Nanometer-sized Particles Research Articles

Process intensification of microplasma nanoparticle synthesis enabled by gas flow design

The wide range of practical uses for nanometer-size metal particles has motivated many lab-scale aerosol synthesis processes. It is well known that the aggregation dynamics of aerosol particles impose a trade-off between particle size and concentration: methods that achieve sub-10 nm particles without aggregation are generally limited by low concentration and low flow rates of order 100 cm3/min. Thus, the intensification of aerosol nanoparticle synthesis and its development for industrial use remains a unique and important manufacturing challenge. We present a microplasma reactor system that has been developed to improve process intensification and reliability. The system utilizes an atmospheric pressure DC microplasma to synthesize iron-carbon particles from a ferrocene vapor precursor. The microplasma incorporates a novel focusing technique using a spatial gradient in gas composition to stabilize short-term fluctuations in performance, achieving an iron yield of up to 0.93. We identify the build-up of deposits between the plasma electrodes as the primary cause of reduced performance over time, and eliminate this build-up by indirectly supplying ferrocene to avoid dissociation in this region of the reactor. Further, we show that the design and conditions downstream of the microplasma have a similar influence on the final particle size distribution as those of the microplasma itself. By tuning the coupled process variables of both the microplasma and this downstream region, we synthesize aerosols with mean diameter from 2 to 7 nm and number concentration of 2 to 8×109 #/cm3 at the system outlet.

Improved Thermoelectric Performance of Sb2Te3 Nanosheets by Coating Pt Particles in Wide Medium-Temperature Zone.

The p-type Sb2Te3 alloy, a binary compound belonging to the V2VI3-based materials, has been widely used as a commercial material in the room-temperature zone. However, its low thermoelectric performance hinders its application in the low-medium temperature range. In this study, we prepared Sb2Te3 nanosheets coated with nanometer-sized Pt particles using a combination of solvothermal and photo-reduction methods. Our findings demonstrate that despite the adverse effects on certain properties, the addition of Pt particles to Sb2Te3 significantly improves the thermoelectric properties, primarily due to the enhanced electronic conductivity. The optimal ZT value reached 1.67 at 573 K for Sb2Te3 coated with 0.2 wt% Pt particles, and it remained above 1.0 within the temperature range of 333-573 K. These values represent a 47% and 49% increase, respectively, compared to the pure Sb2Te3 matrix. This enhancement in thermoelectric performance can be attributed to the presence of Pt metal particles, which effectively enhance carrier and phonon transport properties. Additionally, we conducted a Density Functional Theory (DFT) study to gain further insights into the underlying mechanisms. The results revealed that Sb2Te3 doped with Pt exhibited a doping level in the band structure, and a sharp rise in the Density of States (DOS) was observed. This sharp rise can be attributed to the presence of Pt atoms, which lead to enhanced electronic conductivity. In conclusion, our findings demonstrate that the incorporation of nanometer-sized Pt particles effectively improves the carrier and phonon transport properties of the Sb2Te3 alloy. This makes it a promising candidate for medium-temperature thermoelectric applications, as evidenced by the significant enhancement in thermoelectric performance achieved in this study.

Effect of the addition of 1.5 wt.% of mischmetal in the ZK60 alloy processed by Friction Stir Process (FSP) followed by filing on the H-absorption/desorption kinetics

This work investigates the application of Friction Stir Process (FSP) to the ZK60 alloy enhanced with 1.5 % mischmetal (ZK60–1.5 wt% Mm) combined with manual filing to achieve significant improvement in the hydrogen storage properties of this alloy. Addition of 1.5 wt% Mm to the ZK60 alloy yields a matrix with high thermal stability, attributable to the formation of high melting point intermetallic phases. Post FSP, the ZK60–1.5 wt% Mm material shows a refined, pulverized, and recrystallized structure. Such a structure allows the acquisition of filings with nanometric particle sizes and even more pulverized intermetallic phases post-FSP. This synergistic approach produces a significantly homogeneous microstructure morphology, facilitating the study of the catalytic role Mm plays in the hydrogen storage kinetics of the ZK60 alloy at 350 °C. Currently, among all Severe Plastic Deformation (SPD) techniques, only FSP followed by manual filing has demonstrated a capacity to provide a nanometric, homogeneous microstructure that significantly enhances hydrogen storage kinetics and cycling properties. Additionally, the combination of FSP and manual filing is an industrialization process that can be easily implemented, offering reliability, controllability, and cost-effectiveness compared with alternative methods like High-energy Ball Milling (HEBM). Experimental kinetic data for (de)hydrogenation reactions were analyzed using the Luus-Jaakola optimization method, underscoring the potential applicability of the FSP-manual filing route for hydrogenation temperatures <350 °C.

Silk fibroin and gelatin composite nanofiber combined with silver and gold nanoparticles for wound healing accelerated by reducing the inflammatory response

The design and development of silver and gold nanoparticles incorporated into silk fibroin and gelatin composite nanofibers were prepared using the electrospun method. The functional group, chemical composition, and thermal stability of composite nanofibrous scaffolds were investigated using different characterization techniques. The confirmation of SF/GL/Ag-Au composite nanofibers was achieved through FE-SEM and AFM images, which proved to be highly beneficial for assessing surface morphology, thickness, and roughness area (Ra) with dimensions of 777 nm and 292.71 nm, respectively. Furthermore, HR-TEM images were used to elucidate the morphological structure and size of metal nanoparticles in SF/GL/Ag-Au composite nanofibers, revealing an average diameter length of 220.85 ± 82.65 nm for Ag and Au nanoparticles sizes noted at 6.25 nm and 11.56 nm. In addition, flow cytometry analysis of SF/GL/Ag-Au composite nanofibers was conducted to assess the viability of L929 cells and detect the apoptosis levels. Furthermore, invivo wound healing studies were performed on Sprague-Dawley rat animals. The results demonstrated that SF/GL/Ag-Au composite nanofiber scaffolds significantly accelerated wound closure, achieving a remarkable 99.58 % wound healing rate in the 21 days compared to control groups. In conclusion, our findings highlight that SF/GL/Ag-Au composite nanofiber scaffolds are highly suitable for wound dressing applications.

Bioinspired Multifunctional Silver Nanoparticles for Optical Sensing Applications: A Sustainable Approach.

Silver nanoparticles developed via biosynthesis are the most fascinating nanosized particles and encompassed with excellent physicochemical properties. The bioinspired nanoparticles with different shapes and sizes have attracted huge attention due to their stability, low cost, environmental friendliness, and use of less hazardous chemicals. This is an ideal method for synthesizing a range of nanosized metal particles from plants and biomolecules. Optical biosensors are progressively being fabricated for the attainment of sustainability by using opportunities offered by nanotechnology. This review focuses mainly on tuning the optical properties of the metal nanoparticles for optical sensing to explore the importance and applications of bioinspired silver nanoparticles. Further, this review deliberates the role of bioinspired silver nanoparticles (Ag NPs) in biomedical, agricultural, environmental, and energy applications. Profound insight into the antimicrobial properties of these nanoparticles is also appreciated. Tailor-made bioinspired nanoparticles with effectuating characteristics can unsurprisingly target tumor cells and distribute enwrapped payloads intensively. Existing challenges and prospects of bioinspired Ag NPs are also summarized. This review is expected to deliver perceptions about the progress of the next generation of bioinspired Ag NPs and their outstanding performances in various fields by promoting sustainable practices for fabricating optical sensing devices.

The Investigation of Thermoacoustic Methods for Nanofluid Stability on Heat Exchanger

Due to various engineering applications, nanofluids have gained much attention in the last decade. A Nanofluid is a nanometer-sized particle such as metal, oxide, carbide, etc., dispersed into a base heat transfer fluid. The heat exchanger is a device to transfer heat between fluids. Heat exchanger plays a very important role in modern industry. The new innovative fluid called nanofluid is introduced to improve the overall heat transfer and heat transfer rate. Thermoacoustic is a system which uses sound waves and a non-flammable mixture of inert gases to generate an effect. This paper investigates the enhancement of the heat transfer coefficient of a nanofluid containing alumina (Al2O3) nanoparticle with a volume fraction of 0.4% and sonification at 100 Hz, 500 Hz and 1000 Hz. The addition of Al2O3 nanoparticles will affect the characteristics of the nanofluids, which affect the values of density, specific heat, thermal conductivity, and dynamic viscosity. And the addition of the thermoacoustic method with the sonification of acoustic waves can stabilise the effect of Brownian motion in the nanofluid flow. The maximum results are obtained using acoustic waves at 1000 Hz at high temperatures.

Facile synthesis of nanometer-sized NH2-MIL-101(Fe) decorated BiOBr hybrids for efficient Cr(VI) photoreduction

Using a simple oil bath approach, a nanometer-sized NH2-MIL-101(Fe) (NMF) adorned BiOBr heterojunction photocatalyst was effectively created. Compared with the traditional solvothermal method, the synthesis time is shortened by 10 times. Furthermore, nanometer-sized granular NMF particles are uniformly dispersed on BiOBr surface to form plenty of NMF/BiOBr heterojunctions due to chemical action of oxygen vacancies and –NH2 groups. As a result, the as-synthesized NMF/BiOBr photocatalysts exhibit the improved Cr(VI) reduction performance. In 60 min, the 3%NMF/BiOBr heterostructure reaches a maximum Cr(VI) photoreduction efficiency of 99 %. In the 3%NMF/BiOBr heterostructure, Cr(VI) photoreduction occurs at an apparent rate constant that is 7.6 times higher than that of pure BiOBr and 5.44 times higher than that of NMF. The microstructures and photoelectrochemical characteristics of NMF/BiOBr heterostructures were analyzed through state-of-the-art characterization methods. The results show that charge separation and transfer are promoted by the development of heterojunction, which is brought about by the chemical interaction between oxygen vacancies and –NH2 groups. Furthermore, the intimate contact bonding provides electron transport pathways, considerably increasing photocatalytic activity.

Recent Advances of Seed-Mediated Growth of Metal Nanoparticles: from Growth to Applications.

Unprecedented advances in metal nanoparticle synthesis have paved the way for broad applications in sensing, imaging, catalysis, diagnosis, and therapy by tuning the optical properties, enhancing catalytic performance, and improving chemical and biological properties of metal nanoparticles. The central guiding concept for regulating the size and morphology of metal nanoparticles is identified as the precise manipulation of nucleation and subsequent growth, often known as seed-mediated growth methods. However, since the growth process is sensitive not only to the metal seeds but also to capping agents, metal precursors, growth solution, growth/incubation time, reductants, and other influencing factors, the precise control of metal nanoparticle morphology is multifactorial. Further, multiple reaction parameters are entangled with each other, so it is necessary to clarify the mechanism by which each factor precisely regulates the morphology of metal nanoparticles. In this review, to exploit the generality and extendibility of metal nanoparticle synthesis, the mechanisms of growth influencing factors in seed-mediated growth methods aresystematically summarized. Second, a variety of critical properties and applications enabled by grown metal nanoparticles are focused upon. Finally, the current progress and offer insights on the challenges, opportunities, and future directions for the growth and applications of grown metal nanoparticles are reviewed.

L-Arginine self-delivery supramolecular nanodrug for NO gas therapy.

NO gas therapy is a supplementary approach for tumor treatment due to the advantages of minimal invasion, little drug resistance, low side effect and amplified efficacy. l-Arginine (L-Arg), a natural NO source with good biocompatibility, can release NO under the stimulation of H2O2 in tumor microenvironment. However, the conventional l-Arg delivery systems via noncovalent loading usually lead to inevitable premature leakage of nano-cargos during blood circulation. In this work, an efficient l-Arg self-delivery supramolecular nanodrug (SDSND) for tumor treatment is demonstrated by combining Mannich reaction and π-π stacking. l-Arg links to (-)-epigallocatechin gallate (EGCG) with the assistance of formaldehyde through Mannich reaction, and then assembles into nanometer-sized particles via π-π stacking. The guanidine group of l-Arg and the phenolic hydroxyl groups of EGCG are preserved in the SDSNDs, which allows for accomplishing gas therapy by provoking tumor cell apoptosis and combining with EGCG to amplify apoptosis, respectively. In addition, the SDSNDs exhibit high biocompatibility and avoid the premature leakage of l-Arg in blood circulation, providing an alternative l-Arg delivery system for NO gas therapy. STATEMENT OF SIGNIFICANCE: NO gas therapy has attracted emerging interest in tumor treatment. However, the controlled NO release and the avoidance of premature leakage of NO donors remain challenging. In this work, L-Arginine (L-Arg) self-delivery supramolecular nanodrug for efficient tumor therapy is demonstrated through the Mannich reaction of L-Arg, (-)-epigallocatechin gallate (EGCG) and formaldehyde. Stimulated by tumor microenvironment, the guanidine groups of L-Arg allow for accomplishing NO release and thus provoking tumor cell apoptosis. The nanodrug also avoids the premature leakage of L-Arg in blood circulation. Moreover, the preserved phenolic hydroxyl groups of EGCG combine with L-Arg to amplify apoptosis. The nanodrug exhibits high biocompatibility and good therapeutic effect, providing an alternative L-Arg delivery system for NO gas therapy.

Antifungal activity test of nanosilver combination with lip balm cosmetic preparation

Nanosilveris is a silver-based material with nanometer particle sizes (1-100 nm) predicted to be antifungal or an alternative to preservatives in lip balm preparations that are biocompatible. The nanosilver synthesis process in this study used the bottom-up method by adding sodium citrate as a reducing agent and stabilizer. This study aimed to determine the characteristics of the results of 20 ppm nanosilver synthesis using a UV-Vis and TEM spectrophotometer and to determine the antifungal activity of nanosilver in lip balm cosmetic preparations. Variations in adding 20 ppm nanosilver into lip balm preparations are 5%, 10%, and 15%. The results of characterization using a UV-Vis spectrophotometer, namely 20 ppm nanosilver, were quite stable in storage for 2 months, and the results of characterization using TEM also showed that the formed nanosilver remained stable with a nanometer size range ranging from 11.42 nm to 43.95 nm. The antifungal activity test was carried out using the Direct Microscopic Count (DMC) method by counting directly under a microscope. Based on the data obtained, it shows that the antifungal activity of the combination of nanosilver and lip balm preparations is almost equivalent to the antifungal activity of parabens. It has produced lip balm preparations with nanosilver. This is indicated by the value of the inhibition rate (%). The inhibition of fungal growth produced by lip balm preparations with parabens is almost the same as the inhibition rate (%) produced by lip balm preparations with nanosilver. The inhibition rate of lip balm preparations with parabens was 89.11%. In comparison, the inhibition rate of lip balm preparations with a nanosilver concentration of 15% was 82.31%, so it can be concluded that nanosilver has good antifungal activity and is biocompatible so that nanosilver can be used as an alternative to paraben preservatives.

Traceable methods for calibrating condensation particle counters at concentrations down to 1 cm−3

The concentration of nanometer-sized particles is frequently measured in terms of particle number concentration using well-established measuring instruments, such as condensation particle counters (CPCs). Traceability for these measurements can be achieved by means of calibration against a reference aerosol electrometer starting at concentrations >1000 cm−3. Here, two independent methods for extending traceability down to 1 cm−3 are described. The first method relies on a custom-made, reference optical particle counter while the second method combines electrometer measurements with a series of dilution steps. An inter-comparison of the two methods was carried out using polystyrene spheres with a nominal diameter of 100 nm in the concentration range 1 cm−3–100 cm−3. A CPC Model 3752 (TSI Inc, USA) was used as transfer standard. The obtained results showed a deviation of 1%–4% between the two methods, which was in agreement with the stated uncertainties.

Quantitative 3D Characterization of Functionally Relevant Parameters in Heavy-Oxide-Supported 4d Metal Nanocatalysts.

Accurate 3D nanometrology of catalysts with small nanometer-sized particles of light 3d or 4d metals supported on high-atomic-number oxides is crucial for understanding their functionality. However, performing quantitative 3D electron tomography analysis on systems involving metals like Pd, Ru, or Rh supported on heavy oxides (e.g., CeO2) poses significant challenges. The low atomic number (Z) of the metal complicates discrimination, especially for very small nanoparticles (1-3 nm). Conventional reconstruction methods successful for catalysts with 5d metals (e.g., Au, Pt, or Ir) fail to detect 4d metal particles in electron tomography reconstructions, as their contrasts cannot be effectively separated from those of the underlying support crystallites. To address this complex 3D characterization challenge, we have developed a full deep learning (DL) pipeline that combines multiple neural networks, each one optimized for a specific image-processing task. In particular, single-image super-resolution (SR) techniques are used to intelligently denoise and enhance the quality of the tomographic tilt series. U-net generative adversarial network algorithms are employed for image restoration and correcting alignment-related artifacts in the tilt series. Finally, semantic segmentation, utilizing a U-net-based convolutional neural network, splits the 3D volumes into their components (metal and support). This approach enables the visualization of subnanometer-sized 4d metal particles and allows for the quantitative extraction of catalytically relevant structural information, such as particle size, sphericity, and truncation, from compressed sensing electron tomography volume reconstructions. We demonstrate the potential of this approach by characterizing nanoparticles of a metal widely used in catalysis, Pd (Z = 46), supported on CeO2, a very high density (7.22 g/cm3) oxide involving a quite high-atomic-number element, Ce (Z = 58).

J-GAIN v1.1: a flexible tool to incorporate aerosol formation rates obtained by molecular models into large-scale models

Abstract. New-particle formation from condensable gases is a common atmospheric process that has significant but uncertain effects on aerosol particle number concentrations and aerosol–cloud–climate interactions. Assessing the formation rates of nanometer-sized particles from different vapors is an active field of research within atmospheric sciences, with new data being constantly produced by molecular modeling and experimental studies. Such data can be used in large-scale climate and air quality models through parameterizations or lookup tables. Molecular cluster dynamics modeling, ideally benchmarked against measurements when available for the given precursor vapors, provides a straightforward means to calculate high-resolution formation rate data over wide ranges of atmospheric conditions. Ideally, the incorporation of such data should be easy, efficient and flexible in the sense that same tools can be conveniently applied for different data sets in which the formation rate depends on different parameters. In this work, we present a tool to generate and interpolate lookup tables of formation rates for user-defined input parameters. The table generator primarily applies cluster dynamics modeling to calculate formation rates from an input quantum chemistry data set defined by the user, but the interpolator may also be used for tables generated by other models or data sources. The interpolation routine uses a multivariate interpolation algorithm, which is applicable to different numbers of independent parameters, and gives fast and accurate results with typical interpolation errors of up to a few percent. These routines facilitate the implementation and testing of different aerosol formation rate predictions in large-scale models, allowing the straightforward inclusion of new or updated data without the need to apply separate parameterizations or routines for different data sets that involve different chemical compounds or other parameters.

Coordination complexes as substitutes for metallic powders in ceramic-matrix-composites manufactured by aqueous colloidal processing: Enhanced fracture toughness and quantitative microstructure analysis

In fabrication of metal-reinforced ceramics, metallic powders are used as one of the raw materials, however, they hinder obtaining nanometallic particles in the matrix. The use of metallic nanopowders is inefficient, because they are highly flammable and require special storage and handling conditions (cool, dry inert gas, tightly sealed). Replacing metallic powders with coordination complexes allows to obtain nanocomposites in harmless manufacturing processes. The use of coordination complex of molybdenum (molybdenyl acetylacetonate) allowed to fabricate ZrO2/Mo composites by slip casting and gelcasting. The increase in fracture toughness (ca. 25%) was observed with the little concentration of the metallic phase (up to 1.5 wt%) in a composite. It results from gaining fine metallic particles (ca. 62 nm) in the ceramic matrix. SEM analysis revealed that crack propagation is inhibited by nano-sized metallic particles according to three mechanisms: crack deflection, crack blocking by plastic deformation and interface debonding.

A Review Paper on Properties and Applications of Nanofluids

A nanofluid is a liquid that contains nanometer-sized particles. Nanofluids are obtained by dispersing nanometer-sized particles in conventional base fluids such as water, oil, ethylene glycol, etc. Nanoparticles of materials such as metallic oxides (Al2O3, CuO), nitride ceramics (AlN, SiN), carbide ceramics (SiC, TiC), metals (Cu, Ag, Au), semiconductors (TiO2, SiC), single, double or multi-walled carbon nanotubes, alloyed nanoparticles (Al70, Cu30), etc., were used to prepare the nanofluids. This paper presents a procedure for preparing Nanofluids, the properties of Nanofluids, and their applications in various fields, including energy, mechanics, and biomedicine. Then it defines the parameter that challenges the use of Nanofluids in different applications and finally suggests directions for future research on Nanofluids. The thermal conductivity of the Nanofluids is improved at a very low (< 0.1%) percentage of suspended particles. Nowadays, Nanofluids are used efficiently in non-traditional energy resources in absorbing solar energy to increase the temperature.

Electrodeposition of Carbon from CO2 in Room-Temperature Ionic Liquid Triethylpentylphosphonium Bis(trifluoromethanesulfonyl)imide

The conversion of CO2 to solid carbon by the electrochemical method is an attractive process as a CO2 recycling technology, but the electrolyte has been limited to high-temperature molten salts. In this study, the electrodeposition of solid carbon from CO2 on an Ag substrate in triethylpentylphosphonium bis(trifluoromethanesulfonyl)imide at room temperature and 1 atm CO2 atmosphere was investigated. Cyclic voltammetry with multiple cycles revealed that the three potential steps causing reduction, oxidation, and reduction current are important for the carbon electrodeposition from CO2. Based on the cyclic voltammogram, potentiostatic electrolysis was performed in the three potential steps. Consequently, the Ag substrate was covered with a black film because of the electrodeposited solid carbon. Raman spectroscopy, scanning electron microscopy, and transmission electron microscopy revealed that the deposits were composed of the electrodeposited solid carbon and nanometer-size silver particles coming from the Ag substrate. From the experimental results, we propose a model of the electrochemical formation mechanism of solid carbon from CO2 on the Ag substrate. This study shows that the electrochemical method has the potential to convert CO2 into valuable carbonaceous materials with optimized electrochemical parameters, even at room temperature, and that this technique will contribute to developing a carbon-circulation society.

(Invited) Unique Size-Dependent Electrochemistry of Metal Nanoparticles in Aqueous and Hydrogel Environments

Metal nanoparticles (NPs) exhibit unique size-dependent physical and chemical properties, providing many potential applications including sensing, catalysis, optoelectronics, medical diagnostics and disease therapeutics, among others. Here we describe interesting size-dependent metal oxidation, metal reduction, and electrocatalytic properties for Au and other metal nanoparticles that are coated with relatively weak-binding stabilizers, which is necessary for effective electron transfer at the metal NP surface. Metal oxidation potentials decrease dramatically negative with decreasing NP size, especially below 4 nm down to ~1 nm in radius. Electrocatalytic seeded-growth kinetics also depend strongly on the metal NP size (seed size). The thermodynamics of other oxidation/reduction reactions, such as galvanic replacement, also depend dramatically on metal NP size, resulting in unique alloy nanostructures with improved electrocatalytic reactivity and stability. Size-dependent electrophoretic deposition of metal nanoparticles to form thin films also results from size-dependent electrocatalytic properties, allowing metal NP separations based on electrocatalytic activity. These oxidation, reduction, galvanic replacement, and electrocatalytic properties change dramatically when the metal NPs are coated with strong ligand stabilizers or when placed in a viscous hydrogel environment. The effect of the ligand and environment will be described here. A better understanding of size-dependent reactivity of metal NPs as a function of the type of stabilizer and environment is important to realize their potential for tuning the properties to optimize them for a specific application.

Strong Metal-Support Interactions Stabilize Pt Nanocatalysts for Ceramic Fuel Cells

Nano-sized metal particles are widely used in various chemical/electrochemical fields due to their excellent catalytic activity, but they still suffer from deactivation by sintering, and this leads to serious issues regarding the price and lifespan of catalysts. In this study, we demonstrate that the introduction of nanoscale amorphous TiOx via atomic layer deposition can significantly improve the dispersion and durability of supported Pt nanocatalysts. An ultrathin TiOx layer (< 1 nm) deposited on a conductive Pr0.5Ba0.5MnO3 electrode, with a deposition time of less than 1 min, provides nucleation sites for the Pt nanocrystals impregnated thereon and promotes the migration of TiOx to the Pt surface, creating a metal-oxide interface. As a result, when applied to ceramic fuel cells, the TiOx undercoat achieves remarkable power density increases of over 100% and 400%, respectively, for wet (3% H2O) H2 and CH4 fuels without degradation at 700 °C for 120 h. These observations provide an innovative direction for the design of supported metal catalysts for high-temperature applications.

Life Testing and Redox Cycling of Ni- and Ru-Doped Strontium Iron Titanate Exsolution Fuel Electrodes in Electrolyte-Supported Solid Oxide Cells

Recently perovskite materials have gained much attention as potential candidates for solid oxide cell (SOC) fuel electrodes due to their advantages of redox stability, coking resistance and sulfur resistance over their cermet counterparts. Enhanced electrochemical performance has also been observed for some of these perovskite materials resulting from exsolution, where nano-sized metal particles are formed on the material surface under reducing conditions. However, the degradation mechanism of these perovskite fuel electrodes has yet to be fully understood and the relationship between their long-term stability and operating envrionments (fuel-cell/electrolysis, fuel compositions, redox cycles, operating pressure, etc.) has not been fully investigated.Here, life tests were conducted in open-circuit and reversible operation at 850oC on electrolyte-supported symmetric and full cells with Ni and Ru-doped strontium iron titanate (Sr0.95Ti0.3Fe0.63Ni0.07O3 and Sr0.95Ti0.03Fe0.63Ru0.07O3) as fuel electrodes (SrTi0.3Fe0.6Co0.1O3 used as the air electrode in the full cells). For both materials, higher degradation rate was observed when operated with 97% H2 + 3% H2O compared with 50% H2 + 50% H2O as fuel; an increase in ohmic resistance and gas adsorption/desorption resistance contributed to most of the degradation observed. STFN also showed higher degradation rates than STFRu in both fuel compositions. Exsolution from both compositions was confirmed by scanning electron microscopy (SEM) and scanning transmission electron microscopy (STEM) with both fuel compositions and in situ X-ray Diffraction (XRD) showed the simultaneous perovskite to Ruddlesden-Popper (RP) phase transformation. The faster perovskite-RP phase transformation is believed to be responsible for the higher degradation rates observed for cells using fuel electrode materials with less stable perovskite structure (STFN over STFRu) and tested in more reducing fuel compositions (97% H2 over 50% H2). Moreover, redox cycles were introduced for STFN and STFRu during life tests and partial performance recovery was observed; in situ XRD and SEM microstructural analysis suggests that the recovery resulted from a transformation from RP back to perovskite for both materials. Finally full cell reversible operation durability tests (6 hrs each in fuel cell and electrolysis modes at 0.8 A/cm2) conducted at 850oC with 50% H2 + 50% H2O as fuel at 1 atm showed reasonably good stability over 1000 h. Initial reversible life testing at 3 atm operating pressure showed higher degradation rates, and the possible reasons for this will be discussed.

Electrochemical Applications of Porous Materials Derived from Coal

As the world shifts from the use of coal to alternatives for electricity generation, including renewable energy, interest arises in developing alternative uses for coal. There are vast U.S. coal reserves, much of which are in historically underrepresented or economically depressed regions. This has created environmental concerns in these regions, especially related to legacy impoundments and other waste coal issues. Finding alternative uses for that coal could create new job opportunities in these regions while also addressing climate change. Currently, there are very few applications for coal outside of its traditional use for electricity production.This group has been developing alternative uses for coal, including uses in energy storage applications. This presentation will discuss the development of macroporous coal materials that then can be further processed into micron or nanometer size particles for porous materials. The characterization of these porous materials will be presented. Graphitized materials for use in lithium ion battery electrodes will be presented. Nanoscale materials such as graphene and carbon quantum dots derived from coal will be presented, along with their application in porous electrodes for batteries and capacitors.