Facile electrodeposition of ternary Ni-Fe-Co alloy nanostructure as a binder free, cost-effective and durable electrocatalyst for high-performance overall water splitting.

Development of highly effective and stable electrocatalyst as full water electrolyzers is essential for the energy production process. In this study, binder-free and self-made Ni-Fe-Co nanostructure electrode was developed using electrodeposition method, and its electrocatalytic properties were investigated for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline media. The fabricated electrocatalyst exhibited excellent properties for the evolution of H2 and O2. Ni-Fe-Co nanostructure film required overpotentials of 91 mV for HER and 316 mV for OER in order to create a current density of 10 mA cm-2. Furthermore, the Tafel slope for HER and OER was measured as 86 and 43 mV/dec, respectively. In addition, the resulting electrode showed outstanding electrocatalytic stability, in which following a long period of electrolysis, the necessary overpotential to maintain a current density of 100 mA cm-2 remained constant. This bifunctional electrode enables alkaline water electrolyzers, which can provide a current density of 10 mA cm-2 under a cell voltage of 1.6 V. Such desirable performance of fabricated electrode as an electrocatalyst for full water splitting can be attributed to high active surface area factor, the synergistic effect of the elements, and rapid separation of bubbles from the electrode surface. This study provides a new method for the rapid construction of efficient electrocatalyst for renewable energy sources.

Tribological behaviour of mechanically synthesized titanium-boron carbide nanostructured coating.

In this paper, titanium-boron carbide (Ti/B4C) nanocomposite coatings with different B4C nanoparticles contents were fabricated by surface mechanical attrition treatment (SMAT) method by using B4C nanoparticles with average nanoparticle size of 40 nm. The characteristics of the nanopowder and coatings were evaluated by microhardness test, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Friction and wear performances of nanocomposite coatings and pure titanium substrate were comparatively investigated, with the effect of the boron carbide content on the friction and wear behaviours to be emphasized. The results show the microhardness, friction and wear behaviours of nanocomposite coatings are closely related with boron carbide nanoparticle content. Nanocomposite coating with low B4C content shows somewhat (slight) increased microhardness and wear resistance than pure titanium substrate, while nanocomposite coating with high B4C content has much better (sharp increase) wear resistance than pure titanium substrate. The effect of B4C nanoparticles on microhardness and wear resistance was discussed.

Characterization of Si3N4/TiO2 nanocomposite coatings prepared via micro arc oxidation.

Nanocomposite Si3N4/TiO2 coatings were prepared by micro arc oxidation with Si3N4 nanoparticles in solution and the effects of time and current density on the coatings formation and growth were studied. X-ray diffraction analysis was utilized to detect the nanocrystalline and amorphous characteristics of the composite coatings. Surface morphology and nanostructure of coatings were observed by scanning electron microscopy and atomic force microscopy. The results showed that current density had great effects on phase transformation of Si3N4 nanoparticles in composite coatings. The moderate current density conduced to homogeneous distribution of silicon nitride nanoparticles in the coatings. Moreover, fine nanoparticles that entered and homogeneously distributed in the composite coating led to an increase in the barriers for nucleation of oxide-based grains and inhibition of grain growth. Therefore, the introduction of nanoparticles resulted in the formation of smaller oxide-based grains.

Ti-WC nanocrystalline coating formed by surface mechanical attrition treatment process on 316L stainless steel.

Nanocrystalline coatings were performed on the surface of 316L stainless steel plates mechanically with a mixture of Ti and WC powders under vacuum conditions. The targets were replaced in the end of the high energy milling rig, while Ti-WC mixture was milled as usual. It is shown that the coatings are nanocrystalline in nature with narrow distribution of average size of nanocrystallites. X-ray diffraction and scanning electron microscopy (with energy-dispersive spectrometer) revealed that the top layer of the coatings is uniform. Microhardness, roughness and primary corrosion tests (tafel tests) proved enhancement of coated samples with respect to raw materials. Transmission electron microscope image of deformed surface confirmed surrounding of nanoparticles by dislocation loops after plastic deformation.

Study of nanopores ordering in anodic aluminum oxide templates achieved by three step process.

Enhancement of naturally-occurred self ordering nanopores in anodic aluminum oxide membrane by performing three-step anodic oxidation process has been reported. Naturally-occurred self ordering of nanopores in anodic aluminum oxide membrane has brought it into the applications of template for fabrication of nanoscale materials. Three-step anodic oxidation method was used to achieve self-ordering of nanopores. Effect of duration of first and second steps on the ordering of nanopores was investigated. The current-time curves recorded during anodization elucidate an almost same behavior for all three steps. Scanning electron micrographs show hexagonally arranged 45 nm pores in a manner which contribute into the formation of highly ordered areas, called domains. Larger ones are clearly observed over the surface, for samples with longer first and second anodization steps.

Formation of nanocrystalline layers by surface severe plastic deformation and pulsed plasma electrolytic carburizing.

Surfaces of various kinds of metallic materials spheres were treated by nanocrystalline surface severe plastic deformation and then pulsed nanocrystalline plasma electrolytic carburizing to study nanocrystalline substrate effect on formation and nano-hardness of hard nanocrystalline layer. The surface layers of the metallic materials developed by the nanocrystalline surface severe plastic deformation were characterized by means of high resolution scanning electron microscope. Nearly equiaxed nanocrystals with grain sizes ranging from 15 to 90 nm were observed in the near surface regions of all metallic materials, which are low carbon steel and commercially pure titanium. The effect of substrate nanocrystallization on growth kinetics and hardness of formed nanocrystalline carbide layer was studied with the means of figure analysis and nanohardness tests. Figure analysis show the length to diameter ratio and distribution curve of nanocrystals and it has been found that the achieved properties of hard layer (growth rate, nano-hardness, nanostructure...) are related to these factors. It was also clarified that these techniques and surface nanocrystallization can be easily achieved in most of metallic materials. Results indicate that the resultant hardened carburized layers exhibited excellent hardness profile. Investigation of the layer characteristics showed strong dependence followed from the treatment experimental parameters as well as the shape of nanocrystals.