Enhancement of Photoelectrochemical Hydrogen Production from Hematite Thin Films by the Introduction of Ti and Si

Glasscock, Julie; Barnes, Piers R. F.; Plumb, I. C.; Savvides, N.

doi:10.1021/jp074556l

Cited by 438 publications

(488 citation statements)

References 68 publications

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“…The series resistance, R s , was essentially constant and small, which is consistent with ohmic behavior at the FTO/hematite interface. [46][47][48] We note that the increase of trap C is correlated to the decrease of ct ,trap R , it being the case that both trap C and ct ,trap R shift in concert for the different illumination conditions tested. This clearly indicates that hole transfer for the water splitting reaction takes place through the surface state.…”

Section: Resultsmentioning

confidence: 99%

Water Oxidation at Hematite Photoelectrodes: The Role of Surface States

et al. 2012

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Published asKlahrHowever, the physical-chemical mechanisms responsible for the photoelectrochemical performance of this material ( J(V ) response) are still poorly understood. In the present study we prepared thin film hematite electrodes by Atomic Layer Deposition to study the photoelectrochemical properties of this material under water splitting conditions. We employed Impedance Spectroscopy to determine the main steps involved in photocurrent production at different conditions of voltage, light intensity and electrolyte pH. A general physical model is proposed, which includes the existence of a surface state at the semiconductor/liquid interface where holes accumulate. The strong correlation between the charging of this state with the charge transfer resistance and the photocurrent onset provides new evidence of the accumulation of holes in surface states at the semiconductor/electrolyte interface, which are responsible for water oxidation. The charging of this surface state under illumination is also related to the shift of the measured flat band potential. These findings demonstrate the utility of Impedance Spectroscopy in investigations of hematite electrodes to provide key parameters of photoelectrodes with a relatively simple measurement. 3 I ntroductionAs part of the quest to develop better and cleaner energy conversion and storage systems, the direct conversion of sunlight into chemical fuels has become a subject of renewed interest.One attractive example is the use of semiconductors to harness solar photons to split water, thereby producing hydrogen as a chemical fuel. In order to achieve this, a given material must satisfy a number of stringent requirements including visible light absorption, efficient charge carrier separation and transport, facile interfacial charge-transfer kinetics, appropriate positions of the conduction and valence band energy levels with respect to required reaction potentials and good stability in contact with aqueous solutions. 1 While such systems were heavily investigated several decades ago, no material so far has fulfilled all the required conditions. 2,3 Recent advances in nanotechnology and catalysis, however, greatly increase the prospects of developing a combination of materials capable of efficient conversion of sunlight to chemical fuels. 4 Hematite ( -Fe 2 O 3 ) is a very promising material for photoelectrochemical (PEC) water splitting due to its combination of sufficiently broad visible light absorption, up to 590 nm, and excellent stability under caustic operating conditions. 5,6 However, hematite electrodes are adversely affected by a number of factors including a long penetration depth of visible light due to its indirect band gap transition and a very short minority carrier lifetime and mobility; this combination hinders efficient collection of the minority carriers via the required interfacial charge-transfer reactions. Considerable effort has been devoted to improving the actual efficiency by employing nanostructuring strategies, which disconnects the ligh...

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Section: Resultsmentioning

confidence: 99%

Water Oxidation at Hematite Photoelectrodes: The Role of Surface States

et al. 2012

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“…Often, these will exploit support-metal-supportinteraction (SMSI) modification of photo-catalytic properties [2]. Although TiO 2 is one of the most studied metal oxides in the literature, α-Fe 2 O 3 has come to be of equal, if not more, interest in recent years, due to its relative ubiquity and low cost, with a seemingly ideal bad gap [3][4][5][6][7][8][9][10].…”

Section: Introductionmentioning

confidence: 99%

Photo-active and dynamical properties of hematite (Fe2O3)–water interfaces: an experimental and theoretical study

English

Rahman

Wadnerkar

et al. 2014

Phys. Chem. Chem. Phys.

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The dynamical properties of physically and chemically adsorbed water molecules at pristine hematite-(001) surfaces have been studied by means of equilibrium Born-Oppenheimer molecular dynamics (BOMD) in the NVT ensemble at 298 K. The dissociation of water molecules to form chemically adsorbed species was scrutinised, in addition to 'hopping' or swapping events of protons between water molecules. Particular foci have been dynamical properties of the adsorbed water molecules and OH -and H 3 O + ions, the hydrogen bonds between protons in water molecules and the bridging oxygen atoms at the hematite surface, as well as the interactions between oxygen atoms in adsorbed water molecules and iron atoms at the hematite surface. Experimental results for photoelectrical current generation complement simulation findings of water dissociation.

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“…The resistivity was found to be ~25 Ω·cm at a Ti concentration of 15 cation %. 6 Other methods for synthesizing Ti-doped hematite have also been utilized, including solid-state reaction, 18 sputtering, 19 and sol-gel. 20 However, transport measurements were limited in these investigations.…”

Section: Introductionmentioning

confidence: 99%

Electrical transport properties of Ti-doped Fe2O3(0001) epitaxial films

et al. 2011

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The electrical transport properties for compositionally and structurally well-defined epitaxial α-(Ti x Fe 1-x ) 2 O 3 (0001) films have been investigated for x ≤ 0.09. All films were grown by oxygen plasma assisted molecular beam epitaxy using two different growth rates -0.05 -0.06 Å/s and 0.22 -0.24 Å/s. Despite no detectable difference in cation valence and structural properties, films grown at the lower rate were highly resistive whereas those grown at the higher rate were semiconducting (ρ = ~1 Ω·cm at 25 o C). Hall effect measurements reveal carrier concentrations between 10 19 and 10 20 cm -3 at room temperature and mobilities in the range of 0.1 to 0.6 cm 2 /V·s for films grown at the higher rate. The conduction mechanism transitions from small-polaron hopping at higher temperatures to variable range hopping at a transition temperature between 180 to 140 K. The absence of conductivity in the slow-grown films is attributed to donor electron compensation by cation vacancies, which may form to a greater extent at the lower rate because of higher oxygen fugacity at the growth front.2

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Enhancement of Photoelectrochemical Hydrogen Production from Hematite Thin Films by the Introduction of Ti and Si

Cited by 438 publications

References 68 publications

Water Oxidation at Hematite Photoelectrodes: The Role of Surface States

Water Oxidation at Hematite Photoelectrodes: The Role of Surface States

Photo-active and dynamical properties of hematite (Fe2O3)–water interfaces: an experimental and theoretical study

Electrical transport properties of Ti-doped Fe2O3(0001) epitaxial films

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