Ir Oxide Research Articles

Towards a reliable and high sensitivity O2-independent glucose sensor based on Ir oxidenanoparticles

The primary goal of this work is the development of a rapidly responding, sensitive, and biocompatible Ir oxide (IrOx)-based glucose sensor that regenerates solely via IrOx-mediation in both O2-free and aerobic environments. An important discovery is that, for films composed of IrOx nanoparticles, Nafion® and glucose oxidase (GOx), a Michaelis–Menten constant (K′m) of 20–30mM is obtained in the case of dual-regeneration (O2 and IrOx), while K′m values are much smaller (3–5mM) when re-oxidation of GOx occurs only through IrOx-mediation. These smaller K′m values indicate that the regeneration of GOx via direct electron transfer to the IrOx nanoparticles is more rapid than to O2. Small K′m values, which are obtained more commonly when Nafion® is not present in the films, are also important for the accurate measurement of low glucose concentrations under hypoglycemic conditions. In this work, the sensing film was also optimized for miniaturization. Depending on the IrOx and GOx surface loadings and the use of sonication before film deposition, the imax values ranged from 5to 225μAcm−2, showing very good sensitivity down to 0.4mM glucose.

Comparison of precious metal oxide/titanium monolith catalysts in wet oxidation of wastewaters

CWO (catalytic wet oxidation) of a process wastewater and phenolate solution was carried out at 230°C, 200°C and total pressure of 50bar, with oxygen, in a stainless steel autoclave. Monolith Ti mesh supported precious metal oxide catalysts were characterized with XPS, ICP-MS, SEM and their activity compared in oxidation of model and real wastewaters.The Ru/Ir oxide coated Ti monolith catalysts showed remarkable catalytic activity in wet oxidation both in the overall oxidation expressed by COD (chemical oxygen demand) decrease and in the carbon mineralization expressed by TOC (total organic carbon) decrease. This was valid for the real pharmaceutical wastewater as well as for a phenolate solution too. Meshes containing Ru, Pd and Ir oxide alone were less active than Ru/Ir together on Ti. This observation is in accordance with the electrochemical properties of the same mesh used in hypochlorite production.The commercial mesh was most stable under the conditions of wet oxidation, however the loss of its precious metal content was observed during longer usage. The Ru/Ir monolith catalysts prepared in our laboratories had similar initial activity but they were less stable, the leaching and/or abrasion of the surface precious metal oxide layer was faster, independently of that their had fragmented or continuous structure, resulting from the preparation methods.The loss of activity during longer usage can be the result of deposition of iron and silicon oxides too, as showed by SEM (scanning electron microscopy) analysis.An important feature of the good catalytic activity of the Ru/Ir oxide coated Ti mesh can be the uniform distribution of the two oxides showed by LA–ICPMS (laser ablation–inductive coupled plasma mass spectrometry). According to XPS (X-ray photoelectron spectroscopy) results, the upper surface layer of the catalysts is covered by a mixture of Ru–Ir–Ti oxide of approximately 0.1:0.02:1 atomic ratio for commercial catalyst, and an 0.5:0.7:1.0 atomic ratio for catalysts prepared in our laboratories. We suppose that such mixture of oxides with uniform distribution are the carrier of the good catalytic activity.

Aerobic and Anaerobic Glucose Detection at Films Composed of Ir Oxide Nanoparticles

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Direct Observation of a Hydroperoxide Surface Intermediate upon Visible Light-Driven Water Oxidation at an Ir Oxide Nanocluster Catalyst by Rapid-Scan FT-IR Spectroscopy

A surface hydroperoxide intermediate has been detected upon oxidation of water at an Ir oxide nanocluster catalyst system under pulsed excitation of a [Ru(bpy)(3)](2+) visible light sensitizer by recording of the OO vibrational mode at 830 cm(-1). Rapid-scan FT-IR spectroscopy of colloidal H(2)O, D(2)O, and D(2)(18)O solutions in the attenuated total reflection mode allowed spectral assignment of IrOOH on the basis of an observed D shift of 30 cm(-1), and (18)O shifts of 24 cm(-1) ((16)O(18)O) and 46 cm(-1) ((18)O(18)O). The laser pulse response of the infrared band is consistent with the kinetic relevancy of the intermediate. This is the first observation of a surface intermediate of oxygen evolution at an Ir oxide multielectron catalyst.

Wet oxidation properties of process waste waters of fine chemical and pharmaceutical origin

Wet oxidation was carried out for treating different industrial process wastewaters (PWW’s) of pharmaceutical production, with oxygen in a stainless steel autoclave at 230 and 250 °C and total pressure of 50 bar. Beside non-catalytic, a catalytic reaction was also carried out. The catalyst applied was Ti mesh covered with Ru and Ir oxide. PWW samples were analyzed with respect to their TOC, COD (BOD) content. The tested PWW’s could be oxidized but with rather different conversions. Some effluents were converted with remarkable rate due in some cases to their Fe or Cu ion content, in other cases to the Ti based precious metal oxide catalyst.

Variational Monte Carlo study of two-dimensional strong spin-orbit coupling system: Novel Mott insulating state in Ir oxide

Motivated by the novel 5d Mott insulator Sr2IrO4, we have studied the three-orbital Hubbard model with a spin-orbit coupling (SOC) term in a two-dimensional square lattice. We have found the transition from a paramagnetic metal to an antiferromagnetic (AF) insulator at U = UMI. A large SOC, which is characteristic of 5d electron systems, greatly reduces UMI and even small U can lead the system into the Mott insulator. Moreover, the Hund's coupling induces the anisotropy and stabilizes the in-plane AF order. These mechanisms are considered to be valid for Sr2IrO4.

Microscopic Study of Electronic and Magnetic Properties for Ir Oxide

The exact diagonalization and the variational cluster approximation (VCA) are used to study the nature of a novel Mott insulator induced by a strong spin-orbit coupling for a two-dimensional three-band Hubbard model consisting of the $t_{2g}$ manifold of $5d$ orbitals. To characterize the ground state, we introduce a local Kramer's doublet which can represent a state with effective angular momentum $J_{\rm eff}=|{\bm S}-{\bm L}|=1/2$ as well as spin $S=1/2$. Our systematic study of the pseudo-spin structure factor defined by the Kramer's doublet shows that the $J_{\rm eff}=1/2$ Mott insulator is smoothly connected to the $S=1/2$ Mott insulator. Using the Kramer's doublet as a variational state for the VCA, we examine the one-particle excitations for the Mott insulating phase. These results are compared with recent experiments on Sr$_2$IrO$_4$.

Effects of thermal exposure on Ir-based alloys with and without Pt coating

Isothermal oxidation tests were performed on Ir, Ir–3Hf, Ir/Pt, and Ir–3Hf/Pt in static air at 1100 °C for 200 h. The microstructural evolution and changes in the composition of the alloys were characterisation by performing scanning electron microscopy (SEM) and field-emission electron probe microanalysis (FE-EPMA). The results indicated that the specimens of all the Ir-based alloys exhibited linear mass loss due to the formation/evaporation of gaseous Ir oxide species (mainly IrO 3). The oxidation behaviour, including mass change kinetics, evaporation of gaseous IrO 3, and the role of Hf and Pt are discussed.

Carbon-supported bimetallic PdIr catalysts for ethanol oxidation in alkaline media

Carbon-supported bimetallic PdIr catalysts are synthesized by the simultaneous reduction method using NaBH 4 as reductant and citrate as complexing agent and stabilizer. X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy are used to characterize the PdIr/C catalysts with different Pd/Ir atomic ratios. The catalytic activity and stability of the PdIr/C catalysts for ethanol oxidation in alkaline media are examined and compared with that of the Pd/C catalyst by cyclic voltammetry, linear sweep voltammetry and chronopotentiometry. Results show that Ir addition can significantly improve the ethanol oxidation kinetics on Pd in alkaline media, and the Pd 7Ir/C catalyst exhibits the highest activity and stability than the other samples do. The improvement in catalytic performance is attributed to the fact that Ir addition to Pd can facilitate the removal of adsorbed ethoxi intermediates, as the hydroxyl groups are more easily adsorbed on metallic Ir and iridium oxide (IrO 2) at lower potentials.

Phonon confinement effect in mixed Sn–Ir oxide nanocrystals

Raman spectra in Sn 1− x Ir x O 2 ( x ⩽ 0.15) nanocrystals were investigated to estimate and separate the contributions of phonon confinement and composition effects. To this end, the Raman frequency of the A 1 g bulk-mode of pure SnO 2 and Ir-mixed nanocrystals has been studied in details as a function of the size and the Iridium concentration. As an initial working hypothesis it was assumed a linear dependence of the Raman shift as a function of the Iridium molar concentration, while a quadratic expansion of the dispersion curve has been utilised in the phonon confinement effect. Comparison of predicted and experimental results is reported.

Dual oxygen and Ir oxide regeneration of glucose oxidase in nanostructured thin film glucose sensors

A nanoparticulate iridium oxide (IrOx) thin film has been developed as a redox-active matrix material for an advanced generation glucose biosensor, in which IrOx serves as the non-physiological mediator, replacing oxygen in the enzymatic re-oxidation of glucose oxidase (GOx). Ethanolic solutions of Nafion and an Ir sol were mixed with an aqueous GOx solution and then deposited on a Au support. The Ir nanoparticles were then oxidized electrochemically to IrOx and the resulting films (IrOx–GOx–Nafion) were tested for their glucose response in both oxygen- and argon-saturated solutions, with the oxygen content in both solutions monitored by a Pt electrode. The sensors that are regenerated largely by O 2 are characterized by a Michaelis–Menten K ′ m value of ∼30 mM or more and i max values of at least 20 μA cm −2. Under fully deareated conditions, the sensors lose only ∼50% of their response to glucose, clearly indicating that a dual oxygen-regeneration and IrOx mediation mechanism is operative for the biosensor under these conditions. Under optimized conditions, involving a controlled GOx:Ir ratio, only the Ir oxide sites in the film serve to mediate GOx regeneration, giving K ′ m (10–15 mM) and i max values that are independent of the O 2 content of the solution.

57Fe Mössbauer Spectroscopy of Ir-Fe Catalysts for Preferential CO Oxidation in H2

New insights on the interaction between Ir and Fe oxide are reported. Three Ir-Fe catalysts were prepared by different impregnation sequences of an Al2O3 support. Co-impregnation gave a better catalyst for the preferential CO oxidation in H2 (PROX) reaction. Microcalorimetry data showed that the adsorption of CO and H2 were different. Quasi in situ Mössbauer data of the three catalysts after reduction, reoxidation, and PROX reaction showed that a strong interaction between Ir and Fe affected the redox properties of the Ir-Fe catalysts. CO conversion was proportional to the concentration of the Fe2+(a) species, thus, Fe2+(a) was an active site in the PROX reaction. The impregnation sequence influenced the interaction between Ir and Fe and consequently, the amount of the active Fe2+(a) species. A strong Ir-Fe interaction stabilized the active Fe2+ sites for activating O2. ： 采用不同浸渍顺序制备了三种 Ir-Fe 催化剂, 其 CO 选择氧化 (PROX) 反应活性差别很大, 其中共浸渍的 Ir-Fe 催化剂活性最高. 吸附量热研究表明, 三种催化剂的 H2 和 CO 吸附存在差别. 通过对三种催化剂还原后、再氧化和反应后准原位 57Fe 穆斯堡尔谱的研究, 得到各种 Fe 物种信息. 结果表明, 三种制备方法影响催化剂中 Ir-Fe 相互作用强度, 导致催化剂中 Fe 物种的氧化还原性能不同. 催化剂中 Fe2+(a) 的含量与 CO 转化率呈正比关系, Fe2+(a) 是 PROX 反应过程中活化氧的活性中心. 浸渍顺序改变了 Ir-Fe 间相互作用强度, 从而改变 Fe2+(a) 物种含量, 影响 PROX 反应活性. Ir-Fe 间的相互作用可以稳定活化氧的 Fe2+(a) 物种, 为今后研究金属-金属间的相互作用提供借鉴.

Nanoparticulate Ir Oxide as a Biosensor Matrix Material

not Available.

Nano-porous iridium and iridium oxide thin films formed by high efficiency electrodeposition

The goal of this work has been to fabricate very thin, highly porous Ir films, of use in a wide variety of applications. To achieve this objective, Ir was electrodeposited on a Au-coated quartz crystal, allowing in situ mass measurements to be carried out while concurrently monitoring the charge passed, as a function of the deposition potential, H2IrCl6 concentration, and time. Ir thin films (<5 nm) could be deposited at 100% charge efficiency at an optimum potential of 0.1–0.2 V vs. RHE, all in room temperature 0.5 M H2SO4 containing various concentrations of H2IrCl6. Field emission scanning electron microscopy and in situ surface area measurements showed that the Ir films are uniform and yet highly porous (up to 50%), independent of film thickness. We were also able to efficiently convert the electrodeposited Ir to Ir oxide, without significant loss of metal or diminished coating adhesion, while also maintaining their very high surface area properties. These interesting thin films are very promising for a wide variety of electrocatalytic and sensing applications.

Electrochemical and In Situ Optical Studies of Supported Iridium Oxide Films in Aqueous Solutions

Certain aspects of the dynamic behavior of electrochemically deposited hydrous Ir oxide films supported on Au microelectrodes during charge and discharge have been investigated by a combination of chronocoulometry and simultaneous in situ normalized reflectance spectroscopy techniques in aqueous solutions. Correlations between the reflectance spectra and the optical properties of the films in its various states of oxidation were sought from in situ transmission measurements for films supported on In-doped tin oxide on glass. The current transient response for microelectrodes following a potential step, within the voltage region in which the films display pseudocapacitive characteristics, was found to exhibit a well-defined peak, as opposed to a monotonic decay reported by other groups. Some features of this behavior can be attributed to changes in the conductivity of the film as a function of its state of charge, as has been proposed for electronically conducting polymers. Also presented in this work are data collected over the pH range 0.3–13, which confirm the much faster charge–discharge dynamics in basic compared to acidic media. A primitive model based on proton conductivity within the hydrated oxide lattice is presented which accounts grossly for this pH-induced effect.

In Situ Spectroscopy of Water Oxidation at Ir Oxide Nanocluster Driven by Visible TiOCr Charge-transfer Chromophore in Mesoporous Silica

An all-inorganic photocatalytic unit consisting of a binuclear TiOCr charge-transfer chromophore coupled to an Ir oxide nanocluster has been assembled on the pore surface of mesoporous silica AlMCM-41. In situ FT-Raman and EPR spectroscopy of an aqueous suspension of the resulting IrxOy-TiCr-AlMCM-41 powder reveal the formation of superoxide species when exciting the Ti(IV)OCr(III) --> Ti(III)OCr(IV) metal-to-metal charge-transfer chromophore with visible light. Use of H218O confirms that the superoxide species originates from oxidation of water. Photolysis in the absence of persulfate acceptor leads to accumulation of Ti(III) instead. The results are explained by photocatalytic oxidation of water at Ir oxide nanoclusters followed by trapping of the evolving O2 by transient Ti(III) centers to yield superoxide. Given the flexibility to select donor metals with appropriate redox potential, photocatalytic units consisting of a binuclear charge-transfer chromophore coupled to a water oxidation catalyst shown here constitute a step towards thermodynamically efficient visible light water oxidation units.

Production of hydrogen by the electrochemical reforming of glycerol–water solutions in a PEM electrolysis cell

An alternative method for producing hydrogen from renewable resources is proposed. Electrochemical reforming of glycerol solution in a proton exchange membrane (PEM) electrolysis cell is reported. The anode catalyst was composed of Pt on Ru–Ir oxide with a catalyst loading of 3 mg cm −2 on Nafion. Part of the energy carried by the produced hydrogen is supplied by the glycerol (82%) and the remaining part of the energy originates from the electrical energy (18%) with an energy efficiency of conversion of glycerol to hydrogen of around 44%. The electrical energy consumption of this process is 1.1 kW h m −3 H 2. Compared to water electrolysis in the same cell, this is an electrical energy saving of 2.1 kW h N m −3 H 2 (a 66% reduction). Production rates are high compared with comparable sized microbial cells but low compared with conventional PEM water electrolysis cells.

Influence of oxygen vacancies on Schottky contacts to ZnO

Ni, Ir, Pd, Pt, and silver oxide Schottky contacts were fabricated on the Zn-polar face of hydrothermally grown, bulk ZnO. A relationship was found between the barrier height of the contact and the free energy of formation of its “metal” oxide. This is consistent with the dominating influence of oxygen vacancies (VO) which tend to pin the ZnO Fermi level close to the VO (+2,0) defect level at approximately 0.7eV below the conduction band minimum. Therefore, a key goal in the fabrication of high quality Schottky contacts should be the minimization of oxygen vacancies near the metal-ZnO interface.

Supported Iridium Oxide Films in Aqueous Electrolytes: Charge Injection Dynamics as Monitored by Time-Resolved Differential Reflectance Spectroscopy

Dynamic aspects of the electrochemical charge-discharge of hydrated Ir oxide, IrC x (hyd), films in aqueous 0.5 M H 2 SO 4 have been investigated by simultaneous chronocoulometry and time-resolved, normal incidence (λ = 633 nm) differential reflectance spectroscopy, ΔR/R. Experiments were performed by applying potential steps between two judiciously selected values to IrO x (hyd) films electrodeposited on smooth Au disk microelectrodes to reduce the overall time constant of the cell. The analysis of the results obtained revealed that the rate at which charge is injected into or released from the film, as determined from the chronocoulometric response, is faster than the rate at which Ir sites in the lattice undergo redox transitions, as monitored by AR/R. This behavior appears consistent with the relatively high electronic conductivity of IrC x (hyd), which allows for charge to be stored on the highly convoluted surface of this structurally disorganized material, i.e., strictly capacitive, a process that occurs in parallel and at much higher rates than changes in the oxidation state of the Ir sites, i.e., pseudocapacitive.

Electrochemical formation of Ir oxide/polyaniline composite films

The primary goal of this work has been to electrochemically form and then characterize a composite polyaniline (PANI)/hydrous Ir oxide (IrOx) film. Efforts to electrochemically form IrOx and PANI simultaneously in acidic aniline-containing solutions failed, likely as aniline adsorption on Ir prevents IrOx formation. Successful composite films were therefore made by first forming an anodic IrOx film on bulk Ir and then depositing PANI into its pores. Based on the characteristics of the PANI redox peaks, it is seen that all of the PANI film that is electrochemically active is in direct electrical contact with the Ir surface at the base of the IrOx film pores. This is consistent with the cross-sectional SEM and EDX analyses, showing the formation of films of uniform thickness and composition. Thin films of Ir nanoparticles, subsequently converted to IrOx, were also used as a template for PANI formation within the porous structure. These hybrid films exhibit an enhanced internal porosity, ease of multiple coating formation (up to 20 μm in thickness), high charge densities, unusual electrochromic behavior, and very rapid charge transfer kinetics. The formation of composite IrOx/PANI films also resulted in a widening (by 0.3–0.4 V) of the potential window over which a pseudocapacitive and electrochromic response is seen.