Regulating the Coordination Geometry and Oxidation State of Single-Atom Fe Sites for Enhanced Oxygen Reduction Electrocatalysis.

FeNC catalysts demonstrate remarkable activity and stability for the oxygen reduction reaction (ORR) in polymer electrolyte membrane fuel cells and Zn-air batteries (ZABs). The local coordination of Fe single atoms in FeNC catalysts strongly impacts ORR activity. Herein, FeNC catalysts containing Fe single atoms sites with FeN3 , FeN4 , and FeN5 coordinations are synthesized by carbonization of Fe-rich polypyrrole precursors. The FeN5 sites possess a higher Fe oxidation state (+2.62) than the FeN3 (+2.23) and FeN4 (+2.47) sites, and higher ORR activity. Density functional theory calculations verify that the FeN5 coordination optimizes the adsorption and desorption of ORR intermediates, dramatically lowering the energy barrier for OH- desorption in the rate-limiting ORR step. A primary ZAB constructed using the FeNC catalyst with FeN5 sites demonstrates state-of-the-art performance (an open circuit potential of 1.629 V, power density of 159 mW cm-2 ). Results confirm an intimate structure-activity relationship between Fe coordination, Fe oxidation state, and ORR activity in FeNC catalysts.

Non-Coplanar Diphenyl Fluorene and Weakly Polarized Cyclohexyl Can Effectively Improve the Solubility and Reduce the Dielectric Constant of Poly (Aryl Ether Ketone) Resin.

With the rapid development of high-frequency communication and large-scale integrated circuits, insulating dielectric materials require a low dielectric constant and dielectric loss. Poly (aryl ether ketone) resins (PAEK) have garnered considerable attention as an intriguing class of engineering thermoplastics possessing excellent chemical and thermal properties. However, the high permittivity of PAEK becomes an obstacle to its application in the field of high-frequency communication and large-scale integrated circuits. Therefore, reducing the dielectric constant and dielectric loss of PAEK while maintaining its excellent performance is critical to expanding the PAEK applications mentioned above. This study synthesized a series of poly (aryl ether ketone) resins that are low dielectric, highly thermally resistant, and soluble, containing cyclohexyl and diphenyl fluorene. The effects of cyclohexyl contents on the properties of a PAEK resin were studied systematically. The results showed that weakly-polarized cyclohexyl could reduce the molecular polarization of PAEK, resulting in low permittivity and high transmittance. The permittivity of PAEK is 2.95-3.26@10GHz, and the transmittance is 65-85%. In addition, the resin has excellent solubility and can be dissolved in NMP, DMF, DMAc, and other solvents at room temperature. Furthermore, cyclohexyl provided PAEK with excellent thermal properties, including a glass transition temperature of 239-245 °C and a 5% thermogravimetric temperature, under a nitrogen atmosphere of 469-534 °C. This makes it a promising candidate for use in high-frequency communications and large-scale integrated circuits.

Modulating the Coordination of Single Co Atoms to Trigger the Catalytic Oxidation of Formaldehyde at Room Temperature.

Designing efficient and stable non-precious metal catalysts remains a significant challenge for formaldehyde (HCHO) oxidation, which is an expected way to replace the employment of noble-metal catalysts. Herein, a series of atomically dispersed Co catalysts are optimized by evaporating nitrogen atoms and exploring their HCHO oxidation catalytic performance. The results show that the prepared temperature can effectively control the coordination regulation of the Co atomic site, which in turn affects the catalytic oxidation activity. Our best catalyst, the Co-N/C prepared at 1000 °C, exhibits superior activity with 92.8% of conversion at room temperature at a gas hourly space velocity (GHSV) of 72,000 mL·g-1·h-1. Extensive characterizations combined with theoretical calculations reveal that the high catalytic activity is attributed to the low-coordinated center, which can be tailored by pyrolysis temperature. This work provides an innovative strategy for catalyst design in the catalytic oxidation reaction.

Carbon Nanotubes Grown on the Carbon Fibers to Enhance the Photothermal Conversion toward Solar-Driven Applications.

Photothermal conversion is a directly, sustainable, and green path to use solar energy and the one of the most important keys is the photothermal conversion material. How to obtain the durable and effective material for photothermal conversion with low cost and facile preparation is still a great challenge. In this work, the carbon nanotubes (CNTs) are grown on the carbon fibers (CFs) via the catalysis of trapped Fe and Co. The absorption of the as-prepared CFs/CNTs illustrate the enhancement from the visible light to the near-infrared light range. The photothermal conversion characterization shows the grown CNTs promoting the higher surface temperature and the highest temperature reaches to about 325 °C under 10 sun irradiations. The water evaporation on the CFs/CNTs is measured 1.40 ± 0.03 kg·cm-2·h-1 under 1 sun irradiation and the water evaporation rate is also found depending on the irradiation density. The photothermal conversion applications and the water evaporation under natural irradiation also reveal the suitable candidate of the CFs/CNTs for photothermal conversion application. This work provides a facile path to obtain effective carbon-based materials for photothermal application.

A polyaniline-modified electrode surface for boosting the electrocatalysis towards the hydrogen evolution reaction and ethanol oxidation reaction.

Here, polyaniline (PANI) is reported loaded on carbon paper to modify the carbon paper-PANI-Pt electrode surface, tailoring the electrocatalytic capability towards the hydrogen evolution reaction and ethanol oxidation reaction. The reasons for the enhancement by the PANI layer are attributed to the hydrophilic electrode surface, uniform dispersion of Pt, and large electrochemical active surface.

Positively charged collective oscillations induce efficient Aß1-42 fibril degradation in the presence of novel Au@Cu2-xS core/shell nanorods.

We synthesized Au@Cu2-xS core/shell nanorods (NRs) that have synergistic surface plasmon resonance (SPR) effects using a new cation exchange process in ethylene glycol (EG) phase. The dual effect - NIR photothermal and surface positive charge plasmon - of Au@Cu2-xS NRs, promote the capability to degrade Aß1-42 fibrils into amorphous protein.

Boosting OER performance of IrO2 in acid via urchin-like hierarchical-structure design.

Urchin-like hierarchical IrO2 nanostructures, which are obtained by a surfactant-free, wet-chemical approach, show boosted OER performance in acid with an overpotential of 260 mV @10 mA cm-2geo under optimal pocessing conditions. The overpotential @10 mA cm-2geo can be kept below 285 mV for over 30 hours.

Heat-Resistant and High-Performance Solid-State Supercapacitors Based on Poly(para-phenylene terephthalamide) Fibers via Polymer-Assisted Metal Deposition.

Heat-resistant supercapacitors with excellent mechanical strength are highly required for flexible and wearable electronics in our daily life. Here, high-performance and heat-resistant solid-state supercapacitors based on poly(para-phenylene terephthalamide) fibers/Ag/poly(3,4-ethylenedioxythiophene)/polystyrene sulfonate (PEDOT:PSS)&carbon nanotubes (PPTA/Ag/PCNTs) have been fabricated for the first time. Due to the toughness of the PPTA fibers and the excellent electroconductivity of the composite fiber, the PPTA/Ag/PCNTs-based supercapacitor exhibits good electrochemical performance together with brilliant mechanical strength and bending durability. Moreover, the heat resistance of tough PPTA/Ag/PCNTs fiber and ionic liquid gel electrolyte endow the supercapacitor with stability at temperatures as high as 80 °C and the capacitance can return to more than 80% after the heat treatment. The power density or energy density of the supercapacitor assembled on PPTA/Ag/PCNTs fiber electrodes is higher than that of any other polymer fiber-related supercapacitor. This work adds to the study of high-performance supercapacitors based on polymer fibers and provides the possibility to apply PPTA fiber for energy storage devices with flexibility and heat resistance.

Controlled Synthesis of Co@N-Doped Carbon by Pyrolysis of ZIF with 2-Aminobenzimidazole Ligand for Enhancing Oxygen Reduction Reaction and the Application in Zn-Air Battery.

The Co/N-doped carbon material, as an important electrocatalytic material, has been attracted intense interest in ORR and Zn-air battery. Here, we report an efficient Co@N-doped carbon catalyst (Co@N-C-1) obtained by pyrolysis of ZIF precursor with 2-aminobenzimidazole. The introduction of 2-aminobenzimidazole results in the formation of hierarchical meso/microporous structure of the as-prepared Co@N-C-1, effectively avoiding the aggregation of Co nanoparticles during pyrolysis and the higher N content, which contributes to enhance the ORR electrocatalytic activities. The obtained Co@N-C-1 exhibits remarkable ORR performance with a half-wave potential of 0.938 V vs RHE in alkaline media. As the air catalyst of zinc-air batteries, Co@N-C-1 displays 1.439 V of open-circuit voltage and 1413.3 Wh·kg-1 of energy density.

Preparation, Stabilization and Carbonization of a Novel Polyacrylonitrile-Based Carbon Fiber Precursor.

The quality of polyacrylonitrile (PAN) precursor has a great influence on the properties of the resultant carbon fibers. In this paper, a novel comonomer containing the sulfonic group, 2-acrtlamido-2-methylpropane acid (AMPS), was introduced to prepare P(AN-co-AMPS) copolymers using itaconic acid (IA) as the control. The nanofibers of PAN, P(AN-co-IA), and P(AN-co-AMPS) were prepared using the electrospinning method. The effect of AMPS comonomer on the carbon nanofibers was studied using scanning electron microscopy (SEM), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA) and Raman spectrum. The structural evolutions of PAN-based nanofibers were quantitatively tracked by FTIR and XRD during the thermal oxidative stabilization (TOS) process. The results suggested that P(AN-co-AMPS) nanofibers had the lower heat release rate (ΔH/ΔT = 26.9 J g-1 °C-1), the less activation energy of cyclization (Ea1 = 26.6 kcal/mol and Ea2 = 27.5 kcal/mol), and the higher extent of stabilization (Es and SI) during TOS process, which demonstrated that the AMPS comonomer improved the efficiency of the TOS process. The P(AN-co-AMPS) nanofibers had the better thermal stable structures. Moreover, the carbon nanofibers derived from P(AN-co-AMPS) precursor nanofibers had the better graphite-like structures (XG = 46.889). Therefore, the AMPS is a promising candidate comonomer to produce high performance carbon fibers.

In-Situ Growth of Au on KTaO3 Sub-Micron Cubes via Wet Chemical Approach for Enhanced Photodegradation of p-Nitrophenol.

KTaO3/Au hetero-nanostructures were synthesized by in-situ reduction of HAuCl4 on the surface of hydrothermally-grown KTaO3 sub-micron cubes. The concentration of Au source was found to be a critical factor in controlling the hetero-nucleation of Au nanoparticles on the surface of KTaO3 sub-micron cubes. Loading of Au particles on KTaO3 nanocrystals enriched KTaO3 additional UV-vis absorption in the visible light region. Both KTaO3 and KTaO3/Au nanocrystals were shown to be active in the photo-degradation of p-nitrophenol, while the loading of Au on KTaO3 clearly improved the photo-degradation efficiency of p-nitrophenol compared to that on bare KTaO3 nanocrystals, probably due to the improved light absorption and charge separation.

High Pressure Induced in Situ Solid-State Phase Transformation of Nonepitaxial Grown Metal@Semiconductor Nanocrystals.

Considering the large lattice mismatch induced interface strain between nonepitaxial grown monocrystalline semiconductor shell and metal core, we studied the solid-state phase transformation of such nonepitaxial grown Au@CdS core/shell NCs under high pressure in this paper. Consistent with HRTEM characterizations, the high resolution Raman spectra and synchrotron angle-dispersive X-ray diffraction (ADXRD) spectra evolution were utilized to investigate the hydrostatic pressure (0-24 GPa) induced gradual phase transformation. Due to the strong lattice interactions between Au core and CdS shell, the different behavior and improved stability under high pressure appeared compared to single quantum dots (QDs).

From Indium-Doped Ag2 S to AgInS2 Nanocrystals: Low-Temperature In Situ Conversion of Colloidal Ag2 S Nanoparticles and Their NIR Fluorescence.

Focusing on ternary I-III-VI2 colloidal nanocrystals (NCs) synthesized with precise control of the composition (from doping to ternary composition) and NIR fluorescence performance, monodisperse binary In3+ -doped Ag2 S NCs and ternary AgInS2 NCs have been achieved successfully by facile low-temperature in situ conversion of colloidal Ag2 S nanoparticles. In3+ ions were inserted into the crystal lattice of Ag2 S NCs at a relatively low temperature as dopant and ternary AgInS2 NCs were obtained at a higher temperature following a phase transition. These doped Ag2 S and AgInS2 NCs based on different indium precursor concentrations were explored with respect to the position and intensity of the near-infrared photoluminescent emission at different doping levels and crystal phase evolution.

Colloid-Interface-Assisted Laser Irradiation of Nanocrystals Superlattices to be Scalable Plasmonic Superstructures with Novel Activities.

High-efficient charge and energy transfer between nanocrystals (NCs) in a bottom-up assembly are hard to achieve, resulting in an obstacle in application. Instead of the ligands exchange strategies, the advantage of a continuous laser is taken with optimal wavelength and power to irradiate the film-scale NCs superlattices at solid-liquid interfaces. Owing to the Au-based NCs' surface plasmon resonance (SPR) effect, the gentle laser irradiation leads the Au NCs or Au@CdS core/shell NCs to attach each other with controlled pattern at the interfaces between solid NCs phase and liquid ethanol/ethylene glycol. A continuous wave 532 nm laser (6.68-13.37 W cm-2 ), to control Au-based superlattices, is used to form the monolayer with uniformly reduced interparticle distance followed by welded superstructures. Considering the size effect to Au NCs' melting, when decreasing the Au NCs size to ≈5 nm, stronger welding nanostructures are obtained with diverse unprecedented shapes which cannot be achieved by normal colloidal synthesis. With the help of facile scale-up and formation at solid-liquid interfaces, and a good connection of crystalline between NCs, the obtained plasmonic superstructured films that could be facilely transferred onto different substrates exhibit broad SPR absorption in the visible and near-infrared regime, enhanced electric conductivities, and wide applications as surface enhanced Raman scattering (SERS)-active substrates.

A Flower-Shaped Thermal Energy Harvester Made by Metamaterials.

Harvesting thermal energy from arbitrary directions has become an exciting theoretical possibility. However, an exact 3D thermal energy harvester is still challenging to achieve for the stringent requirement of highly anisotropic and symmetrical structures with homogenous materials, as well as absence of effective characterization. In this Communication, a flower-shaped thermal harvesting metamaterial is originally promoted. Numerical simulations imply that heat flux can be concentrated into the target core and a temperature gradient turns out to be more than two times larger than the applied one without obvious distortion or perturbation to the temperature profile outside the concentrator. Temperature transitions of the actual device are experimentally measured to validate the novel structure with consistency of the simulated results with original methods. With ultraefficiency independent of geometrical size, the flower-shaped thermal harvester facilitates multiple scale energy harvesting with splendid efficient and might help to improve thermoelectric devices efficiency in a totally new perspective.

Hierarchical Self-Assembly of Cu7Te5 Nanorods into Superstructures with Enhanced SERS Performance.

This paper reports a strategy to get self-assembly of Cu7Te5 nanorods into hierarchical superstructures: the side-by-side self-assembly of nanorods into microscale one-dimensional (1D) nanowires (primary structure), the side-by-side alignments of the 1D nanowires into two-dimensional (2D) nanowire bundles (secondary structure), and the further rolling up of the 2D bundles into three-dimensional (3D) microtubes (tertiary structure). It was found that the oleylamine (OLA)/n-dodecanethiol (DDT) mixture as a binary capping agent was key to produce Cu7Te5 nanorods in the quantum size regime with high monodispersity, and this was a prerequisite for their hierarchical self-assembly based on elaborate control of the solvent evaporation process. The obtained Cu7Te5 microtube superstructures were used as SERS substrate and showed much stronger SERS enhancement than the as-prepared Cu7Te5 nanorods before assembly. This was probably ascribed to the remarkably enhanced local electromagnetic field arising from the plasmon coupling of Cu7Te5 nanorods in the well-assembled superstructures.

Structurally Well-Defined Au@Cu2- x S Core-Shell Nanocrystals for Improved Cancer Treatment Based on Enhanced Photothermal Efficiency.

Au@Cu2- x S core-shell nanocrystals (NCs) have been synthesized under large lattice mismatch with high crystallinity, controllable shape, and nonstoichiometric composition. Both experimental observations and simulations are used to verify the flexible dual-mode plasmon coupling. The enhanced photothermal effect is harnessed for diverse HeLa cancer cell ablation applications in the NIR-I window (750-900 nm) and the NIR-II window (1000-1400 nm).

Aqueous oxidation reaction enabled layer-by-layer corrosion of semiconductor nanoplates into single-crystalline 2D nanocrystals with single layer accuracy and ionic surface capping.

A controllable aqueous oxidation reaction enabled layer-by-layer corrosion has been proposed to prepare high-quality two-dimensional (2D) semiconductor nanocrystals with single layer accuracy and well-retained hexagonal shapes. The appropriate oxidizing agent, such as H2O2, Fe(NO3)3, and HNO3, could not only corrode the layered-crystalline-structured Bi2Te3 nanoplates layer-by-layer to be a single quintuple layer, but also replace the organic barriers to be ionic ligands on the surface synergistically. AFM analysis was used to confirm the layer-by-layer exfoliation from the side to the center. Together with precise XRD, LRTEM and HRTEM characterizations, the controllable oxidation reaction enabled aqueous layer-by-layer corrosion mechanism has been studied.

Plasmon enhanced photoelectrochemical sensing of mercury (II) ions in human serum based on Au@Ag nanorods modified TiO2 nanosheets film.

Taking advantages of the monodisperse TiO2 nanosheets (NSs) with high active crystal face exposure and the tunable localized surface plasmon resonance (LSPR) properties of Au@Ag nanorods (NRs), this study demonstrated that TiO2 NSs film with trace amount of Au@Ag NRs modification possess a strong enhancement of photocurrent response, which was remarkably inhibited with the addition of mercury (II) ions (Hg(2+)). Based on the selective decrease of photocurrent with the addition of Hg(2+), a simple photoelectrochemical (PEC) sensor has been assembled. The PEC sensor exhibits wide linear range (0.01-10nM), low detection limit (2.5 pM), satisfying selectivity, reproducibility and acceptable stability for Hg(2+) detection. The feasibility of this method for practical application in human serum has been evaluated and the result was satisfactory. This PEC sensing method would provide a potential application for Hg(2+) detection in clinical diagnosis.