Atomic‐Scale Origin of Long‐Term Stability and High Performance of <i>p</i>‐GaN Nanowire Arrays for Photocatalytic Overall Pure Water Splitting

Kibria, Golam; Qiao, Ruimin; Yang, Wanli; Boukahil, Idris; Kong, Xianghua; Chowdhury, Faqrul A.; Trudeau, Michel; Ji, Wei; Guo, Hong; Himpsel, F. J.; Vayssières, Lionel; Mi, Zetian

doi:10.1002/adma.201602274

Cited by 119 publications

(108 citation statements)

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“…[30][31][32] Even though GaN nanowire-based devices, including tunnel-injected DUV light-emitting diodes (LEDs) 33 and LEDs for monolithic metal-optoelectronics 34 and high-power light emitters, 35 have recently been realized, understanding and optimizing the electrothermal characteristics 36,37 of GaN-based nanowires is critical for identifying and achieving their full potential in opto-electrothermal device applications. 38,39 As a consequence of the thermal activation of non-radiative recombination channels, we observed an increasing trend in the amount of generated photoinduced entropy of the InGaN nanowire system as its temperature approached room temperature, which is a valid assessment of the thermodynamic disorder in photoluminescent semiconducting materials. 40 Furthermore, the non-radiative photocarrier recombination lifetimes in nanostructured materials are naturally shorter than those of bulk structures owing to their higher surface-to-volume ratios.…”

Section: Introductionmentioning

confidence: 77%

Thermodynamic photoinduced disorder in AlGaN nanowires

Alfaraj

Muhammed

et al. 2017

AIP Advances

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In this study, we examine thermodynamic photoinduced disorder in AlGaN nanowires through their steady-state and transient photoluminescence properties. We correlate the energy exchange during the photoexcitation and photoemission processes of the light–solid reaction and the generation of photoinduced entropy of the nanowires using temperature-dependent (6 K to 290 K) photoluminescence. We observed an oscillatory trend in the generated entropy of the system below 200 K, with an oscillation frequency that was significantly lower than what we have previously observed in InGaN/GaN nanowires. In contrast to the sharp increase in generated entropy at temperatures close to room temperature in InGaN/GaN nanowires, an insignificant increase was observed in AlGaN nanowires, indicating lower degrees of disorder-induced uncertainty in the wider bandgap semiconductor. We conjecture that the enhanced atomic ordering in AlGaN caused lower degrees of disorder-induced uncertainty related to the energy of states involved in thermionic transitions; in keeping with this conjecture, we observed lower oscillation frequency below 200 K and a stable behavior in the generated entropy at temperatures close to room temperature.

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Section: Introductionmentioning

confidence: 77%

Thermodynamic photoinduced disorder in AlGaN nanowires

Alfaraj

Muhammed

et al. 2017

AIP Advances

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“…As aforementioned, the polar structure of GaN consists of a hexagonal close packing of nitrogen (N) and gallium (Ga) atoms arranged in space group P6 3 mc with Ga atoms in tetrahedral sites (point group 3 m ), which exhibits a c ‐elongated hexagon with a polar plane (Ga‐ or N‐ polar) and C 6 v ‐symmetric nonpolar side plane. Accordingly, the exposed surfaces of the GaN nanorod arrays are schematically represented in Figure h. The polar c ‐plane is perpendicular to c ‐axis while the nonpolar a ‐plane and m ‐plane are parallel to the c ‐axis ([0001]).…”

Section: Resultsmentioning

confidence: 99%

Surface‐Polarity‐Induced Spatial Charge Separation Boosts Photocatalytic Overall Water Splitting on GaN Nanorod Arrays

Zhang

Liu

et al. 2019

Angewandte Chemie

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Photocatalytic overall water splitting has been recognized as a promising approach to convert solar energy into hydrogen. However, most of the photocatalysts suffer from low efficiencies mainly because of poor charge separation. Herein, taking a model semiconductor gallium nitride (GaN) as an example, we uncovered that photogenerated electrons and holes can be spatially separated to the nonpolar and polar surfaces of GaN nanorod arrays, which is presumably ascribed to the different surface band bending induced by the surface polarity. The photogenerated charge separation efficiency of GaN can be enhanced significantly from about 8 % to more than 80 % via co‐exposing polar and nonpolar surfaces. Furthermore, spatially assembling reduction and oxidation cocatalysts on the nonpolar and polar surfaces remarkably boosts photocatalytic overall water splitting, with the quantum efficiency increased from 0.9 % for the film photocatalyst to 6.9 % for the nanorod arrays photocatalyst.

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“…Moreover,operando ambient pressure X-ray photoelectron spectroscopy (APXPS) has also show groundbreaking ability for instanceb ys patially-resolvingt he surfacechemical states of aworkingsolid state electrochemical cell (SOC), providing critical understanding for the rational design of such devices. [75] Finally,t he combinationo fn ovel and smart energy materials design studied at atomics cale and in "real" operating conditions by operando X-ray spectroscopies at synchrotron radiation facilities worldwide is an ideal situation for the current and future generation of scientists to unravel new phenomena as well as establishing quantitative correlations between structural properties, electronic structure and physical/chemical properties of materials [76][77][78] to not only improveour fundamental knowledge but also going beyond as imple incremental increase of device efficiency by breakthrough fundamental and appliedd iscoveries in materials science, condensed matter physics,c hemistry and biology.S uch advances in energy materials, characterizations techniques as wella sb etter fundamental and applied understanding should allow scientists and engineers of all origins to efficiently contribute( and potentially solve) current societal and environmental crucial issues that is, novel carbon-zero sustainable energy resources such as stable and efficient hydrogen generation from (sea)water splitting [79,80] for ac leanerand safer world.…”

Section: Discussionmentioning

confidence: 99%

In Situ/Operando X‐ray Spectroscopies for Advanced Investigation of Energy Materials

Dong

Vayssières

2018

Chemistry A European J

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Issues relatedt oe nergy and the environment have now become of central and crucial importance in our societies. Low-carbon green energy will have ac ritical role in an ecessary third industrial revolution.T or educe global greenhouse gas emissions in response to globalization and increasingly stringent carbone mission policies, large scale green energy production technologiesm ust be established worldwide. An ew age of human demandf or green energy is thus cominga nd scientists are focusedo nf inding new functional efficient and low-cost materialst ogenerate clean and sustainable energy.I mproving the energy conversion, generation, and storagee fficiency of energy materials has always been ad aunting challenge. For many important energy materials ystems, such as nanostructured catalysts, artificial photosynthetic systems, smart energy saving materials, and energy storaged evices, monitoring the atomica nd electronic structures close to the interfacial region in ar eal working environment is of paramount importance.D esigning ab etter-performing materialw ithoutc omprehendingi ts fundamentalp roperties such as chemical states, atomica nd electronic structures and how they are altered close to the interfacial regions during the physical and chemicalr eactions involved in their applications is very challenging. Understanding, controlling and tuning the interfaces in energy conversion and storagem aterials requires in situ/operando characterization tools, of which synchrotron X-ray spectroscopies, whichh ave severalu nique features, are very suitable ones. X-ray absorption spectroscopy can be used to elucidate the local unoccupied electronic structure in the con-ductionb and, and X-ray emission spectroscopy can be used to characterizet he occupied electronic structurei nt he valence band. The derived resonanti nelastic X-ray scattering reveals inter-and/ori ntra-electric transitions (i.e. d-d, f-f excitation and charge-transfer excitation) that reflect intrinsic chemicala nd physicalp roperties. Scanning transmission Xray microscopy is ac hemicalm apping technique with elemental sensitivity and spatial selectivity,w hich can therefore yield information about chemical composition in various spatialr egions. This unique characteristic makest he method effectivef or investigating interfacial phenomena (such as electront ransport, interface formation/deformation,d efects, doping etc.). In situ/operandoa pproaches have made the probinga nd understanding of changes in the atomica nd electronic structures of energy materials in an operational environment feasible. This article presentsaperspective of the pioneering developments as wella st he recent achievements in in situ/operando synchrotron X-ray spectroscopies for the advanced investigationo fe nergy materials. Four major energy materials ystems are identified:e nergy storage, energy generation,e nergy conversion,a nd energy saving materials ystems. Selected representative investigations of each systems are showcased and discussed demonstratingt hat in situ/operando sy...

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Atomic‐Scale Origin of Long‐Term Stability and High Performance of p‐GaN Nanowire Arrays for Photocatalytic Overall Pure Water Splitting

Cited by 119 publications

References 70 publications

Thermodynamic photoinduced disorder in AlGaN nanowires

Thermodynamic photoinduced disorder in AlGaN nanowires

Surface‐Polarity‐Induced Spatial Charge Separation Boosts Photocatalytic Overall Water Splitting on GaN Nanorod Arrays

In Situ/Operando X‐ray Spectroscopies for Advanced Investigation of Energy Materials

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