NiFe Research Articles

Spectral properties of ablating meteorite samples for improved meteoroid composition diagnostics

Emission spectra and diagnostic spectral features of a diverse range of ablated meteorite samples with a known composition are presented. We aim to provide a reference spectral dataset to improve our abilities to classify meteoroid composition types from meteor spectra observations. The data were obtained by ablating meteorite samples in high-enthalpy plasma wind tunnel facilities recreating conditions characteristic of low-speed meteors. Near-UV to visible-range (320–800 nm) emission spectra of 22 diverse meteorites captured by a high-resolution Echelle spectrometer were analyzed to identify the characteristic spectral features of individual meteorite groups. The same dataset captured by a lower-resolution meteor spectrograph was applied to compare the meteorite data with meteor spectra observations. Spectral modeling revealed that the emitting meteorite plasma was characterized by temperatures of 3700–4800 K, similar to the main temperature component of meteors. The studied line intensity variations were found to trace the differences in the original meteorite composition and thus can be used to constrain the individual meteorite classes. We demonstrate that meteorite composition types, including ordinary chondrites, carbonaceous chondrites, various achondrites, stony-iron and iron meteorites, can be spectrally distinguished by measuring relative line intensities of Mg I, Fe I, Na I, Cr I, Mn I, Si I, H I, CN, Ni I, and Li I. Additionally, we confirm the effect of the incomplete evaporation of refractory elements Al, Ti, and Ca, and the presence of minor species Co I, Cu I, and V I.

In situ synthesis of FeNi3/(Fe,Ni)9S8/Ni4S3/C nanorods and enhancement of oxygen evolution reaction properties

NiFe-based nanomaterials have emerged as highly promising catalysts to replace platinum, ruthenium and iridium for oxygen evolution reaction (OER), in “green hydrogen” production process through water splitting. Using iron (2+) sulfate and nickel acetate as the raw materials, with the molar ratio of Ni acetate to iron (2+) sulfate controlled at 8:5, the concentration of metal-ion was 0.6 mol/L, and precursor fibers rich in Ni2+, Fe2+, and SO4 2− were prepared using electrospinning technology, with polyvinyl alcohol acting as the colloid. Subsequently, composite nanorods rich in the elements of Ni, Fe, S, and C were successfully obtained at a heat treatment temperature of 1000°C in an Ar gas atmosphere. The results demonstrate that the nanorod samples possessed a surface diameter of ~200 nm, and the main phases of the nanorods after heat treatment at 1000°C included FeNi3 alloy, (Fe,Ni)9S8, Ni4S3, and amorphous C. Electrochemical performance tests conducted in a 1.0 mol/L KOH solution exhibited excellent oxygen evolution reaction properties of the catalysts prepared using FeNi3/(Fe,Ni)9S8/Ni4S3/C nanorods as the materials. The overpotential was about 258.6 mV of the catalyst material at 10 mAcm−2.

First widespread occurrence of rare phosphate chladniite in a meteorite, winonaite Graves Nunataks (GRA) 12510: Implications for phosphide–phosphate redox buffered genesis in meteorites

Abstract The first widespread occurrence of rare Na-, Ca-, and Mg, Mn, Fe-bearing phosphate chladniite was observed in meteorite Graves Nunataks (GRA) 12510, which is a primitive achondrite that sits within the winonaite class. Numerous 1–500 µm chladniite grains were found, often on the margins between silicate clasts and the kamacite portions of the large metal veins that permeated through the sample. The largest chladniite grains are associated with merrillite, kamacite, taenite, troilite, albite, forsterite, diopside, and enstatite, with a few tiny chladniite grains and an apatite grain enclosed within merrillite. GRA 12510s average chladniite composition is Na2.7Ca1.25(Mg10.02Mn0.69Fe0.20)Σ10.91(PO4)9. Electron backscattered diffraction (EBSD) patterns indicate varying degrees of nucleation and growth of chladniite grains. Additionally, the first pure Raman spectrum of chladniite is described here, revealing primary ν1 bands at 954, 974, and especially 984 cm–1. The co-occurrence and close association of merrillite, apatite, chladniite, and P-bearing metallic phases within GRA 12510 suggests that the fO2 of IW-2 to IW-4 is an intrinsic property of the precursor chondritic material, and the phosphate-phosphide reaction may have buffered the final winonaite and IAB iron meteorite phase assemblages. Altogether, chladniite appears to form alongside other phosphates, with their chemistries reflecting the diverse environment of their formation. Meteoritic chladniite likely formed through subsolidus oxidation of schreibersite, scavenging Na from albite, Ca from diopside, Mg from enstatite/forsterite, Fe from kamacite/taenite, and Mn from alabandite/chromite when available. A P0-P5+ redox-buffered environment also has implications for thermometry and fast cooling rates, although more experiments are needed to extrapolate powder reaction rates to those of larger crystals. Furthermore, phosphide-phosphate buffered experiments may aid in investigating equilibrium chemistry at fO2 values between IW-2 and IW-4, which have been challenging to explore experimentally due to the limited availability of solid metal-metal oxide buffers between IW (Fe-FeO) and IW-5 (Cr-Cr2O3) at temperatures and pressures relevant to planetary interiors. Future investigations of phosphide-phosphate redox-buffered genesis at fO2 values between IW-2 and IW-4 have important implications for primitive meteorite constituents (e.g., CAI values), partially differentiated planetesimals and planets, including Mercury and core formation on Earth.

Quantification of evaporative loss of volatile metals from planetary cores and metal-rich planetesimals

The processes responsible for the isotopic compositions and abundances of volatile elements in the early solar system remain highly debated. Orders of magnitude variation of (highly) volatile elements exist between different magmatic iron meteorite groups, but it is unclear to what extent their depletions can be explained by evaporation from metal melts during parent body accretion and/or subsequent break up. To this end, we present 86 new evaporation experiments with the aim of constraining the volatility of most volatile metals from metallic melts. The results confirm the previously proposed important effects of S in metal melt on the volatility of the elements of interest governed by their S-loving or S-phobic behavior. Nominally S-loving elements In, Sn, Te, Pb and Bi are significantly more volatile in Fe melt relative to FeS liquid, whereas nominally S-avoiding elements Ga and Sb are more volatile in FeS liquid relative to Fe melt, at a given pressure and temperature. The newly derived volatility sequences for S-free/poor and S-rich metallic melts were also compared with commonly used volatility models based on condensation temperatures. The results indicate significant differences between the latter, including the much more volatile behavior of Te, relative to Se, in both explored bulk compositions, which are traditionally assumed to be equally volatile. The (minimum) degree of volatile element depletion due to evaporation was quantified using the new experimental results and models. A comparison between the volatile element depletions in magmatic iron meteorites and the predicted depletions appropriate for evaporation from Fe melts shows that the latter depletions can be easily reconciled with (an) evaporation event(s). Altogether, the new data and models will provide an important framework when more accurate and precise estimates of magmatic iron meteorite bulk volatile element contents are available.

Nickel single-atom synergistic iron-nitrogen sites for efficient CO2 electroreduction at a wide potential range

Recently, diatomic site catalysts (DASCs) by introducing a second metal active site have become a research focus in electrochemical CO2 reduction reaction (eCO2RR), as can regulate electronic structure of metal centers and optimize reaction free energies. However, hitherto the studies on the origin of the outstanding performance of DASCs and the accurate identification of active centers are not still clear. Herein, we designed a nickel–iron diatomic site catalyst by loading highly dispersed iron phthalocyanine (FePc) on a nickel single-atom with ultrathin porous nitrogen-doped carbon nanosheet substrate (denoted as FePc/M-LNi-NC). Experimental and calculational results prove that the synergistic catalysis of FePc and carbon nanosheet based Ni single-atom endowed FePc/M-LNi-NC achieving excellent CO2 reduction performance with a maximum CO Faradaic efficiency of 98.8 % at –0.8 V vs. RHE. In particular, the current density of FePc/M-LNi-NC at −1.0 V vs. RHE in an H-type cell (−20.9 mA/cm2) is 5.6 times that of FePc (3.7 mA/cm2). Compared with M-LNi-NC, the potential range of FePc/M-LNi-NC when FECO above 95 % expands from 0.31 to 0.43 V. Density functional theory calculations reveal that the Fe site in FePc/M-LNi-NC has a lower free energy change for *COOH formation (ΔG*COOH) and CO desorption (ΔGCO) than Ni site, thus exhibits higher electrocatalytic activity. Furthermore, the ΔG*COOH on FePc/M-LNi-NC declines from 0.78 to 0.08 eV compared to M-LNi-NC, and the ΔGCO lowers from 1.36 to 0.33 eV compared to FePc, thus FePc/M-LNi-NC achieves high performance for eCO2RR at a wide potential range.

Iron-promoted rapid self-reconstruction of nickel-based catalysts for efficient oxygen evolution

High-performance oxygen evolution reaction (OER) catalyst is critical for improving the water splitting efficiency. In this work, an efficient self-supported OER catalyst was prepared by electrodeposition of nickel–iron layered double hydroxide nanosheets on titanium mesh substrate (NiFe-LDH/Ti-mesh). This self-supporting design exposes abundant active sites. At 100 mA cm−2, the NiFe-LDH/Ti-mesh shows a low overpotential of 310 mV in 1.0 M KOH. When assembled into an anion exchange membrane water electrolyzer, it can run stably over 200 h. In-situ Raman reveals that the NiFe-LDH/Ti-mesh surface was reconstructed into NiFeOOH active species. In-situ infrared shows that the introduction of Fe promotes the evolution of oxygen intermediates. Theoretical calculations reveal a weakened binding strength of *OH and accelerated formation of *O in OER by the introduction of Fe. This study provides a facile approach for developing self-supported high-performance OER electrocatalyst, and advances the understanding on the origin of NiFe-based catalysts as well.

Surface Modification of Chromium–Nickel Steel by Electrolytic Plasma Nitriding Method

Electrolytic plasma nitriding is an attractive chemical heat treatment used to improve the surface properties of steel by implementing nitrogen saturation. This method is widely applied to steel and iron-based alloys operating under various operating conditions. In this work, using liquid-phase plasma nitriding technology, a nitrided layer was obtained on the surface of 40CrNi steel in electrolytes of different concentrations. The microstructure and phase composition of the nitrided layer were investigated and analyzed using scanning electron microscopy (SEM) and X-ray diffraction (XRD), and we performed Vickers hardness and wear resistance tests using the ball-on-disc method. The microhardness and wear resistance of nitrided 40CrNi steel were significantly improved due to the lubricating properties of the ε-Fe2N phase formed on its surface.

Microstructures of iron meteorites

Abstract Meteorites originate from the early phase of our solar system and are wonderfully undefined and inhomogeneous. In terms of its composition and microstructure, one single meteorite has quite a few surprises in store. The iron meteorite microstructure depends essentially on the initial solidification of the melt in a larger asteroid or minor planet. The solidification process itself is a function of local element concentrations and the very slow cooling rate. Various collisions in space resulted in the fragmentation of the asteroids and the deformation of the microstructure. However, whether visible microstructural changes occur or not depends on the microstructure itself. And finally, corrosion may also occur in the Earth’s atmosphere. An attempt is made to explain the different microstructures on the example of three iron meteorites, namely those found in Canyon Diablo, Gebel Kamil, and Dronino.

Fe2O3/γ-Al2O3 and NiO/γ-Al2O3 catalysts for the selective catalytic oxidation of ammonia

Ammonia, a significant atmospheric pollutant, requires effective emission control due to its inherent toxicity and the generation of secondary pollutants like particulate matter. This control can be achieved through various methods, including catalytic processes. Therefore, our study focuses on evaluating the potential of catalysts based on iron oxide and nickel oxide supported on γ–Al2O3 for the selective catalytic oxidation of NH3 to N2 (NH3-SCO). The γ–Al2O3 was obtained by thermal decomposition of aluminum hydroxide, and 5 or 10 wt% of Fe or Ni was added through wetness incipient impregnation. XRD diffractograms confirmed the formation of the γ–Al2O3 phase. XRD, H2-TPR, and UV–vis DRS data showed the presence of Fe2O3, NiO, and NiAl2O4 in the catalysts. Introducing metal oxides onto the support led to a drop in the specific area, pore size, pore volume, and NH3 desorption, which was higher for the catalysts containing Fe. The catalysts were active in NH3-SCO, and the insertion of Fe or Ni was essential because it promoted a significant increase in the NH3 conversion (∼75 % Fe and ∼55 % Ni), compared to pure support (∼8 %), mainly from 400 °C. However, doubling the metal content has not resulted in a considerable increase in NH3 conversion. The N2 selectivity was higher for the catalysts containing Ni (∼85 %) from 400 °C compared to catalysts containing Fe (∼76 %). Such behavior was due to the larger surface area of the Ni-containing catalysts. Despite that, the 5Fe/γ–Al2O3 catalyst emerged as the most effective option for NH3-SCO applications, combining higher NH3 conversion and good N2 selectivity.

Recent Advances in the Compositional and Mapping Analysis of Iron Meteorites Using a Handheld Laser‐Induced Breakdown Spectroscopy Instrument

Analytical techniques are essential in investigating the unique features of extra‐terrestrial geomaterials, and the use of in situ analytical tools is becoming increasingly common, as it facilitates a quick initial bulk chemical analysis, identification and classification. In this work, a handheld laser‐induced breakdown spectroscopy (hLIBS) instrument has been used to identify the qualitative and quantitative composition, and generate compositional micro‐maps, of a suite of iron meteorite samples representative of the different chemical and structural classes by analysing the spectra released from the plasma formed by the laser impact. Furthermore, the analytical performance of hLIBS was compared with that of portable X‐ray fluorescence spectrometry (pXRF). The analytical precision and accuracy of the calibration curves previously built in the laboratory for a set of certified reference metal alloys was assessed, so that the same protocol could be used to measure those of the investigated iron meteorites. A good agreement was achieved between hLIBS and reference data in the quantitative estimate of the elements Fe, Ni, Co and Cu. An attempt to quantify Ga by LIBS in two classified iron meteorites was also successful.

Engineering Robust Triazine Crosslinked and Pyridine Capped Anion Exchange Membrane for Advanced Water Electrolysis.

Exploring high-performance anion exchange membranes (AEM) for water electrolyzers (AEMWEs) is significant for green hydrogen production. However, the current AEMWEs are restricted by the poor mechanical strength and low OH- conductivity of AEMs, leading to the low working stability and low current density. Here, we develop a robust AEM with polybiphenylpiperidium network by combining the crosslinking with triazine and the capping with pyridine for advanced AEMWEs. The AEM exhibits an excellent mechanical strength (79.4 MPa), low swelling ratio (19.2 %), persistent alkali stability (» 5,000 hours) and high OH- conductivity (247.2 mS cm-1) which achieves the state-of-the-art AEMs. Importantly, when applied in AEMWEs, the corresponding electrolyzer equipped with commercial nickel iron and nickel molybdenum catalysts obtained a current density of up to 3.0 A cm-2 at 2 Vand could be stably operated ~430 h at a high current density of 1.6 A cm-2, which exceeds the most of AEMWEs. Our results suggest that triazine crosslinking and pyridine capping can effectively improve the overall performance of the AEMWEs.

Engineering Robust Triazine Crosslinked and Pyridine Capped Anion Exchange Membrane for Advanced Water Electrolysis

Exploring high‐performance anion exchange membranes (AEM) for water electrolyzers (AEMWEs) is significant for green hydrogen production. However, the current AEMWEs are restricted by the poor mechanical strength and low OH‐ conductivity of AEMs, leading to the low working stability and low current density. Here, we develop a robust AEM with polybiphenylpiperidium network by combining the crosslinking with triazine and the capping with pyridine for advanced AEMWEs. The AEM exhibits an excellent mechanical strength (79.4 MPa), low swelling ratio (19.2 %), persistent alkali stability (» 5,000 hours) and high OH‐ conductivity (247.2 mS cm‐1) which achieves the state‐of‐the‐art AEMs. Importantly, when applied in AEMWEs, the corresponding electrolyzer equipped with commercial nickel iron and nickel molybdenum catalysts obtained a current density of up to 3.0 A cm‐2 at 2 V and could be stably operated ~430 h at a high current density of 1.6 A cm‐2, which exceeds the most of AEMWEs. Our results suggest that triazine crosslinking and pyridine capping can effectively improve the overall performance of the AEMWEs.

Preparation of high quality carbon nanotubes by catalytic pyrolysis of waste plastics using FeNi-based catalyst

Plastic waste pollution is the serious environmental problem, and catalytic pyrolysis of waste plastics is an effective way to solve this problem. Carbon nanotubes (CNTs) are prepared by catalytic pyrolysis of low-density polyethylene (LDPE) waste plastics by one-stage method using iron nitrate and nickel nitrate as catalyst. The growth mechanism of CNTs is analyzed in detail. TPO, XRD, SEM and Raman analyses show that increasing Ni content contributes to the production of CNTs with good morphology and high graphitization degree. While the increasing Fe content contributes to improving the yield of CNTs. The outer and inner diameters of the FeNi12-CNTs-800 are about 21 nm and 8 nm with the length of 18.9 μm, respectively. LDPE pyrolysis gases are analyzed to determine that the primary carbon source required for CNTs growth is C2H4. The C2H4 adsorption and decomposition processes on FeNi alloys are performed to reveal the growth mechanism of CNTs, based on density functional theory calculation. Three kinds of the growth models are proposed to explain the difference of the CNTs tubular shape. FeNi12-CNTs-800 are used to remove microplastics from wastewater due to existence of magnetic. PVC can be quickly removed from wastewater with removal of 100 % at 20 min. This study provides an effective way for recycling and treatment of waste plastic.

Polypyrrole as photo-thermal-assisted modifier for BiVO4 photoanode enables high-performance photoelectrochemical water splitting

Herein, iron nickel oxide (FeNiOx) and conductive polymer polypyrrole (PPy) with excellent hole transport property and catalytic oxidation ability combine with bismuth vanadate (BiVO4) based photoanode to obtain a remarkable improvement of photocurrent density. More importantly, due to the photo-thermal effect of PPy, the operating temperature of the photoanode reaches 323.15 K under AM 1.5G illumination without infrared light source, thus activating the photoanode surface and accelerating the water splitting reaction. As a result, when the temperature of electrolyte reaches 323.15 K, the photocurrent density of BiVO4/FeNiOx/PPy photoanode achieves 6.91 mA cm−2 at 1.23 V versus reversible hydrogen electrode (vs. RHE), which is 3.04 folds of pristine BiVO4 (2.27 mA cm−2). Such a photo-thermal-assisted enhancement strategy based on the temperature sensitivity of BiVO4 provides a new way for the breakthrough of the performance bottleneck of BiVO4 photoanode and the design of the next generation PEC catalyst materials.

Electrochemical reconfiguration of iron-modified Ni3S2 surface induced oxygen vacancies to immobilize sulfate for enhanced oxygen evolution reaction

There is an urgent need for highly active, durable, and low-cost electrocatalysts to overcome the shortcomings of high overpotential in the oxygen evolution reaction (OER) process. In this work, the nickel–iron hydroxysulfate rich in sulfate and oxygen vacancies (SO42−@Fe-NiOOH-Ov/NiS) is legitimately constructed. SO42−@Fe-NiOOH-Ov/NiS only requires a low overpotentials of 190 mV and 232 mV at 10 mA cm−2 and 100 mA cm−2 current densities in 1 M KOH, with excellent stability for 200 h at 100 mA cm−2 current density. In situ Raman spectroscopy and Fourier transform infrared spectroscopy demonstrated the stable adsorption of more SO42− on the surface of catalyst. Density functional theory calculations testify surface reconstruction, doped Fe and oxygen vacancies significantly reduced the adsorption energy of sulfate on the surface. More importantly, the formation of *OOH to O2 is facilitated by the highly hydrogen bonding between SO42− and *OOH, accelerating the OER process.

Rotating Disk Slurry Electrodeposition of Trimetallic Nickel-Cobalt-Iron Nanoparticles Electrocatalyst on Vulcan Xc-72R for the Oxygen Reduction Reaction in Alkaline Media

Although platinum and platinum group metals (PGMs) catalysts are the most efficient for oxygen reduction reaction, the cost and scarcity of the metals are the reason to look for alternative electrocatalysts. Transition metals, such as cobalt, iron, and nickel, have shown promise as an alternative catalyst to oxygen reduction reactions (ORR). In this work, we electrochemically synthesized nickel-cobalt-iron trimetallic alloy nanoparticles dispersed on carbon Vulcan using Rotating Disk Slurry Electrodeposition (RoDSE). This technique is an energy-efficient green method to synthesize well-dispersed catalysts on carbon and oxide supports for various applications including the oxygen reduction reaction (ORR) for fuel cell applications. Cobalt-nickel iron nanoparticles have been well dispersed in 20 mg carbon Vulcan XC-72R using a negative potential (-1.05V vs Ag/AgCl-sat KCl) in a saturated Argon environment. The electrodeposition potential was obtained from cyclic voltammetry analysis of the metal salts in 0.1m KClO4 solution with an electrochemically cleaned glassy carbon electrode. The starting material precursors were iron chloride, nickel acetate, and cobalt acetate in 0.1 M KClO4 aqueous solution. A 500 micromolar metal salt solution aliquot was added for the electrodeposition every 20 minutes, with a total of 12 aliquots.Compared with commercially available 20% Pt/Vulcan, the synthesized catalyst shows comparable mass activity and durability with an onset potential of 0.78V vs RHE(@0.01mA/cm2), limiting current density of 5.56mA/cm2 and half wave potential of 0.66V vs RHE.The X-ray diffraction (XRD) studies and transmission electron microscopy showed that trimetallic nanoparticles are formed and deposited on the carbon Vulcan support. Moreover, scanning electron microscopy, X-ray fluorescence studies, and transmission emission microscopy show the presence of trimetallic nanoparticles. The RDE and RRDE studies show that the synthesized material is active and may lead to a good and inexpensive catalyst for ORR.

Electrolyte-Induced Fe-Doping of LaNiO3 Model Surfaces for Water Electrolysis

Renewable energy needs to be store in different energy forms for the energy transition away from fossil fuels. One of most promising forms is chemicals such as H2 and C-based fuels obtained via electrochemical reactions. The common hinderance in such reactions is the sluggish oxygen evolution reaction (OER), which causes low energy efficiency in conversion devices. Developing highly active, earth-abundant OER electrocatalysts in alkaline media is necessary to boost the performance of such devices. Fe ion content in electrolyte is known to influence the OER-activity of metal oxide electrocatalysts. For example, the Fe incorporation in NiOOH is a well-established and important effect for OER.[1] Here, we present the effect of absorbed Fe on the OER activity of the epitaxial Ni-surface terminated LaNiO3 thin films. The correlation between surface species and OER activity of electrocatalysts was investigated using surface-sensitive low-energy ion scattering and X-ray photoemission spectroscopies. We observe more than an order-of-magnitude boost in OER activity during initial cycling, from 0.15 mAcm-2 to 3.40 mAcm-2 at 1.60 V vs. reversible hydrogen electrode. The activity increase was mainly caused by the incorporation of up to 5 % Fe at the top surface of LaNiO3 film (less than ~1 nm) even though only a very trace amount of Fe ion, 30 ppb, is present in the 0.1 M electrolyte of high purity KOH 99.99 %. Our results demonstrate that the disordered active surface phase, which develops even on single crystalline surfaces, is a complex interplay between the as-prepared (surface) crystalline structure, composition of the solid electrocatalyst and the liquid electrolyte, and has strong impact on the final OER activity, implying that we need to think differently about the crystalline electrocatalysts: crystalline bulk and dynamically changing surface layer.[1] L. Trotochaud, S.L. Young, J.K. Ranney, S.W. Boettcher, Nickel–Iron Oxyhydroxide Oxygen-Evolution Electrocatalysts: The Role of Intentional and Incidental Iron Incorporation, J. Am. Chem. Soc. 136 (2014) 6744–6753.

Encapsulating Nickel-Iron Alloy Nanoparticles in a Polysilazane-Derived Microporous Si-C-O-N-Based Support to Stimulate Superior OER Activity.

The in situ confinement of nickel (Ni)-iron (Fe) nanoparticles (NPs) in a polymer-derived microporous silicon carboxynitride (Si-C-O-N)-based support is investigated to stimulate superior oxygen evolution reaction (OER) activity in an alkaline media. Firstly, we consider a commercial polysilazane (PSZ) and Ni and Fe chlorides to be mixed in N,N-dimethylformamide (DMF) and deliverafter overnight solvent reflux a series of Ni-Fe : organosilicon coordination polymers. The latter are then heat-treated at 500 °C in flowing argon to form the title compounds. By considering a Ni : Fe ratio of 1.5, face centred cubic (fcc) NixFey alloy NPs with a size of 15-30 nm are in situ generated in a porous Si-C-O-N-based matrixdisplaying a specific surface area (SSA) as high as 237 m2 ⋅ g-1. Hence, encapsulated NPs are rendered accessible to promote electrocatalytic water oxidation. An OER overpotential as low as 315 mV at 10 mA ⋅ cm-2 is measured. This high catalytic performance (considering that the metal mass loading is as low as 0.24 mg cm-2) is rather stable as observed after an activation step; thus, validating our synthesis approach. This is clearly attributed to both the strong NP-matrix interaction and the confinement effect of the matrix as highlighted through post mortem microscopy observations.

Characterization of Particulate Emissions From Thermal Runaway of Lithium-Ion Cells

Abstract Over the past decade, there has been a significant acceleration in the adoption of lithium-ion (Li-ion) batteries for various applications, ranging from portable electronics to automotive, defense, and aerospace applications. Lithium-ion batteries are the most used energy storage technologies due to their high energy densities and capacities. However, this battery technology is a potential safety hazard under off-nominal conditions, which may result in thermal runaway events. Such events can release toxic gaseous and particulate emissions, posing a severe risk to human health and the environment. Particulate emissions from the failure of two different cell chemistries—lithium iron phosphate (LFP) and nickel manganese cobalt oxide (NMC)—were studied. Experiments were conducted at multiple states of charge (SOC), and three repeats were performed at each SOC for each cell chemistry to examine the repeatability/variability of these events. Particulate emissions were characterized in terms of particulate matter mass (PM2.5), black carbon, and particle number (PN)/size. Failure of a single cell led to a significant release of particulate emissions, with peak emission levels being higher at the higher SOCs. A high level of variability was observed for a specific SOC for LFP cells, while NMCs exhibited relatively less variability. In general, much higher particulate emissions were observed for NMCs compared to LFPs at each SOC. For NMCs at 100% SOC, peak PN levels were ∼2.5 × 10+09 particles/cc (part/cc), and black carbon levels were ∼60 mg/m3. For LFPs at 100% SOC, peak PN levels were ∼9.0 × 10+08 part/cc, and black carbon levels were 2.5 mg/m3.

Fatigue Crack Propagation Across the Multiple Length Scales of Technically Relevant Metallic Materials

The fundamentals of our understanding of fatigue crack propagation were formed more than 60 years ago by Paul C. Paris. Since then, the run toward new metallic materials and alloys with ever finer-grained microstructures has had a large impact on research. Along with enormous variation of the microstructural length scales (i.e., grain size), the essential parameters for the description of fatigue crack growth, such as the crack propagation rate and plastic zone size, also exhibit an immense change from the subnanometer to the micrometer regime. These enormous variations in the fatigue crack growth behavior's controlling parameters motivate this contribution. This article presents an overview of the effect of grain size, from the millimeter to the nanometer grain-size regime, on fatigue crack propagation of mainly ductile metals and alloys with an attempt to summarize the most important findings and underlying physical phenomena, including with respect to selected materials such as pure iron, nickel, and austenitic and pearlitic steel.