2D layered materials with sensitive surfaces are promising materials for use in chemical sensing devices, owing to their extremely large surface‐to‐volume ratios. However, most chemical sensors based ...on 2D materials are used in the form of laterally defined active channels, in which the active area is limited to the actual device dimensions. Therefore, a novel approach for fabricating self‐formed active‐channel devices is proposed based on 2D semiconductor materials with very large surface areas, and their potential gas sensing ability is examined. First, the vertical growth phenomenon of SnS2 nanocrystals is investigated with large surface area via metal‐assisted growth using prepatterned metal electrodes, and then self‐formed active‐channel devices are suggested without additional pattering through the selective synthesis of SnS2 nanosheets on prepatterned metal electrodes. The self‐formed active‐channel device exhibits extremely high response values (>2000% at 10 ppm) for NO2 along with excellent NO2 selectivity. Moreover, the NO2 gas response of the gas sensing device with vertically self‐formed SnS2 nanosheets is more than two orders of magnitude higher than that of a similar exfoliated SnS2‐based device. These results indicate that the facile device fabrication method would be applicable to various systems in which surface area plays an important role.
A novel approach for fabricating self‐formed active‐channel devices based on 2D semiconductor materials with very large surface areas is proposed and their potential gas sensing ability is examined. The device exhibits extremely high response values and this novel fabrication method is expected to find use in various applications where surface area plays an important role in function.
Transparent electrodes have been widely used in electronic devices such as solar cells, displays, and touch screens. Highly flexible transparent electrodes are especially desired for the development ...of next generation flexible electronic devices. Although indium tin oxide (ITO) is the most commonly used material for the fabrication of transparent electrodes, its brittleness and growing cost limit its utility for flexible electronic devices. Therefore, the need for new transparent conductive materials with superior mechanical properties is clear and urgent. Ag nanowire (AgNW) has been attracting increasing attention because of its effective combination of electrical and optical properties. However, it still suffers from several drawbacks, including large surface roughness, instability against oxidation and moisture, and poor adhesion to substrates. These issues need to be addressed before wide spread use of metallic NW as transparent electrodes can be realized. In this study, we demonstrated the fabrication of a flexible transparent electrode with superior mechanical, electrical and optical properties by embedding a AgNW film into a transparent polymer matrix. This technique can produce electrodes with an ultrasmooth and extremely deformable transparent electrode that have sheet resistance and transmittance comparable to those of an ITO electrode.
High‐performance electrocatalysts, especially those consisting of earth abundant elements with low cost, are highly desirable for oxygen reduction reaction (ORR). However, design of well‐dispersed ...ORR catalysts that are efficient in both acidic and alkaline media remains challenging. Herein, we report a phosphate‐regulated synthesis with phytic acid, by dispersing the active sites in the carbon nanosheets to obtain Fe2P/FeP nanoparticles encapsulated in P, N‐doped carbon (PNC). The active sites of Fe2P/FeP particles and P, N‐doping sites have a synergistic effect on the ORR reaction. The Fe2P/FeP‐PNC catalyst exhibits good ORR performance and stability in alkaline media. The half‐wave potential (0.85 V), and 5 mV shift after 5000 cycles of stability test for Fe2P/FeP‐PNC catalyst exceed those of commercial Pt/C (E1/2=0.84 V, 20 mV shift) under alkaline condition. The catalyst presents a half‐wave potential of 0.70 V and limited current density of 5.31 mA cm−2 in acidic media. We demonstrate a Zn‐air battery and a PEMFC with the Fe2P/FeP‐PNC as the cathodes, showing a high power density of 156.68 mW cm−2 and 144 mW cm−2 respectively in either the alkaline or acidic electrolytes.
Fe2P/FeP nanoparticles dispersed on P, N co‐doped carbon nanosheets with a balance between graphitization and defects present good ORR activity and durability in both alkaline and acidic conditions.
Small machines are highly promising for future medicine and new materials. Recent advances in functional nanomaterials have driven the development of synthetic inorganic micromachines that are ...capable of efficient propulsion and complex operation. Miniaturization and large‐scale manufacturing of these tiny machines with true nanometer dimension are crucial for compatibility with subcellular components and molecular machines in operation. Here, block copolymer lithography is combined with atomic layer deposition for wafer‐scale fabrication of ultrasmall coaxial TiO2/Pt nanotubes as catalytic rocket engines with length below 150 nm and a tubular reactor size of only 20 nm, leading to the smallest man‐made rocket engine reported to date. The movement of the nanorockets is examined using dark‐field microscopy particle tracking and dynamic light scattering. The high catalytic activity of the Pt inner layer and the reaction confined within the extremely small nanoreactor enable highly efficient propulsion, achieving speeds over 35 µm s−1 at a low Reynolds number of <10−5. The collective movements of these nanorockets are able to efficiently power the directional transport of significantly larger passive cargo.
Atomic layer deposition is combined with block copolymer lithography for wafer‐scale fabrication of ultrasmall coaxial TiO2/Pt nanotubes as catalytic nanorockets, leading to the smallest man‐made rocket engines reported to date. The high catalytic activity of the Pt inner layer and the reaction confined within the 20 nm nanoreactor enable an efficient propulsion at a low Reynolds number of <10−5.
The performance of proton exchange membrane fuel cells (PEMFCs) depends on the controlled size, dispersion and density of Pt nanoparticles (NPs) on carbon supports, which are strongly affected by the ...carbon characteristics and fabrication methods. Here, we demonstrated a high-performance Pt/carbon catalyst for PEMFCs using fluidized bed reactor atomic layer deposition (FBR-ALD) that was realized by an effective matching of the carbon supports for the FBR-ALD process and an optimization of the ionomer content during the preparation of the membrane electrode assembly (MEA). For this, the synthesis of Pt NPs was conducted on two porous supports (Vulcan XC-72R and functionalized carbon) by FBR-ALD. The functionalized carbon possessed a higher surface area with a large pore volume, abundant defects in a disordered structure and a large number of oxygen functional groups compared to those of the well-known Vulcan carbon. The favorable surface characteristics of the functionalized carbon for nucleation produced Pt particles with an increased uniformity and density and a narrow size range, which led to a higher electrochemical surface area (ECSA) than that of Pt/Vulcan carbon and commercial Pt/carbon. The PEMFC test of the respective Pt/carbon samples was investigated, and highly dense and uniform Pt/functionalized-carbon showed the highest performance through optimization of the higher ionomer content compared to that for the ALD Pt growth on Vulcan carbon and commercial Pt/carbon. In addition, the Pt catalyst using ALD demonstrated a significant long-term stability for the PEMFC. This finding demonstrates the remarkable advantages of FBR-ALD for the fabrication of Pt/carbon and the ability of functionalized carbon supports to achieve a high PEMFC efficiency and an enhanced durability.Fuel cells: giving nanocatalysts some much-needed supportSmall tweaks to techniques used to manufacture platinum catalysts can have a big impact on the long-term stability of fuel cells. Platinum nanoparticle catalysts help fuel cells turn hydrogen and oxygen into water and electricity, but their small size makes them tricky to manipulate. Se-Hun Kwon from Pusan National University in Busan, South Korea, and colleagues have now optimized a high-tech procedure for attaching these tiny nanocatalysts to large, porous materials known as carbon supports. Their process coats various supports with platinum nanoparticles, less than one monolayer at a time, until the desired thicknesses are reached. Various factors including the physical textures of the supports and leftover chemical impurities were shown to significantly affect coating uniformity. Adjusting these factors enabled the team to generate supports with greater durability than commercial platinum–carbon composites.
We report the successful synthesis of surface defective small size (SS) SnO₂ nanoparticles (NPs) by adopting a low temperature surfactant free solution method. The structural properties of the NPs ...were analyzed using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM). The presence of surface defects, especially oxygen vacancies, in the sample were characterized using micro-Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and photoluminescence emission. The Brunauer⁻Emmet⁻Teller (BET) nitrogen adsorption⁻desorption isotherms demonstrated the superior textural properties (high surface area and uniform pore size) of SS SnO₂ compared to large size (LS) SnO₂. A comparable study was drawn between SS SnO₂ and LS SnO₂ NPs and a significant decrease in the concentration of surface defects was observed for the LS sample. The results showed that surface defects significantly depend upon the size of the NPs. The surface defects formed within the band gap energy level of SnO₂ significantly participated in the recombination process of photogenerated charge carriers, improving photochemical properties. Moreover, the SS SnO₂ showed superior photoelectrochemical (PEC) and photocatalytic activities compared to the LS SnO₂. The presence of a comparatively large number of surface defects due to its high surface area may enhance the photochemical activity by reducing the recombination rate of the photogenerated charges.
Green hydrogen fuel generation via the photoelectrochemical (PEC) approach has attracted considerable attention recently for its sustainability and eco‐friendliness. Photoelectrocatalysts are the key ...component of the PEC process. To produce green hydrogen by this approach at a reasonable rate from water splitting and waste valorization, proper design and electronic structure modulation of the photoelectrocatalysts are of utmost importance. Therefore, in this review, we discuss the materials selection, design, and engineering of photoanode materials to efficiently harvest and convert solar energy into green hydrogen fuel and value‐added chemicals. In this regard, we introduce the fundamentals and the mechanistic insights of the PEC solar energy conversion and storage technologies, which would provide knowledge to novices to gain insight into this field while designing a new photoanode. Moreover, we mention the importance of various semiconducting materials and their surface/interface engineering aspects to improve the PEC properties for selective water oxidation to value‐added chemicals and waste valorization coupled with green hydrogen generation. Finally, we discuss the conclusions and prospects of this technology by highlighting the major challenges and its potential for commercialization.
This review summarizes the rational design and recent progress of photoanode materials for solar fuel production via the photoelectrochemical (PEC) approach. A comprehensive survey has been performed on selective water oxidation to value‐added chemicals production utilizing solar energy. In addition, this review demonstrates current challenges and future prospects of PEC solar fuel/chemical production.
The dielectric properties of the Si-doped Zr1-xHfxO2 thin films were investigated over a broad compositional range with the goal of improving their properties for use as DRAM capacitor materials. The ...Si-doped Zr1-xHfxO2 thin films were deposited on TiN bottom electrodes by atomic layer deposition using a TEMA-Zr/TEMA-Hf mixture precursor for deposition of Zr1-xHfxO2 film and Tris-EMASiH as a Si precursor. The Si stabilizer increased the tetragonality and the dielectric constant; however, at high fractions of Si, the crystal structure degraded to amorphous and the dielectric constant decreased. Doping with Si exhibited a larger influence on the dielectric constant at higher Hf content. A Si-doped Hf-rich Zr1-xHfxO2 thin film, with tetragonal structure, exhibited a dielectric constant of about 50. This is the highest value among all reported results for Zr and Hf oxide systems, and equivalent oxide thickness (EOT) value of under 0.5 nm could be obtained with a leakage current of under 10(-7) A·cm(-2), which is the lowest EOT value ever reported for a DRAM storage capacitor system without using a noble-metal-based electrode.
Ultrathin films or particles of atomic layer deposition (ALD) on high surface can improve the activity and durability of catalyst fields, so depending on the surface state, the ALD growth mechanism ...on porous materials should be systematically investigated and optimized to improve their characteristics of catalysts. Herein, a Pt catalyst used in polymer electrode membrane fuel cell (PEMFC) applications is synthesized through fluidized‐bed‐reactor ALD on carbon black whose surface is modified through treatment with citric acid. The functional groups, analyzed through X‐ray photoelectron spectroscopy (XPS), are found to be maximized after 60 min of acid treatment with stirring. Compared with bare carbon (untreated), the acid‐treated carbon presents rich oxidized functional groups and abundant defects but lower surface areas and pore volumes. After ALD Pt deposition, highly dense, uniform, and well‐dispersed Pt nanoparticles (NPs) are observed on the carbon black subjected to acid treatment, because of the favorable surface modifications for ALD growth resulting from the acid treatment. The ALD‐Pt NPs on the acid‐treated carbon exhibit larger electrochemical active surface areas, improved oxygen reduction reactions, and PEMFC performances, when compared with that of NPs on bare carbon with similar Pt weight loading.
Pt nanoparticles (NPs) on carbon black with/without the citric acid treatment are synthesized by fluidized‐bed‐reactor atomic layer deposition (FBR‐ALD). The growth characteristics, electrochemical properties, and proton‐exchange membrane fuel cell (PEMFC) performance of Pt catalyst are investigated depending on the carbon with/without acid treatment. The uniform and dense ALD‐Pt NPs on acid‐treated carbon provided improved electrochemical properties and PEMFC performance.
Hybrid tandem solar cells comprising an inorganic bottom cell and an organic top cell have been designed and fabricated. The interlayer combination and thickness matching were optimized in order to ...increase the overall photovoltaic conversion efficiency. A maximum power conversion efficiency of 5.72% was achieved along with a Voc of 1.42 V, reaching as high as 92% of the sum of the subcell Voc values.
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