TEM Grids Research Articles

Synthesis of Highly Oriented Nanocrystal Thin-Films and Their Applications to Electrochemical Devices

The precisely defined particle assembly at the nanoscale with simultaneously scalable patterning at the microscale is indispensable for enabling functionality and improving the performance of devices. While synthetic advances in the past decades now allow precise control of their size, shape, and composition, they must be processed from dispersion into functional films for many applications, which presents additional challenges. In this work, we introduce the self-assembly of inorganic nanoubes (Co3O4 NCs) and we also describe the fabrication of centimeter-scale NC superlattice thin-films on silicone substrate with anisotropic NC building blocks, thin-film patterning, and the supercrystal formation of superlattice structures. As a result, the Raman spectra of Co3O4 NC thin-films clearly exhibits the distinct feature of vibration modes of Co3O4 and synchrotron-based X-ray diffraction techniques showed the Co3O4 NCs order into [100] aligned arrays. Also, the uniformly prepared Co3O4 NC building blocks and thin-films were examined by field-emission scanning electron microscopy analysis and it shows well-defined nanostructures with ~13nm-side of NCs and ~3nm space between self-assembled NCs. To investigate the distinct feature of functional films, we prepared various type of device structures (memory, electrode, gas sensor) and examined the performances. In case of memristor, the device exhibits excellent bipolar resistance switching characteristics with better reliability and stability over various polycrystalline metal oxide nanostructures. Utilizing our approach enables the creation of miniaturized devices, followed by the transfer of NC thin-films onto TEM grids. Subsequent in-situ TEM analysis offers the potential to observe unique phenomena at the nano-scale, unveiling phase transitions in nanocrystalline materials or electrochemical reaction mechanisms previously unexplored by researchers.

Facile preparation of graphene–graphene oxide liquid cells and their application in liquid-phase STEM imaging of Pt atoms

Graphene–graphene oxide (GO) hybrid liquid cells (LCs) for liquid-phase scanning transmission electron microscopy (STEM) were fabricated using a facile method with commercial graphene on a polymethyl methacrylate sheet and GO on a TEM grid. LCs containing Pt nanoparticles (NPs) and pure water were efficiently produced and observed via STEM. Their composition and thickness were characterized by STEM-electron energy-loss spectroscopy. High-resolution (HR) STEM revealed slow-moving Pt NPs’ atomic structures and fast-moving single Pt atoms at the LC’s thin edges. Minimal damage during HR STEM indicated stable LCs because of their excellent electrical and thermal conductivities and radiolysis species scavenging ability.

Electrochemical Synthesis of Hollow Nanoparticles via Anodic Transformation of Metastable Core-Shell Precursors.

Recent advances in electrosynthesis of nanomaterials expanded structural and compositional variations accessible by the electrochemical method; however, reliably synthesizable morphological variety fall shy of that available by conventional solvothermal synthesis. In this communication, electrochemical preparation of surfactant-free hollow nanoparticles is demonstrated. By anodic conversion of core-shell precursors with metastable cores, hollowed nickel nanoparticles with uniform dimensions were synthesized and characterized. Implementation of TEM grids as the working electrodes, identical location tracking of the morphological evolution of single particles to anodic stimulus has been demonstrated. The synthesized nanoparticles were employed as catalysts for the alkaline hydrogen evolution reaction and exhibited catalytic rates that compare favorably to the Pt/C benchmark. This marks the first pure electrochemical synthesis of hollow nanoparticles and shall contribute to the structural diversification of electrosynthesized nanomaterials.

Bismuth tri-iodide – Graphene 2D material

In recent years, a multitude of 2D materials has been extensively studied, and new ones continue to emerge. Among these, bismuth tri-iodide-graphene material has been reported in both theoretical and experimental studies, displaying intriguing properties. These findings suggest potential photovoltaic applications for BiI3 layers and van der Waals superstructures. In this context, the present work explores the growth of van der Waals superstructures BiI3–graphene, obtained through physical vapor deposition. These structures are achieved by nucleating BiI3 and allowing it to grow on graphene-covered TEM grids and ultra-flat silicon substrates.When the structures are directly grown on grids and substrates covered with graphene, twisted BiI3 structures are formed, leading to Moiré interference, indicating the presence of two or more BiI3 layers and non-uniformity. However, when the structures are grown on grids pre-treated with UV/O3, and then subjected to annealing and post-growth, they become more uniform and aligned, without observable twisting. Structures obtained on substrates with this treatment and post-growth result in thinner layers, as thin as 7.59 ± 0.16 nm, with a roughness of 0.435 ± 0.018 nm. As the thickness decreases, the position of the (003) reflection peak in the diffraction pattern shifts to lower values and broadens, indicating an expansion of the cell along the c-axis. The obtained bandgap values, ranging from 1.55 ± 0.04 to 1.62 ± 0.04 eV, closely align with theoretical predictions. The obtained structures become part of the 2D universe of other similar materials, such as TMDs-graphene, and open up exciting possibilities for new properties and applications.

Investigations on ion irradiation induced microstructural changes in Gd2O3 nanorods

Ion irradiation induced phase transformations in Gd2O3 nanorods dispersed on TEM grids, are investigated using synchrotron X-ray diffraction and transmission electron microscopy. Ion irradiation induced cubic (C) to monoclinic (B) phase transformation is observed in Gd2O3 nanorods. Gd2O3 nanorods are partially transformed to monoclinic phase at 0.63 dpa (5 × 1016 ions/cm2) itself. The C→B phase transformation is reconstructive type transformation where the role of O-vacancies and diffusion are very important. During He+ ion irradiation, the displacement cascades produced O-vacancies and during the non-melting thermal spike regime, diffusion was assisted and it resulted in the phase transformation. In addition to phase transformation, TEM investigations shows formation of amorphous carbon layer around the nanorods and welding of the nanorods, upon ion irradiation. These observations are explained based on the mechanisms of GOLF (giant onion like fullerene) formation and the localized surface melting during thermal spike.

Impact of flash boiling spray on soot generation of a rich fuel–air mixture under various ambient pressures

Particulate emission is one of the critical challenges for the modern gasoine direct injection (GDI) engines. Especially under cold start conditions, the global equivalence ratio inside the cylinder is often set quite rich, leading to the generation of a large amount of soot. The fuel distribution state, such as homogeneous mixing and heterogeneous mixing with local rich pockets prior to the combustion is the key factor affecting soot generation under cold start conditions in GDI engines. Flash boiling injection, as a method to promote fuel air mixing, could be a potential solution to sooting problems of rich mixture combustion under cold start conditions. However, the unclear influences of flash boiling spray to fuel–air mixing state and subsequent soot generation pose a challenge to soot reduction in GDI engines. This work aims to study the effect of various flash boiling degrees on fuel–air mixture formation and subsequent soot generation utilizing a customized constant volume combustion chamber (CVCC) incorporated with the gasoline direct injection scheme under moderately cold start ambient temperature of 30 °C. A global high equivalence ratio of 1.7 representing extremely rich combustions under cold start conditions is selected for strong sooting propensity. By setting different fuel temperatures (Tf= 30 °C and 120 °C) and various ambient pressures (Pa= 40 kPa, 100 kPa and 160 kPa), various spray flash boiling states (subcooled, transitional flash boiling and flare flash boiling sprays) are achieved, and finally various fuel distribution states of rich mixtures prior to combustion are obtained. High speed color camera and soot sampling TEM grids were used to capture and evaluate the characteristics of spray atomization, combustion and soot aggregate structures. Based on this investigation, the effect of flash boiling degree on fuel–air mixing and subsequent soot generation is analyzed. The results show that flash boiling spray enhances fuel atomization and produces much more homogeneous rich mixture with smaller local rich pockets and richer global premixed gaseous portion. Over-rich global premixed mixture combustion is prone to nuclei inception and agglomeration, producing soot aggregates with small primary particles. While the local rich pocket combustion is prone to surface growth, producing larger primary particles. Flash boiling spray could reduce the size of soot particles under cold start conditions by generating smaller local rich pockets.

Three-dimensional surface lattice plasmon resonance effect from plasmonic inclined nanostructures via one-step stencil lithography

Abstract Plasmonic nanostructures allow the manipulation and confinement of optical fields on the sub-wavelength scale. The local field enhancement and environmentally sensitive resonance characteristics provided by these nanostructures are of high importance for biological and chemical sensing. Recently, surface lattice plasmon resonance (SLR) research has attracted much interest because of its superior quality factor (Q-factor) compared to that of localized surface plasmon resonances (LSPR), which is facilitated by resonant plasmonic mode coupling between individual nanostructures over a large area. This advantage can be further enhanced by utilizing asymmetric 3D structures rather than low-height (typically height < ∼60 nm) structure arrays, which results in stronger coupling due to an increased mode volume. However, fabricating 3D, high-aspect ratio, symmetry-breaking structures is a complex and challenging process even with state-of-the-art fabrication technology. Here, we report a plasmonic metasurface of 3D inclined structures produced via commercial TEM grid–based stencil lithography with a Q-factor of 101.6, a refractive index sensitivity of 291 nm/RIU, and a figure of merit (FOM) of 44.7 in the visible wavelength range at a refractive index of 1.5 by utilizing the 3D SLR enhancement effect, which exceeds the performance of most LSPR systems (Q < ∼10). The symmetry-breaking 3D inclined structures that are fabricated by electron beam evaporation at an angle increase the polarizability of the metasurface and the directionality of the diffractively scattered radiative field responsible for SLR mode coupling. Additionally, we explore the role of spatial coherence in facilitating the SLR effect and thus a high-Q plasmonic response from the nanostructures. Our work demonstrates the feasibility of producing 3D inclined structure arrays with pronounced SLR enhancement for high biological sensitivity by utilizing the previously unexplored inclined stencil lithography, which opens the way to fabricate highly sensitive plasmonic metasurfaces with this novel simple technique.

Transition-Metal Interdiffusion in Solid-State Batteries Revealed By Cryo-TEM

Solid-state lithium-ion batteries are being considered as a future energy-storage technology, with superior energy/power density and improved safety over conventional lithium-ion batteries. However, their commercial implementation is hampered by side reactions and electro-chemo-mechanical degradation occurring during cycling (mostly at the positive electrode side). Many efforts have been made to reveal the underlying mechanisms in order to alleviate such problems.In the current study, the Thermo Scientific IGST workflow solution was used to enable a DualBeam to TEM workflow by protecting both bulk sample and prepared lamella under argon atmosphere with a CleanConnect transfer module. Because of the beam and temperature sensitivity of the superionic lithium thiophosphate solid electrolyte and the cathode interphases formed during cycling, the lamella preparation process (incl. bulk milling, lift out, attachment to the TEM grid, and final thinning) was carried out at cryogenic temperature (−178 °C). The lamella was then transferred to a Talos F200X CFEG for TEM analysis using an inert gas sample transfer workflow.STEM and EELS investigations revealed Ni, Co, and Mn dissolution from a Ni-rich cathode and subsequent solid electrolyte poisoning. Transition-metal dissolution/migration during cycling operation has previously only been reported for conventional (liquid-electrolyte-based) batteries.

(Invited) High-Throughput Local Electrochemistry Coupled with (in-situ) microscopy to Advance on the Fundamentals of Electrochemical Nucleation and Growth

Electrochemical nucleation and growth (EN&G) are the cornerstone for many (nano)material growth routes and the main factor limiting battery durability. The in-depth experimental assessment of the process is very challenging due to the random nature of initiation events (nucleation), the heterogeneity of surfaces and the (very) fast kinetics across several length scales. For all that, our understanding of the mechanisms involved is inaccurate and incomplete [1].During the last years, we have developed an approach based on using carbon coated TEM grids as electrodes to combine ex-situ atomic-scale TEM characterization with electron tomography and macroscale electrochemical measurements [2,3]. This approach has brought valuable evidence of non-classical growth pathways such as growth mediated by nanocluster aggregation [3,4]. Yet, it does not capture the influence of the heterogeneous nature of the surface where EN&G proceeds, nor the dynamics before, during and after nucleation [5].In this contribution, we present our recent work in which we combine high-throughput local electrochemistry by Scanning Electrochemical Cell Microscopy (SECCM), with ex-situ and in-situ characterization, including electrochemical transmission electron microscopy (EC-TEM), to study the electrochemical nucleation and growth of metals on carbon surfaces [6,7].The spatially resolved electrochemical characterization enables a one-to-one correlation between the electrochemical data and the local surface properties, which can be evaluated by different surface analytical tools (SEM, AFM, ...) in identical locations to where the local electrochemical measurements have been performed. In addition, EC-TEM allows the study of the early-stage growth/dissolution dynamics of the metallic phase.The combination of both methods opens new opportunities for fully understanding the complex nature of EN&G phenomena. In the longer run, this can be exploited for the rational design (electrodeposition) of functional nanostructured materials considering the heterogeneous nature of the supports and the differences within nanomaterial ensembles.

Morphology and nanostructure of soot particles from diesel engine under transient and steady-state operating conditions with a microalgae fuel component, dioctyl phthalate biofuel

In order to adhere to strict emissions standards, it is necessary to reduce diesel particulate emissions under real driving conditions. This can be achieved by reducing the production of soot particles and optimising the combustion process within the combustion chamber. This investigation examines the impact of engine operating conditions (transient and steady-state) on the characterisation of the soot particles. Soot samples from a common rail direct injection (CRDI), turbocharged six-cylinder diesel engine without any aftertreatment devices were collected on TEM grids. This investigation utilised both pure diesel and diesel-dioctyl phthalate (DOP) blends (D90DOP10 and D80DOP20). To correlate the soot characterisation results, diesel particulate emissions were also measured using a fast particle analyser (DMS500). The results indicate that emissions from transient cycles are higher in comparison to steady-state engine operation. Smaller primary particle diameter with a compact structure were observed for transient cycles when compared to steady-state operating conditions. Parameters such as number of primary particles within a single aggregate, radius of gyration, and soot aggregate area were also studied. Nanostructure analysis reveals that the soot particles from transient cycles could have lower oxidation reactivity and longer fringes with less curvature and interplanar spacing.

Facile hermetic TEM grid preparation for molecular imaging of hydrated biological samples at room temperature

Although structures of vitrified supramolecular complexes have been determined at near-atomic resolution, elucidating in situ molecular structure in living cells remains a challenge. Here, we report a straightforward liquid cell technique, originally developed for real-time visualization of dynamics at a liquid-gas interface using transmission electron microscopy, to image wet biological samples. Due to the scattering effects from the liquid phase, the micrographs display an amplitude contrast comparable to that observed in negatively stained samples. We succeed in resolving subunits within the protein complex GroEL imaged in a buffer solution at room temperature. Additionally, we capture various stages of virus cell entry, a process for which only sparse structural data exists due to their transient nature. To scrutinize the morphological details further, we used individual particle electron tomography for 3D reconstruction of each virus. These findings showcase this approach potential as an efficient, cost-effective complement to other microscopy technique in addressing biological questions at the molecular level.

Nanoscale Lithium Distribution within a Secondary Cathode Particle for Li-Ion Battery Using Identical Location (S)TEM-EELS

Energy density of LIBs are primarily limited by cathodes and further development of cathode materials requires in-depth understanding of the structural and compositional changes spanning across various length scales involved during electrochemical delithiation/lithiaton. Cathode materials are usually synthesized as secondary particles (∼10 µm) that are sintered agglomerates of smaller primary particles (∼100s µm). Lithium distribution may not necessarily be uniform across the entirety of these particles in typical state-of-the-art layered cathodes during electrochemical cycling. A detailed knowledge of lithium distribution within secondary particles is crucially important for obtaining a comprehensive understanding of the energy storage system. To truly understand the structural changes taking place at the nano and atomic scales, high spatial resolution techniques are of paramount importance for understanding the lithium distribution and optimizing/developing future LIB cathodes. STEM-EELS is ideally suited for obtaining such information at the desired (atomic) spatial resolution. In the present work, nanoscale lithium-ion distribution was investigated among various primary particles within a secondary particle of state-of-the-art Ni-rich layered LIB cathode using identical location scanning transmission electron microscopy with electron energy loss spectroscopy (IL-STEM-EELS) by making use of a specially designed electrochemical cell employing TEM grids. Identical location allows for the imaging of the same location before and after electrochemical testing to evaluate localized changes. Nanoscale lithium-ion distribution along with the electron beam dose effects on the nanoscale/atomic structure of layered NMC532 cathodes at various charge stages will be presented.

Deposition of graphenic nanomaterials from elevated temperature premixed stagnation flames

The work examines the unique nanostructure of carbon nanoparticles deposited from sooting premixed flames with flame temperatures exceeding 2200 K. This flame temperature regime has previously been shown to transition from typical soot formation conditions to a regime whereby the flame-form carbon adopts a nanostructure considerably more ordered than soot. Graphenic carbon deposits observed by High-resolution TEM (HRTEM) are reported here corroborating previous Raman spectroscopy evidence. The use of premixed stretch-stabilized flames enables particle production in the high-temperature regime under a flow field amenable to low-dimensional flame modeling. Although the flame flow configuration is relatively simple, three sample preparation methods are used to assess the representation of true carbon properties as they exist in the flame. HRTEM imaging is carried out on carbon particle samples prepared by rapid-insertion deposition, aerosol dilution probe deposition and carbon particle film deposition. Images from rapid-insertion samples show amorphous particles in the lightly sooting flame and turbostratic particles in the heavy sooting flame. There is trace evidence of graphenic structure in rapid-insertion samples but the most striking particles on the TEM grid are graphite nanocrystals presumably formed by a new artificial crystallization process. HRTEM images of particles collected over time by diluted aerosol deposition and film deposition show clear graphenic structures. Overall, the carbon nanostructure observed by HRTEM is a mixture of amorphous, turbostratic and graphenic carbon lattices depending on the flame condition and sampling method. The current work highlights potential impacts of higher flame temperatures and higher equivalence ratio on deposited flame-formed carbon. Namely, graphenic particle structure is observed in rapid-insertion deposition samples but graphene portions are most abundant in aerosol dilution and carbon particle film deposition samples. This may indicate that graphene structures grow on the deposition surface over time.

Non-Covalent Free-Standing Monolayer Nanoarchitectonics of Heterocoronene-Based Discotic Liquid Crystal Molecules

With excellent charge carrier mobility, tendency to form long-range assembly with self-healing ability, and remarkable chemical and mechanical stability, highly conjugated discotic molecules constitute an important class of materials for electronic applications. Here, we report formation of the stable free-standing molecular film of heterocoronene-based discotic liquid crystal (DLC) molecules, held solely by supra-molecular non-covalent interactions. The films of monolayer thickness (∼4 nm) were lifted from Langmuir trough directly onto a circular ring of diameter up to 2 mm as well as onto TEM grids. Films remain free-standing up to a macroscopic length scale, as revealed by optical and secondary electron microscopy, presumably due to the synergistic effect of intermolecular π–π interactions and the dispersion forces between the peripheral alkyl chains as well as their interdigitation. The monolayer is more than 97% transparent in the visible range. Further, resistive switching measurements carried out on the monolayer DLC film transferred on a silver substrate revealed electrochemical metallization to be the governing process. The switching time was found to decrease exponentially with voltage indicating nucleation to be a possible rate-limiting step. We anticipate that the method presented here will facilitate utilization of such non-covalent free-standing films in flexible memristor and nano-electromechanical systems.

29 Fugitive Emissions from Carbon Dioxide Laser Cutting Activities

Abstract Carbon Dioxide laser cutters are used to cut and engrave on various types of materials, including metals, wood, and plastics. Although many are equipped with fume extractors for removing airborne substances generated during laser cutting, gases and particulate matter can be released upon opening the lid after completion. Real-time instruments were utilized to monitor both particulate concentrations and size distributions, while the novel Tsai Diffusion Sampler was used to collect particulate samples on a polycarbonate membrane and TEM grid. Preliminary detection of released gases consisted of the use of gas sampling with Teflon Gas Bags and followed with analysis using Gas Chromatography-Mass Spectrometry (GC-MS). A portable ambient infrared air analyzer was used to quantify the concentrations of the chemicals released by the laser cutting activities. Results of the study found that a significant concentration of particulate matter ranging 15.4 - 86 nm in particle sizes were released each time the laser cutter lid was opened and were observed to gradually increase in concentration for a period of at least 20 minutes after the completion of a cut. The GC-MS gaseous samples primarily contained methyl methacrylate at a low level close to the detection limit of the infrared air analyzer.

Measuring cryo-TEM sample thickness using reflected light microscopy and machine learning

In cryo-transmission electron microscopy (cryo-TEM), sample thickness is one of the most important parameters that governs image quality. When combining cryo-TEM with other imaging methods, such as light microscopy, measuring and controlling the sample thickness to ensure suitability of samples becomes even more critical due to the low throughput of such correlated imaging experiments. Here, we present a method to assess the sample thickness using reflected light microscopy and machine learning that can be used prior to TEM imaging of a sample. The method makes use of the thin-film interference effect that is observed when imaging narrow-band LED light sources reflected by thin samples. By training a neural network to translate such reflection images into maps of the underlying sample thickness, we are able to accurately predict the thickness of cryo-TEM samples using a light microscope. We exemplify our approach using mammalian cells grown on TEM grids, and demonstrate that the thickness predictions are highly similar to the measured sample thickness. The open-source software described herein, including the neural network and algorithms to generate training datasets, is freely available at github.com/bionanopatterning/thicknessprediction. With the recent development of in situ cellular structural biology using cryo-TEM, there is a need for fast and accurate assessment of sample thickness prior to high-resolution imaging. We anticipate that our method will improve the throughput of this assessment by providing an alternative method to screening using cryo-TEM. Furthermore, we demonstrate that our method can be incorporated into correlative imaging workflows to locate intracellular proteins at sites ideal for high-resolution cryo-TEM imaging.

Iridium Stabilizes Ceramic Titanium Oxynitride Support for Oxygen Evolution Reaction.

Decreasing iridium loading in the electrocatalyst presents a crucial challenge in the implementation of proton exchange membrane (PEM) electrolyzers. In this respect, fine dispersion of Ir on electrically conductive ceramic supports is a promising strategy. However, the supporting material needs to meet the demanding requirements such as structural stability and electrical conductivity under harsh oxygen evolution reaction (OER) conditions. Herein, nanotubular titanium oxynitride (TiON) is studied as a support for iridium nanoparticles. Atomically resolved structural and compositional transformations of TiON during OER were followed using a task-specific advanced characterization platform. This combined the electrochemical treatment under floating electrode configuration and identical location transmission electron microscopy (IL-TEM) analysis of an in-house-prepared Ir-TiON TEM grid. Exhaustive characterization, supported by density functional theory (DFT) calculations, demonstrates and confirms that both the Ir nanoparticles and single atoms induce a stabilizing effect on the ceramic support via marked suppression of the oxidation tendency of TiON under OER conditions.

Structure Determination Feasibility of Three-Dimensional Electron Diffraction in Case of Limited Data

During the last two decades, three-dimensional electron diffraction (3D ED) has undergone a renaissance, starting with the introduction of precession (Precession Electron Diffraction Tomography, PEDT) that led to variations on the idea of collecting as much of the diffraction space as possible in order to solve crystal structures from sub-micron sized crystals. The most popular of these acquisition methods is based on the continuous tilting/rotation of the crystal (so-called Microcrystal Electron Diffraction, MicroED) akin to the oscillating crystal method in X-ray crystallography, which was enabled by the increase of sensitivity and acquisition speed in electron detectors. While 3D ED data is more complex than the equivalent X-ray data due to the higher proportion of dynamical scattering, the same basic principles of what is required in terms of data quality and quantity in order to solve a crystal structure apply; high completeness, high data resolution and good signal-to-noise statistics on measured reflection intensities. However, it may not always be possible to collect data in these optimum conditions, the most common limitations being the tilt range of the goniometer stage, often due to a small pole piece gap or the use of a non-tomography holder, or the position of the sample on the TEM grid, which may be too close to a grid bar and then the specimen of interest becomes occluded during tilting. Other factors that can limit the quality of the acquired data include the limited dynamic range of the detector, which can result on truncated intensities, or the sensitivity of the crystal to the electron beam, whereby the crystallinity of the particle is changing under the illumination of the beam. This limits the quality and quantity of the measured intensities and makes structure analysis of such data challenging. Under these circumstances, traditional approaches may fail to elucidate crystal structures, and global optimization methods may be used here as an alternative powerful tool. In this context, this work presents a systematic study on the application of a global optimization method to crystal structure determination from 3D ED data. The results are compared with known structure models and crystal phases obtained from traditional ab initio structure solution methods demonstrating how this strategy can be reliably applied to the analysis of partially complete 3D ED data.

Stability and Degradation of Pt/C Catalysts Explored with IL-TEM

Industrial application of fuel cells, while, hopefully, inevitable, is still hindered by various aspects, one of them being the issue with oxygen reduction reaction (ORR) catalysts. Current state of the art platinum catalysts, while extraordinarily active, still have a long way to go when it comes to stability. In this work we have decided to tackle this problem by employing FW200 carbon black as a support for platinum nanoparticles. The carbon support was treated in 3000 °C to obtain highly ordered, graphitic structure. We’ve discovered that our catalyst, while initially exhibiting lower electrochemical surface area (ECSA) than it’s commercial, Vulcan-based counterpart, degraded with substantially slower rate than the industrial catalyst. We’ve came to that conclusion after subjecting the catalysts to accelerated degradation tests (ADT) on the rotating ring disk electrode in various potential ranges and performing ECSA and activity measurements during and after said tests. Additionally, to explore degradation mechanisms of the catalysts we’ve used identical localization transmission electron microscopy (ILTEM). This technique allows us to track the behaviour of each platinum nanoparticle, before and after electrochemical measurements, by performing ADT on TEM grids covered with catalyst. ILTEM experiments allowed us to prove, that the crystalline structure of graphitized FW200 hinders nanoparticles’ movement across the carbon support, leading to increased resistance to agglomeration. We used inductively coupled plasma optical emission spectroscopy to investigate platinum dissolution’s part in reducing catalyst activity by measuring the amount of platinum left in electrolyte after ADT. Lastly, we’ve investigated the influence of heat treatment in 3000 °C on the structure and electronic properties of the FW200 carbon black using Raman spectroscopy and X-ray photoelectron spectroscopy. Thorough electrochemical and structural study of platinum catalyst deposited on graphitized FW200 carbon black allowed us to confirm, that our material is highly competitive, in the terms of stability, to commercially available Vulcan-based catalysts. We also think that ILTEM, while exceptionally powerful, is still quite an underutilized technique and we would like to present how joint efforts of microscopists and electrochemists can push the boundaries of knowledge in ORR electrochemistry.

Surface Enhanced Raman Spectroscopy of methylene blue deposited on Ag nanostructured substrates prepared by pulsed laser deposition

Pulsed laser deposition has proven to be a suitable technique to fabricate nanostructures of noble metals with different sizes and morphologies on glass substrates. Generally, this is done by varying the number of laser pulses impinging on the target. However, it is well known that the produced plasma plume has an inhomogeneous angular distribution and the quantity/density of material deposited on the substrate is higher in the center than in the periphery. Actually, a noble metal (silver in the present case, gold or copper) density gradient starting with a continuous region in its center and progressively evolving to complicate nanostructures and finally to spherical nanoparticles is obtained. Taking advantage of this morphological variation, drops of highly diluted methylene blue were deposited radially. Furthermore, TEM grids were placed in the same way. This technique gives the possibility of directly correlate the SERS signal, the underlying noble metal morphology and the optical absorption in very similar regions. In the present work we develop this method and discuss the obtained results.