Ir Nanoparticles Research Articles

Photodeposited IrO2 on TiO2 support as a catalyst for oxygen evolution reaction

A simple, alternative, catalyst preparation method was proposed in order to combine the properties of photoactive and stable TiO2 with state-of-the art of IrO2 for the oxygen evolution reaction (OER). IrO2 nanoparticles were obtained in the process of photodeposition on the surface of TiO2 powder by UV illumination from appropriate Ir salt aqueous solution. Physicochemical characterization of the resulting IrO2/TiO2 composite, containing 25% w/w Ir, was carried out by transmission electron microscopy (TEM), energy-dispersive spectrometry (EDS), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The electrochemical behaviour of the prepared IrO2/TiO2 catalyst was compared with that of commercial unsupported IrO2. Cyclic voltammetry (CV), linear sweep voltammetry (LSV) and chronoamperometry (CA) were performed to identify the surface electrochemistry and OER of the IrO2/TiO2 catalyst. Electrochemical impedance spectroscopy (EIS) was used to determine uncompensated and charge transfer resistance. CA experiments were carried out in order to evaluate the stability of the IrO2/TiO2 composite during OER in the dark and under UV light irradiation. The photodeposition method on a TiO2 support resulted in 1–2 nm Ir nanoparticles, very well dispersed on the surface and in their oxidized state (IrO2). Electrochemical results indicated that despite its lower conductivity, the IrO2/TiO2 composite exhibits comparable intrinsic electrocatalytic activity for OER with that of the commercial IrO2 catalyst. It was found that under UV light irradiation there has been improvement of the stability of the IrO2/TiO2 performance during oxygen evolution (presumably due to sustained activation of reactive species via photogenerated holes or OH radicals) as well as current enhancement (due to the interaction between the photogenerated holes in TiO2 support and IrO2 nanoparticles). These would be beneficial effects in prolonged water photo-electrolysis.

Kinetic Synergy between Supported Ir Single Atoms and Nanoparticles during CO Oxidation Light-Off

Kinetic Synergy between Supported Ir Single Atoms and Nanoparticles during CO Oxidation Light-Off

Support Induced Effects on the Ir Nanoparticles Activity, Selectivity and Stability Performance under CO2 Reforming of Methane.

The production of syngas (H2 and CO)—a key building block for the manufacture of liquid energy carriers, ammonia and hydrogen—through the dry (CO2−) reforming of methane (DRM) continues to gain attention in heterogeneous catalysis, renewable energy technologies and sustainable economy. Here we report on the effects of the metal oxide support (γ-Al2O3, alumina-ceria-zirconia (ACZ) and ceria-zirconia (CZ)) on the low-temperature (ca. 500–750 °C) DRM activity, selectivity, resistance against carbon deposition and iridium nanoparticles sintering under oxidative thermal aging. A variety of characterization techniques were implemented to provide insight into the factors that determine iridium intrinsic DRM kinetics and stability, including metal-support interactions and physicochemical properties of materials. All Ir/γ-Al2O3, Ir/ACZ and Ir/CZ catalysts have stable DRM performance with time-on-stream, although supports with high oxygen storage capacity (ACZ and CZ) promoted CO2 conversion, yielding CO-enriched syngas. CZ-based supports endow Ir exceptional anti-sintering characteristics. The amount of carbon deposition was small in all catalysts, however decreasing as Ir/γ-Al2O3 > Ir/ACZ > Ir/CZ. The experimental findings are consistent with a bifunctional reaction mechanism involving participation of oxygen vacancies on the support’s surface in CO2 activation and carbon removal, and overall suggest that CZ-supported Ir nanoparticles are promising catalysts for low-temperature dry reforming of methane (LT-DRM).

Sacrificial Cu Layer Mediated the Formation of an Active and Stable Supported Iridium Oxygen Evolution Reaction Electrocatalyst.

The production of hydrogen via a proton-exchange membrane water electrolyzer (PEM-WE) is directly dependent on the rational design of electrocatalysts for the anodic oxygen evolution reaction (OER), which is the bottleneck of the process. Here, we present a smart design strategy for enhancing Ir utilization and stabilization. We showcase it on a catalyst, where Ir nanoparticles are efficiently anchored on a conductive support titanium oxynitride (TiONx) dispersed over carbon-based Ketjen Black and covered by a thin layer of copper (Ir/CuTiONx/C), which gets removed in the preconditioning step. Electrochemical OER activity, stability, and structural changes were compared to the Ir-based catalyst, where Ir nanoparticles without Cu are deposited on the same support (Ir/TiONx/C). To study the effect of the sacrificial less-noble metal layer on the catalytic performance of the synthesized material, characterization methods, namely X-ray powder diffraction, X-ray photoemission spectroscopy, and identical location transmission electron microscopy were employed and complemented with scanning flow cell coupled to an inductively coupled plasma mass spectrometer, which allowed studying the online dissolution during the catalytic reaction. Utilization of these advanced methods revealed that the sacrificial Cu layer positively affects both Ir OER mass activity and its durability, which was assessed via S-number, a recently reported stability metric. Improved activity of Cu analogue was ascribed to the higher surface area of smaller Ir nanoparticles, which are better stabilized through a strong metal–support interaction (SMSI) effect.

Electronic properties of Ir3Li and ultra-nanocrystalline lithium superoxide formation

Current lithium-oxygen (Li-O2) batteries suffer from large charge overpotentials related to electronic resistivity of the insulating lithium peroxide (Li2O2) discharge product. One potential solution to this challenge is the stabilization of the lithium superoxide (LiO2) discharge intermediate, which has much higher electronic conductivity compared to Li2O2. Cathodes based on small iridium (Ir) nanoparticles have been recently used in a Li-O2 battery to successfully stabilize the LiO2 product, however, the LiO2 had a short lifetime. In the previous study, researchers found that the LiO2 was stabilized on Ir3Li surfaces which were formed from Ir nanoparticles during battery operation. Little is known about the electronic properties of Ir3Li and its role in stabilizing LiO2 product formation. This work provides the first study of the electronic properties of Ir3Li, which was thermally synthesized in bulk prior to implementation on the reduced graphene oxide (rGO) cathode of a Li-O2 cell. The bulk Ir3Li was found to have comparable electrical conductivity to Ir metal, possess metal-like magnetic properties, and has an affinity towards O2 adsorption. The LiO2 discharge product formed from the Li-O2 battery discharge was characterized using Raman spectroscopy, titration, along with a comprehensive transmission electron microscopy (TEM) study. This analysis revealed the formation of ultra-nanocrystalline LiO2 particles greater than 200 nm. This result was attributed to the use of large micron sized Ir3Li particles, which could stabilize larger LiO2 particles compared to previous cathodes that utilized Ir nanoparticles that partially converted to Ir3Li during cycling. These results demonstrate that cathode properties can be modified to stabilize the bulk LiO2 discharge product, which can be useful for the further development of LiO2-based Li-O2 batteries.

Enhancing Iridium Nanoparticles’ Oxygen Evolution Reaction Activity and Stability by Adjusting the Coverage of Titanium Oxynitride Flakes on Reduced Graphene Oxide Nanoribbons’ Support

AbstractHydrogen production from solar energy is currently considered the best alternative to fossil fuels. Thus, materials enabling efficient and sustainable energy conversion and storage need to be developed. Iridium is still the only material used in proton exchange membrane electrolyzers that efficiently catalyze hydrogen evolution counter‐reaction, namely, the oxygen evolution reaction (OER) for electrochemical water splitting in acidic media. With no practical alternatives that can sustain the harsh reaction conditions, new approaches need to be developed to increase the utilization of this scarce metal. Hereby, a carbon–ceramic nanocomposite material is investigated, where Ir nanoparticles and nanoflakes of titanium oxynitride (TiONx) are deposited on the surface of reduced graphene oxide nanoribbons (rGONRs). OER performance is shown to be dependent on the mutual distribution of the Ir–TiONx–rGONR phases and in the best case leads up to 30 times higher activity relative to the commercial IrO2 benchmark. Adjusting the domains of different chemical nature within the same hybrid nanocomposite material through the formation of heterojunctions is shown to boost OER performance. This work demonstrates how fine‐tuning of morphology, composition, and particle distribution of the carbon–ceramic catalytic material can introduce a strong synergistic effect on OER activity and stability of iridium.

Ultra-responsive and selective of formic acid sensors based on flame-made SnO2 nanoparticles loaded with core-shell Ir-IrO2 nanocatalysts

0.1–2 wt% Ir-loaded tin dioxide (SnO2) nanoparticles were prepared via flame spray pyrolysis and investigated for sensing of formic acid (CH2O2). The structural morphologies of the materials were investigated by various X-ray spectroscopic and electron microscopic analyses. The results revealed that very fine secondary core-shell nanoparticles containing Ir° and Ir4+ species were decorated on the surfaces of cassiterite SnO2 nanoparticles, resulting in an increase of specific surface area and a small reduction of SnO2 crystallize size. The gas-sensing performances of all fabricated sensors were evaluated towards several volatile organic acids particularly CH2O2, volatile organic compounds and hydrocarbon gases at working temperature in the range of 200–400 °C in dry and humid air. The data revealed that the 1 wt% Ir-loaded SnO2 provided the optimal sensor response of ∼1.43 × 105 to 1000 ppm CH2O2 at an optimum working temperature of 350 °C. In addition, the sensors presented moderately low humidity effect on CH2O2 response and high CH2O2 selectivity against C2H5OH, CH3OH, C3H6O, C7H8, C6H6, C8H10, HCHO, CH4, H2, C2H4O2, C3H6O2, C4H8O2, C5H10O2 and C3H6O3. The electronic and gas-sensing mechanisms could be primarily ascribed to metal-metal-semiconductor heterojunctions and catalytic effects of Ir-IrO2 via oxygen spill-over and oxygen evolution reaction mechanisms. Therefore, the loading of catalytic core-shell Ir nanoparticles on SnO2 nanostructures was a highly promising approach to achieve ultrasensitive and selective sensing of formic acid.

Single-Atom Doping and High-Valence State for Synergistic Enhancement of NiO Electrocatalytic Water Oxidation.

The NiO-based electrocatalytic oxygen evolution reaction (OER) of water splitting is recognized as a promising approach to produce clean H2 fuel. However, the OER performance is still low, and especially, the overpotential is larger than 200mV at the current density of 10mA cm-2 . Herein, an Ir@IrNiO sample is prepared with single-atom (SA) Ir4+ doping and surface metallic Ir nanoparticles loaded onto the NiO. Owing to the bonding of the loaded Ir with surface-exposed Ni2+ , the nearby Ni atoms exist in the +3valence state, that is, the surface-loaded Ir particles behave like a stabilizer for the Ni3+ sites. Under the synergistic effect of SA Ir4+ and high-valance-state Ni3+ , the Ir@IrNiO nanostructure effectively reduces the overpotential to 195mV at acurrent density of 10mA cm-2 . Moreover, it gives an Ir-content-normalized current density of 0.0457 A mgIr -1 , 72.1 times higher than that of the best commercialized IrO2 (6.33 × 10-4 A mgIr -1 ), under the condition of 1.5V versus reversible hydrogen electrode. Operando Raman and X-ray absorption fine-structure (XAFS) measurements reveal that there are more surface-active species of Ni3+ , which adsorb and activate water molecules to form Ni3+ -*OH at low voltage, the intermediate of Ni4+ -•O is then formed at a relatively high bias voltage, and then the •O is transferred to the SA Ir4+ sites to generate Ir4+ -O-O with OH at increased voltage. This work can help design more SA-based highly active OER materials.

Recyclable Ir Nanoparticles for the Catalytic Hydrogenation of Biomass-Derived Carbonyl Compounds

The valorisation of biomass-derived platform chemicals via catalytic hydrogenation is an eco-friendly tool which allows us to recover bio-based building blocks and produce fine chemicals with high industrial appeal. In the present study, a novel surfactant-type triazolyl-thioether ligand was prepared, showing excellent catalytic activity in the presence of bis(1,5-cyclooctadiene)diiridium(I) dichloride [Ir(COD)Cl]2 for the hydrogenation of furfural, cinnamaldehyde, levulinic acid, 5-hydroxymethylfurfural, vanillin, and citral. Easy recovery by liquid/liquid extraction allowed us to recover the catalyst, which could then be efficiently recycled up to 11 times for the hydrogenation of furfural. In-depth analysis revealed the formation of spherical structures with metal nanoparticles as big as 2–6 nm surrounded by the anionic ligand, preventing iridium nanoparticle degradation.

Surfactant-free colloidal strategies for highly dispersed and active supported IrO2 catalysts: Synthesis and performance evaluation for the oxygen evolution reaction

Water electrolysis is a pivotal technology to drive the energy transition towards a system based on renewable resources. The scarce Ir is a crucial element for the synthesis of heterogeneous catalysts for the oxygen evolution reaction (OER). Carbon supported Ir oxide catalysts obtained from surfactant-free colloidal Ir nanoparticles (NPs) synthesized in alkaline methanol (MeOH), ethanol (EtOH), and ethylene glycol (EG) are investigated and compared. The comparison of independent techniques such as transition electron microscopy (TEM), small angle X-ray scattering (SAXS), and electrochemistry allows shedding light on the parameters that affect the dispersion of the active phase as well as the initial catalytic activity. The colloidal dispersions obtained are suitable to develop supported OER catalysts with little NP agglomeration on a carbon support. Due to the high dispersion of the active phase, initial catalytic activities of more than 400 A g−1Ir are reached at 1.5 VRHE when using carbon as a model support. While the more common surfactant-free alkaline EG synthesis requires flocculation and re-dispersion leading to Ir loss, the main difference between methanol and ethanol as solvent is related to the dispersibility of the support material. The choice of the suitable monoalcohol determines the maximum achieved Ir loading on the support without detrimental particle agglomeration. This simple consideration on catalyst design can readily assist the implementation of more relevant support materials for technical applications and significantly improved catalysts.

Transition Metal Oxide-Modified Ir Nanoparticles Supported on SBA-15 Silica for Selective Hydrogenation of Substituted Nitroaromatics

Modification of active metals with metal oxide modifiers has attracted considerable attention in heterogeneous catalysis due to their synergistic effect. However, a controllable synthesis of highly reactive and stable metal–metal oxide hybrid nanocatalysts is difficult. To solve this problem, presynthesized IrM (M = Fe, Co, and Ni) bimetallic nanoparticles were initially confined in the mesopores of SBA-15 and were then in situ transformed to Ir-MOx hybrids. The obtained Ir-MOx/SBA-15 nanocatalysts show superior activity and selectivity in the hydrogenation of substituted nitroaromatics to corresponding aromatic amines compared to Ir/SBA-15. Among these Ir-based catalysts, Ir-FeOx/SBA-15 exhibits the highest activity and selectivity and has a wider substrate scope due to the interaction between Ir and FeOx. Therefore, our research provides a way to design reactive and stable hydrogenation catalysts.

Glucose-oxidase like catalytic mechanism of noble metal nanozymes

Au nanoparticles (NPs) have been found to be excellent glucose oxidase mimics, while the catalytic processes have rarely been studied. Here, we reveal that the process of glucose oxidation catalyzed by Au NPs is as the same as that of natural glucose oxidase, namely, a two-step reaction including the dehydrogenation of glucose and the subsequent reduction of O2 to H2O2 by two electrons. Pt, Pd, Ru, Rh, and Ir NPs can also catalyze the dehydrogenation of glucose, except that O2 is preferably reduced to H2O. By the electron transfer feature of noble metal NPs, we overcame the limitation that H2O2 must be produced in the traditional two-step glucose assay and realize the rapid colorimetric detections of glucose. Inspired by the electron transport pathway in the catalytic process of natural enzymes, noble metal NPs have also been found to mimic various enzymatic electron transfer reactions including cytochrome c, coenzymes as well as nitrobenzene reductions.

Pt, Ir, Ru, and Rh Nanoparticles Supported on ZIF-67 Nanocubes for Evaluation of Hydrogen Spillover Ability of Noble Metals

Pt, Ir, Ru, and Rh Nanoparticles Supported on ZIF-67 Nanocubes for Evaluation of Hydrogen Spillover Ability of Noble Metals

Recent advances in ruthenium(II) and iridium(III) complexes containing nanosystems for cancer treatment and bioimaging

• Three main strategies for the fabrication of nanosystems are summarized. • How to produce novel Ru and Ir complexes containing nanosystems is summarized. • The recent developments in Ru and Ir complexes containing nanosystems are outlined. • The existing opportunities and challenges in nanosystems are highlighted. Ruthenium(II) and iridium(III) coordination compounds display excellent structural, photophysical, and biological properties which make them highly promising as anticancer and bioimaging agents. When nanoparticles are functionalized with Ru(II) and Ir(III) complexes, enhanced performance and synergistic effects can be produced in the resultant nanosystems. This review begins by describing the three main strategies for the fabrication of Ru(II) and Ir(III) complex containing nanosystems. This is followed by a discussion of the ways in which Ru(II) and Ir(III) complexes and nanoparticles combine and interact to produce novel materials with efficacies exceeding the sum of their parts. The main body of the review then outlines the recent developments in Ru(II) and Ir(III) complex containing nanosystems for cancer treatment and bioimaging. To conclude, some of the future challenges and opportunities in this field are highlighted.

Unravelling the Role of Strong Metal-Support Interactions in Boosting the Activity toward Hydrogen Evolution Reaction on Ir Nanoparticle/N-Doped Carbon Nanosheet Catalysts.

Pt-based catalysts are commercial electrocatalysts for the hydrogen evolution reaction (HER), but their shortcomings of expensive and imperfect efficiency hinder their large-scale application. Here, we report an Ir-based HER catalyst supported by N-doped carbon nanosheets (Ir-NCNSs). The NCNSs, with a high surface area and unique atomic composition, enable Ir nanoparticles (NPs) to disperse at 2-3 nm and strongly coordinate to the Ir through Ir-N bonds, which exposes many active sites and strengthens their durability. The catalyst displays a low overpotential and a small Tafel slope of 46.3 mV at 10 mA cm-2 and 52 mV dec-1 in 0.5 M H2SO4, respectively. When used in 1.0 M KOH, Ir-NCNSs also show excellent electrocatalytic activity with a low overpotential of 125 mV at 10 mA cm-2. The calculated results further suggest that Ir NPs and NCNSs have excellent selectivity for strong metal-support interactions, corresponding to a significant and stable HER characteristic. Our findings provide insight into the design of high-efficiency Ir-based HER catalysts.

Widening Temperature Window for CO Preferential Oxidation in H2 by Ir Nanoparticles Interaction with Framework Fe of Hexaaluminate

It is important to develop an efficient noble-metal-based catalyst that has a wide work temperature window and good stability for CO preferential oxidation in H2 (CO-PROX), a key step to purify ind...

Pt and Ir supported on mixed Ce0.97Ru0.03O2 oxide as low-temperature CO oxidation catalysts

Pt and Ir catalysts (3% w/w) supported on Ce0.97Ru0.03O2 were synthesized and successfully tested in a low-temperature CO oxidation process. The CO oxidation was followed in-operation, by FTIR spectroscopy. The catalysts were characterized by SEM-EDS, HTEM, XRD, DRS UV–vis, XPS techniques and BET isotherms. It was found that Pt and Ir nanoparticles on Ce0.97Ru0.03O2 drastically improved the CO oxidation in comparison to CeO2, showing the best performance the Pt/ Ce0.97Ru0.03O2 system. From the FTIR studies, a route for CO oxidation was proposed. The CO oxidation pathway in Ce0.97Ru0.03O2 considers that CO was adsorbed at the Ce and Ru sites, while O2 is adsorbed on the surface oxygen vacancies, being activated by nearby Ru species. Subsequently, the activated oxygen reacts with CO linked to Ce and Ru to produce CO2. Also, Pt and Ir promotes oxygen vacancies, increasing the activation-adsorption of O2 and, consequently, the activity of the catalyst was improved.

Comparative characterization of iridium loading on catalyst assessment under different conditions

To discuss the potential role of iridium (Ir) nanoparticles loaded under atmospheric and high pressures, we prepared a series of catalysts with the same active phase but different contents of 10wt%, 20wt%, and 30wt% on gamma-alumina for decomposition of hydrazine. Under atmospheric pressure, the performance of the catalyst was better when 30wt% of the Ir nanoparticles was used with chelating agent that had greater selectivity of approximately 27%. The increase in the reaction rate from 175 to 220 h−1 at higher Ir loading (30wt%) was due to a good dispersion of high-number active phases rather than an agglomeration surface. As a satisfactory result of this investigation at high pressure, Ir catalysts with different weight percentages showed the same stability against crushing and activity with a characteristic velocity of approximately 1300 m/s.

Single Ir Atoms Anchored on Ordered Mesoporous WO3 Are Highly Efficient for the Selective Catalytic Reduction of NO with CO under Oxygen‐rich Conditions

AbstractUnder oxygen‐rich conditions, achieving a selective and efficient reduction of NO by CO is always challenging. Here, we report the synthesis of the catalyst consisting of single Ir atoms anchored on mesoporous WO3 (denoted as Ir1/m‐WO3) using a facile template method followed by wet impregnation. X‐ray diffraction and transmission electron microscope studies indicated that the Ir atoms were distributed uniformly on the internal surface of m‐WO3. When tested for the reduction of NO by CO, the Ir1/m‐WO3 catalyst with a low Ir loading of 0.28 wt % exhibited excellent catalytic performance in the presence of 2 vol % O2 (volume ratio of CO to O2 being 1 : 10), achieving a NO conversion of 73 % and N2 selectivity of 100 % at 350 °C. In particular, its turnover frequency (TOF) value reached 0.30 s−1 at 200 °C, which is six times higher than that of the catalyst with Ir nanoparticles supported on mesoporous WO3 (0.05 s−1). The superior catalytic performance of Ir1/m‐WO3 is attributed to the formation of the isolated Ir atoms and the more newly generated Ir‐WO3 interfaces that can promote the adsorption and activation of NO, and the presence of accessible mesopores in m‐WO3 that facilitates the mass transfer of NO and CO. This study brings a new fundamental understanding of active sites in Ir‐based catalysts for the CO+NO reaction and provides a new way to the design and synthesis of single‐atom catalysts, especially precious metal catalysts for emissions control.

Highly Efficient Ir-CoOx Hybrid Nanostructures for the Selective Hydrogenation of Furfural to Furfuryl Alcohol.

Decoration of noble metals with transition-metal oxides has been intensively studied for heterogeneous catalysis. However, controllable syntheses of metal-metal oxide heterostructures are difficult, and elucidation of such interfaces is still challenging. In this work, supported IrCo alloy nanoparticles are transformed into supported Ir-CoOx close-contact nanostructures by in situ calcination and following selective reduction. Relative to Ir/Al2O3, Ir-CoOx/Al2O3 shows greatly enhanced activities for the hydrogenation of furfural derivatives to the corresponding furfuryl alcohol derivatives with more than 99% selectivity and demonstrates significantly improved activities and selectivity for hydrogenations of α,β-unsaturated aldehydes to α,β-unsaturated alcohols. The modification of Ir surfaces with CoOx prevents Ir nanoparticles from growing, achieving high thermal and catalytic stabilities. Theoretic calculation suggests that the better catalytic performance of Ir-CoOx/Al2O3 is ascribed to the Ir-CoOx interaction, which promotes the absorption of furfural as well as desorption of furfuryl alcohol, resulting in enhanced catalytic activities.