Search

Molybdenum disulfide (MoS 2 ) has attracted considerable attentions in the application of catalysis. However, the chemically inert property of the basal plane in MoS 2 retards the catalytic efficiency. Highly exposing active edge sites and optimizing the electronic structure are the two effective ways to improve MoS 2 electrocatalytic activity. Here, we report the synthesis of one dimensional (1D) single-crystal MoS 2(1−x) Se 2x nanobelts with controllable Se and S content, formed by the vertically aligned basal planes perpendicular to the substrate. The top and bottom surfaces of this 1D structure are fully covered by the active edge sites. The single crystalline nanobelt was characterized by high resolution transmission electron microscopy, atomic force microscopy, Raman, photoluminescence and X-ray photoemission spectroscopy. The introduction of Se into MoS 2 optimizes the electronic structures of MoS 2(1−x) Se 2x nanobelts by tuning the oxidation state of Mo. As a result, the enhanced catalytic activity for hydrogen generation was obtained in the 1D MoS 2(1−x) Se 2x nanobelts (a low onset overpotential of 139 mV at an electrocatalytic current density of 20 mA/cm 2 and a Tafel slope of 65 mV/decade). [ABSTRACT FROM AUTHOR]

Abstract: Amorphous, anodically grown tantalum pentoxide serves as a dielectric layer in capacitors using anodes constructed from tantalum. These capacitors are extensively used in demanding high-reliability applications such as military, aerospace and medical systems. One of the degradation mechanisms in this oxide layer is crystallization induced by applied electric fields. Previous studies have described many attributes of this process. However, the role of stress and strain in the crystallization process has not been explicitly studied to date. The purpose of the present study is to directly monitor the stress evolution and understand its role in the field-induced crystallization of anodic tantalum oxide (ATO). To this end, tantalum was deposited onto quartz substrates by electron beam evaporation and subsequently anodized in acidic electrolytes. A multi-beam optical technique was then used for the in situ measurement of stress evolution in the anodic thin films during the application of electric fields whose strengths are on the order of 5.5×106 V/cm. The salient features of field-driven crystallization in acidic electrolytes were additionally tracked using microscopy. The results indicate that field-induced crystallization of ATO is associated with compressive stresses. The methods used in the present study offer a promising new approach for a detailed mechanistic understanding of the stresses associated with the field crystallization process in ATO. [Copyright &y& Elsevier]

Abstract: In this paper, carbon nanotubes (CNTs) were modified by ethylene diamine (ED) and then used as the support of the Pt–Ru catalyst. The cyclic voltammetry (CV) and Fourier transform infrared spectroscopy were employed to study the interaction between ED and CNTs. The morphology and elemental composition of the as-prepared Pt–Ru/ED/CNT electrode were characterized by scanning electron microscopy and energy dispersive X-ray spectroscopy. The electrocatalytic properties of the Pt–Ru/ED/CNT electrode for methanol electro-oxidation were investigated by CV, polarization method and electrochemical impedance spectroscopy. The long-term stability of the Pt–Ru/ED/CNT electrode was also evaluated. Compared with the Pt–Ru/CNT electrode, the Pt–Ru/ED/CNT electrode exhibits excellent electrocatalytic properties and long-term stability. These results show that the ED-grafted CNTs are the promising catalyst support for methanol electro-oxidation. [Copyright &y& Elsevier]

The effect of the reduction half reaction of Cu(II) complexes on passivation and gold dissolution in the copper-ammonia-thiosulfate system were studied using electrochemistry and density functional theory (DFT). The results show that the cathodic process accounts for the surface passivation, aside from contributions made by thiosulfate decomposition during the anodic process. Copper sulfide and polysulfide are formed in the passivation layer during the reduction half reaction of Cu(II) complexes. The addition of common additives, such as ethylenediamine (EN) and ethylenediamine tetraacetic acid (EDTA), are able to not only remove the passive layer but also change the Cu(II) reduction half reaction. Tafel curves show that the gold leaching current in the EDTA-supplemented solution is higher than that in the EN-supplemented solution. Linear sweep voltammetry demonstrated that the reduction half reaction of Cu(II) complexes is controlled by the diffusion process, and the diffusion coefficient of the Cu(II) complex in the EN-supplemented solution and EDTA-supplemented solution is 0.64 × 10−6 cm2/s and 1.44 × 10−6 cm2/s, respectively. Density functional theory (DFT) studies showed that the lowest unoccupied molecular orbital (LUMO) of the mixed Cu(II)-ammonia-EDTA complex has lower energy than that of the mixed Cu(II)-ammonia-EN complex. Additionally, gold atoms on the surface that adsorbed the Cu(II)-ammonia-EDTA complex have higher relaxation degrees than those in the Cu(II)-ammonia-EN complex system. This explains why the gold concentration in the EDTA-supplemented solution is higher than that in the EN- supplemented solution. This study provides insight into the differences in gold dissolution during the cathodic process. [ABSTRACT FROM AUTHOR]

• Strong complexing agents decrease the discharge potential of Mg anode. • Weak Mg2+ complexing agents improve the utilization efficiency and specific capacity. • The utilization efficiency reaches 72.3% after addition of 0.1 M sodium salicylate. • Discharge performance depends on the weight loss caused by self-corrosion and chunk effect. Deposition of discharge products on the surface of magnesium (Mg) anode and high self-corrosion rate are the main obstacles that limit the application of Mg-air batteries. Tailoring electrolyte additives in Mg-air batteries has been proved to be an efficient way to improve the discharge performance of Mg-air batteries. In this work, the influence of several complexing agents on the discharge potential and utilization efficiency of Mg anode is studied by means of half-cell discharge test. The results show that strong Mg2+ complexing agents can significantly lower the discharge potential of Mg anode. Mg2+complexing agents with low stability constant can improve the utilization efficiency and specific capacity of the anode compared to complexing agents with strong complexation ability. The utilization efficiency of anode reaches 72.3% at 10 mA cm−2 after addition of 0.1 mol/L sodium salicylate. Moreover, salicylate deposits on the anode surface after discharge, which has a negative influence on the discharge potential of Mg anode. [ABSTRACT FROM AUTHOR]

In this paper, the single-doped (Ni-WO 3 and Ti-WO 3) and binary-doped (Ni-Ag-WO 3 and Ti-Ag-WO 3) amorphous WO 3 thin films were respectively prepared on indium-doped tin oxide conductive glass substrates by radio-frequency magnetron sputtering. Among the single-doped WO 3 thin films, the electrochromic (EC) properties of films can be enhanced by the presence of Ni or Ti. However, the low conductivity of WO 3 limits its application in EC devices. A novel approach was proposed to ameliorate this disadvantage which has not been explored, that is, the highly conductive Ag was introduced into WO 3 films with Ni or Ti. The experimental results show that the addition of Ag reduces the charge transfer resistance and shortens the ion diffusion path length, thereby improving the EC response time (Ni-Ag-WO 3 : t b =1.16 s; Ti-Ag-WO 3 : t c =4.14 s), electrochemical active area, and ion diffusion coefficients (Ni-Ag-WO 3 : D a =3.032 × 10−9 cm2/s; Ti-Ag-WO 3 : D c =7.737 × 10−9 cm2/s). Based on these work, the feasibility of Ni-Ag and Ti-Ag binary-doped WO 3 films was confirmed. These discoveries contribute to the exploration of preparing high-performance WO 3 EC films for the practical applications of EC devices such as in automatic anti-glare rearview mirrors. [ABSTRACT FROM AUTHOR]

Abstract In this paper, aqueous solution of reduced graphene oxide has been prepared assisted by the graphene quantum dot, which is then mixed with aqueous polyaniline solution to form water-borne reduced graphene oxide/polyaniline composite powder. The resultant graphene quantum dot-reduced graphene oxide/polyaniline shows a specific morphology of nanosized polyaniline firmly attached on reduced graphene oxide layer, due to the good dispersion of reduced graphene oxide and polyaniline in water. The monodispersion leads to the close contact between reduced graphene oxide sheets and polyaniline particles, significantly depressing the accumulation. It leads to the enhanced conductivity, supercapacitance and cycling stability for graphene quantum dot-reduced graphene oxide/polyaniline, with capacitance as high as 648 F g−1. After 5000 charge-discharge cycles, the capacitance of as-prepared reduced graphene oxide/polyaniline composite shows just 3.7% decay while it reaches 68% for polyaniline. Furthermore, driven by the strong electrostatic forces between the electropositive polyaniline and the electronegative graphene quantum dot-reduced graphene oxide as well as the π−π interactions, the obtained nanosized graphene quantum dot-reduced graphene oxide/polyaniline films from the controllable layer-by-layer method show the morphology of interconnected-layer networks and exhibit good electrochemical activity on H 2 O 2 in the range of 5.0 × 10−7–3.5 × 10−5 M. The detection limit is as low as 1.1 μM. Graphical abstract Image 1 Highlights • Water-borne rGO/polyaniline composite from powder to layer-by-layer film derived from aqueous rGO and polyaniline solution. • The aqueous rGO solution is prepared assisted by graphene quantum dot. • The enhanced synergistic electrochemical property benefit from the strong p-p and electrostatic interactions. • The approach evidences high cycling stability and electrochemical catalysis for the rGO/polyaniline composites. [ABSTRACT FROM AUTHOR]

In this study, low temperature strategy for the synthesis of Ta 3 N 5 and electrochemical deposition of Ag 3 PO 4 to modify TiO 2 nanorods were proposed to construct a heterogeneous structural system with enhanced interfacial charge transfer. Introduction of n-type Ta 3 N 5 suitable for the reduction reaction and p-type Ag 3 PO 4 suitable for the oxidation reaction pose effect on photoelectrochemical (PEC) performance of Ag 3 PO 4 /Ta 3 N 5 -TiO 2. This provides important insights into PEC performance by testing the optical absorption, carrier concentration, band gap, photocurrent density and stability of Ag 3 PO 4 /Ta 3 N 5 -TiO 2. Compared with the bare TiO 2 , Ag 3 PO 4 /Ta 3 N 5 -TiO 2 with a bandgap of 1.89 eV enhances absorption on the red side of the visible light spectrum. The optimised Ag 3 PO 4 /Ta 3 N 5 -TiO 2 photoelectrode with the uniform morphology exhibits an enhanced photocurrent density of 15.08 mA cm−2 at 1.88 V vs. reversible hydrogen electrode (RHE), with 8.7 times enhancement compared with bare TiO 2 (1.55 mA cm−2). Both the PEC performance and stability of the Ag 3 PO 4 /Ta 3 N 5 -TiO 2 photoanode could be enhanced by the decoration of Ag 3 PO 4 nanoparticles and Ta 3 N 5. In addition, the synthesis of Ta 3 N 5 materials by hydrothermal methods under low temperature strategies can be used as a reference to guide the preparation of more efficient photoelectrodes. [ABSTRACT FROM AUTHOR]

• Both metallic Ag and Ag oxide exist in the coating. • A nano-sized Ag-rich layer exists at the substrate/coating interface. • PEO affects corrosion morphology and susceptibility of Mg-Ag alloy. • A sustained Ag+ release is achieved after PEO of Mg-Ag alloy. The application of biodegradable Mg alloys as implanted devices has been hindered by their low corrosion resistance and potential risk associated with microbial infection. In the present work, a rolled Mg-Ag alloy was studied, which was subjected to plasma electrolytic oxidation (PEO) to achieve a favoured balance between corrosion resistance and antimicrobial capability. The Ag distribution, corrosion resistance and Ag ionic release behaviour have been examined in details. It is revealed that PEO process leads to both incorporated Ag+ and Ag-rich nanoparticles in forms of metallic Ag and Ag oxide across the coating. In addition, a nano-sized Ag-enriched layer also exists at the substrate/coating interface. The microstructural modification associated with PEO process results in an increased corrosion resistance and a sustained Ag ionic release, indicating that it is a promising surface modification technique for antibacterial Mg-Ag alloy. [Display omitted] [ABSTRACT FROM AUTHOR]

• The structure and properties of SCBC were studied as cathodes for IT-SOFCs. • The introduction of Ca significantly improved the TEC and conductivity. • The SCBC exhibited good chemical compatibility and electrochemical properties. • The SCBC exhibited good anti-carbon dioxide poisoning capability. Here, Sm 1– x Ca x BaCo 2 O 5+ δ (x = 0–0.4; SCBC) oxygen-deficient perovskites were synthesized by a sol–gel method and studied as potential novel cathodes for intermediate-temperature solid oxide fuel cells (IT-SOFCs). As an effective doping strategy, partial substitution of Ca for Sm in SmBaCo 2 O 5+ δ could reduce the thermal expansion coefficient (TEC) and improve the conductivity and catalytic activity of the oxygen reduction reaction (ORR). The x = 0–0.2 samples obtained after sintering at 1100 °C crystallized in an orthorhombic structure with the space group Pmmm and had good chemical compatibility with CeO 2 -based electrolytes at 1000 °C for 10 h. The TECs of the SCBC samples decreased from 20.2 × 10−6 K−1 (x = 0) to 17.7 × 10−6 K−1 (x = 0.2). The area-specific resistances (ASRs) of the x = 0–0.4 cathodes were 0.163, 0.114, 0.075, and 0.090 Ω cm2 at 700°C. Additionally, the x = 0.2 cathode showed good electrochemical stability in a CO 2 -containing atmosphere. All results clearly indicated that double perovskite SCBC (x = 0–0.3) are promising cathode materials for IT-SOFCs. [Display omitted] [ABSTRACT FROM AUTHOR]