Small Amount Of Ir Research Articles

New Electrocatalyst with the Content of Ir

Introduction Proton exchange membrane (PEM) water electrolysis (WE) is a promising technology for hydrogen production. However, the local environment of the anode in PEMWE is highly acidic and high potential due to the oxygen evolution reaction (OER; 2H2O → O2 + 4H+ + 4e-), and the available anode materials are limited to precious metal elements such as Pt, Ru and Ir. In the current technology, Ir-based materials are the mainstream anode catalysts, and Ir loading of 1-2 mg/cm2 is necessary to achieve both activity and durability. On the other hand, the annual production of Ir is said to be only 5-7 tons. The demand for hydrogen is expected to increase to the GW scale in the future. For example, if water electrolysis is operated at 2 A/cm2 and 2 V with Ir loading of 2 mg/cm2 (0.5 mgIr/W), it is difficult to meet the demand with the existing Ir resources. Tosoh have been engaged in the electrolytic manganese dioxide (EMD) business. EMD is synthesized thorough anodic oxidation of Mn2+ ion (Mn2+ + 2H2O → MnO2 + 4H+ + 2e-) under acidic conditions, therefore it is potentially suitable for the anode environment of PEMWE. In this study, a very small amount of Ir (<0.1 mg/cm2) was successfully composited with EMD. The resulting composite consisting of Ir and EMD showed more active than commercial Ir oxide with the same Ir content, and operated stably for at least 1000 h. Experiment EMD thin film was electrodeposited anodically on Pt-coated Ti fibers (Pt/Ti) thorough electrolyzing a mixed solution of MnSO4 and H2SO4. The obtained EMD-coated Pt/Ti were immersed in an Ir-containing solution, and then annealed to obtain Ir-containing EMD (hereinafter referred to as "Ir-EMD"). The Pt-coated Ti fibers are used as a porous transport layer (PTL) in PEMWE cells, and our developed material serves as both an OER catalyst and a PTL. OER property was evaluated using a PEMWE cell at 80°C in a two-electrode system. Pt-supported carbon was used as the cathode catalyst and Nafion®-115 as the PEM. See Fig. 1 for PEMWE cell construction flow. Result and discussion The Ir content in Ir-EMD was determined to be 0.1 mg/cm2 by ICP-AES. This Ir content is 10-20 times lower than that used in current PEMWE electrolyzers. The OER activity of Ir-EMD was evaluated by linear sweep voltammetry (LSV) (Fig. 2). For comparison, EMD (with no Ir) and Ir oxide (commercial product) with an Ir content of 0.1 mg/cm2 were evaluated in the same way. The slow OER property of EMD was improved dramatically by introducing Ir into EMD. Also, at the same amount of Ir, Ir-EMD exhibited higher OER activity than that of Ir oxide. The inset in Fig. 2 shows Tafel plots corresponding to LSVs, and the slope of the linear region (Tafel slope) can be used to predict which elementary reaction is the rate-limiting step in the OER. The Tafel slope of Ir-EMD is 58 mV/dec., which is close to the Tafel slope of Ir oxide, 50 mV/dec. This suggests that OER on Ir-EMD proceeds by the same mechanism as Ir oxide. The durability of Ir-EMD and Ir oxide was tested at a current density of 2 A/cm2 (Fig. 3). Ir oxide was deactivated within only 8 days, and it is confirmed that Ir have disappeared after electrolysis. On the other hand, Ir-EMD has operated stably for more than 42 days (≈1000 h), with a degradation rate of only 13 μV/h. In other words, Ir-EMD has practical durability while reducing the amount of Ir by more than 10 times compared to current technology.Acknowledgements : This presentation is based on results obtained from a project, JPNP20003, subsidized by the New Energy and Industrial Technology Development Organization (NEDO). Figure 1

Highly reversal-tolerant anodes using Ti4O7-supported platinum with a very small amount of water-splitting catalyst

Gross fuel starvation can seriously damage the anode of polymer electrolyte fuel cells (PEFCs) due to the exceptionally high anodic potential induced by oxygen evolution and carbon corrosion reactions to generate protons, instead of hydrogen oxidation. In this report, we describe a highly effective reversal-tolerant anode catalyst (RTA) based on Pt/Ti4O7 with a very small amount of Ir. A membrane electrode assembly (MEA) using a Pt/Ti4O7 RTA including 0.04 mgIr cm−2 shows almost no performance loss even after severe cell reversal. This is in clear contrast with the results obtained with an Pt/C RTA including the same amount of Ir, for which a significant voltage loss is observed after a cell reversal test. Moreover, the reversal-tolerance of Pt/Ti4O7 RTA is considerably high even with a very small amount of Ir, as low as 0.014 mgIr cm−2. An Ir/Ti4O7 based anode also shows superior RTA property as well as the mitigation of start-up/shut-down degradation due to the limited activity of Ir for the oxygen reduction reaction. A post-mortem analysis of the tested MEA confirmed that Pt/Ti4O7 RTA alleviates damage to not only the catalyst layer but also the micro porous layer, which leads to a better RTA property for the Pt/Ti4O7.

Highly Reversal Tolerant Anodes Using Ti4O7-Supported Platinum with a Very Small Amount of Water Splitting Catalyst

Gross fuel starvation (cell reversal) event are known to damage the anode of PEFC seriously due to exceptionally high anodic potential (> 2 V vs RHE) when the anode gas channel or manifolds are clogged with water or ice. This high potential is due to oxygen evolution and/or carbon corrosion reactions (OER & COR) at anode to generate protons, instead of hydrogen oxidation reaction. Especially, COR may lead to rapid destruction of the anode structure so that promotion of OER instead of COR would be better way to mitigate serious damages by the fuel starvation. Thus, reversal tolerant anode (RTA), which includes water splitting catalyst to promote OER is one of the solution from material side to mitigate these serious damages. So far, water splitting catalyst (iridium and/or ruthenium) mixed Pt/C has been proposed as RTA, however a significant amount of iridium is indispensable to mitigate the damages. Here we will present oxidation-resistant and electro-conductive titanium oxide (Ti4O7) supported Pt (Pt/Ti4O7) catalyst-based RTA with very small amount of Ir without compromising RTA properties. For example, MEAs using a conventional Pt/C RTA including 0.04 mgIr cm-2 showed significant voltage loss after severe cell reversal test (0.2 A cm-2 load @H2-starved anode for 7,200 seconds), however, almost no performance loss was observed for the Pt/Ti4O7 RTA including the same amount of Ir. Moreover this superior reversal tolerant property of Pt/Ti4O7 RTA was found to be kept at as low as 0.014 mgIr cm-2. Detailed data about electrochemical and post mortem analyses of the tested MEAs will be discussed at the Meeting.

Screening for the best detergent for the isolation of placental membrane proteins

Although membrane proteins (MPs) play crucial roles in physiological processes, information on them are insufficient, mostly due to their peculiar nature and surrounding which demand specific procedures for their extraction (using detergents) and analysis. A pallet of ten detergents and β-cyclodextrin was employed to investigate their efficiency in extracting total placental MPs, glycoproteins and insulin-like growth factor receptors (IR/IGF1R/IGF2R). Regardless of detergent used, the identity of major extracted proteins was the same. Glycoproteins extracted with Triton X-100 contained the greatest variety and quantity of glycans recognised by fifteen lectins, pointing to this detergent as universal medium for the extraction of membrane glycoproteins. Glycoproteins extracted using Brij 35 exhibited weak interaction with only seven lectins and were differently recognised by lectins of the similar glycan specificity. Brij 35, Tween 20, saponin and digitonin selectively extracted IGF2R compared to other two receptors. Pilot experiments should be conducted in order to choose adequate detergent for the extraction of specific MP. To obtain preparations enriched in specific receptor of the insulin/IGF system sequential solubilisation of placental MPs can be proposed: to use Brij 35 to extract IGF2R and subject the insoluble remaining suspension to Triton X-114 in order to extract most of IGF1R with small amounts of IR.

Charge conduction study of phosphorescent iridium compounds for organic light-emitting diodes application

The charge conduction properties of a series of iridium-based compounds for phosphorescent organic light-emitting diodes (OLEDs) have been investigated by thin-film transistor (TFT) technique. These compounds include four homoleptic compounds: Ir(ppy)3, Ir(piq)3, Ir(Tpa-py)3, Ir(Cz-py)3, and two heteroleptic compounds Ir(Cz-py)2(acac) and FIrpic. Ir(ppy)3, Ir(piq)3 and FIrpic are commercially available compounds, while Ir(Tpa-py)3, Ir(Cz-py)3 and Ir(Cz-py)2(acac) are specially designed to test their conductivities with respect to the commercial compounds. In neat films, with the exception of FIrpic, all Ir-compounds possess significant hole transporting capabilities, with hole mobilities in the range of about 5×10−6–2×10−5cm2V−1s−1. FIrpic, however, is non-conducting as revealed by TFT measurements. We further investigate how Ir-compounds modify carrier transport as dopants when they are doped into a phosphorescent host material CBP. The commercial compounds are chosen for the investigation. Small amounts of Ir(ppy)3 and Ir(piq)3 (<10%) behave as hole traps when they are doped into CBP. The hole conduction of the doped CBP films can be reduced by as much as 4 orders of magnitude. Percolating conduction of Ir-compounds occurs when the doping concentrations of the Ir-compounds exceed 10%, and the hole mobilities gradually increase as their values reach those of the neat Ir films. In contrast to Ir(ppy)3 and Ir(piq)3, FIrpic does not participate in hole conduction when it is doped into CBP. The hole mobility decreases monotonically as the concentration of FIrpic increases due to the increase of the average charge hopping distance in CBP.

Probability of twin boundary formation associated with the nucleation of equiaxed grains on icosahedral quasicrystal templates

Recently, we have shown that minute Cr additions (typically 0.1 wt%) to Al-Zn alloys solidified in a uniform temperature field lead to the formation of fine equiaxed fcc Al grains [1]. Furthermore, these grains exhibit an unexpectedly large number of twin, or neartwin, relationships with their nearest neighbors and some of them even show a 5-fold symmetry multi-twin relationship with a common (110) direction. Similar observations have been made for yellow gold alloys (Au-12.5wt%Cu-12.5wt%Ag) inoculated with very small amounts of Ir (5-200 ppm) [2]. These results become fully consistent when one considers that the primary fcc phase forms on facets of icosahedral quasicrystals (iQC's), either by heteroepitaxy solidification or by peritectic transformation, with the following relationship: 〈111〉fcc || 3-fold symmetry iQC axes, 〈110〉fcc ⊥ 2-fold symmetry iQC axes. The present study contributes to a better understanding of the frequency of twin boundary formation by the nucleation of fcc phase from an iQC template. A simple stereological model for the formation of equiaxed grains on such iQC templates has been derived. It is based on a 3D Voronoi tessellation of randomly distributed and oriented iQC template centers. Each iQC nucleation template site is the origin of 20 fcc grains with the heteroepitaxy relationships mentioned above on the 20 facets of the iQC. Therefore, the neighboring grains having a common iQC nucleation site contributes to the twin boundary frequency, while those coming from different iQC sites have random grain boundary orientations. The twin boundary frequency of the grains nucleated from iQC templates seen in 2D metallographic sections is compared with that measured in EBSD reconstructed grain structures.

Age hardening and softening related to ordering and first and second grain boundary reaction in dental low carat gold alloy

A commercial dental Au–Ag–Cu–Pd alloy with small amounts of Ir and Zn was examined to elucidate the age hardening and softening mechanisms by characterising the phase transformation and microstructural changes via a first and second grain boundary reaction by means of a hardness test, X-ray diffraction study, field emission scanning electron microscopy and energy dispersive spectrometry. The hardness increased to the maximum value without an incubation period, and the overaging process showed a softening course in two steps. The increase in hardness was caused primarily by lattice distortion along the c axis due to the tetragonality of the metastable AuCu I′ and stable AuCu I phases, and secondarily by the coherence or semicoherence strain in the interfaces of the metastable AuCu I′ phase with the parent α0, product α1 and stable AuCu I phases. The fine lamellar forming first grain boundary reaction did not result in hardening, because it was not related directly to the phase separation process. The softening was in proportion to the quantity of lamellar structures by the first and second grain boundary reaction, and the softening effect of the fine lamellar forming first grain boundary reaction was larger than that of the coarse lamellar forming second grain boundary reaction.

Change of magnetic ground state by light electron doping in CeOs2Al10

The effect of Ir substitution for Os in CeOs${}_{2}$Al${}_{10}$, with an unusually high N\'eel temperature of ${T}^{*}\ensuremath{\sim}28.5$ K, has been studied by high-resolution neutron diffraction and magnetization measurements. A small amount of Ir ($\ensuremath{\sim}$$8%$) results in a pronounced change of the magnetic structure of the Ce sublattice. The induced magnetic ground state is controlled by single ion anisotropy and implies an antiferromagnetic arrangement of the Ce moments along the $a$ axis, as expected from the anisotropy of the paramagnetic susceptibility. The value of the ordered moments, 0.92(1)${\ensuremath{\mu}}_{B}$, is substantially bigger than in the undoped compound, whereas the transition temperature is reduced down to 21 K. A comparison of the observed phenomena with the recently studied CeRu${}_{1.9}$Rh${}_{0.1}$Al${}_{10}$ system, exhibiting similar behavior [Kondo et al., J. Phys. Soc. Jpn. 82, 054709 (2013)], strongly suggests the electron doping as the main origin of the ground state changes. This provides additional ways for exploring the anomalous magnetic properties of the Ce(Ru/Os)${}_{2}$Al${}_{10}$ compounds.

Spectroscopic Characterization of Alumina-Supported Bis(allyl)iridium Complexes: Site-Isolation, Reactivity, and Decomposition Studies

The covalent attachment of tris(allyl)iridium to partially dehydroxylated gamma-alumina is found to proceed via surface hydroxyl group protonation of one allyl ligand to form an immobilized bis(allyl)iridium moiety, (=AlO)Ir(allyl)(2), as characterized by CP-MAS (13)C NMR, inductively coupled plasma-mass spectrometry, and Ir L(3) edge X-ray absorption spectroscopy. Extended X-ray absorption fine-structure (EXAFS) measurements taken on unsupported Ir(allyl)(3) and several associated tertiary phosphine addition complexes suggest that the eta(3)-allyl ligands generally account for an Ir-C coordination number of 2 rather than 3, with an average Ir-C distance of 2.16 A. Using this knowledge, combined EXAFS and X-ray absorption near-edge structure studies reveal that a small amount of Ir(0) is also formed upon reaction of Ir(allyl)(3) with the surface. It was found that the addition of either 2,6-dimethylphenyl isocyanide or carbon monoxide to the supported complex allows spectroscopic identification of the supported bis(allyl)iridium complexes, (=AlO)Ir(allyl)(2)(CNAr) [Ar = 2,6-(CH(3))(2)C(6)H(4)] and (=AlO)Ir(allyl)(2)(CO)(2), respectively. Although samples of the supported bis(allyl)iridium complex are active for the dehydrogenation of cyclohexane to benzene at temperatures between 180 and 220 degrees C, in situ temperature-programmed reaction XAFS and continuous-flow reactor studies suggest that Ir(0) nanoparticles, rather than a well-defined Ir(3+) complex, are responsible for the observed activity.

Morphology and Oxygen Sensor Response of Luminescent Ir-Labeled Poly(dimethylsiloxane)/Polystyrene Polymer Blend Films

Polymer films consisting of a linear poly(dimethylsiloxane) end-functionalized with a luminescent Ir(III) complex (Ir-PDMS), blended with polystyrene (PS), function as optical oxygen sensors. The sensor response arises by quenching of the luminescence from the Ir(III) chromophore by oxygen that permeates into the polymer film. The morphology and luminescence oxygen sensor properties of blend films consisting of Ir-PDMS and PS have been characterized by fluorescence microscopy, atomic force microscopy, and scanning electron microscopy. The investigations demonstrate that microscale phase segregation occurs in the films. In blends that contain a relatively small amount of Ir-PDMS in PS (ca. 10 wt %), the Ir-PDMS exists as circular domains, with diameters ranging from 2 to 5 mum, surrounded by the majority PS phase. For larger weight fractions of Ir-PDMS in the blends, the film morphology becomes bicontinuous. A novel epifluorescence microscopy method is applied that allows the construction of Stern-Volmer quenching images that quantify the oxygen sensor response of the blend films with micrometer spatial resolution. These images provide a map of the oxygen permeability of the polymer blend films with a spatial resolution of ca. 1 mum. The results of this investigation show that the micrometer-sized Ir-PMDS domains display a 2-3-fold higher oxygen sensor response compared to the surrounding PS matrix. This result is consistent with the fact that PDMS is considerably more gas permeable compared to PS. The relationship of the microscale morphology of the blends to their performance as macroscale optical oxygen sensors is discussed.

スパッタ法による成形型用白金合金膜

Pt-Ir and Pt-Rh alloy films were deposited on a cemented carbide substrate by RF magnetron sputtering and film characteristics were examined to determined a candidate for the molds used for molding optical glass elements.XRD showed a highly oriented (111) texture for both the Pt-Ir and Pt-Rh films.Tensile stress existed in pure Pt films deposited in the present experiment. In Pt-Ir films, tensile stress decreased with increases in Ir content up to 20wt%. Film stress changed in sign from tension to compression, and the compressive stress increased with increases in Ir content. In Pt-Rh films, on the contrary, tensile stress increased only slightly with increases in Rh content up to approximately 40wt%.The Vickers hardness of the alloy films increased with increases in either Ir or Rh content, and this tendency is marked in the Pt-Ir alloy system Pt-80wt% Ir films shows a Vickers hardness of approximately 1200.Molds coated with pure Pt film or alloy films containing a small amount of Ir or Rh were degrated markedly by heat treatment at 600°C for 5hrs. Molds coated with Pt-Ir alloy films containing more than 30wt% of Ir, however, exhibited excellent performance despite heat treatment. No degradation was observed for molds coated with Pt-Ir alloy films containing more than 30wt% Ir.