The importance of nickel oxyhydroxide deprotonation on its activity towards electrochemical water oxidation

Widespread application of solar water splitting for energy conversion is largely dependent on the progress in developing not only efficient, but also cheap and scalable photoelectrodes. Metal oxides, which can be deposited with scalable techniques and are relatively cheap, are particularly interesting, but high efficiency is still hindered by the poor carrier transport properties (i.e., carrier mobility and lifetime). In this paper, a mild hydrogen treatment is introduced to bismuth vanadate (BiVO4), which is one of the most promising metal oxide photoelectrodes, as a method to overcome the carrier transport limitations. Timeresolved microwave and terahertz conductivity measurements reveal more than two-fold enhancement of the carrier lifetime for the hydrogen-treated BiVO4, without significantly affecting the carrier mobility. This is in contrast to the case of tungsten-doped BiVO4, although hydrogen is also shown to be a donor type dopant in BiVO4. The enhancement in carrier lifetime is found to be caused by significant reduction of trap-assisted recombination, either via passivation of deep trap states or reduction of trap state density, which can be related to vanadium anti-site on bismuth or vanadium interstitials according to density functional theory calculations. Overall, these findings provide further insights on the interplay between defect modulation and carrier transport in metal oxide photoelectrodes, which will benefit the development of low-cost, highly-efficient solar energy conversion devices.

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“…[36,37] The same effect may also occur in BiVO4; further studies are needed to confirm this, which is beyond the scope of this paper.…”

Section: Resultsmentioning

confidence: 80%

Enhancing Charge Carrier Lifetime in Metal Oxide Photoelectrodes through Mild Hydrogen Treatment

Jang

Friedrich

Müller

et al. 2017

Advanced Energy Materials

119

164

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“…In contradistinction to an Fe active site model for Fe:Ni oxides, although Mössbauer studies of Fe:Ni layered double hydroxides provide direct evidence for the formation of Fe 4+ in Fe:Ni oxide catalysts during OER, these Fe 4+ sites do not account for the observed catalytic activity (24). Moreover, the formed "active oxygen" species have been found to be adsorbed on nickel sites in Fe:Ni films in borate buffer (25)(26)(27), suggesting Ni centers as active sites for OER. These results together suggest that the presence of Fe active sites may not be the primary reason for the enhanced activity of Fe:Ni catalysts films and point to another chemical role for Fe in oxidic Ni films.…”

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confidence: 92%

Influence of iron doping on tetravalent nickel content in catalytic oxygen evolving films

Bediako

Hadt

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

532

401

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Iron doping of nickel oxide films results in enhanced activity for promoting the oxygen evolution reaction (OER). Whereas this enhanced activity has been ascribed to a unique iron site within the nickel oxide matrix, we show here that Fe doping influences the Ni valency. The percent of Fe 3+ doping promotes the formation of formal Ni 4+ , which in turn directly correlates with an enhanced activity of the catalyst in promoting OER. The role of Fe 3+ is consistent with its behavior as a superior Lewis acid.water splitting | renewable energy | electrocatalysis | oxygen evolution reaction | catalysis

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“…57,58 Specifically, the substitution of hydrogen with deuterium has been carried out extensively due to the large differences in reaction rates arising from the reduced mass differences between the isotopes. 59 68 Therefore, we seek to expand the use of KIE studies to further understand the OER on NPM catalysts at the molecular level.…”

Section: Introductionmentioning

confidence: 99%

Observation of an Inverse Kinetic Isotope Effect in Oxygen Evolution Electrochemistry

et al. 2016

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Earth-abundant and inexpensive catalysts with low overpotential and high durability are central to the development of efficient water splitting electrolyzers. However, improvements in catalyst design and preparation are currently hampered by the lack of detailed understanding of the reaction mechanisms of the oxygen evolution reaction (OER) facilitated by non-precious metal (NPM) catalysts. In this manuscript, we conducted a kinetic isotope effect (KIE) study in an effort to identify the rate-determining step (RDS) of these intricate electrocatalytic reactions involving multiple proton-coupled electron transfer (PCET) processes. We observed an inverse KIE for OER catalyzed by Ni and Co electrodes. These results contribute to a more complete understanding of the OER mechanism and allow for the future development of improved NPM catalysts.

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The importance of nickel oxyhydroxide deprotonation on its activity towards electrochemical water oxidation

Abstract: The OER activity of NiOOH enhances at pH > 11 due to formation of superoxo-like species on its surface.

Cited by 567 publications

References 48 publications

Enhancing Charge Carrier Lifetime in Metal Oxide Photoelectrodes through Mild Hydrogen Treatment

Enhancing Charge Carrier Lifetime in Metal Oxide Photoelectrodes through Mild Hydrogen Treatment

Influence of iron doping on tetravalent nickel content in catalytic oxygen evolving films

Observation of an Inverse Kinetic Isotope Effect in Oxygen Evolution Electrochemistry

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