Effects of NiO-loading on n-type GaN photoanode for photoelectrochemical water splitting using different aqueous electrolytes

Koike, Kayo; Yamamoto, Kazuhiro; Ohara, Satoshi; Kikitsu, Tomoka; Ozasa, Kazunari; Nakamura, Shinichiro; Sugiyama, Masakazu; Nakano, Yoshiaki; Fujii, K.

doi:10.1016/j.ijhydene.2016.12.141

Cited by 22 publications

(19 citation statements)

References 14 publications

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“…The photocurrents were continuously monitored under illumination at 0.5 V for 60 min, as shown in Figure d. For the composite porous GaN, the initial photocurrent is ∼0.41 mA/cm 2 , which slightly decreases to ∼0.33 mA/cm 2 with a degeneration rate of 1.3 μA/cm 2 min –1 because of the photocorrosion caused by UV light and applied voltage. ,− Although the photocurrent initially decreased for the composite porous GaN compared with the other two samples, according to our measurement for a longer period, the decrease became slow with further increasing the time, and this composite structure can still possess the best performance after 3 h. The photocorrosion can be reduced by reducing the applied voltage and the electrolyte concentration, and a high stability with good performance was also observed in the composite porous GaN (Figure S2). The good stability of the composite porous GaN compared to other untreated nanostructured GaN , is due to the low porosity of the laterally porous GaN and the low-damage ICP etching for vertical nanoholes.…”

Section: Resultsmentioning

confidence: 71%

Light Modulation and Water Splitting Enhancement Using a Composite Porous GaN Structure

Yang

et al. 2018

ACS Appl. Mater. Interfaces

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On the basis of the laterally porous GaN, we designed and fabricated a composite porous GaN structure with both well-ordered lateral and vertical holes. Compared to the plane GaN, the composite porous GaN structure with the combination of the vertical holes can help to reduce UV reflectance and increase the saturation photocurrent during water splitting by a factor of ∼4.5. Furthermore, we investigated the underlying mechanism for the enhancement of the water splitting performance using a finite-difference time-domain method. The results show that the well-ordered vertical holes can not only help to open the embedded pore channels to the electrolyte at both sides and reduce the migration distance of the gas bubbles during the water splitting reactions but also help to modulate the light field. Using this composite porous GaN structure, most of the incident light can be modulated and trapped into the nanoholes, and thus the electric fields localized in the lateral pores can increase dramatically as a result of the strong optical coupling. Our findings pave a new way to develop GaN photoelectrodes for highly efficient solar water splitting.

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Section: Resultsmentioning

confidence: 71%

Light Modulation and Water Splitting Enhancement Using a Composite Porous GaN Structure

Yang

et al. 2018

ACS Appl. Mater. Interfaces

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“…Another common method named metal–organic chemical vapor deposition strategy was applied to deposit NiO onto GaN. The band alignment between them offered efficient carrier separation and fast hole transport, making its PEC performance significantly outperform that of pure GaN . Besides, an n‐silicon photoanode coated by a NiO x layer was successfully synthesized via a pulsed laser deposition method for efficient PEC oxygen evolution .…”

Section: Cocatalysts For Photoanodes: Construction and Regulationmentioning

confidence: 99%

Rational Design and Construction of Cocatalysts for Semiconductor‐Based Photo‐Electrochemical Oxygen Evolution: A Comprehensive Review

et al. 2018

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Photo‐electrochemical (PEC) water splitting, as an essential and indispensable research branch of solar energy applications, has achieved increasing attention in the past decades. Between the two photoelectrodes, the photoanodes for PEC water oxidation are mostly studied for the facile selection of n‐type semiconductors. Initially, the efficiency of the PEC process is rather limited, which mainly results from the existing drawbacks of photoanodes such as instability and serious charge‐carrier recombination. To improve PEC performances, researchers gradually focus on exploring many strategies, among which engineering photoelectrodes with suitable cocatalysts is one of the most feasible and promising methods to lower reaction obstacles and boost PEC water splitting ability. Here, the basic principles, modules of the PEC system, evaluation parameters in PEC water oxidation reactions occurring on the surface of photoanodes, and the basic functions of cocatalysts on the promotion of PEC performance are demonstrated. Then, the key progress of cocatalyst design and construction applied to photoanodes for PEC oxygen evolution is emphatically introduced and the influences of different kinds of water oxidation cocatalysts are elucidated in detail. Finally, the outlook of highly active cocatalysts for the photosynthesis process is also included.

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“…Several protective layers and catalysts have been tested for such photoanodes to suppress photocorrosion. [ 17–25 ] In particular, the loading of p‐type NiO cocatalysts enhances the stability of GaN during the oxygen evolution reaction (OER). [ 19–25 ] However, the mechanism of the protection against photocorrosion is not well understood.…”

Section: Figurementioning

confidence: 99%

Protection Mechanism against Photocorrosion of GaN Photoanodes Provided by NiO Thin Layers

et al. 2020

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The photoelectrochemical properties of n‐type Ga‐polar GaN photoelectrodes covered with NiO layers of different thicknesses in the range 0–20 nm are investigated for aqueous solution. To obtain layers of well‐defined thickness and high crystal quality, NiO is grown by plasma‐assisted molecular‐beam epitaxy. Stability tests reveal that the NiO layers suppress photocorrosion. With increasing NiO thickness, the onset of the photocurrent is shifted to more positive voltages and the photocurrent is reduced, especially for low bias potentials, indicating that hole transfer to the electrolyte interface is hindered by thicker NiO layers. Furthermore, cathodic transient spikes are observed under intermittent illumination, which hints at surface recombination processes. These results are inconsistent with the common explanation of the protection mechanism that the band alignment of GaN/NiO enables efficient hole‐injection, thus preventing hole accumulation at the GaN surface that would lead to anodic photocorrosion. Interestingly, the morphology of the etch pits as well as further experiments involving the photodeposition of Ag indicate that photocorrosion of GaN photoanodes is related to reductive processes at threading dislocations. Therefore, it is concluded that the NiO layers block the transfer of photogenerated electrons from GaN to the electrolyte interface, which prevents the cathodic photocorrosion.

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Effects of NiO-loading on n-type GaN photoanode for photoelectrochemical water splitting using different aqueous electrolytes

Cited by 22 publications

References 14 publications

Light Modulation and Water Splitting Enhancement Using a Composite Porous GaN Structure

Light Modulation and Water Splitting Enhancement Using a Composite Porous GaN Structure

Rational Design and Construction of Cocatalysts for Semiconductor‐Based Photo‐Electrochemical Oxygen Evolution: A Comprehensive Review

Protection Mechanism against Photocorrosion of GaN Photoanodes Provided by NiO Thin Layers

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