Iridium Content Research Articles

Abu Hureyra, Syria, Part 3: Comet airbursts triggered major climate change 12,800 years ago that initiated the transition to agriculture

This study investigates the hypothesis that Earth collided with fragments of a disintegrating comet, triggering Younger Dryas climate change 12,800 years ago. This collision created environmental conditions at Abu Hureyra, Syria, that favored the earliest known continuous cultivation of domestic-type grains and legumes, along with animal management, adding to the pre-existing practice of hunting-and-gathering. The proposed airburst coincided with a significant decline in local populations and led to architectural reorganizations of the village. These events immediately followed the deposition of the Younger Dryas Boundary layer that contains peak concentrations of high-temperature meltglass, nanodiamonds, platinum, and iridium. These proxies provide evidence of a nearby low-altitude airburst by a comet-like fragment of a former Centaur, one of many <300-km-wide bodies in unstable orbits between the giant planets. This large body is proposed to have undergone cascading disintegrations, thus producing the Taurid Complex containing Comet Encke and ~90 asteroids with diameters of ~1.5 to 5 km. Here, we present substantial new quantitative evidence and interpretations supporting the hypothesis that comet fragments triggered near-global shifts in climate ~12,800 years ago, and one airburst destroyed the Abu Hureyra village. This evidence implies a causative link between extraterrestrial airbursts, environmental change, and transformative shifts in human societies.

The effect of iridium content in boron carbide-supported iridium catalyst on the activity and stability of proton exchange membrane water electrolyzer

One of the major obstacles to proton exchange membrane water electrolyzer (PEMWE) for large-scale applications is the cost of iridium for oxygen evolution reaction (OER). To resolve this issue, boron carbide-supported iridium catalysts are prepared by varying the iridium content from 10 to 60 wt%. Increasing the iridium content on the boron carbide support affects the physical properties of the catalysts and the electronic structure of iridium. At the content of 40%, Ir/B4C showed the highest catalytic activity mainly due to its high electrochemical surface area. 40%-Ir/B4C showed outstanding cell performance of 1.0 A/cm2 at 1.61 V with a loading of 0.5 mg⋅Ir/cm2 which has the same performance with 3.0 mg⋅Ir/cm2 of unsupported commercial catalyst. 40%-Ir/B4C also showed excellent durability in a half-cell as well as in a single cell. The presence of Ir (IV) and the metal-support interaction help 40%-Ir/B4C to be stable.

Lattice Strain Enhances the Activity of Ir−IrO2/C for Acidic Oxygen Evolution Reaction

AbstractLattice strain plays a critical role in regulating the electronic structure and improving the performance of catalysts. Here, Ir−IrO2/C catalysts with different iridium content are obtained by annealing Ir/C in air. The growth of IrO2 on Ir nanoparticles can form a core–shell structure and introduces strain at their interface. The local compressive strain on Ir nanoparticles is 7.2 % in the optimal Ir−IrO2/C sample with Ir content of 14.3 % (Ir−IrO2/C‐3), which regulates the adsorption energy of intermediates and improves the catalytical performance of oxygen evolution reaction (OER). The overpotential of Ir−IrO2/C‐3 at 10 mA ⋅ cm−2 is 264 mV in acidic electrolyte, 35 mV lower than that of Ir−IrO2/C with no lattice strain. Ir−IrO2/C‐3 also exhibits the highest mass activity of 1304 A ⋅ gIr−1 at 1.55 V vs. RHE, which is higher than those of commercial catalysts. Furthermore, the activity of Ir−IrO2/C‐3 can maintain 42 h with the potential increase of only 18 mV at 10 mA ⋅ cm−2, proving that the lattice strain can also effectively improve the electrochemical stability.

The role of extraterrestrial phenomena in extinction

In the several years since the Alvarez report of anomalously high iridium concentrations at the Cretaceous-Tertiary boundary, evidence for the involvement of meteorite impacts in biological extinction has increased dramatically. Much more research will be needed, however, before meteorite impact is established as a general causal factor in extinction. Of ever greater long-term interest is the possibility that other extraterrestrial forces have had important influences on the evolution of life. To recognize the effects of such forces, it will be necessary to coordinate the research of astronomy and paleontology so that testable predictions can be formulated. It is possible that known, systematic changes in the Solar System or Galaxy have had effects on global biology and that these effects have been preserved in the paleontological record.

N-Heterocyclic Carbene-Based Iridium and Ruthenium/Iridium Nanoparticles for the Hydrogen Isotope Exchange Reaction through C–H Bond Activations

Suppressing aromatic ring reduction in noble-metal-catalyzed H/D exchange reactions remains a challenge. This drawback may be overcome by finding a synergetic effect in bimetallic nanoparticles (NPs). Herein, we report the synthesis of bimetallic lipo- and water-soluble Ru/Ir NPs. They were characterized by state-of-the-art techniques such as transmission electron microscopy (TEM), high-resolution TEM, attenuated total reflection Fourier transform infrared, powder X-ray diffraction, and solid-state nuclear magnetic resonance. These NPs were found to disperse in both organic and aqueous media because of the stabilization and coordination of adequate N-heterocyclic carbene (NHC) ligands to the NP surface. They were tested in the deuteration of 2-phenylpyridine, 2-methyl-naphthylamine, 5,6,7,8-tetrahydro-naphthtylamine, and l-lysine using D2 as the isotopic source. Bimetallic NPs showed an unusual selectivity toward the H/D exchange of 2-phenylpyridine, deuterating not only the expected C–H positions close to the N atom but also remote positions on the heterocycle. Additionally, reduction of the aromatic rings, which is a common undesired side reaction catalyzed by Ru NPs, was not observed. These outcomes, rationalized by a synergetic effect of both metals, are enhanced when NHC ligands are on the surface in comparison to model catalysts stabilized by polyvinylpyrrolidone. With regard to non-aromatic substrates, CH2-α and CH2-ε positions with respect to the amino acid group of l-lysine were fully deuterated, while moderate deuteration of the γ position was observed as the iridium content was increased in the bimetallic system.

Electrochemical Properties of Ti/SnO2-Sb-Ir Electrodes Doped with a Low Iridium Content for the Oxygen Evolution Reaction in an Acidic Environment

Electrochemical Properties of Ti/SnO₂-Sb-Ir Electrodes Doped with a Low Iridium Content for the Oxygen Evolution Reaction in an Acidic Environment

714 nm emission with 12.25% efficiency from iridium complexes with low iridium content by the strategy of rigid coordination core and amplifying shell

A novel core–shell-typed Ir(iii) complex with a rigid C^N coordinated core of DBPz and an amplifying peripheral shell of tBuTPA. Its doped OLEDs exhibited a 714 nm emission with an outstanding EQE of 12.25% and a recorded radiance emittance of 45 330 mW Sr−1 m−2.

Selective determination of rhodium and iridium in the urban environment using the catalytic method

The problem of studying the level of technogenic pollution of the environment with platinum group metals is attributed first to the release of platinum metals into the environment together with the exhaust gases of cars using afterburning catalysts containing Pt, Pd, Rh. The pharmaceutical, electronics and jewelry industries the waste of which contains PGMs also contribute to the pollution of the environment. A number of studies have shown the toxic effects of PGM on humans. The goal of the study is to obtain new information about the level of technogenic pollution of the environment with platinum group metals (such as water-washings from roads, bio-collector plants, roadside dust), which necessitates developing of the method for sample preparation and determination of rhodium and iridium. A technique of sample opening and determination of rhodium and iridium in environmental objects, water-washings from roads, bio-collector plants, roadside dust is proposed. To increase the selectivity of rhodium determination, the samples were treated with a mixture of concentrated perchloric acid and sodium periodate when heated to boiling, which provided more than 5-fold increase the rhodium signal. Moreover, the permissible excess of iridium and ruthenium was increased by 5 and 20 times, respectively, due to the conversion of other PGMs into catalytically inactive forms. The indicator reaction of sulfarsazen oxidation by periodate was used in the kinetic determination of rhodium and iridium. The correctness of the results obtained by the developed method was confirmed by the ETAAS method. The determined content of Rh and Ir: in roadside waters (μg/liter) up to 0.015 and 0.005; in collector plants (g/ton) up to 0.030 Rh and 0.022; in street dust (g/ton) up to 0.05 and 0.025, respectively. The standard deviation of the repeatability of the determination results does not exceed 0.07 (Rh) and 0.12 (Ir). The developed method of opening samples and determining rhodium and iridium in environmental objects provided a great bulk of information about the content of rhodium and iridium in water-flushes from Moscow roads, bio-collector plants, roadside dust, which correlate fairly well with the scarce data from other geographic regions available in the literature and our earlier results on rhodium content in dust. The developed technique made it possible to obtain data on the level of technical pollution of the environment with PGMs in places with different traffic density in Moscow.

Tuning the hybridization state of Ir-O to improve the OER activity and stability of iridium pyrochlore via Zn doping

Developing high-active, stable, and cost-efficient electrocatalysts for oxygen evolution reaction (OER) is urgent task in water splitting. Recently, iridium pyrochlores (A2Ir2O7) have attracted broad attention as promising catalysts due to their unique electronic properties and the less iridium content relative to IrO2, while in iridium pyrochlores, the relatively high concentration of oxygen vacancies decreases the Ir-O hybridization, hindering the OER process. The electronic states of iridium-based pyrochlore M2Ir2O7 (M = Lu, Pr) are rationally tuned through partial substitution in A-site of Zn2+ for Lu3+ or Pr3+, efficiently promoting its intrinsic activity. The optimal Pr1.8Zn0.2Ir2O7 and Lu1.8Zn0.2Ir2O7 electrocatalysts exhibit 114.6 and 135.32 A gIr−1 high mass activity at 1.58 V vs. RHE. Combining X-ray absorption spectrum with DFT calculations, we demonstrate that the doping of Zn2+ reduces the defective oxygen and regulates the electron distribution. The decrease of defective oxygen leads to the O-2p band center upshift, resulting in the Ir–O covalency promotion and the decrease of the binding energy between oxygen intermediates and Ir to accelerate the OER process. This work provides a fresh idea introducing small ionic radius Zn to solve the problem of high concentration of oxygen vacancies inevitably produced in the synthesis of pyrochlores.

Investigating the Effect of Iridium Based Water Electrolysis Catalysts on the Performance and Durability of the Catalyst Layer in PEMFCs

Hydrogen-based polymer electrolyte fuel cells (PEMFCs), are becoming very popular, especially for automobile applications, given their high power density, high efficiency and zero emissions characteristics. However, they still face durability issues of the catalyst layer. Catalysts supported on carbon based materials show high electrochemically active surface area and performance [1] but are, at the same time, susceptible to carbon based degradation. To avoid carbon corrosion, it has recently become common strategy to include a water electrolysis catalyst like Ir or IrO2 to preferentially promote water electrolysis reaction since it is electrochemically more favourable than the harmful carbon corrosion reaction, thus improving the durability of the catalyst layer [2,3].In our group, a series of Ir(IrOx)-Pt/Vulcan catalysts (Fig. 1) were developed by varying Ir/Pt atomic ratio, 0.21 to 1.20. It was used on the cathode side, and the durability test simulating the stop/start cycle of FCVs was evaluated. Ir(IrOx)-Pt/Vulcan catalysts showed a slight decrease in the initial performance relative to Pt/Vulcan due to the presence of Ir, but there was a point after which a further increase in Iridium content did not noticeably affect the performance any longer. In contrast to the initial performance, post durability-test performance was expected to be higher for catalysts with higher Ir content, but our results showed the worst performance in the most Ir-rich catalyst after 10000 cycles. This was attributed to water electrolysis products trapped in small pores of the catalyst layer thereby affecting mass transport. We confirmed this by studying the various losses in each catalyst type, and found the highest concentration overvoltage in the Ir-rich catalyst. On repeating durability experiments for Ir-rich catalyst, but this time purging it with N2 gas overnight, results showed much higher performance relative to other samples for the same number of durability test cycles, supporting our hypothesis.We also consider water electrolysis catalysts on the anode side as well, since fuel starvation is commonly encountered in the anode under extreme operating conditions. Specifically, we explore Iridium-based corrosion tolerant anode catalysts and outline several strategies to reduce degradation at high humidity and loads where carbon corrosion becomes more preferable to water electrolysis. Our findings in understanding and addressing these durability issues could greatly aid in better catalyst design.

High sensitivity determination of iridium contents in ultra-basic rocks by INAA with coincidence gamma-ray detection

Very low contents (in the range of 10−9 g/g) of Ir in mantle-derived rock samples (komatiites) were non-destructively determined by INAA coupled with coincidence gamma-ray spectrometry using 16 Ge detectors. Aliquots of the same samples were analyzed by NiS fire-assay ICP-MS for Ir and other platinum group elements. Because the INAA procedure used in this study is non-destructive and is almost free from spectral interference in gamma-ray spectrometry, the INAA values of Ir contents obtained in this study can be highly reliable. Iridium values obtained by ICP-MS were consistent with the INAA values, implying that the ICP-MS values of Ir obtained in this study are equally reliable. Under the present experimental conditions, detection limits were estimated to be 1 pg/g, which corresponds to 0.1 pg for a sample mass of 0.1 g. These levels can be even lowered by an order of magnitude, if necessary, which cannot be achieved by ICP-MS carried out in this study.

Extraction and separation of iridium(IV) and rhodium(III) from hydrochloric acid media by a quaternary ammonium-based hydrophobic eutectic solvent

• Efficient extraction of critical metals by a hydrophobic eutectic solvent. • Efficient separation of iridium(IV) and rhodium(III) in hydrochloric acid media. • Mathematical modeling of the extraction mechanism. • Calculation of the fundamental extraction constants. The extraction and separation of iridium(IV) and rhodium(III) from hydrochloric acid solutions by a hydrophobic eutectic solvent composed of tetraheptylammonium chloride and decanoic acid have been studied for the first time. This eutectic solvent selectively extracts iridium(IV) over rhodium(III), the highest separation factor obtained is approximately 20. The effects of the main experimental factors (shaking time, the volume ratio of aqueous to organic phase, hydrochloric acid concentration, and the initial metal concentration in the aqueous phase) on the extraction behavior of iridium(IV) and rhodium(III) have been investigated. Ultraviolet–visible (UV–Vis) spectroscopy was applied to reveal the [IrCl 6 ] 2− complex to be a predominant species attributed to iridium(IV) extraction. To understand the underlying extraction mechanism, the initial iridium(IV) concentration in the aqueous phase has been varied and a corresponding mathematical model has been developed.

Globally distributed iridium layer preserved within the Chicxulub impact structure.

The Cretaceous-Paleogene (K-Pg) mass extinction is marked globally by elevated concentrations of iridium, emplaced by a hypervelocity impact event 66 million years ago. Here, we report new data from four independent laboratories that reveal a positive iridium anomaly within the peak-ring sequence of the Chicxulub impact structure, in drill core recovered by IODP-ICDP Expedition 364. The highest concentration of ultrafine meteoritic matter occurs in the post-impact sediments that cover the crater peak ring, just below the lowermost Danian pelagic limestone. Within years to decades after the impact event, this part of the Chicxulub impact basin returned to a relatively low-energy depositional environment, recording in unprecedented detail the recovery of life during the succeeding millennia. The iridium layer provides a key temporal horizon precisely linking Chicxulub to K-Pg boundary sections worldwide.

Highly Efficient and Selective N‐Formylation of Amines with CO2 and H2 Catalyzed by Porous Organometallic Polymers

AbstractThe valorization of carbon dioxide (CO2) to fine chemicals is one of the most promising approaches for CO2 capture and utilization. Herein we demonstrated a series of porous organometallic polymers could be employed as highly efficient and recyclable catalysts for this purpose. Synergetic effects of specific surface area, iridium content, and CO2 adsorption capability are crucial to achieve excellent selectivity and yields towards N‐formylation of diverse amines with CO2 and H2 under mild reaction conditions even at 20 ppm catalyst loading. Density functional theory calculations revealed not only a redox‐neutral catalytic pathway but also a new plausible mechanism with the incorporation of the key intermediate formic acid via a proton‐relay process. Remarkably, a record turnover number (TON=1.58×106) was achieved in the synthesis of N,N‐dimethylformamide (DMF), and the solid catalysts can be reused up to 12 runs, highlighting their practical potential in industry.

Highly Efficient and Selective N-Formylation of Amines with CO2 and H2 Catalyzed by Porous Organometallic Polymers.

The valorization of carbon dioxide (CO2 ) to fine chemicals is one of the most promising approaches for CO2 capture and utilization. Herein we demonstrated a series of porous organometallic polymers could be employed as highly efficient and recyclable catalysts for this purpose. Synergetic effects of specific surface area, iridium content, and CO2 adsorption capability are crucial to achieve excellent selectivity and yields towards N-formylation of diverse amines with CO2 and H2 under mild reaction conditions even at 20 ppm catalyst loading. Density functional theory calculations revealed not only a redox-neutral catalytic pathway but also a new plausible mechanism with the incorporation of the key intermediate formic acid via a proton-relay process. Remarkably, a record turnover number (TON=1.58×106 ) was achieved in the synthesis of N,N-dimethylformamide (DMF), and the solid catalysts can be reused up to 12 runs, highlighting their practical potential in industry.

Layered Distribution of Platinum Group Elements in Ferromanganese Nodules from the Cape Basin, Atlantic Ocean

The paper presents data on contents of the platinum group elements (Pt, Ir, Pd, and Ru) and Au in Fe–Mn nodules of different morphology and in their separate layers from the Cape Basin, Atlantic Ocean. The Layer-by-layer analysis of the Fe–Mn nodules and crusts shows that the platinum group elements (PGE) are accumulated in the ferromanganese oxyhydroxide layers relative to the clayey nuclei and the substrate of the crust. Among oxyhydroxide layers, PGE are more significantly concentrated in the hydrogenetic (sedimentation) layers of the nodules than in layers with predominant oxic and suboxic diagenetic material. Gold is demonstrated not to be accumulated in the Fe–Mn nodules. The reason for the predominant accumulation of platinum relative to palladium in nodules is the oxidative sorption on manganese oxyhydroxides suspended in seawater. An increase in the growth rate of the nodules due to the input of diagenetic material from sediments is accompanied by an increase in the Mn/Fe value in the nodules. The increase of Mn/Fe value in nodules is shown to be associated with a decrease in the Pt/Pd ratio, which indicates a dominant role of the hydrogenetic input of PGE to the nodule. The contents of iridium and ruthenium correlate with the contents of platinum and cerium.

The local atomic structure and thermoelectric properties of Ir-doped ZnO: hybrid DFT calculations and XAS experiments

We combined the hybrid density functional theory (DFT) calculations and X-ray absorption spectroscopy (XAS) experiments in the study of the local atomic structure around Ir ions in ZnO thin films with different iridium content.

Pulsed electrodeposition of iridium catalyst nanoparticles on titanium suboxide supports for application in PEM electrolysis

In this work recent progress on a novel preparation route for iridium-based electrodes applied in PEM-electrolysis cells is communicated. Substoichiometric titanium oxide (TiO2-x) particles have been synthesized to prepare a nano porous coating on top of a titanium electrode substrate. The TiO2-x-material is stabilized on the substrate by laser sintering and utilized as an electrically conductive support for iridium catalyst particles, which were deposited via electrochemical methods. The influence of the deposition current density and iridium concentration in the electrolyte were analyzed, resulting in samples with increased catalytic activity when compared to reference samples in linear sweep voltammetry.

Kinetic Oxidation Studies of Pentoxifylline by N-Chlorosuccinimide in Acidic Medium Using Iridium(III) Chloride as Inhibitor

In present study, the kinetics and mechanism of oxidation of pentoxifylline (PTX) by N-chlorosuccinimide (NCS) in acidic conditions at 40 ± 0.1 ºC is reported. The reaction depicts first-order kinetics in regard to [NCS], [PTX] and [HClO4]. The reaction rate goes on decreasing as the concentration of iridium(III) chloride is increased. This shows that iridium(III) chloride plays the role of an inhibitor in the reaction under investigation. Nil impact of [Hg(OAc)2], [NHS] and dielectric constant (D) of the medium on the rate of oxidation of pentoxifylline have been observed. This reaction has been investigated from 308-323 K and the monitored rate of reaction suggests a direct relationship between temperature and the rate of reaction. From the graph between log k and 1/T, value of activation energy (Ea) was numerated and more activation parameters like enthalpy of activation (ΔH#), entropy of activation (ΔS#) and free energy of activation (ΔG#) were calculated with the help of activation energy (Ea). On account of experimentally determined the kinetic orders and activation parameters, a most plausible reaction path has been suggested for the oxidation of pentoxifylline in presence of Ir(III) as an inhibitor.

Voltammetric determination of iridium(IV) using 5-hydroxyimino-4-imino-1,3-thiazolidin-2-one

The influence of the medium acidity on the voltammetric characteristics of the peak of hydrogen catalytic currents in iridium(IV) solutions in the presence of azolidone derivative, viz. 5-hydroxyimino-4-imino-1,3-thiazolidin-2-one was studied. It is shown that the growth of the peak of hydrogen catalytic currents in iridium(IV) solutions in the presence of 5-hydroxyimino-4-imino-1,3-thiazolidin-2-one is observed in the whole studied range of the medium acidity. The optimal conditions were established and the sensitive method for the voltammetric determination of iridium(IV) using the peak of hydrogen catalytic currents was developed (LOD = 1.7×10 -7 M) by means of 5-hydroxyimino-4-imino-1,3-thiazolidin-2-one on the background of 0.3 M sodium chloride at pH 1.00 ± 0.05 (adjusted with hydrochloric acid); scan rate was V = 1 V/s; potentials scan range was E c in . = −0.70 V, E c fin . = −1.50 V; the potential of hydrogen catalytic currents peak was E c p = −1.185 V (relatively to saturated calomel electrode). The developed technique has two intervals of analytical signal linearity, and each of them covers one concentration order (0.3–2.0)×10 -6 M and (0.2–2.0)×10 -5 M. Significant concentration excess of ions of concomitant metals do not interfere the voltammetric determination of iridium(IV), except for the commensurate amounts of Rh(III), Pd(II) and Os(IV); but Ru(IV) and Pt(IV) ions interfere the determination. The significant interfering effect of ions of almost all platinum group elements does not allow us to recommend the developed method for the determination of iridium in samples of natural origin (e.g. rocks, ores, minerals). Instead, the developed technique can be recommended for the analytical control of iridium content in various industrial samples, where it is at the level of microquantities in the absence of other platinum group metals (spark plugs, balls in ballpoint pens, etc.). Keywords: iridium, voltammetric determination, azolidone, oxime.