Showing papers by "Shuit-Tong Lee published in 2019"

Single atom tungsten doped ultrathin α-Ni(OH)2 for enhanced electrocatalytic water oxidation

Abstract: Electrocatalytic water oxidation is a rate-determining step in the water splitting reaction. Here, we report one single atom W6+ doped Ni(OH)2 nanosheet sample (w-Ni(OH)2) with an outstanding oxygen evolution reaction (OER) performance that is, in a 1 M KOH medium, an overpotential of 237 mV is obtained reaching a current density of 10 mA/cm2. Moreover, at high current density of 80 mA/cm2, the overpotential value is 267 mV. The corresponding Tafel slope is measured to be 33 mV/dec. The d0 W6+ atom with a low spin-state has more outermost vacant orbitals, resulting in more water and OH− groups being adsorbed on the exposed W sites of the Ni(OH)2 nanosheet. Density functional theory (DFT) calculations confirm that the O radical and O-O coupling are both generated at the same site of W6+. This work demonstrates that W6+ doping can promote the electrocatalytic water oxidation activity of Ni(OH)2 with the highest performance. Electrocatalytic water splitting for hydrogen and oxygen generation provides an attractive path to obtain clean energy, but the half reaction of oxygen evolution remains the bottleneck for the progress. Here, the authors show single atom tungsten doped ultrathin α-Ni(OH)2 exhibits enhanced performance in electrocatalytic water oxidation.

Carbon dots: advances in nanocarbon applications

Abstract: Carbon dots (C-Dots), defined by characteristic sizes of <10 nm, have become a rising star in carbon nanomaterials. C-Dots possess many unique physiochemical and photochemical properties which make them a promising platform for imaging, environmental, catalytic, biological and energy-related applications. To date, C-Dots have been investigated extensively, and their related applications have developed rapidly. However, quantitative understanding of the physiochemical properties of C-Dots still remains a difficult challenge because of their complex structures. Here, we will highlight the recent progress in the practical applications of C-Dots, with particular attention to the research in light-emitting devices, bioimaging and biodetection, catalysis, functional materials, and agriculture.

High-Efficiency Perovskite Light-Emitting Diodes with Synergetic Outcoupling Enhancement.

Abstract: Perovskite light-emitting diodes (PeLEDs) show great application potential in high-quality flat-panel displays and solid-state lighting due to their steadily improved efficiency, tunable colors, narrow emission peak, and easy solution-processing capability. However, because of high optical confinement and nonradiative charge recombination during electron-photon conversion, the highest reported efficiency of PeLEDs remains far behind that of their conventional counterparts, such as inorganic LEDs, organic LEDs, and quantum-dot LEDs. Here a facile route is demonstrated by adopting bioinspired moth-eye nanostructures at the front electrode/perovskite interface to enhance the outcoupling efficiency of waveguided light in PeLEDs. As a result, the maximum external quantum efficiency and current efficiency of the modified cesium lead bromide (CsPbBr3 ) green-emitting PeLEDs are improved to 20.3% and 61.9 cd A-1 , while retaining spectral and angular independence. Further reducing light loss in the substrate mode using a half-ball lens, efficiencies of 28.2% and 88.7 cd A-1 are achieved, which represent the highest values reported to date for PeLEDs. These results represent a substantial step toward achieving practical applications of PeLEDs.

Approaching the Volcano Top: Iridium/Silicon Nanocomposites as Efficient Electrocatalysts for the Hydrogen Evolution Reaction.

Abstract: Electrolysis of water to generate hydrogen is an important issue for the industrial production of green and sustainable energy. The best electrocatalyst currently available for the hydrogen evolution reaction (HER) is platinum. We herein show that iridium can be manipulated to achieve a record high HER activity surpassing platinum in every aspect: a lower overpotential at any given current density, a higher current density, and mass activity for all bias potentials applied and a catalyst cost reduction of 50% for the same hydrogen generation rate. The superior HER activity was achieved by a binary Ir/Si nanowire catalyst design in which (as density functional theory calculations show) two distinct strategies act in synergy: (i) decreasing the size of the iridium nanoparticles to ∼2.2 nm and (ii) dividing the H2-generation process to three steps occurring on two different catalysts: H adsorption on iridium, H diffusion to silicon, and H2 desorption from silicon.

Enhanced RuBisCO activity and promoted dicotyledons growth with degradable carbon dots

Abstract: The ∼ 5 nm degradable carbon dots (CDs) were synthesized directly from carbon rod by a one-step electrochemical method at room temperature. The as-prepared CDs can effectively enhance the ribulose bisphosphate carboxylase oxygenase (RuBisCO) activity, and then promote the dicotyledons growth (soybean, tomato, eggplant and so on) and finally increase their yields. Here, we used Arabidopsis thaliana and Trifolium repens L. as model plants to systematically study the beneficial effects of CDs on plant growth. These include: (i) accelerating seed germination; (ii) enlarging root elongation; (iii) increasing metal ions absorption and delivery; (iv) improving enzymes activity; (v) enhancing the carbohydrate content; (vi) degradation into plant hormone analogues and CO2; and finally (vii) enhancing the grain production by about 20%.

Dual-Band, High-Performance Phototransistors from Hybrid Perovskite and Organic Crystal Array for Secure Communication Applications

Abstract: High-performance phototransistors made from organic semiconductor single crystals (OSSCs) have attracted much attention due to the high responsivity and solution-processing capability of OSSCs. However, OSSC-based phototransistors capable of dual-band spectral response remain a difficult challenge to achieve because organic semiconductors usually possess only narrow single-band absorption. Here, we report the fabrication of high-performance, dual-band phototransistors from a hybrid structure of a 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) single-crystal array coated with CH3NH3PbI3 nanoparticles (NPs) synthesized by a simple, one-step solution method. In contrast to C8-BTBT and CH3NH3PbI3 NPs with respective absorption in the ultraviolet (UV) and visible (vis) region, their hybrid structure shows broad absorption covering the entire UV–vis range. The hybrid-based phototransistors exhibit an ultrahigh responsivity of >1.72 × 104 A/W in the 252–780 nm region, which represents the best perfo...

Memory phototransistors based on exponential-association photoelectric conversion law.

Abstract: Ultraweak light detectors have wide-ranging important applications such as astronomical observation, remote sensing, laser ranging, and night vision. Current commercial ultraweak light detectors are commonly based on a photomultiplier tube or an avalanche photodiode, and they are incompatible with microelectronic devices for digital imaging applications, because of their high operating voltage and bulky size. Herein, we develop a memory phototransistor for ultraweak light detection, by exploiting the charge-storage accumulative effect in CdS nanoribbon. The memory phototransistors break the power law of traditional photodetectors and follow a time-dependent exponential-association photoelectric conversion law. Significantly, the memory phototransistors exhibit ultrahigh responsivity of 3.8 × 109 A W−1 and detectivity of 7.7 × 1022 Jones. As a result, the memory phototransistors are able to detect ultraweak light of 6 nW cm−2 with an extremely high sensitivity of 4 × 107. The proposed memory phototransistors offer a design concept for ultraweak light sensing devices. CdS nanostructures can enable memory based photodetection by charge-storage accumulative effect. Here, the authors report CdS nanoribbons-based memory phototransistors with high responsivity of 3.8 × 109 A/W and detectivity of 7.7 × 1022 Jones that can detect weak light of 6 nW/cm2.

Synergistic Cu@CoOx core-cage structure on carbon layers as highly active and durable electrocatalysts for methanol oxidation

Abstract: Active and inexpensive electrocatalysts for methanol oxidation reaction (MOR) are highly required for the practical application of direct methanol fuel cells (DMFCs). However, efficient MOR is limited by using the expensive and rare noble metal-based catalysts. Here we report a Cu@CoOx core-cage nanostructure on carbon layers (CLs) for superior electrocatalysis of MOR in the alkaline media, which shows an excellent specific activity of 150.41 mA cm−2 and a high mass activity of 467.94 mA mg-1 at the potential of 0.8 V vs. SCE (1.85 V vs. RHE) in 1 M KOH + 1 M CH3OH. It represents the highest MOR activity ever reported for noble metal-free catalysts. Synchrotron radiation based in-situ X-ray absorption spectroscopy reveals that the outside CoOx cage can form a high Co4+ state to easily oxidize methanol, while the adsorption experiments indicate that Cu can act as the methanol adsorption center. The capture-catalysis process on the core-cage structure thus leads to the excellent MOR activity. The CLs can also anchor the Cu@CoOx particles and accelerate the charge transport to enhance the performance. The Cu@CoOx-CLs catalyst is economical, abundant, highly active and stable, which has the potential to act as a good alternate material for noble metal-based catalysts in DMFCs.

Nano as a Rosetta Stone: The Global Roles and Opportunities for Nanoscience and Nanotechnology.

Abstract: Opportunities for Nanoscience and Nanotechnology As we have for the last six years, nano center directors and leaders in nanoscience and nanotechnology from around the world met in Beijing, the day before ChinaNano. We shared our experiences on how our fields are perceived by our colleagues, institutions, countries, the public, and each other. We discussed our goals and strategieswhere we are headed and how we interact with others in and beyond our fields. Here, we report some of the highest level issues that we face around the world. We also highlight some of the interesting areas now being explored at nano centers. An overarching comment, and the title feature here “Nano as a Rosetta Stone”, is that nanoscience and nanotechnology connect fields together. As nanotechnology has grown as a field, we have taught each other approaches and languages, taken on each other’s problems, and have developed new capabilities, tools, and methods to explore existing and newly uncovered opportunities. Nanoscientists were key to developing the BRAIN Initiative in the U.S., its partner efforts in other countries, and the microbiome initiatives around the world. Among the many new efforts being explored in nano centers are the nanoscale and larger contributions to the origins of life, developing world research and applications in and for nano, how nanotechnology can contribute to the UN Sustainable Development goals, and more. We often return to the idea that the nanoscale is the scale of function in biology. The consequences are that the tools and materials that we develop can give us new insights into the biological world. It also means that the interactions between nanomaterials and biological systems can be strong, with important consequences in both medicine and environmental health and safety. One point that came up repeatedly was that, given the unlimited variety of nanomaterials that are accessible, it should be possible to defeat the threat of drug resistance by coming up with materials to which pathogens and diseases have not previously been exposed. Nanomedicine continues to grow as a research field, but moving to the clinic requires significant efforts to pass through regulatory approval. Taking this important step into account early in the design of nanomedicines can significantly improve the likelihood of real impact in medicine. In the areas of nanomaterials and devices, exciting new and hybrid materials with newly discovered and extraordinary properties open a world of possibilities. How new devices will be constructed and integrated into or even displace existing technologies all remain open questions. Again, we will draw on our expertise in and connection to many fields to address these issues. In some cases, the production of nanomaterials has already been scaled up and will rival that of conventional materials. For example, carbon nanotubes, which were relatively recently considered exotic materials, are now produced at the scale of hundreds of tons per year and widely used in Li-ion batteries.