Amorphous Carbon Support Research Articles

Stepwise emergence of CO gas sensing response and selectivity on SnO2 using C supports and PtOx decoration.

Room temperature gas sensing is crucial for practical devices used in indoor environments. Among various materials, metal oxides are commonly used for gas sensing, but their strong insulating properties limit their effectiveness at room temperature. To address this issue, many studies have explored diverse methods such as nanoparticle decoration or conductive support, etc. Here, we report the emergence of gas-sensing functionality at room temperature with improved CO gas selectivity on SnO2 nanoparticles through sequential steps by using amorphous carbon (a-C) support and PtOx decoration. The SnO2 decorated on amorphous carbon shows enhanced gas adsorption compared to inactive gas sensing on SnO2 decorated carbon support. The higher Vo site of SnO2 on a-C induces gas adsorption sites, which are related to the higher sp2 bonding caused by the large density of C defects. The ambiguous gas selectivity of SnO2/a-C is tailored by PtOx decoration, which exhibits six values of sensing responses (Rg/Ra or Ra/Rg) under CO gas at room temperature with higher selectivity. Compared to PtOx/a-C, which shows no response, the enhanced CO gas sensing functionality is attributed to the CO adsorption site on PtOx-decorated SnO2 particles. This report not only demonstrates the applicability of CO gas sensing at room temperature but also suggests a strategy for using SnO2 and carbon compositions in gas sensing devices.

Cryo-electron microscopy at the Faculty of Biology of Lomonosov Moscow State University

This paper demonstrates an example of a successful upgrade of a JEOL JEM-2100 analytical transmission electron microscope to a low-resolution cryo-electron microscope designed for routine tasks of sample preparation and quality evaluation. As a result of the upgrade, the instrument allows the subnanometer resolution of protein molecule reconstructions (within 8 Å). The influence of graphene and amorphous carbon support films to prevent the effect of preferred orientation of protein particles in the frozen sample is discussed.

One-pot aerobic conversion of fructose to 2,5-diformylfuran using silver-decorated carbon materials

The synthesis of 2,5-diformylfuran (DFF) from fructose is a simultaneous process using two distinct catalysts, including fructose dehydration to 5-hydroxymethylfurfural (5-HMF) accelerated by an acid catalyst, followed by 5-HMF oxidation to DFF mediated by a redox catalyst. In this study, various catalysts with Ag metal decorated on sulfonated amorphous carbon supports (AC-SO3H@Ag) were performed, and their structures were characterized via different characterization techniques such as X-ray diffraction, scanning electron microscopy, X-ray fluorescence spectroscopy, thermogravimetric analysis, Boehm's titration, inductively coupled plasma mass spectroscopy, energy-dispersive X-ray spectroscopy, elemental mapping analysis and Fourier-transform infrared spectroscopy. The catalytic performance of the prepared AC-SO3H@Ag bifunctional catalysts with various wt% of Ag/AC-SO3H was determined for the one-pot transformation of fructose into DFF. The influence of solvent, substrates, reaction time, and catalyst loading were also examined thoroughly to optimize the reaction, and a mechanism was proposed. 5-HMF formed by the dehydration of fructose was converted entirely to DFF, and the highest DFF yield of 77.9 % was obtained after 18 h of reaction time at 150 °C in dimethyl sulfoxide with 3 wt% of the AC-SO3H@Ag catalyst and without the use of any additives, traditional hydrogen acceptors, or oxidants. The reusability of the catalysts was also tested.

(Keynote) Insight into Carbon Corrosion of Different Carbon Supports for Pt-Based Electrocatalysts for Polymer Electrolyte Fuel Cells from Interfacial Perspective

A mechanistic understanding of carbon corrosion in polymer electrolyte fuel cells (PEFCs) is required to design catalyst layers that are durable. Electrochemical oxidation of carbon occurs during uncontrolled startup and shutdown events of PEFCs leading to multitude of degradation events, including loss of electrochemical surface area (ECSA), pore structure collapse, Pt detachment, loss in ionomer and others. To understand carbon corrosion physics and resulting degradation mechanisms a detailed electrochemical characterization is needed to probe interfaces between Pt-ionomer, carbon-ionomer and to measure transport properties and the ECSA in the catalyst layer. In this presentation we will provide an overview of carbon corrosion understanding and our approaches to quantify the sequence of events. In these studies, PEFCs were subjected to the Department of Energy carbon corrosion accelerated stress test (AST) protocol. Various electrochemical techniques were used to describe interfaces and morphology, as well as transport properties for the cells at different stages of the AST. ECSA measurements, polarization curves, CO-displacement/stripping to determine sulfonic acid group coverage in dry and wet conditions, electrochemical impedance spectroscopy, oxygen transport resistance measurements and other techniques were used. In addition, physical characterization methods at the beginning of life (BOL) and end of life (EOL) were used, such as micro x-ray fluorescence mapping, focused ion beam scanning electron microscopy, transmission electron microscopy, x-ray photoelectron spectroscopy and Raman spectroscopy. A combination of electrochemical and physicochemical methods revealed that amorphous carbon oxidizes first, after which Pt detach resulting in the loss of the ECSA, followed by severe structure collapse, resulting in a poor oxygen transport resistance. We extend the study to carbon supports that are more graphitized to alleviate some of the issues observed with amorphous carbon support.

Partial oxidation of methane to methyl oxygenates with enhanced selectivity using a single-atom copper catalyst on amorphous carbon support

In this study, we report a single-atom Cu catalyst on the amorphous carbon support for direct methane partial oxidation. The catalyst was prepared by the carbonization of Cu-doped ZIF-8 to implant single-atom Cu active centers that coordinate with four nitrogen (CuN4) on the amorphous N-doped carbon. Carbonization enhanced the oxidation resistance of the catalyst by preventing the oxidation of Cu-coordinating ligands, leading to a 40% reduction in CO2 production. Our prepared catalyst showed higher methanol selectivity than other single-atom copper catalysts. Mechanistic studies revealed that Cu and the surface carbon atom facilitated the dissociation of H2O2 into OOH and H, which further transformed into Cu–O and led to proton abstraction from methane. We highlight a simple approach to prepare a single-atom catalyst that is supported on amorphous N-doped carbon, derived from a metal-doped ZIF. This catalyst exhibits enhanced selectivity and stability for the partial oxidation of methane.

Machine learning for classifying narrow-beam electron diffraction data.

As an alternative approach to X-ray crystallography and single-particle cryo-electron microscopy, single-molecule electron diffraction has a better signal-to-noise ratio and the potential to increase the resolution of protein models. This technology requires collection of numerous diffraction patterns, which can lead to congestion of data collection pipelines. However, only a minority of the diffraction data are useful for structure determination because the chances of hitting a protein of interest with a narrow electron beam may be small. This necessitates novel concepts for quick and accurate data selection. For this purpose, a set of machine learning algorithms for diffraction data classification has been implemented and tested. The proposed pre-processing and analysis workflow efficiently distinguished between amorphous ice and carbon support, providing proof of the principle of machine learning based identification of positions of interest. While limited in its current context, this approach exploits inherent characteristics of narrow electron beam diffraction patterns and can be extended for protein data classification and feature extraction.

Selective and Stable CO2 Electroreduction to CH4 via Electronic Metal-Support Interaction upon Decomposition/Redeposition of MOF.

The CO2 electroreduction to fuels is a feasible approach to provide renewable energy sources. Therefore, it is necessary to conduct experimental and theoretical investigations on various catalyst design strategies, such as electronic metal-support interaction, to improve the catalytic selectivity. Here a solvent-free synthesis method is reported to prepare a copper (Cu)-based metal-organic framework (MOF) as the precursor. Upon electrochemical CO2 reduction in aqueous electrolyte, it undergoes in situ decomposition/redeposition processes to form abundant interfaces between Cu nanoparticles and amorphous carbon supports. This Cu/C catalyst favors the selective and stable production of CH4 with a Faradaic efficiency of ≈55% at -1.4V versus reversible hydrogen electrode (RHE) for 12.5h. The density functional theory calculation reveals the crucial role of interfacial sites between Cu and amorphous carbon support in stabilizing the key intermediates for CO2 reduction to CH4 . The adsorption of COOH* and CHO* at the Cu/C interface is up to 0.86eV stronger than that on Cu(111), thus promoting the formation of CH4 . Therefore, it is envisioned that the strategy of regulating electronic metal-support interaction can improve the selectivity and stability of catalyst toward a specific product upon electrochemical CO2 reduction.

C-shaped dipper: A novel useful auxiliary tool for preparation of specimen grids for transmission electron microscopy.

The transmission electron microscopy (TEM) has played a pivotal role in visualizing and detailing the morphology of nanoscale objects of observation, but care must be taken to ensure that the object is in its original, unperturbed state. This is because not all objects under the observation are necessarily robust and structurally stable, and if the object being observed is so delicate and easily changeable in shape, one may be observing structural artifacts leading to wrong interpretations. I here present a novel prototype of an easy-to-use and reliable auxiliary tool, the C-shaped dipper, developed for the preparation of specimen grids for TEM, along with its handling instructions for diverse applications. Some nanostructures are so delicate and fragile that their nanocomplexes are easily destroyed when aspirated by a pipette with a narrow tip diameter. Using the C-shaped dipper, the observation objects can be scooped up in a droplet formed by the surface tension of the liquid, keeping their intact shapes, and placed on a grid precovered with a support film. The C-shaped dipper has proven to be excellent for handling soft assemblies having delicate structures, such as nano-scale composites, for facilitating thin layered formations with molecular constituent blocks, and for preparing a grid individually covered with a collodion film or an amorphous carbon support film.

Carbonaceous FexP Synthesized via Carbothermic Reduction of Dephosphorization Slag as Hydrogen Evolution Catalyst for Water Splitting

Developing the high-efficiency and cheap non-noble catalysts towards hydrogen evolution reaction (HER) is of significance for water splitting. Herein, for the first time, we report a simple method of acid leaching combined with carbothermic reduction with dephosphorization slag to construct a carbonaceous FexP/C catalyst. In alkaline medium, the corresponding overpotential when the output current density was 10 mA cm−2 (η10) was only 145 mV. Additionally, there was no obvious attenuation after 3000 cycles, which showed significantly better activity and stability than that of non-carbonaceous FexP catalysts prepared by gas–solid phosphating. The structure and composition of FexP/C were characterized by X-ray diffraction, scanning electron microscope, energy dispersive spectroscopy, and inductively coupled plasma atomic emission spectrometer. The electrochemical properties of the electrode were evaluated by cyclic voltammetry, linear scanning voltammetry, electrochemical impedance spectroscopy, and cyclic stability. The results showed that the prepared FexP/C was composed of FeP-Fe2P mixed nanocrystals supported on amorphous carbon. Compared with FexP, the synergistic catalysis of the FeP and Fe2P phases as well as the interactive support effect between the FeP-Fe2P mixed nanocrystals and the amorphous carbon support will attribute the rich active sites for electrocatalytic reaction and reduce the charge transfer resistance. Thus, FexP/C has good hydrogen evolution activity and stability. Overall, the preparation of catalysts with high additional value based on dephosphorization slag was preliminarily explored.

Zif-Derived Single-Atom Copper Catalyst on Amorphous Carbon Support for Partial Oxidation of Methane with Enhanced Methanol Selectivity

Zif-Derived Single-Atom Copper Catalyst on Amorphous Carbon Support for Partial Oxidation of Methane with Enhanced Methanol Selectivity

Atomically resolved tomographic reconstruction of nanoparticles from single projection: Influence of amorphous carbon support

Nanoparticles have a wide range of applications due to their unique geometry and arrangement of atoms. For a precise structure-property correlation, information regarding atomically resolved 3D structures of nanoparticles is utmost beneficial. Though modern aberration-corrected transmission electron microscopes can resolve atoms with the sub-angstrom resolution, an atomic-scale 3D reconstruction of a nanoparticle using Scanning Transmission Electron Microscopy (STEM) based tomographic method faces hurdles due to high electron irradiation damage and “missing-wedge”. Instead, inline 3D holography based tomographic reconstructions from single projection registered at low electron doses is more suitable for defining atomic positions at nanostructures. Nanoparticles are generally supported on amorphous carbon film for Transmission Electron Microscopy (TEM) experiments. However, neglecting the influence of carbon film on the tomographic reconstruction of the nanoparticle may lead to ambiguity. To address this issue, the effect of amorphous carbon support was quantitatively studied using simulations and experiments and it was revealed that increasing thickness and/or density of carbon support increases distortion in tomograms.

Ultra-Low Platinum Nano-Alloy Encapsulated in Carbon Nanotube Matrix: A Practical PEM Fuel Cell Electrocatalyst

Hydrogen oxidation reaction (HOR) and oxygen reduction reaction (ORR) are the crucial PEM fuel cell reactions. However, the sluggish kinetics of these reactions particularly ORR require efficient catalysts to reduce the larger voltage losses and boost the electrochemical activity. Hence developing efficient and durable platinum (Pt)-based electrocatalysts is of enormous significance for practical PEM fuel cell. The state-of the-art carbon black supported Pt nanoparticles (Pt/C) catalyst has sever activity and stability issues. The tiny Pt nanoparticles often undergo the dissolution and redeposition under electrochemical operation, which would destroy their initial state of highly uniform dispersion and high activity. Meanwhile, the amorphous carbon support suffers from the corrosion and oxidation at the cathodic working conditions, which leads to the initial interaction disruption of Pt and carbon support. It causes Pt nanoparticles detachment and agglomeration with a consequent significant activity degradation. Herein we report an integrated ultra-low Pt nanoalloy encapsulated in nitrogen-doped carbon nanotubes matrix (PtCoNi@NCNTs) for efficient oxygen reduction in practical fuel cell. This hybrid Pt-based catalyst achieves a higher mass activity of 3.46 A mgPt -1 at 0.9 V vs. RHE with a negligible stability decay after 10,000 cycles. More importantly, this excellent half-cell activity can be fully transformed into practical full cell. The fuel cell based on this hybrid electrocatalyst delivers a power density of 11.2 W mgPt -1 cathode, which is 8 times of commercial Pt/C 20 % based cells (1.4 W mgPt -1 cathode). Furthermore, PtCoNi@NCNTs also demonstrates an excellent fuel-cell durability by retaining its initial current after 10 h operation at the constant voltage of 0.7 V without any loss. This excellent performance is ascribed to the synergetic response by the integration of encapsulated Pt nano-alloy and hierarchical nitrogen-doped carbon nanotube matrix. It is well acknowledged that the fine tuning of transition metals in the PtM alloy offers extra Pt structural strain that controls the weakening of surface bonds and results in a hike in the electrocatalytic activity. Moreover, the incorporation of metal-nitrogen-carbon (M-N-C) sites also additionally boosts catalytic activity, where the hierarchical architecture is not only the robust substrate to anchor/embed ternary alloy nanoparticles but also ensures sufficient contact of the reactant on the catalysts, which is always ignored in the previous catalysts for fuel cells. Respectable hydrophilic NCNTs matrix restricts comprehensive contact between electrolyte and active sites thereby regulating the oxygen diffusion to the active sites and avoid flooding, hence the enhanced mass transport boosts fuel cell performance. Decent hydrophilic nature of the PtCoNi@NCNTs catalyst facilitates the three-phase interface at the cathode that offers efficient mass transport and excellent conductivity for efficient oxygen reduction reaction. Higher graphitic properties offer advanced durability to the NCNTs support against corrosion and oxidation at cathodic working conditions, while few layers carbon coatings shield the Pt nanoalloy against dissolution in acidic conditions thereby offering pronounced durability for long term fuel cell operation. Therefore, such novel graphitic NCNTs support material endows superior durability to the electrocatalyst in real working conditions of PEM fuel cell. In this work the existing gaps between the RDE activity and fuel cell performance have been investigated and optimized magnificently, which endorses the complete transformation of RDE activity to the MEAs level. This work may provide significant insights in designing the low-Pt integrated highly durable electrocatalysts for practical PEM fuel cells. Figure 1

Investigation of the Effects of Low-Energy Plasma Treatment on Amorphous Carbon and Graphene Support Films for Cryo-Electron Microscopy

Journal Article Investigation of the Effects of Low-Energy Plasma Treatment on Amorphous Carbon and Graphene Support Films for Cryo-Electron Microscopy Get access MJ Campin, MJ Campin E.A. Fischione Instruments, Inc., Export, PA, USA Corresponding author: mj_campin@fischione.com Search for other works by this author on: Oxford Academic Google Scholar M Stumpf, M Stumpf E.A. Fischione Instruments, Inc., Export, PA, USA Search for other works by this author on: Oxford Academic Google Scholar PE Fischione PE Fischione E.A. Fischione Instruments, Inc., Export, PA, USA Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 25, Issue S2, 1 August 2019, Pages 996–997, https://doi.org/10.1017/S1431927619005713 Published: 01 August 2019

Phase Separation in Liquid Metal Nanoparticles

Nanoparticles produced from gallium-based liquid metal alloys have been explored for developing applications in the fields of electronics, catalysis, and biomedicine. Nonetheless, physical properties, such as phase behavior at micro-/nanosize scale, are still significantly underexplored for such nanoparticles. Here, we conduct an in situ investigation of phase behavior for gallium-based liquid metal nanoparticles and discover the unprecedented coexistence of solid particles in spherical liquid metal shells without the support of a crystalline substrate. The particles can also transform into solid Janus nanoparticles after temperature cycling. In addition, we investigate the optical properties of the nanoparticles before and after phase separation using in situ electron energy-loss spectroscopy. Most importantly, we discover that increasing the content of indium within the nanoparticle can stabilize the solid-core/liquid-shell structure at room temperature. This study provides a foundation to engineer liquid metal nanoparticles for developing new applications in nanoscale optical platforms and shape-configurable transformers.Although various electronic, chemical, and biomedical applications have been demonstrated for nanoparticles made from gallium-based liquid metal alloys, fundamental physical properties such as phase behavior of such nanoparticles are still significantly underexplored. Here, Tang and coworkers present the in situ investigation of phase separation in binary and ternary spherical liquid metal nanoparticles upon cooling, and demonstrate the coexistence of solid core/liquid shell without the support of a crystalline substrate. This study provides insight into engineering such nanoparticles for the development of new applications.Despite gallium-based liquid metal alloys attracting extensive attention for various applications, their phase behavior at the nanoscale is still underexplored. Understanding the impact of phase separation in nanoparticles can be extremely useful for developing new structures and exploring suitable applications. Here, we report on the investigation of phase behavior for spherical nanoparticles made from gallium-based liquid metal alloys upon cooling. We discover the thermally stable coexistence of solid cores in spherical liquid metal shells without the support of a crystalline substrate at room temperature. Given the unique properties of liquid metal, together with the facile process for producing core-shell and Janus nanoparticles, this work will encourage further investigation of the properties of such nanoparticles for developing applications in the fields of electronics, catalysis, nanomedicine, and beyond.

Defect formation in multiwalled carbon nanotubes under low-energy He and Ne ion irradiation.

The mechanical, structural, electronic and magnetic properties of carbon nanotubes can be modified by electron or ion irradiation. In this work we used 25 keV He+ and Ne+ ion irradiation to study the influence of fluence and sample thickness on the irradiation-induced damage of multiwalled carbon nanotubes (MWCNTs). The irradiated areas have been characterised by correlative Raman spectroscopy and TEM imaging. In order to preclude the Raman contribution coming from the amorphous carbon support of typical TEM grids, a new methodology involving Raman inactive Au TEM grids was developed. The experimental results have been compared to SDTRIMSP simulations. Due to the small thickness of the MWCNTs, sputtering has been observed for the top and bottom side of the samples. Depending on thickness and ion species, the sputter yield is significantly higher for the bottom than the top side. For He+ and Ne+ irradiation, damage formation evolves differently, with a change in the trend of the ratio of D to G peak in the Raman spectra being observed for He+ but not for Ne+. This can be attributed to differences in stopping power and sputter behaviour.

Modelling electron beam induced dynamics in metallic nanoclusters

We present a computational scheme to simulate beam induced dynamics of atoms in surface dominated, metallic systems. Our approach is based on molecular dynamics and Monte Carlo techniques. The model is tested with clusters comprised of either Ni, Ag or Au. We vary their sizes and apply different electron energies and cluster temperatures to elucidate fundamental relations between these experimental parameters and beam induced displacement probabilities. Furthermore, we demonstrate the capability of our code to simulate beam driven dynamics by using Ag and Au clusters as demonstration systems. Simulations of beam induced displacement and sputtering effects are compared with experimental results obtained via scanning transmission electron microscopy. The clusters in question are synthesised with exceptional purity inside inert superfluid He droplets and deposited on amorphous carbon supports. The presented results may help to understand electron beam driven processes in metallic systems.

Atomic-Scale Understanding of Gold Cluster Growth on Different Substrates and Adsorption-Induced Structural Change

To fully understand the properties of functional nanocatalysts including nanoclusters and nanoparticles, it is necessary to know the geometric and electronic structures of the nanostructure. The catalytic properties of noble metal nanoclusters can often be improved by the formation of heterostructures on different support, but little is known about their atomic-scale structures and their interaction with the support materials. Here, we report the size- and support-dependent structures for Au nanoclusters by combining aberration-corrected scanning transmission electron microscopy and density functional theory calculations. We demonstrate lattice-induced epitaxial coherence growth for Au nanoclusters on crystalline substrate of (110) MgO, different from the chainlike or random structures on amorphous carbon support. The time sequential atomic scale observations confirm that Au clusters tend to easily migrate on crystalline MgO support. DFT calculations based on the experiment results imply the CO adsorption...

Observation of metal nanoparticles at atomic resolution in Pt-based cancer chemotherapeutics.

The chemotherapeutics cisplatin and oxaliplatin are important tools in the fight against cancer. Both compounds are platinum complexes. Aberration-corrected scanning transmission electron microscopy using the annular dark-field imaging mode now routinely provides single-atom sensitivity with atomic number contrast. Here, this imaging mode is used to directly image the platinum within the two drugs in their dried form on an amorphous carbon support film. The oxaliplatin is found to have wetted the supporting amorphous carbon, forming disordered clusters suggesting that the platinum has remained within the complex. Conversely, the cisplatin sample reveals 1.8-nm-diameter metallic platinum clusters. The size and shape of the clusters do not appear to be dependent on drying rate nor formed by beam damage, which may suggest that they were present in the original drug solution.

Ultra-low Pt loading catalyst layers prepared by pulse electrochemical deposition for PEM fuel cells

We report the production of efficient, ultra-low Pt loading catalyst layers on fuel cell electrodes via pulse potential deposition (PPD) from a H2Pt(OH)6 plating solution. We show that by optimizing the off time in the PPD pulse sequence, it is possible to deposit very small, crystalline Pt nanoparticles with narrow size distribution (1.36 ± 0.360 nm) on amorphous carbon supports. Electrodes fabricated from these high surface area electrocatalysts display increased fuel cell performance compared to commercial electrodes with up to an order of magnitude less Pt. The improved performance of our electrodes is attributed to a combination of the optimized size of the deposited nanoparticles as well as the decreased thickness of the catalyst layer. In our deposited electrodes the catalyst layers are very thin (<10 μm) and as a result achieve up to twelve times the gravimetric power of commercial electrodes.

Statistical analysis of support thickness and particle size effects in HRTEM imaging of metal nanoparticles

High-resolution transmission electron microscopy (HRTEM) examination of nanoparticles requires their placement on some manner of support – either TEM grid membranes or part of the material itself, as in many heterogeneous catalyst systems – but a systematic quantification of the practical imaging limits of this approach has been lacking. Here we address this issue through a statistical evaluation of how nanoparticle size and substrate thickness affects the ability to resolve structural features of interest in HRTEM images of metallic nanoparticles on common support membranes. The visibility of lattice fringes from crystalline Au nanoparticles on amorphous carbon and silicon supports of varying thickness was investigated with both conventional and aberration-corrected TEM. Over the 1–4nm nanoparticle size range examined, the probability of successfully resolving lattice fringes differed significantly as a function both of nanoparticle size and support thickness. Statistical analysis was used to formulate guidelines for the selection of supports and to quantify the impact a given support would have on HRTEM imaging of crystalline structure. For nanoparticles ≥1nm, aberration-correction was found to provide limited benefit for the purpose of visualizing lattice fringes; electron dose is more predictive of lattice fringe visibility than aberration correction. These results confirm that the ability to visualize lattice fringes is ultimately dependent on the signal-to-noise ratio of the HRTEM images, rather than the point-to-point resolving power of the microscope. This study provides a benchmark for HRTEM imaging of crystalline supported metal nanoparticles and is extensible to a wide variety of supports and nanostructures.