Formation of internal p–n junctions in Ta<sub>3</sub>N<sub>5</sub>photoanodes for water splitting

Wang, Yi Chieh; Chang, Chih Yung; Yeh, Te Fu; Lee, Yuh Lang; Teng, Hsisheng

doi:10.1039/c4ta04501g

Cited by 58 publications

(37 citation statements)

References 60 publications

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“…These results strongly suggest that Co 3 O 4 has minimized the Ta 5+ /Ta 4+ redox process and the holes are efficiently scavenged by Co 3 O 4 . Furthermore, a slight negative shift of the flat band can be observed from the photocurrent onset (Figure S4, Supporting Information) as compared to Figure afor pristine Ta 3 N 5 NTs, which is also contributing to the improvement in PEC performance from Co 3 O 4 /Ta 3 N 5 . EIS was performed to compare the interfacial charge transportation of Ta 3 N 5 NTs after loading Co 3 O 4 (Figure S5, Supporting Information).…”

Section: Resultsmentioning

confidence: 98%

Pristine Ta₃N₅ Nanotubes: Trap‐Driven High External Biasing Perspective in Semiconductor/Electrolyte Interfaces

Khan

Santos

Malfatti

et al. 2016

Chemistry A European J

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Ta N is a promising photoelectrode for solar hydrogen production; however, to date pristine Ta N electrodes without loading co-catalysts have presented limited photoelectrochemical (PEC) performance. In particular, large external biasing has been required to run water oxidation, the origin of which is investigated herein. Ta N nanotubes (NTs) prepared by nitridation were characterized by a wide range of techniques. The bandgap was confirmed by a novel PEC technique. Nondestructive synchrotron-excited XPS has shown the presence of reduced Ta species deeper in the Ta N surface. Lower photocurrent and transient spikes that were intense at lower applied biasing were observed under water oxidation; however, spikes were inhibited in the presence of a sacrificial agent and photocurrent was improved even at low biasing. It was observed for the first time that the lower PEC performance under water oxidation can be attributed to the presence of interband trapping states associated with pristine Ta N NTs/electrolyte junction. These states correspond to the structural defects in Ta N , devastate PEC performance, and present the necessity to apply higher biasing. The key to circumvent them is to use a sacrificial agent in the electrolyte or to load a suitable co-catalyst to avoid hole accumulation under water oxidation, thereby improving the phootocurrent. The findings on the interband states could also provide guidance for the investigation of PEC properties of new types of semiconducting devices.

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Section: Resultsmentioning

confidence: 98%

Pristine Ta₃N₅ Nanotubes: Trap‐Driven High External Biasing Perspective in Semiconductor/Electrolyte Interfaces

Khan

Santos

Malfatti

et al. 2016

Chemistry A European J

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“…42,43 The crossing point of the lines was used as the capacitance values of the space-charge regions. 42,43 The crossing point of the lines was used as the capacitance values of the space-charge regions.…”

Section: Resultsmentioning

confidence: 99%

Activated carbon-based gas sensors: effects of surface features on the sensing mechanism

et al. 2015

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Ammonia sensing capability of a commercial wood-based activated carbon (BAX) and its oxidized counterpart (BAX-O) was studied. The materials were exposed to continuous cycles of various ammonia concentrations, followed by purging with air, and changes in a normalized resistance were analyzed. When initially exposed to the reducing gas, chemical interactions between ammonia and the carbons generated an irreversible signal change, which was stronger in the case of the initial carbon. After equilibration and reactive adsorption the sensors were further tested with ammonia. During the reversible sensing, the two carbons exhibited opposite trends in their signal. This indicates that oxidation changed the electrical properties of the carbon sample, leading to a different sensing mechanism. For the initial material holes play the predominant role in a current transport, while their depletion upon the exposure to the reducing gas leads to a decrease in the conductivity. In the case of the oxidized sample, the presence of electron donating nitro groups causes a hole annihilation in the carbon itself converting it to a predominantly n-type material. Here the exposure to ammonia increases the conductivity of the chip owing to the electron donating properties of the gas. Physical interactions, such as hydrogen bonding, polar interactions with surface functional groups, and dispersive interactions of ammonia with the carbon matrix, lead to the pore filling, which governs the extent of the response signal. The sensor signal changes linearly with the ammonia concentration.

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“…Among many cocatalysts reported, the low cost Co-based catalysts CoO x , CoPi and CoB i have shown good performance as photoelectrochemical or photocatalytic oxidation cocatalysts. [24][25][26][27][28] Especially, CoO x has proved to be an excellent cocatalyst for TiO 2 . 29,30 The rate of hydrogen generation, photocatalytic activity and the photocurrent density of TiO 2 exhibit obvious enhancement with the addition of CoO x .…”

Section: Introductionmentioning

confidence: 99%

Direct evidence of the efficient hole collection process of the CoO_x cocatalyst for photocatalytic reactions: a surface photovoltage study

Hou

Zhang

et al. 2015

J. Mater. Chem. A

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The authentic effect of a cocatalyst in photocatalytic reaction is one of the major to issues in photocatalysis research. Herein, the efficient hole-collecting role of CoOx cocatalyst grown on TiO2-nanotubes has been directly proved by surface photovoltage (SPV) spectroscopy. Transient SPV measurement provides evidence for the CoOx cocatalyst that could significantly prolong the life-time of photogenerated holes. Furthermore, it is proposed the hole-collecting effect can be attributed to the work function difference between TiO2 and CoOx interface. These findings demonstrates that the development of cocatalyst with suitable work function can be a general strategy for photoconversion applications.

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Formation of internal p–n junctions in Ta₃N₅photoanodes for water splitting

Abstract: Internal electrical fields created in Co-doped Ta3N5 photoanodes facilitate hole injection into the solution phase for O2 evolution.

Cited by 58 publications

References 60 publications

Pristine Ta₃N₅ Nanotubes: Trap‐Driven High External Biasing Perspective in Semiconductor/Electrolyte Interfaces

Pristine Ta₃N₅ Nanotubes: Trap‐Driven High External Biasing Perspective in Semiconductor/Electrolyte Interfaces

Activated carbon-based gas sensors: effects of surface features on the sensing mechanism

Direct evidence of the efficient hole collection process of the CoO_x cocatalyst for photocatalytic reactions: a surface photovoltage study

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Formation of internal p–n junctions in Ta3N5photoanodes for water splitting

Abstract: Internal electrical fields created in Co-doped Ta3N5 photoanodes facilitate hole injection into the solution phase for O2 evolution.

Cited by 58 publications

References 60 publications

Pristine Ta3N5 Nanotubes: Trap‐Driven High External Biasing Perspective in Semiconductor/Electrolyte Interfaces

Pristine Ta3N5 Nanotubes: Trap‐Driven High External Biasing Perspective in Semiconductor/Electrolyte Interfaces

Activated carbon-based gas sensors: effects of surface features on the sensing mechanism

Direct evidence of the efficient hole collection process of the CoOx cocatalyst for photocatalytic reactions: a surface photovoltage study

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Formation of internal p–n junctions in Ta₃N₅photoanodes for water splitting

Pristine Ta₃N₅ Nanotubes: Trap‐Driven High External Biasing Perspective in Semiconductor/Electrolyte Interfaces

Pristine Ta₃N₅ Nanotubes: Trap‐Driven High External Biasing Perspective in Semiconductor/Electrolyte Interfaces

Direct evidence of the efficient hole collection process of the CoO_x cocatalyst for photocatalytic reactions: a surface photovoltage study