Ultra-small MnCo2O4 nanocrystals decorated on nitrogen-enriched carbon nanofibers as oxygen cathode for Li-O2 batteries

2020 ◽  
Vol 13 (06) ◽  
pp. 2051035
Author(s):  
Xiaoping Jiang ◽  
Ronghua Wang ◽  
Ning Hu ◽  
Chaohe Xu
Keyword(s):  
Particle Size ◽  
Cathode Materials ◽  
Nitrogen Doping ◽  
Carbon Nanofiber ◽  
Nucleation And Growth ◽  
Ex Situ ◽  
Aprotic Electrolyte ◽  
High Level ◽  
Oxygen Cathode

Ultra-small MnCo2O4 nanocrystals/nitrogen enriched carbon nanofiber composites, with particle size as small as 2–4[Formula: see text]nm and nitrogen content as high as [Formula: see text][Formula: see text]at.%, were designed and used as oxygen cathode materials for Li-O2 batteries, with an aprotic electrolyte. Via an in-situ nucleation and growth, the morphology, size and distribution of MnCo2O4 nanocrystals were well controlled on surface of nanofibers, with strong interfacial interactions between the two components. Benefitting from the unique microstructure and high-level nitrogen doping, the MnCo2O4/NCF composite can deliver discharge and charge capacities of 4147.8 and 3842.8[Formula: see text]mAh/g as oxygen cathode materials, and columbic efficiencies are about 92.6%. More importantly, the discharge products can completely decompose in charging process as evidenced by an ex-situ FESEM investigation, while for pure NCF cathode, particle and plate-like Li2O2 were still observed on its surface, which confirmed that the MnCo2O4/NCF composite has a superior electrocatalytic activity that that of NCF.

scholarly journals In Situ Synthesis of Core-Shell-Structured SiCp Reinforcements in Aluminium Matrix Composites by Powder Metallurgy

Metals ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 1201
Author(s):  
Xinghua Ji ◽  
Cheng Zhang ◽  
Shufeng Li
Keyword(s):  
Particle Size ◽  
Powder Metallurgy ◽  
Shell Structure ◽  
Ex Situ ◽  
Aluminium Matrix ◽  
Core Shell ◽  
Matrix Composites ◽  
Aluminium Matrix Composites ◽  
Core Shell Structure

SiCp reinforced aluminium matrix composites (AMCs), which are widely used in the aerospace, automotive, and electronic packaging fields along with others, are usually prepared by ex situ techniques. However, interfacial contamination and poor wettability of the ex situ techniques make further improvement in their comprehensive performance difficult. In this paper, SiCp reinforced AMCs with theoretical volume fractions of 15, 20, and 30% are prepared by powder metallurgy and in situ reaction via an Al-Si-C system. Moreover, a combined method of external addition and an in situ method is used to investigate the synergistic effect of ex situ and in situ SiCp on AMCs. SiC particles can be formed by an indirect reaction: 4Al + 3C → Al4C3 and Al4C3 + 3Si → 3SiC + 4Al. This reaction is mainly through the diffusion of Si, in which Si diffuses around Al4C3 and then reacts with Al4C3 to form SiCp. The in situ SiC particles have a smooth boundary, and the particle size is approximately 1–3 μm. A core-shell structure having good bonding with an aluminium matrix was generated, which consists of an ex situ SiC core and an in situ SiC shell with a thickness of 1–5 μm. The yield strength and ultimate tensile strength of in situ SiCp reinforced AMCs can be significantly increased with a constant ductility by adding 5% ex situ SiCp for Al-28Si-7C. The graphite particle size has a significant effect on the properties of the alloy. A criterion to determine whether Al4C3 is a complete reaction is achieved, and the forming mechanism of the core-shell structure is analysed.

Inferring suspended sediment carbon content and particle size at high frequency from the optical response of a submerged spectrometer 

2021 ◽  
Author(s):  
Dhruv Sehgal ◽  
Núria Martínez-Carreras ◽  
Christophe Hissler ◽  
Victor Bense ◽  
AJF (Ton) Hoitink
Keyword(s):  
Particle Size ◽  
Absorption Spectrum ◽  
Carbon Content ◽  
Suspended Sediment ◽  
High Frequency ◽  
Suspended Sediments ◽  
Ex Situ ◽  
Frequency Measurements ◽  
Component Form

<p>Manual and unattended sampling in the field and laboratory analysis are common practices to measure suspended sediment (SS) carbon content and particle size. However, one of the major drawbacks of these ex-situ methods is that they make high frequency measurements challenging. This includes restricted data collection due to limited access to the sampling locations during turbulent conditions or high flows, when the largest amount of sediments is transported downstream, introducing uncertainty in quantification of SS properties (particle size and carbon content) and sediment loads. Knowledge on SS carbon content and particle size is also important to better understand the multi-component form of suspended sediments (i.e. flocs) that directly affect sediment transport and other sediment properties (e.g. settling velocity and density). Moreover, SS carbon content and particle size exert an impact on the optical sensor readings that are traditionally used to measure turbidity. In that respect, high frequency measurements of SS carbon content and particle size could eventually help us to move from ‘local’ calibrations towards ‘global’ dependencies based on in-situ SS characterization.</p><p>In this study, we propose to use a submerged UV-VIS spectrometer to infer SS carbon content and particle size. The sensor measures the entire light absorption spectrum of water between 200 nm and 750 nm at sampling intervals as short as 2-minutes. To this end, we first test our approach under controlled conditions with an experimental laboratory setup consisting of a cylindrical tank (40-L) with an open top. An UV-VIS spectrometer and a LISST-200X sensor (to measure particle size distribution) are installed horizontally. A stirrer facilitates the homogeneous mixing of SS and prevents the settling of heavy particles at the bottom. We use the sediments sampled from 6 sites in Luxembourg with contrasting composition and representing different land use types and geological settings. The sampled sediments were wet sieved into 3 size classes to clearly recognize the effect of particle size on absorption. In our investigation, we use specific wavelengths, chemometric techniques and carbon content specific absorbance indices to infer SS composition and particle size from the absorption spectrum. Results are then validated using in-situ field data from two instrumented field sites in Luxembourg. Amid the challenge of associating laboratory and field results, the preliminary results indicate that the absorption spectrum measured with a submerged UV-VIS spectrometer can be used to estimate SS particle size and carbon content.</p>

TEM/STEM characterization of industrial type supported Pd catalysts: Effect of an in situ hydrogen activation

1988 ◽  
Vol 46 ◽  
pp. 700-701
Author(s):  
R. Szymanski ◽  
J. Lynch
Keyword(s):  
Particle Size ◽  
Particle Shape ◽  
Local Information ◽  
Ex Situ ◽  
Supported Metal Catalysts ◽  
Metal Dispersion ◽  
Pd Catalysts ◽  
Supported Pd Catalysts ◽  
Induced Changes

TEM is routinely used to control the metallic dispersion of industrial supported metal catalysts, since in complement to the chemisorptive methods it provides unique local information about particle size distribution, i.e. about the quality of the metal dispersion. An evaluation by TEM of the mean particle size can be useful to quantify the metal dispersion assuming a simple model for the particle shape, e.g. spherical or cubic. However, except for the cases where chemisorption fails (e.g. poisonning), this evaluation is mainly considered as a mean of checking the representativity of the statistical distribution of local information in comparison with chemisorption results. Discrepancies are often observed between the two techniques and many reasons can be advanced for these such as statistics, particle shape models, electron beam induced changes, chemisorption assumptions (cf coverage), etc... In fact, we consider that in a number of cases one of the primary limitations is likely to be due to the in situ problem in TEM, which is inherent to most techniques involving an ex situ characterization.

scholarly journals Investigating Processes of Nanocrystal Formation and Transformation via Liquid Cell TEM

2014 ◽  
Vol 20 (2) ◽  
pp. 425-436 ◽  
Author(s):  
Michael H. Nielsen ◽  
Dongsheng Li ◽  
Hengzhong Zhang ◽  
Shaul Aloni ◽  
T. Yong-Jin Han ◽  
...  
Keyword(s):  
Direct Evidence ◽  
Nucleation And Growth ◽  
Ex Situ ◽  
Bulk Solution ◽  
Dynamic Information ◽  
Transmission Electron ◽  
Classical Models ◽  
Liquid Cell ◽  
Temporal And Spatial

AbstractRecent ex situ observations of crystallization in both natural and synthetic systems indicate that the classical models of nucleation and growth are inaccurate. However, in situ observations that can provide direct evidence for alternative models have been lacking due to the limited temporal and spatial resolution of experimental techniques that can observe dynamic processes in a bulk solution. Here we report results from liquid cell transmission electron microscopy studies of nucleation and growth of Au, CaCO3, and iron oxide nanoparticles. We show how these in situ data can be used to obtain direct evidence for the mechanisms underlying nanoparticle crystallization as well as dynamic information that provide constraints on important energetic parameters not available through ex situ methods.

A study of ruthenium ultrathin film nucleation on pretreated SiO2 and Hf–silicate dielectric surfaces

2007 ◽  
Vol 22 (8) ◽  
pp. 2254-2264 ◽  
Author(s):  
Filippos Papadatos ◽  
Steven Consiglio ◽  
Spyridon Skordas ◽  
Eric T. Eisenbraun ◽  
Alain E. Kaloyeros
Keyword(s):  
Grain Size ◽  
Rutherford Backscattering Spectrometry ◽  
Substrate Surface ◽  
Compressive Strain ◽  
Chemical Vapor ◽  
Nucleation And Growth ◽  
Ex Situ ◽  
Organic Chemical ◽  
Nucleation Density

This study explored the effects of substrate surface pretreatments on the nucleation and growth of metal–organic chemical vapor deposited ruthenium. In situ plasma (dry), featuring O2, Ar, and H2/Ar chemistries, and ex situ (wet) treatments, consisting of a standard RCA bath, were examined in the nucleation and growth of up to 50-nm-thick metallic Ru films on SiO2 and Hf–silicate surfaces. The resulting surface morphology, grain size, and roughness of the metallic films were examined by scanning electron microscopy (SEM) and atomic force microscopy (AFM), while Rutherford backscattering spectrometry (RBS) was used for compositional measurements. It was determined that an in situ plasma treatment using a H2/Ar yielded metallic Ru films with the highest nucleation density, smallest grain size, and lowest resistivity. Film buckling was also observed for the Ru films deposited on H2/Ar pretreated surfaces. The behavior was attributed to the presence of compressive strain. The films deposited on RCA-cleaned and Ar plasma treated surfaces exhibited very similar physical and electrical characteristics to the films grown on untreated substrates. Alternatively, the use of O2 plasma surface treatment adversely affected Ru nucleation on the SiO2 surface. Relevant mechanisms for Ru nucleation and growth on SiO2 and Hf–silicate nontreated surfaces are discussed in the context of the various predeposition dry and wet treatments.

scholarly journals Processing Methods Used in the Fabrication of Macrostructures Containing 1D Carbon Nanomaterials for Catalysis

Processes ◽  
2020 ◽  
Vol 8 (11) ◽  
pp. 1329
Author(s):  
João Restivo ◽  
Olívia Salomé Gonçalves Pinto Soares ◽  
Manuel Fernando Ribeiro Pereira
Keyword(s):  
Carbon Nanotubes ◽  
Carbon Nanomaterials ◽  
Carbon Nanofiber ◽  
Ex Situ ◽  
Processing Methods ◽  
Structured Catalysts ◽  
Operation Conditions ◽  
Potential Applications ◽  
Multi Walled Carbon Nanotubes

A large number of methodologies for fabrication of 1D carbon nanomaterials have been developed in the past few years and are extensively described in the literature. However, for many applications, and in particular in catalysis, a translation of the materials to a macro-structured form is often required towards their use in practical operation conditions. This review intends to describe the available methods currently used for fabrication of such macro-structures, either already applied or with potential for application in the fabrication of macro-structured catalysts containing 1D carbon nanomaterials. A review of the processing methods used in the fabrication of macrostructures containing 1D sp2 hybridized carbon nanomaterials is presented. The carbon nanomaterials here discussed include single- and multi-walled carbon nanotubes, and several types of carbon nanofibers (fishbone, platelet, stacked cup, etc.). As the processing methods used in the fabrication of the macrostructures are generally very similar for any of the carbon nanotubes or nanofibers due to their similar chemical nature (constituted by stacked ordered graphene planes), the review aggregates all under the carbon nanofiber (CNF) moniker. The review is divided into methods where the CNFs are synthesized already in the form of a macrostructure (in situ methods) or where the CNFs are previously synthesized and then further processed into the desired macrostructures (ex situ methods). We highlight in particular the advantages of each approach, including a (non-exhaustive) description of methods commonly described for in situ and ex situ preparation of the catalytic macro-structures. The review proposes methods useful in the preparation of catalytic structures, and thus a number of techniques are left out which are used in the fabrication of CNF-containing structures with no exposure of the carbon materials to reactants due to, for example, complete coverage of the CNF. During the description of the methodologies, several different macrostructures are described. A brief overview of the potential applications of such structures in catalysis is also offered herein, together with a short description of the catalytic potential of CNFs in general.

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