Chiral Effect on the Electrochemistry of Magnetic Ferrite Colloidal Nanocrystal Assembly Modified by Amino Acids.

Chirality on the molecular or nanometer scale is particularly significant in chemistry, materials science, and biomedicine. Chiral electrochemical reactions on solid surfaces are currently a hot research topic. Herein, a chiral solid surface is constructed in aqueous solutions by mixing chiral molecules, d- and l-glutamic, with γ-Fe2O3 and Fe3O4 nanoparticles (NPs) and MnFe2O4 colloidal nanocrystal assembly (CNA). Cyclic voltammetry and differential pulse voltammetry measurements are conducted in a phosphate buffer solution (PBS) containing ascorbic acid (AA) or isoascorbic acid (IAA), and a chiral effect appears on the electroreduction of ferric ions of amino acid-modified magnetic samples. A negative or positive potential shift is observed, respectively, for magnetic structures modified by l- and d-glutamic acid in aqueous AA electrolyte, while the opposite is observed for these samples in IAA electrolyte. The reduction peak current increases by 0.8-1.2 times for the electrodes modified with l- and d-glutamate molecules, improving the electron transport efficiency. The chiral effect is absent when the electrolytes contain achiral uric acid or dopamine, or even chiral l-/d-/ld-tartaric acid. The chiral recognition between d-/l-glutamic acid and AA/IAA at the electrochemical interface is suggested to be related to their spinal configurations. These observations will be helpful for the rational design of inorganic functional chiral micro/nanostructures.

A highly stretchable smart dressing for wound infection monitoring and treatment.

Smart dressings integrated with bioelectronics have attracted considerable attention and become promising solutions for skin wound management. However, due to the mechanical distinction between human body and the interface of electronics, previous smart dressings often suffered obvious degradation in electrical performance when attached to the soft and curvilinear wound sites. Here, we report a stretchable dressing integrated with temperature and pH sensor for wound status monitoring, as well as an electrically controlled drug delivery system for infection treatment. The wound dressing was featured with the deployment of liquid metal for seamless connection between rigid electrical components and gold particle-based electrodes, achieving a stretchable soft-hard interface. Stretching tests showed that both the sensing system and drug delivery system exhibited good stretchability and long-term stable conductivity with the resistance change rate less than 6 % under 50 % strain. Animal experiments demonstrated that the smart dressing was capable of detecting bacterial infection via the biomarkers of temperature and pH value and the infection factors of wound were significantly improved with therapy through electrically controlled antibiotics releasing. This proof-of-concept prototype has potential to significantly improve management of the wound, especially those with dynamic strain.

Synthesis of Monodispersed Pd Nanoparticles and Ultrathin Twisty Pd Nanowire Networks for Electrooxidation of Ethanol.

In recent years, preparing precious metal catalysts with a controllable morphology has become a hot research topic for researchers. In this study, monodispersed palladium (Pd) nanoparticles (NP) and ultrathin Pd twisty nanowire networks (TNN) were synthesized in a solvothermal system using N,N-dimethylformamide (DMF) and oleylamine (OAm) as solvents, Transmission electron microscopy (TEM) images reveal the successful synthesis of nanoparticles and ultrathin TNN microstructures. Electrochemical data show that the current densities of Pd-NP and Pd-TNN for the ethanol oxidation reaction (EOR) reach 1878 mA mg-1 and 1765 mA mg-1, respectively. Compared to commercial Pd/C, Pd-TNN and Pd-NP exhibit better catalytic stability, lower electron transfer barriers, and more resistance to catalyst poisoning. Temperature, pH value, and ethanol concentration are all favorable for the EOR. According to the experimental data, the mechanism of enhanced electrocatalytic activity of Pd-NP and Pd-TNN catalysts for ethanol oxidation is discussed. This paper presents a method for preparing catalysts with stabilized structures to develop Pd-based catalysts for electrocatalytic oxidation reactions.

Assembly of Alloyed PdM (Ag, Cu, and Sn) Nanosheets and Their Electrocatalytic Oxidation of Ethanol and Methanol.

Direct alcohol fuel cells are popular due to their high energy density, abundant sources, and ease of transportation and storage. Palladium-based nanosheet self-assembled materials have emerged as an effective catalyst for alcohol oxidation reactions. In this work, nanosheets were synthesized with the same feeding ratio assembly of alloyed PdM (M = Ag, Cu, and Sn). The introduction of the second element was able to enhance the catalytic response of the catalysts to alcohol electrooxidation. Among them, the PdCu alloy exhibited the best performance in terms of catalytic activity, toxicity resistance, and stability to ethanol oxidation reaction (EOR) and methanol oxidation reaction (MOR). The catalytic current densities for EOR can reach 2226, 2518, and 1598 mA mg-1 for PdAg, PdCu, and PdSn nanosheet assemblies, respectively. These are mainly attributed to better electronic effects, altered atomic distances within the cell for the d-band centers of Pd, and a larger electrochemical active surface area (ECSA). The optimized d-band center is beneficial to promote the catalytic performance of EOR and MOR. Experimental data also demonstrated that higher electrocatalytic temperature, higher pH, and higher alcohol concentration can accelerate the rate of alcohol electrooxidation. These results have the potential to be extended to Pd-M (M = other metals) nanosheets and help for a wider range of catalytic applications.

Pd-Enriched-Core/Pt-Enriched-Shell High-Entropy Alloy with Face-Centred Cubic Structure for C1 and C2 Alcohol Oxidation.

High-entropy alloy nanoparticles (HEA NPs) have aroused great interest globally with their unique electrochemical, catalytic, and mechanical properties, as well as diverse activity and multielement tunability for multi-step reactions. Herein, a facile low-temperature synthesis method at atmospheric pressure is employed to synthesize Pd-enriched-HEA-core and Pt-enriched-HEA-shell NPs with a single phase of face-centred cubic structure. Interestingly, the lattice of both Pd-enriched-HEA-core and Pt-enriched-HEA-shell enlarge during the formation process of HEA, with tensile strains included in the core and shell of HEA. The as-obtained PdAgSn/PtBi HEA NPs show excellent electrocatalytic activity and durability for methanol oxidation reaction (MOR) and ethanol oxidation reaction (EOR). The specific (mass) activity of PdAgSn/PtBi HEA NPs for MOR is 4.7 mA cm-2 (2874 mA mg(Pd+Pt) -1 ), about 1.7 (5.9) and 1.5 (4.8) times higher than that of commercial Pd/C and Pt/C catalysts, respectively. Additional to high-entropy effect, Pt sites and Pd sites on the interface of the HEA act synergistically to facilitate the multi-step process towards EOR. This study offers a promising way to find a feasible route for scalable HEA manufacturing with promising applications.

Self-Assembled Nanocomposites and Nanostructures for Environmental and Energic Applications.

With the rapid development of nanotechnology, nanocomposites and nanostructures have attracted significant attention due to their unique physical and chemical properties and variable functionalities [...].

Unveiling the Synergistic Effects of Monodisperse Sea Urchin-like PdPb Alloy Nanodendrites as Stable Electrocatalysts for Ethylene Glycol and Glycerol Oxidation Reactions.

In recent times, the fabrication of noble metal-based catalysts with controllable morphologies has become a research hotspot. Electrocatalytic devices with excellent catalytic performance and enhanced durability for the ethylene glycol oxidation reaction (EGOR) and the glycerol oxidation reaction (GOR) are significant for commercial direct fuel cells. Herein, a series of PdPb sea urchin-like nanodendrite (ND) structures with controllable molar ratios were synthesized as EGOR and GOR electrocatalysts of high efficiency. The optimized structurally regular Pd3Pb NDs exhibit the best electrocatalytic activity and outstanding stability compared to other samples and commercial Pt/C. In addition, the integrated Pb on Pd3Pb NDs can mitigate the bond energy the intermediates generate and further boost the electrooxidation of the intermediates by supplying enough active sites without considering its intrinsic structure, which is beneficial to the enhanced EGOR and GOR activity and stability. With the assistance of electrochemical measurement, the mechanism of the enhanced alloy was further investigated. This paper presents a promising strategy to fabricate catalysts with stable structures, which will elucidate a very promising approach for developing Pd-based catalysts for further applications in fuel cells.

Assembly of Alloyed PdCu Nanosheets and Their Electrocatalytic Oxidation of Ethanol.

Two-dimensional (2D) nanostructured catalysts have attracted great attention in many important fields, including energy applications and chemical industry. In this study, PdCu nanosheet assemblies (NSAs) have been synthesized and investigated as electrocatalysts for direct ethanol fuel cells in an alkaline medium. A great number of active sites on the nanosheets of PdCu NSAs for ethanol electro-oxidation are exposed, where the electron structures are optimized combined with the second element copper. Electrochemical measurements show that PdCu NSA1 exhibits excellent catalytic activity (2536 mA mg-1) and cyclic stability compared to PdCu NSA2 (1700 mA mg-1) and PdCu NSA3 (1436 mA mg-1), much higher than commercial Pd/C. Kinetics studies on the electrolysis of ethanol suggest that PdCu NSAs should be more favorable at higher catalytic temperatures, higher concentrations of ethanol, and low pH value environments. The unique composition and structures PdCu NSA1 would result in the lowest energy barrier in the rate-controlling step of the ethanol oxidation reaction (EOR), confirmed by density functional theory (DFT). The formation mechanism of PdCu NSAs and their excellent electrocatalytic activity toward EOR have been discussed and analyzed.

A soft intelligent dressing with pH and temperature sensors for early detection of wound infection.

Wound infection is a common clinical problem. Traditional detection methods can not provide infection early warning information in time. With the development of flexible electronics, flexible wearable devices have been widely used in the field of intelligent monitoring. Here, we describe the development of a soft wound infection monitoring system with pH sensors and temperature sensors. The measurement range of pH was 4-10, the fitting accuracy was 99.8%, and the response time was less than 6 s. The temperature sensor array showed good accuracy and short response times in the range of 30 °C to 40 °C. A series of in vitro tests and the use of a rat model of Staphylococcus aureus infection confirmed that this flexible detection system can monitor the pH and temperature changes occurring in the early stage of infection, which provides an effective reference for clinical application.

Alloyed Palladium-Lead Nanosheet Assemblies for Electrocatalytic Ethanol Oxidation.

Synthesizing alloyed bimetallic electrocatalysts with a three-dimensional (3D) structure assembly have arouse great interests in electrocatalysis. We synthesized a class of alloyed Pd3Pb/Pd nanosheet assemblies (NSAs) composed of a two-dimensional (2D) sheet structure with adjustable compositions via an oil bath approach at a low temperature. Both the scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images reveal the successful formation of the nanosheet structure, where the morphology of Pd3Pb/Pd NSAs can be regulated by adjusting the atomic mole ratio of Pb and Pb metal precursors. The power X-ray diffraction (XRD) pattern shows that Pd3Pb/Pd NSA catalysts are homogeneously alloyed. Electrochemical analysis and the density functional theory (DFT) method demonstrate that the electrocatalytic activity of the alloyed Pd3Pb/Pd NSAs can be improved by the doping of the Pb element. As a result of the addition of element Pb and change of the electron structure, the electrocatalytic activity toward ethanol oxidation of alloyed Pd3Pb/Pd-15 NSA can reach up to 2886 mA mg-1, which is approximately 2.8 times that of the pure Pd NSA counterpart (1020 mA mg-1). The Pd3Pb/Pd NSAs are favorable in a high catalytic temperature, high KOH concentration, and high ethanol concentration.

Enhanced Electrocatalytic Activity of Alloyed Palladium-Lead Nanoparticles toward Electrooxidation of Ethanol.

Although many researchers have made great efforts to pursue promising high-efficiency electrocatalysts, a formidable challenge remains for designing excellent palladium-based electrocatalysts for commercializing direct liquid fuel cells. This study reports the synthesis of bimetallic PdPb nanoparticles (NPs) via a mixed solution containing cetyl trimethyl ammonium bromide as the capping agent. Alloyed PdPb NPs are formed, where the size of the NPs increases as Pb atoms are introduced gradually. However, Pd3Pb NPs are obtained with the same molar ratio of Pd and Pb in the raw systems. Among all of the as-made NPs, Pd9Pb1 NPs exhibit superior catalytic activity (2620 mA mg-1) toward ethanol electrooxidation, 4.3 times higher than commercial Pd/C catalysts (613 mA mg-1). The overall rate of the EOR for PdPb NPs is determined, demonstrating that the electrocatalytic activity of the PdPb NPs increases at high catalytic temperatures, in high pH environments, and/or at high ethanol concentrations.

Surfactant-Assisted Synthesis of Palladium Nanosheets and Nanochains for the Electrooxidation of Ethanol.

The synthesis of metal nanometer electrocatalysts with a two-dimensional (2D) structure or rich active sites has become a research hotspot in electrocatalysis. In this work, surfactant hexadecyltrimethylammonium bromide (CTAB) was used to assist the synthesis and assembly of Pd ultrathin nanosheet with the help of Mo(CO)6 in the start system. Pd nanochain composed of nanoparticles is obtained under the same condition, replacing CTAB with carrageenan only. Electrochemical measurements showed that the catalytic peak current density for the electrooxidation of ethanol can reach 2145 mA mg-1 for the Pd nanosheet assembly (NSA) and 1696 mA mg-1 for Pd nanochains. Pd nanosheet assembly also has a lower electron-transfer barrier, better catalytic stability, and antipoisoning performance than that of Pd nanochains. The mechanism of Pd nanosheets and nanochains catalysts the enhanced electrocatalytic activity toward ethanol oxidation has been discussed based on the experimental data.

Assembly of Bimetallic PdAg Nanosheets and Their Enhanced Electrocatalytic Activity toward Ethanol Oxidation.

The direct ethanol fuel cells in an alkaline medium have a broad vision of applications because of their large energy density, reasonable power density, and environmentally friendly features. Herein, we present a facile one-step method to synthesize PdAg nanosheet assemblies (NSAs) in a mixed solution of N,N-dimethylformamide and water with the addition of molybdenum hexacarbonyl and cetyltrimethylammonium bromide. Pure Pd NSA shows an irregular shape while PdAg NSAs gradually undergo a process from solid assembly to a hollow structure with the Pd/Ag molar ratio changing from 3:1 to 2:1 to 1:1. The formation of alloy nanosheets in the assemblies combined with the introduction of Ag in the Pd catalyst enhances the catalytic activity toward ethanol electrooxidation from 1524 mA mg-1 of pure Pd NSA to 1866 mA mg-1 of PdAg NSA with a Pd/Ag molar ratio of 2:1. On the basis of the experimental data, compared with pure Pd structures, both the nature of a thin nanosheet of PdAg NSAs and the structural changes in the alloy assemblies play key roles in determining the electrocatalytic activity of these Pd-based catalysts.

Bimetallic PdCu Nanoparticles for Electrocatalysis: Multiphase or Homogeneous Alloy?

Crystal phase structure of bimetallic alloy is an important factor determining the electrocatalytic activity toward oxidation of energy molecules. In this paper, PdCu bimetallic NPs with similar element composition and different crystal phase structural features have been synthesized hydrothermally by adjusting the content of ethylenediaminetetraacetic acid disodium salt (EDTA-2Na). Multiphase PdCu NPs composed of pure Pd and alloy phase are obtained with a low concentration (even as low as zero) of EDTA-2Na in synthetic systems while homogeneous PdCu alloy NPs are formed in the presence of EDTA-2Na with a high concentration. The catalytic activity of ethanol electrooxidation is increased from 3.1 mA·cm-2 of pure Pd NPs, to 3.6 mA·cm-2 of multiphase PdCu NPs, and to 5.0 mA·cm-2 of homogeneous PdCu alloy NPs (about 2360 mA mgPd-1). The surface composition and structural stability of homogeneous PdCu NPs were much less damaged during electrochemical measurements. Based on the experimental data, the formation mechanism of multiphase and homogeneous PdCu NPs and their structure-property relationship have been discussed.

Assembly of large-area reduced graphene oxide films for the construction of Z-scheme over single-crystal porous Bi5O7I nanosheets.

In this work, we have firstly achieved the construction of bismuth oxyiodide (Bi5O7I)/reduced graphene oxide (rGO)/ZnO Z-scheme photoelectrochemical (PEC) system without backward reactions through loading large-area ZnO quantum dots (QDs)/rGO films on Bi5O7I nanosheets. Single-crystal porous Bi5O7I nanosheets with numerous oxygen vacancies (OVs) were firstly fabricated through the calcination of BiOI in reductive glycols. The single-crystal facilitates charge transport, nanoporous structure promotes light absorption and OVs improves charge separation efficiency. As a result, single-crystal porous Bi5O7I nanosheets with OVs exhibited higher PEC performance than other morphologies reported before. Moreover, The PEC activity of Bi5O7I can be further enhanced through loading large-area ZnO QDs/rGO films to construct a pure Z-scheme charge transfer system, which not only achieves efficient separation of electron-hole pairs but also retains its excellent redox ability. To the best of our knowledge, the photocurrent density of Bi5O7I/rGO/ZnO heterostructures is the highest among Bi5O7I-based samples. For comparison, an opposite Z-scheme model has also been built up by replacing Bi5O7I with WO3, in which the photocurrent density decreased conversely. Therefore, it can be known that a pure Z-scheme system without backward reactions can be successfully prepared through loading ZnO QDs/rGO films on photoelectrodes.

Highly Conductive Graphene Paper with Vertically Aligned Reduced Graphene Oxide Sheets Fabricated by Improved Electrospray Deposition Technique.

Because of its notable electrical and mechanical properties, the highly conductive graphene paper has great potential applications in future flexible electronics. In this study, we report a simple and effective method to prepare vertically aligned graphene oxide papers from graphene oxide suspensions by an improved electrospray deposition technique with a moving stage, which is controlled by computer. Then, the flexible reduced graphene oxide papers are successfully synthesized after reduction by using hydroiodic acid. The obtained reduced graphene oxide paper has an electrical conductivity as high as 6180 S/m, which is more than one and a half times of the reduced graphene oxide paper film, which was fabricated by using the electrospray deposition technique without the moving stage. The experimental results approved for the first time that the degree of alignment of reduced graphene oxide sheets can affect the conductivity of the reduced graphene oxide papers. Further electrochemical measurements for a symmetrical supercapacitor device based on the prepared reduced graphene oxide paper indicate that it has great capacitive performance and electrochemical stability. It exhibited relatively high specific capacitance (174 F·g-1) at a current density of 1 A·g-1 in 6 M KOH aqueous solution, and its capacitance can retain approximately 86% after 1000 cycles. In addition, patterned freestanding reduced graphene oxide papers, which have potential applications in many fields such as stretchable electronics and wearable devices, also can be fabricated by using this method.

Insights into the Role of Poly(vinylpyrrolidone) in the Synthesis of Palladium Nanoparticles and Their Electrocatalytic Properties.

Four types of palladium (Pd) nanoparticles were prepared from the systems containing PdCl2 or Na2PdCl4 with or without the assistance of poly(vinylpyrrolidone) (PVP). Two types of Pd nanoparticles obtained in the absence of PVP were obviously larger than those synthesized with the assistance of PVP. The former large Pd particles showed typical features in cyclic voltammetry in H2SO4 solution, whereas two types of small Pd nanoparticles did not. However, small nanoparticles treated first in an electrochemical way in 0.5 M KOH solution displayed the adsorption and desorption peaks similar to those of typical Pd-modified electrodes in H2SO4 solution. Large Pd nanoparticles from the PdCl2 synthesis system showed a catalytic specific current of 629 mA/mg in the electrocatalysis of ethanol, whereas large particles from the Na2PdCl4 system showed a current of 262 mA/mg. The maximum catalytic currents of small Pd nanoparticles without surface cleaning treatment were 1382 and 1019 mA/mg for samples from the Na2PdCl4 and PdCl2 systems, respectively, higher than those being treated in KOH solution first, and the electrocatalytic stability of the two untreated samples was better. However, small nanoparticles after the electrochemical treatment can reach the maximum catalytic current faster. The synthesis and structure-property relation of four types of Pd nanoparticles have been discussed and analyzed on the basis of systematically experimental data.

In situ fabrication of nanoporous BiVO4/Bi2S3 nanosheets for enhanced photoelectrochemical water splitting.

Nanoporous BiVO4/Bi2S3 nanosheets have been firstly fabricated through a two-step annealing followed by hydrothermal method using BiOI two-dimensional nanosheets as precursors, which could greatly improve the photoelectrochemical performances of BiVO4 due to the enhanced charge separation efficiency and the enlarged absorption range. The optimal content of Bi2S3 in the BiVO4/Bi2S3 nanocomposites has been explored by tuning the reaction time. In addition, it is found that loading co-catalysts FeOOH could further optimize the hole transfer pathway and thus enhance the photoelectrochemical water splitting ability.

One-Pot Decoration of Graphene with SnO2 Nanocrystals by an Elevated Hydrothermal Process and Their Application as Anode Materials for Lithium Ion Batteries.

Tin dioxide (SnO2), with a high theoretical storage capacity of 782 mAhg-1, is a potential alternative anode for rechargeable lithium ion batteries (LIBs). However, its low electronic conductivity and poor stability during cycling (due to a change in volume) hinder its practical applications for energy storage. Composite materials of SnO2-nanocrystal-decorated graphene, which show excellent electrochemical characteristics, were prepared using a one-pot elevated hydrothermal method at 250 °C without subsequent carbonization treatment. The effects of graphene, solvent composition, and temperature on the morphology, structure, and electrochemical properties of the SnO2/graphene composites were investigated using XRD, SEM, TEM, and N2 adsorption-desorption techniques. The as-prepared SnO2/graphene composites deliver a high initial discharge capacity of 1734.1 mAh g-1 at 200 mA g-1 and exhibit a high reversible capacity of 814.7 mAh g-1 even after 70 cycles at a current density of 200 mA g-1. The composites also exhibit a high rate capability of 596 mAh g-1 at 2000 mAg-1, indicating a long cycle life and promising capability when used as anode materials for lithium ion batteries and suggesting that SnO2/graphene composites have wide application prospects in LIBs.

Carbon Wrapped Ni3S2 Nanocrystals Anchored on Graphene Sheets as Anode Materials for Lithium-Ion Battery and the Study on Their Capacity Evolution.

Ni3S2 nanocrystals wrapped by thin carbon layer and anchored on the sheets of reduced graphene oxide (Ni3S2@C/RGO) have been synthesized by a spray-coagulation assisted hydrothermal method and combined with a calcination process. Cellulose, dissolved in Thiourea/NaOH aqueous solution is chosen as carbon sources and mixed with graphene oxide via a spray-coagulation method using graphene suspension as coagulation bath. The resulted cellulose/graphene suspension is utilized as solvent for dissolving of Ni(NO3)2 and then used as raw materials for hydrothermal preparation of the Ni3S2@C/RGO composites. The structure of the composites has been investigated and their electrochemical properties are evaluated as anode material for lithium-ion batteries. The Ni3S2@C/RGO sample exhibits increasing reversible capacities upon cycles and shows a superior rate performance as well. Such kinds of promising performance have been ascribed to the wrapping effect of carbon layer which confines the dislocation of the polycrystals formed upon cycles and the enhanced conductivity as the integration of RGO conductive substrate. Discharge capacities up to 850 and 630 mAh·g-1 at current densities of 200 and 5000 mA·g-1, respectively, are obtained. The evolution of electrochemical performance of the composites with structure variation of the encapsulated Ni3S2 nanocrystals has been revealed by ex-situ TEM and XRD measurements.