Modulated anodization synthesis of Sn-doped iron oxide with enhanced solar water splitting performance

Lv, Xincong; Rodrı́guez, Ingrid; Hu, Chen-Yan; Shang, Jin; Sit, Patrick H.‐L.; Ye, Changhui; Oskam, Gerko; Teoh, Wey Yang

doi:10.1016/j.mtchem.2018.11.012

Cited by 14 publications

(14 citation statements)

References 43 publications

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“…Charge accumulation in such intra-bandgap states has previously been reported for hematite in several studies, and proposed to drive water oxidation. [13][14][15][16] In contrast, the data herein shows that charge accumulating in these states does not contribute significantly to water oxidation, most likely due to their modest oxidation potentials relative to hematite's valence band. These intra-bandgap states have been suggested to be catalytically inactive, 38 instead, they are likely involved in competing trapping processes that can be mitigated with increasing applied potentials.…”

Section: Rhecontrasting

confidence: 62%

Impact of the Synthesis Route on the Water Oxidation Kinetics of Hematite Photoanodes

Mesa

Steier

Moss

et al. 2020

J. Phys. Chem. Lett.

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Operando spectroelectrochemical analysis is used to determine the water oxidation reaction kinetics for hematite photoanodes prepared using four different synthetic procedures. Whilst these photoanodes exhibit very different current / voltage performance, their underlying water oxidation kinetics are found to be almost invariant. Lower photoanode performance was found to correlate with the observation of optical signals indicative of charge accumulation in mid-gap oxygen vacancy states, indicating these states do not contribute directly to water oxidation. Photoelectrochemical water splitting is attracting extensive interest as a promising solar-to-fuel process to store solar energy in chemical bonds (i.e., hydrogen). In solar-driven water splitting, it is widely accepted that the oxygen evolution reaction (OER) is the most kinetically demanding process, especially when using earth abundant metal-oxide photoanodes. 1,2 Consequently, one of the primary limitations to efficiency in such photoanodes is the kinetic mismatch between the lifetimes of photogenerated charges, limited by recombination processes on ps to ms timescales, and the slow kinetics of OER catalysis, occurring usually on the ms-s timescale. 3-5 The efficiency of such photoanodes is strongly dependent on not only the selection of metal oxide, but also the methodology used to synthesize the photoanode, attributed to variations in nanomorphology, surface facet, doping and surface state densities and surface / co-catalyst treatments. 2 However, it is often unclear whether such variations in photoelectrochemical performance result from differences in the underlying kinetics of OER catalysis or rather from differences in competing bulk or surface recombination processes. In this study, we address this issue for one of the most widely studied metal oxides for light driven oxygen evolving photoanodes, hematite (a-Fe2O3). The kinetic mismatch between charge recombination and water oxidation is particularly severe in hematite. Consequently, analyzing the connection between overall performance and the underlying OER kinetics in hematite photoanodes synthesized by different deposition methods, yielding different morphologies, may inform strategies to further narrow the kinetic mismatch between reaction and recombination. One of the key considerations for water oxidation on metal oxides, including hematite, is the potential role of intra-bandgap surface states. 6-9 Such surface states have often been related to oxygen vacancies and structural imperfections / defect sites. 10,11 Surface holes on hematite have been assigned to Fe IV =O species, with these states being proposed as the first intermediate species of the OER. 12 Some studies, including electrochemical impedance analyses, have provided evidence that mid-gap surface states participate as intermediates in the OER catalysis on such photoanodes. 13-16 Other studies, including transient absorption analyses, have suggested OER catalysis is driven by valence band holes localized at the metal oxide surface, w...

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Section: Rhecontrasting

confidence: 62%

Impact of the Synthesis Route on the Water Oxidation Kinetics of Hematite Photoanodes

Mesa

Steier

Moss

et al. 2020

J. Phys. Chem. Lett.

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“…Regarding PEC systems, the anodization of iron substrates was performed in EG + water + fluoride ions via potentiostatic (50 V, 15 min) [ 77 ] or pulsed [ 22 ] methods. Fe 2 O 3 film annealing was carried out at 500 °C for 1 h in an Ar atmosphere to form the hematite phase [ 77 ].…”

Section: General Aspects Of Anodic Oxide Synthesis For Energy Applmentioning

confidence: 99%

“…The recent papers describing the water-splitting devices using anodic oxides mainly explored photoanodes based on TiO 2 -NT [ 10 , 19 , 54 , 82 , 102 , 103 , 104 ], WO x [ 20 , 21 , 51 , 69 , 70 , 71 , 101 ], Fe 2 O 3 [ 22 , 77 ], and ZnO [ 73 , 74 ]. These studies focus on improving the photocurrent density and overall PEC efficiency by developing electrodes with specific bandgap properties, crystallinity, and morphology.…”

Section: Photoelectrochemical Devices For H 2 Pmentioning

confidence: 99%

“…In general, TiO 2 -NT is the preferred anodic oxide explored in dye-sensitized solar cells and PEC water-splitting systems [ 10 , 17 , 18 , 19 ]. Due to its photocatalytic properties, chemical stability, and unidirectional orientation, this semiconductor is frequently used as the photoanode; exceptions include reports of WO 3 [ 20 , 21 ] and Fe 2 O 3 [ 22 ]. The use of copper oxides as photocathodes is emerging [ 23 , 24 ].…”

Section: Introductionmentioning

confidence: 99%

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The Use of Anodic Oxides in Practical and Sustainable Devices for Energy Conversion and Storage

et al. 2021

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This review addresses the main contributions of anodic oxide films synthesized and designed to overcome the current limitations of practical applications in energy conversion and storage devices. We present some strategies adopted to improve the efficiency, stability, and overall performance of these sustainable technologies operating via photo, photoelectrochemical, and electrochemical processes. The facile and scalable synthesis with strict control of the properties combined with the low-cost, high surface area, chemical stability, and unidirectional orientation of these nanostructures make the anodized oxides attractive for these applications. Assuming different functionalities, TiO2-NT is the widely explored anodic oxide in dye-sensitized solar cells, PEC water-splitting systems, fuel cells, supercapacitors, and batteries. However, other nanostructured anodic films based on WO3, CuxO, ZnO, NiO, SnO, Fe2O3, ZrO2, Nb2O5, and Ta2O5 are also explored and act as the respective active layers in several devices. The use of AAO as a structural material to guide the synthesis is also reported. Although in the development stage, the proof-of-concept of these devices demonstrates the feasibility of using the anodic oxide as a component and opens up new perspectives for the industrial and commercial utilization of these technologies.

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“…12 Some studies, including electrochemical impedance analyses, have provided evidence that mid-gap surface states participate as intermediates in the OER catalysis on such photoanodes. [13][14][15][16] Other studies, including transient absorption analyses, have suggested OER catalysis is driven by valence band holes localized at the metal oxide surface, with intra-bandgap (e.g. : oxygen vacancy) states primarily function as electron / hole trapping sites, impacting upon bulk and back electron-hole recombination.…”

mentioning

confidence: 99%

Impact Of Synthesis Route on the Water Oxidation Kinetics of Hematite Photoanodes

Mesa

Moss²,

Francàs³

et al. 2020

Preprint

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<p><i>Operando</i> spectroelectrochemical analysis is used to determine the water oxidation reaction kinetics for hematite photoanodes prepared using four different synthetic procedures. Whilst these photoanodes exhibit very different current / voltage performance, their underlying water oxidation kinetics are found to be almost invariant. Lower photoanode performance was found to correlate with the observation of optical signals indicative of charge accumulation in mid-gap oxygen vacancy states, indicating these states do not contribute directly to water oxidation.</p>

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Modulated anodization synthesis of Sn-doped iron oxide with enhanced solar water splitting performance

Cited by 14 publications

References 43 publications

Impact of the Synthesis Route on the Water Oxidation Kinetics of Hematite Photoanodes

Impact of the Synthesis Route on the Water Oxidation Kinetics of Hematite Photoanodes

The Use of Anodic Oxides in Practical and Sustainable Devices for Energy Conversion and Storage

Impact Of Synthesis Route on the Water Oxidation Kinetics of Hematite Photoanodes

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