Biomass wood-derived efficient Fe–N–C catalysts for oxygen reduction reaction

Journal of Materials Science - Efficient and low-cost electrocatalysts for oxygen reduction reaction (ORR) were the key for scalable application of metal–air batteries and fuel cells. Herein,...     

Transition metal–nitrogen–carbon nanostructured catalysts for the oxygen reduction reaction: From mechanistic insights to structural optimization

Accelerating the rate-limiting oxygen reduction reaction (ORR) at the cathode remains the foremost issue for the commercialization of fuel cells.Transition metal-nitrogen-carbon (M-N/C,M =Fe,Co,etc.) nanostructures are the most promising class of non-precious metal catalysts (NPMCs) with satisfactory activities and stabilities in practical fuel cell applications.However,the long-debated nature of the active sites and the elusive structure-performance correlation impede further developments of M-N/C materials.In this review,we present recent endeavors to elucidate the actual structures of active sites by adopting a variety of physicochemical techniques that may provide a profound mechanistic understanding of M-N/C catalysts.Then,we focus on the spectacular progress in structural optimization strategies for M-N/C materials with tailored precursor architectures and modified synthetic routes for controlling the structural uniformity and maximizing the number of active sites in catalytic materials.The recognition of the right active centers and site-specific engineering of the nanostructures provides future directions for designing advantageous M-N/C catalysts.     

WS2@Co9S8@N/C core–shell as multifunctional electrocatalysts for dye-sensitized solar cell,oxygen reduction reaction and oxygen evolution reaction

Journal of Materials Science - It is promising strategy in recent years to design and prepare metal/carbon-based functional materials with different structures using metal–organic framework...     

Core–shell nanostructure supported Pt catalyst with improved electrocatalytic stability in oxygen reduction reaction

Core–shell nanostructure electrode (TiO₂@C) for oxygen reduction reaction is prepared with TiO₂ nanoparticles at 900 °C in a methane atmosphere. The TiO₂@C supported Pt catalyst (Pt/TiO₂@C) contains Pt nanoparticles on TiO₂@C nanostructure electrodes consisting of TiO₂ as a core and carbon as a shell. In the accelerated stability test, the Pt/TiO₂@C exhibits a superior ORR stability to conventional carbon supported Pt catalyst. It is likely that the enhanced catalytic properties of the nanostructure supported Pt catalyst may be due to graphite-like carbon and an improved electronic conductivity of the core–shell nanostructure.     

Fe/Co/C–N nanocatalysts for oxygen reduction reaction synthesized by directly pyrolyzing Fe/Co-doped polyaniline

Development of precious metal-free catalysts for oxygen reduction reaction (ORR) is of great significance for the practical application of fuel cells. In this article, we report the finding that the C–N composites containing Fe and/or Co (C–PANI, Fe/C–PANI, Co/C–PANI, and FeCo/C–PANI), produced by directly pyrolyzing the Fe- and/or Co-doped polyaniline (PANI) precursors, show efficient electroactivity for ORR both in acidic and in alkaline media. Among the prepared catalysts, Fe/C–PANI and Co/C–PANI present the most positive ORR onset potential that is 0.61 V (vs. SCE) in 0.5 mol L^?1 H₂SO₄ solution or ?0.1 V (vs. SCE) in 1 mol L^?1 NaOH solution. In addition, the Fe/C–PANI catalyst shows the largest limiting-diffusion current density for ORR both in acidic and in alkaline media. A four-electron reaction of ORR on the Fe/C–PANI and Co/C–PANI catalysts is more dominant than a two-electron reaction. Fe/C–PANI catalyst also presents good electrocatalytic activity stability for ORR both in acidic and in alkaline media.     

Facet-controlled Pt–Ir nanocrystals with substantially enhanced activity and durability towards oxygen reduction

Nanocrystals made of Pt–Ir alloys are fascinating catalysts towards the oxygen reduction reaction (ORR), but the lack of control over their surface atomic structures hinders further optimization of their catalytic performance. Here we report, for the first time, a class of highly active and durable ORR catalysts based on Pd@Pt–Ir nanocrystals with well-controlled facets. With an average of 1.6 atomic layers of a Pt₄Ir alloy on the surface, the nanocrystals can be made in cubic, octahedral, and icosahedral shapes to present Pt–Ir {1 0 0}, {1 1 1}, and {1 1 1} plus twin boundaries, respectively. The Pd@Pt–Ir nanocrystals exhibit not only facet-dependent catalytic properties but also substantially enhanced ORR activity and durability relative to a commercial Pt/C and their Pd@Pt counterparts. Among them, the Pd@Pt–Ir icosahedra deliver the best performance, with a mass activity of 1.88 A·mg⁻¹_Pt at 0.9 V, which is almost 15 times that of the commercial Pt/C. Our density functional theory (DFT) calculations attribute the high activity of the Pd@Pt–Ir nanocrystals, and the facet dependence of these activities, to easier protonation of O* and OH* under relevant OH* coverages, relative to the corresponding energetics on clean Pd@Pt surfaces. The DFT calculations also indicate that incorporating Ir atoms into the Pt lattice destabilizes OH–OH interactions on the surface, thereby raising the oxidation potential of Pt and greatly improving the catalytic durability.     

Co₃O₄ nanocrystals on graphene as a synergistic catalyst for oxygen reduction reaction

Catalysts for oxygen reduction and evolution reactions are at the heart of key renewable-energy technologies including fuel cells and water splitting. Despite tremendous efforts, developing oxygen electrode catalysts with high activity at low cost remains a great challenge. Here, we report a hybrid material consisting of Co?O? nanocrystals grown on reduced graphene oxide as a high-performance bi-functional catalyst for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Although Co?O? or graphene oxide alone has little catalytic activity, their hybrid exhibits an unexpected, surprisingly high ORR activity that is further enhanced by nitrogen doping of graphene. The Co?O?/N-doped graphene hybrid exhibits similar catalytic activity but superior stability to Pt in alkaline solutions. The same hybrid is also highly active for OER, making it a high-performance non-precious metal-based bi-catalyst for both ORR and OER. The unusual catalytic activity arises from synergetic chemical coupling effects between Co?O? and graphene.     

Reaction products and growth kinetics during diffusion bonding of SiC ceramic to Ni–Cr alloy

Abstract

Vacuum diffusion bonding of SiC ceramic to Ni–25 at.-%Cr alloy was carried out at 1223–1323 K for 0.9–3.6 ks under a pressure of 7.2 MPa. The kinds of the reaction products and the interface structures of the joints were investigated by scanning electron microscopy (SEM), electron probe microanalysis (EPMA), and X-ray diffraction (XRD), and the kinetic parameters describing the growth of reaction layers were calculated. The experiment and analysis identify that four kinds of reaction products, namely Ni₂Si, graphite (G), Ni₅Cr₃Si₂ and Cr₃Ni₂SiC, have formed during the diffusion bonding of SiC ceramic to Ni–25 at.-%Cr alloy. The interface structure of the SiC/Ni–Cr joints is SiC/(Ni₂Si+G)/(Cr₃Ni₂SiC + Ni₅Cr₃Si₂)/Ni₅Cr₃Si₂/Ni- Cr, and each reaction layer in this structure grows according to a parabolic law. The activation energies for growth of (Ni₂Si+G), (Cr₃Ni₂SiC+Ni₅Cr₃Si₂), and Ni₅Cr₃Si₂ are 217, 248, and 233 kJ mol ­ 1, respectively.     

α-Fe2O3/alkalinized C3N4 heterostructure as efficient electrocatalyst for oxygen reduction reaction

Journal of Materials Science - A nanocomposite of α-Fe2O3/alkalinized C3N4 (α-Fe2O3/A-C3N4) electrocatalyst for oxygen reduction reaction (ORR) was synthesized by a simple in situ...     

Adhesion characteristics of Cu/Ni–Cr/polyimide flexible copper clad laminates according to Ni:Cr ratio and Cu electroplating layer thickness

The adhesion strength of Cu/Ni–Cr/polyimide flexible copper clad laminate (FCCL) was evaluated according to the composition ratio of the Ni–Cr layer and the thickness of the Cu electroplating layer, by using a 90° peel test. The changes in the morphology, chemical bond and adhesion property were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The peel strength of the FCCL increased with increasing Cr content and increasing Cu electroplating layer thickness. This increasing FCCL peel strength was attributed to a lower C–N bond and higher C–O and carbonyl (C=O) bonds in the polyimide surface compared to the FCCL with a lower adhesion strength. The adhesion property of the FCCLs was significantly affected by the Ni:Cr ratio.     

Exploiting H-induced lattice expansion in β-palladium hydride for enhanced catalytic activities toward oxygen reduction reaction

We have developed an efficient strategy to synthesize an active and durable electrocatalyst of Pd hy-dride nanocubes(NCs).Instead of the traditional chemical me...     

To be nano or not to be nano?

Nanomaterials, nanostructures, nanostructured materials, nanoimprint, nanobiotechnology, nanophysics, nanochemistry, radical nanotechnology, nanosciences, nanooptics, nanoelectronics, nanorobotics, nanosoldiers, nanomedecine, nanoeconomy, nanobusiness, nanolawyer, nanoethics to name a few of the nanos. We need a clear definition of all these burgeoning fields for the sake of the grant attribution, for the sake of research program definition, and to avoid everyone being lost in so many nanos.     

Microstructure stability and mechanical properties of an age-hardenable Ni–Mo–Cr alloy subjected to long-term exposure to elevated temperature

This paper characterizes the microstructure and mechanical properties of a nickel-based superalloy with a nominal composition of Ni–25Mo–8Cr (wt.%) after long-term exposures to elevated temperatures. The alloy is strengthened by long-range-ordered precipitates of an oI6 metastable phase with the Ni₂(Mo,Cr) stoichiometry. The alloy was annealed at 650 °C for 1000, 2000 and 4000 h, after it had been plastically deformed in order to accelerate diffusion processes occurring at elevated temperature and consequently to ease the formation of stable phases. The microstructure was characterized using TEM, SEM and X-ray phase analyses; mechanical properties were measured in tensile tests.It has been determined that the alloy loses its phase stability upon plastic deformation and subsequent long-term annealing at 650 °C. The microstructure, composed initially of a dispersed Ni₂(Mo,Cr) strengthening phase in a Ni-based solid solution, decomposes during annealing into a mixture of Ni₃Mo- and Ni₄Mo-type phases, Mo-lean Ni-based solid solution and a complex intermetallic P phase. The dominant new phase is a plate-shaped Ni₃Mo-type phase while the P phase appears as singular small precipitates. The Ni₃Mo phase is formed mainly in regions of highly localized deformation, e.g., in shear bands, and only occasionally nucleates in regions where the deformation was relatively uniform (dislocations or twins in one system). Regions adjacent to the plates of the Ni₃Mo phase are recrystallized and free from an Ni₂(Mo,Cr) strengthening phase. Changes in microstructure of the deformed alloy during long time annealing at 650 °C result in the decrease in the yield strength as well as tensile elongation at both room temperature and 650 °C. A significant decrease in elongation at 650 °C occurs only in specimens tested in air but not those tested in vacuum.     

To publish or not to publish? On the aggregation and drivers of research performance

This paper presents a methodology to aggregate multidimensional research output. Using a tailored version of the non-parametric Data Envelopment Analysis model, we account for the large heterogeneity in research output and the individual researcher preferences by endogenously weighting the various output dimensions. The approach offers three important advantages compared to the traditional approaches: (1) flexibility in the aggregation of different research outputs into an overall evaluation score; (2) a reduction of the impact of measurement errors and a-typical observations; and (3) a correction for the influences of a wide variety of factors outside the evaluated researcher's control. As a result, research evaluations are more effective representations of actual research performance. The methodology is illustrated on a data set of all faculty members at a large polytechnic university in Belgium. The sample includes questionnaire items on the motivation and perception of the researcher. This allows us to explore whether motivation and background characteristics (such as age, gender, retention, etc.,) of the researchers explain variations in measured research performance.     

Damage analysis in Fe–Cr–Ni centrifugally cast alloy tubes for reforming furnaces

Reformer furnaces tubes work under high temperature and pressure for a long time, which are very critical conditions for creep deformation and life of most common materials. Cast austenitic Fe–Cr–Ni alloys in the widely know HP grades are used for reformer tubes to allow a good service at temperatures that can be close to 1000 °C. This paper reports a study devoted to the damage analysis of reformer furnace tubes after more than 100,000 h of service. Tubes, made of a HP grade modified with Nb and Ti additions, were inspected in situ by a laser optic system to measure their internal diameter and evaluate creep deformation. With the aim of developing a criterion for deciding the substitution of components, samples of as cast material and samples, cut from the most deformed tubes put out of service, were considered to check changes of mechanical properties and metallurgical characteristics. Tensile and creep tests were carried out; moreover the metallographic observations included optical and scanning electron microscopy and energy dispersive X-ray microanalysis in order to measure locally the chemical composition.     

Ni–Cu alloy for diffusion bonding cermet/steel in air

Microstructural and mechanical evaluation for joints obtained by static and dynamic diffusion bonding of a 90MnCrV8 high strength steel coated with WC–Co, using a Ni–Cu alloy as interlayer, are shown in the present work. In all joints different reacted zones generated during the bonding process can be distinguished by means of scanning electron microscopy and dispersive X-ray spectrometry. The maximum tensile strength obtained using dynamic diffusion bonding process confirms a very promising technology for industrial applications.     

Thermal-Conductivity Measurements and Predictions for Ni–Cr Solid Solution Alloys

Thermal conductivities of Ni–Cr solid solution alloys have been measured to develop a prediction equation for thermal conductivities as functions of temperature and chemical composition. Samples used were Ni–x at% Cr (0 ≤ x ≤ 22) and commercial alloys of Nichrome Nos. 1 and 2. Thermal conductivity measurements were carried out using the transient hot-strip method over a temperature range from 293 K to 1273 K. The thermal conductivities of the alloys increased with increasing temperature and decreased with increasing Cr concentration at constant temperature. The Smith–Palmer equation has been examined to relate the thermal conductivities of the alloys to the electrical resistivities. The thermal conductivity and electrical-resistivity data, respectively, in the present work and in the literature have confirmed that the Smith–Palmer equation applies to Ni–Cr solid solutions and Nichrome alloys. On the basis of this equation, the thermal conductivity of Ni–Cr solid solution alloys has been expressed as a function of temperature and chemical composition. This analysis has also been applied to Ni–Fe and Cu–Ni solid solution alloys.