Enhanced Water Splitting on Thin-film Hematite Photoanodes Functionalized with Lithographically Fabricated Au Nanoparticles

Iandolo, Beniamino; Zäch, Michael

doi:10.1071/ch11453

Cited by 19 publications

(18 citation statements)

References 24 publications

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“…Then, we employed RTP to oxidize the Fe into Fe 2 O 3 . In previous work2728, electrodes with a Fe 2 O 3 thickness of 40 nm converted from Fe at 350 °C in a flow furnace yielded highest performance. In this work, we retained the Fe 2 O 3 thickness of 40 nm and investigated the effect of varying the oxidation temperature T ox in an RTP step on the physical and PEC properties of the fabricated electrodes.…”

Section: Resultsmentioning

confidence: 89%

Iron Oxide Films Prepared by Rapid Thermal Processing for Solar Energy Conversion

Wickman

Fanta

Burrows

et al. 2017

Sci Rep

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Hematite is a promising and extensively investigated material for various photoelectrochemical (PEC) processes for energy conversion and storage, in particular for oxidation reactions. Thermal treatments during synthesis of hematite are found to affect the performance of hematite electrodes considerably. Herein, we present hematite thin films fabricated via one-step oxidation of Fe by rapid thermal processing (RTP). In particular, we investigate the effect of oxidation temperature on the PEC properties of hematite. Films prepared at 750 °C show the highest activity towards water oxidation. These films show the largest average grain size and the highest charge carrier density, as determined from electron microscopy and impedance spectroscopy analysis. We believe that the fast processing enabled by RTP makes this technique a preferred method for investigation of novel materials and architectures, potentially also on nanostructured electrodes, where retaining high surface area is crucial to maximize performance.

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Section: Resultsmentioning

confidence: 89%

Iron Oxide Films Prepared by Rapid Thermal Processing for Solar Energy Conversion

Wickman

Fanta

Burrows

et al. 2017

Sci Rep

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“…[28] All the PEC characterization (cyclic voltammetry, open circuit potential measurements, EIS and MS characterization) were performed in a standard three-electrode configuration with the hematite film as working electrode, a Pt wire as counter-electrode, and a Ag/AgCl electrode as reference. [28] All the PEC characterization (cyclic voltammetry, open circuit potential measurements, EIS and MS characterization) were performed in a standard three-electrode configuration with the hematite film as working electrode, a Pt wire as counter-electrode, and a Ag/AgCl electrode as reference.…”

Section: Methodsmentioning

confidence: 99%

“…The atom-resolved DOS indicates that the valence band is formed by p-band contribution from O atoms, whereas the conduction band has mostly a Fe dband character, in excellent agreement with previous results. These films are polycrystalline [28] and with a relatively flat surface (Supporting Information, Figure S2 and S3), which makes the interpretation of EIS results less complicated than in the case of nanostructured electrodes. [9,27] It is clear that the OH termination introduces occupied mid-gap surface states in a broad energy range extending about 1.5 eV from the bottom of the conduction band.…”

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confidence: 99%

The Role of Surface States in the Oxygen Evolution Reaction on Hematite

Iandolo

Hellman

2014

Angewandte Chemie

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Hematite (a-Fe 2 O 3 ) is an extensively investigated semiconductor for photoelectrochemical (PEC) water splitting. The nature and role of surface states on the oxygen evolution reaction (OER) remain however elusive. Firstprinciples calculations were used to investigate surface states on hematite under photoelectrochemical conditions. The density of states for two relevant hematite terminations was calculated, and in both cases the presence and the role of surface states was rationalized. Calculations also predicted a Nerstian dependence on the OER onset potential on pH, which was to a very good extent confirmed by PEC measurements on hematite model photoanodes. Impedance spectroscopy characterization confirmed that the OER takes place via the same surface states irrespective of pH. These results provide a framework for a deeper understanding of the OER when it takes place via surface states.Sunlight-driven photoelectrochemical (PEC) water splitting carries the promise of an efficient, sustainable method for harvesting solar energy and storing it in chemical bonds in form of fuels. [1][2][3] To make PEC water splitting economically competitive, we need photoelectrodes that are inexpensive, stable against corrosion, as well as efficient in converting solar energy into chemical energy. [4] The latter requirement translates into: broad absorption of sunlight, high yield of charge carriers delivered to the appropriate semiconductor/electrolyte interface, and high catalytic activity for both hydrogen and oxygen evolution reactions (HER and OER, respectively). Since no photoelectrode has been found so far to satisfy all these requirements simultaneously, [5] research has focused on identifying materials that efficiently address some of the processes taking place in a PEC cell. In this context, hematite (a-Fe 2 O 3 ) has attracted great interest as photoanode for the OER, [6][7][8][9][10][11][12][13][14] being an inexpensive semiconductor, stable in electrolytic environment of pH higher than 3, [15] and capable of absorbing a significant amount of visible light thanks to its bandgap energy of around 2 eV. [16] The microscopic mechanism of the OER on hematite is currently the object of intense investigation. It is generally agreed that surface states play an important role in determining the OER efficiency. [9,17] The latter is usually limited by recombination at these surface states. However, the chemical identity and role of the states are not fully understood. [18] In particular, it is not clear whether they are intermediates in the OER, or instead participate in parasitic reactions. Herein, we used a unique combination of first-principles calculations and PEC characterization to investigate the role of surface states on the OER on hematite. Density functional theory (DFT) calculations were employed to resolve the density of states (DOS) for OH-terminated and O-terminated hematite surfaces. The OH-terminated surface is associated with occupied surface states extending over a broad range of energies in the bandgap, whi...

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“…[1] Owing to the global abundance of hematite, efforts have been made to explore practical uses of this material. [10][11][12][13][14][15] In both photocatalysis and water-splitting applications, electrons and holes must be separated and used to perform chemical reactions, and the longer the excitons live, the more likely they are to be separated. Moreover, hematite possesses a narrower band gap, allowing it to absorb more solar light than the other related materials.…”

Section: Introductionmentioning

confidence: 99%

Ultrafast Transient Absorption Studies of Hematite Nanoparticles: The Effect of Particle Shape on Exciton Dynamics

et al. 2013

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Much progress has been made in using hematite (α‐Fe2O3) as a potentially practical and sustainable material for applications such as solar‐energy conversion and photoelectrochemical (PEC) water splitting; however, recent studies have shown that the performance can be limited by a very short charge‐carrier diffusion length or exciton lifetime. In this study, we performed ultrafast studies on hematite nanoparticles of different shapes to determine the possible influence of particle shape on the exciton dynamics. Nanorice, multifaceted spheroidal nanoparticles, faceted nanocubes, and faceted nanorhombohedra were synthesized and characterized by using SEM and XRD techniques. Their exciton dynamics were investigated by using femtosecond transient absorption (TA) spectroscopy. Although the TA spectral features differ for the four samples studied, their decay profiles are similar, which can be fitted with time constants of 1–3 ps, approximately 25 ps, and a slow nanosecond component extending beyond the experimental time window that was measured (2 ns). The results indicate that the overall exciton lifetime is weakly dependent on the shape of the hematite nanoparticles, even though the overall optical absorption and scattering are influenced by the particle shape. This study suggests that other strategies need to be developed to increase the exciton lifetime or to lengthen the exciton diffusion length in hematite nanostructures.

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Enhanced Water Splitting on Thin-film Hematite Photoanodes Functionalized with Lithographically Fabricated Au Nanoparticles

Cited by 19 publications

References 24 publications

Iron Oxide Films Prepared by Rapid Thermal Processing for Solar Energy Conversion

Iron Oxide Films Prepared by Rapid Thermal Processing for Solar Energy Conversion

The Role of Surface States in the Oxygen Evolution Reaction on Hematite

Ultrafast Transient Absorption Studies of Hematite Nanoparticles: The Effect of Particle Shape on Exciton Dynamics

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