described elsewhere, 4 and the back contacts were made with silver paste (Ecolit). The surfaces were polished to 0.25 Apm with diamond paste (Winter Corp.).…”

Section: Methodsmentioning

confidence: 99%

“…Upon illumination, photogenerated valence-band holes are transferred to Ru surface states where oxidation of water to molecular oxygen occurs via an interfacial coordination chemical reaction. 4 On crystal surfaces, one to two monolayers of RuO,_, species were detected by x-ray photoelectron spectroscopy (XPS) after being exposed to air. Although this result should be taken with caution when extrapolating to a solid-liquid contact, the presence of an interfacial compound must be considered to explain the complicated electrochemical behavior of RuS,: strong Fermi-level pinning is deduced from electrochemical impedance spectroscopy 6 and a complicated dependence of the photocurrent on the dc applied potential (V) is always observed.…”

Section: Introductionmentioning

confidence: 99%

Dynamics of the Oxygen‐Evolving RuS2/Electrolyte Interface: An Electroreflectance Study

Chaparro¹,

Salvador²,

Tributsch³

1997

J. Electrochem. Soc.

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Systematic studies of electrolyte electroreflectance (EER) on n-type RuS 2 electrodes in contact with acqueous electrolyte makes it possible to distinguish between two different signals from phases which compete for applied electrical potential. They could be attributed to the space-charge region (EER-b) and to a surface oxide layer (EER-s), respectively. Both signals coexist on electroactivated RuS 2 samples with moderate doping level, where EER-s is observable under accumulation of photogenerated holes at the RuS 2 /RuO,2, interface. On degenerate RuS, samples, the EER-s signal is the only one observed in the spectrum, whereas on low-doped samples EER-b predominates. A minimum observed for the intensity of the EER-s signal on potentiodynamic measurements is attributed to the condition of zero electric field at the surface oxide. A change of sign of this electric field is necessary for oxygen to evolve from water at the RuS,/electrolyte interface. According to the EER measurements, this happens at more negative potentials on the degenerate rather than the moderately doped RuS, sample, explaining why oxygen evolution in the dark is more efficient for highly doped RuS,.

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“…'5 It has to be emphasized that the interfacial ruthenium states, S2Ru,, which capture photogenerated holes, may interact with water molecules forming adsorbed species such as: S2Ru,OH, S2Ru,(OH)2, S2Ru,00H, S2Ru,02, giving rise to surface states within the forbidden energy gap. 6 In reality these complexes should be tential, E° (S2Ru,02/RuS2) may be similar to E°( Ru04/Ru02) or more negative. The RuS2 surface oxidation process can be considered to take place in several steps.…”

Section: Discussionmentioning

confidence: 98%

“…The faradaic process (oxygen evolution) under illumination is only visible for RuS2 a CH = 80 p.F cm2, similar to that estimated for Ru02, 12 we obtain that Q0 2 X io-C cm2, which is approximately the charge needed for oxidizing the io' cm2 Ru states existing at the RuS2 surface. 6 The energy diagram of Fig. 10 illustrates the bandedges position of RuS2, both in the dark and under illumination.…”

Section: Discussionmentioning

confidence: 99%

Photoelectrocatalytic Study of Water Oxidation at n ‐ RuS2 Electrodes

Salvador

Tributsch

1998

J. Electrochem. Soc.

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A kinetic study of the photocatalytic oxidation of water at a n-Ru52 semiconducting single crystal has been undertaken on the basis of photocurrent transients (photocurrent-time behavior as a function of the polarization potential, illumination intensity, and temperature) and electrolyte electroreflectance experiments. The main factor defining the catalytic activity of Ru53 for water oxidation, both in the dark and under illumination, is a low overpotential (i 0.3 V), which is comparable to that of the Ru02 catalyst for oxygen evolution at darkness. Evidence has been given that ris determined by the E°(Ru,-OH°/Ru,-H30) redox potential, which strongly depends on the bonding energy of Ru surface species with OH° radicals generated by direct oxidation of adsorbed water molecules (interfacial Ru-peroxo-type complex formation). This bonding energy increases as the Ru52 surface becomes oxidized under anodic polarization and reaches its maximum value at the potential of the S2Ru02/Ru53 transition (VIII Ru oxidation state). Further oxidation of the Ru-peroxo-type complexes leads to oxygen evolution at a rate which increases with the degree of oxidation of the Ru surface active centers. Although 02 evolution probably already takes place on Ru(VI) surface sites, high evolution rates (current densities) are only reached under oxidation state VIII. However, in this state (idealized S2Ru(VIII)02) Ru-S surface bonds are weakened and occasionally broken, contributing to Ru53 dissolution with generation of volatile Ru04 and S0 soluble ions as the main corrosion products. This phenomenon may be attributed to the reaction in acidic medium of H20 molecules with Ru(VIII) surface species, giving rise to the formation of unstable intermediate complexes. InfroductionRu52 is the first discovered semiconducting material which is able to evolve oxygen from water under infrared illumination.1'2 This is, of course, only possible with a supporting bias potential, since thermodynamics restrains nonassisted photoelectrolysis of water to semiconductors with an energy gap of Eg = 2.1 eV The key requirement for the applicability of semiconductor (sc) electrodes to oxidation of water is that photoinduced minority carriers have to react with H20 molecules via metal-centered interfacial mechanisms.3 Minority carriers trapped at interface metal states not only produce oxidation of these states but induce coordination chemical reactions involving water molecules. When sufficiently high oxidation states are reached, oxygen can be liberated from water. This is the case for Ru52 but not for Fe52, in spite of the fact that both materials have the same crystalline and electronic structure, because Ru can reach high oxidation states that Fe cannot reach. During electrochemical polarization of Ru52, its surface becomes charged with a high density of surface states able to react with water molecules. The consequence is a significant Fermi level pinning and an energetic downward shift of the sc bands with respect to the electrolyte (el) energy levels. When an ...

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Influence of low temp. and electrical field strength on oxygen evolution (photo)catalysis with n-ruthenium disulfide electrodes

Cited by 16 publications

References 5 publications

Ruthenium sulphide thin layers as catalysts for the electrooxidation of water

Ruthenium sulphide thin layers as catalysts for the electrooxidation of water

Dynamics of the Oxygen‐Evolving RuS2/Electrolyte Interface: An Electroreflectance Study

Photoelectrocatalytic Study of Water Oxidation at n ‐ RuS2 Electrodes

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