Electrochemical Properties of a Rhodium(III) Mono-Terpyridyl Complex and Use as a Catalyst for Light-Driven Hydrogen Evolution in Water

Molecular hydrogen (H₂) is considered one of the most promising fuels to decarbonize the industrial and transportation sectors, and its photocatalytic production from molecular catalysts is a research field that is still abounding. The search for new molecular catalysts for H₂ production with simple and easily synthesized ligands is still ongoing, and the terpyridine ligand with its particular electronic and coordination properties, is a good candidate to design new catalysts meeting these requirements. Herein, we have isolated the new mono-terpyridyl rhodium complex, [Rh^III(tpy)(CH₃CN)Cl₂](CF₃SO₃) (Rh-tpy), and shown that it can act as a catalyst for the light-induced proton reduction into H₂ in water in the presence of the [Ru(bpy)₃]Cl₂ (Ru) photosensitizer and ascorbate as sacrificial electron donor. Under photocatalytic conditions, in acetate buffer at pH 4.5 with 0.1 M of ascorbate and 530 μM of Ru, the Rh-tpy catalyst produces H₂ with turnover number versus catalyst (TON_Cat*) of 300 at a Rh concentration of 10 μM, and up to 1000 at a concentration of 1 μM. The photocatalytic performance of Ru/Rh-tpy/HA^–/H₂A has been also compared with that obtained with the bis-dimethyl-bipyridyl complex [Rh^III(dmbpy)₂Cl₂]⁺ (Rh2) as a catalyst in the same experimental conditions. The investigation of the electrochemical properties of Rh-tpy in DMF solvent reveals that the two-electrons reduced state of the complex, the square-planar [Rh^I(tpy)Cl] (Rh^I-tpy), is quantitatively electrogenerated by bulk electrolysis. This complex is stable for hours under an inert atmosphere owing to the π-acceptor property of the terpyridine ligand that stabilizes the low oxidation states of the rhodium, making this catalyst less prone to degrade during photocatalysis. The π-acceptor property of terpyridine also confers to the Rh-tpy catalyst a moderately negative reduction potential (Ep_c(Rh^III/Rh^I) = −0.83 V vs. SCE in DMF), making possible its reduction by the reduced state of Ru, [Ru^II(bpy)(bpy^•−)]⁺ (Ru⁻) (E_1/2(Ru^II/Ru⁻) = −1.50 V vs. SCE) generated by a reductive quenching of the Ru excited state (*Ru) by ascorbate during photocatalysis. A Stern–Volmer plot and transient absorption spectroscopy confirmed that the first step of the photocatalytic process is the reductive quenching of *Ru by ascorbate. The resulting reduced Ru species (Ru⁻) were then able to activate the Rh^III-tpy H₂-evolving catalyst by reduction generating Rh^I-tpy, which can react with a proton on a sub-nanosecond time scale to form a Rh^III(H)-tpy hydride, the key intermediate for H₂ evolution.     

Abkömmlinge der TiSi2-Struktur — ein neues Bauprinzip

Zusammenfassung Weitere Beispiele für das Auftreten des neuartigen Bauprinzips der Defektdisilicide werden in den pseudohomogenen Bereichen Rh(Ga,Ge)_2–x und Ir(Ga,Ge)_2–x aufgefunden. Eine vollständige Bestimmung der Struktur und damit der Vervielfachung (n) mit Hilfe von Einkristallen wird für Rh₁₀Ga₁₇, Ir₃Ga₅ und Rh₃₉ (Ga_0,5Ge_0,5)₅₈ gegeben. Ein beschränkter pseudohomogener Bereich wird bei Ru(Ga,Ge)_2–x beobachtet, während im System Mo–Ga–Ge die Verbindungen Mo(Ga_0,3Ge_0,7)₂ und Mo(Ga_0,7Ge_0,3)₂ mit TaSi₂- bzw. TiSi₂-Typ auftreten. Die Abhängigkeit zwischenV. E. K. und Ga-bzw. Ge-Defekt wird diskutiert.

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Novel examples for the existence of a particular structural pattern shown for defect disilicides have been observed within the pseudo-homogeneous regions of Rh(Ga,Ge)_2–x and Ir(Ga,Ge)_2–x . Structural data, especially the mode of multiplicity (n) of the subcell, have been determined from single crystals for Rh₁₀Ga₁₇, Ir₃Ga₅ and Rh₃₉ (Ga_0,5Ge_0,5)₅₈. A limited domain of pseudo-homogeneity also occurs for Ru(Ga,Ge)_2–x, while in the system Mo–Ga–Ge two ternary phases do exist, namely Mo(Ga_0,3Ge_0,7)₂ having TaSi₂-type and Mo(Ga_0,7Ge_0,3)₂ crystallizing with TiSi₂-type. Relations between theV. E. C. and the amount of the respective Ga- and Ge-defect of the various phases can be established.

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Implanting Atomic Dispersed Ru in PtNi Colloidal Nanocrystal Clusters for Efficient Catalytic Performance in Electro-oxidation of Liquid Fuels

Although PtRu alloy nanocatalysts have been certified to possess excellent electrocatalytic performance and CO-poisoning tolerance toward formic acid and methanol electro-oxidation, the unaffordable usages of ruthenium (Ru) and platinum (Pt) have greatly limited their widespread adoption. Here, a facile one-pot method is reported for implanting atomic dispersed Ru in PtNi colloidal nanocrystal clusters with different Ru/Pt/Ni molar ratios, greatly reducing the dosages of Pt and Ru, and further improving the catalytic performances for the electro-oxidation of formic acid and methanol. Through simple control of the amount of Ni(acac)₂ precursor, trimetallic Ru_0.3Pt_70.5Ni_29.2, Ru_0.6Pt_55.9Ni_43.5, Ru_0.2Pt_77.3Ni_22.5, and Ru_0.9Pt_27.3Ni_71.8 colloidal nanocrystal clusters (CNCs) are obtained. In particular, the Ru_0.3Pt_70.5Ni_29.2 CNCs exhibit excellent specific activities for formic acid and methanol electro-oxidation, that is, 14.2 and 15.3 times higher, respectively, than those of the Pt/C catalyst. Moreover, the Ru_0.3Pt_70.5Ni_29.2 CNCs also possess better anti-CO-poisoning properties and diffusion ability than the other RuPtNi CNCs. The excellent formic acid and methanol electro-oxidation activities of RuPtNi CNCs are ascribed to the optimal ligand effects derived from the Pt, Ni, and atomic dispersed Ru atoms, which can improve the OH adsorption ability and further the anti-CO-poisoning capability. This research opens a new door for increasing the electro-oxidation properties of liquid fuels by using lower dosages of noble metals in Pt-based catalysts.     

Neue komplexboride

V_0.5Ru_0.5B and Ni_0.5Ru_0.5B crystallize with FeB-type structure. The stability of these compounds with respect to the participating metals will be discussed within the structurally related monoborides. Fe_2.2Rh_0.8B and Fe_2.2Ir_0.8B crystallize with Fe₃C-type structure. The stabilizing influence ofT=Mo, W, Re, Ru, Os, Co, Rh, Ir, Pd and Pt will be investigated.

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Herrn Professor Dr.G. Brauer zum 65. Geburtstag mit herzlichen Wünschen gewidmet.     

Preparation and properties of the systems Co1−xRhxS2, Co1−xRuxS2, and Rh1−xRuxS2

Members of the systems Co_1−xRh_xS₂ (0 ≤ x ≤ 0.6) were prepared, and their crystallographic and magnetic properties studied. The observed ferromagnetic moments for compositions where x ≤ 0.2 indicate a ferromagnetic alignment between Co(3d⁷) and Rh(4d⁷) electrons. This is the first observation of localized behavior of 4d electrons in the pyrite structure. Members of the systems Co_1−xRu_xS₂ (0 ≤ x ≤ 1) and Rh_1−xRu_xS₂ (0.5 ≤ x ≤ 1) were also prepared and their crystallographic and magnetic properties studied. From comparison with the Co_1−xRh_xS₂ system, it appears that the 4d electrons of Rh(4d⁷) are localized in the presence of Co(3d⁷) but are delocalized in the presence of Ru(4d⁶). The magnetic susceptibility of the Co_1−xRu_xS₂ system is sensitive to the homogeneity of the products and indicates that Ru(4d⁶) behaves as a diamagnetic ion.     

Synthesis of nickel sulfide and nickel–iron sulfide nanoparticles from nickel dithiocarbamate complexes and their photocatalytic activities

[ Ni(dtc)₂] (dtc = N-(pyrrole-2-ylmethyl)-N-thiophenemethyldithiocarbamate ( 1 ), N-methylferrocenyl-N-(2-phenylethyl)dithiocarbamate ( 2 ), N-furfuryl-N-methylferrocenyldithiocarbamate ( 3 ), and (N-[pyrrole-2-ylmethyl]-N-thiophenemethyldithiocarbamato-S,S′)(thiocyanato-N)(triphenylphosphine)nickel(II) ( 4 ) complexes were prepared and characterized by elemental analysis, infrared, ultraviolet–visible, and nuclear magnetic resonance (¹H and ¹³C) spectroscopies. The data were consistent with the formation of square planar nickel(II) complexes, which was confirmed by single-crystal X-ray diffraction studies on 2 and 4 . Fe···Fe interactions exhibited by complex 2 led to supramolecular aggregation. The structure of 4 reveals intermolecular and intramolecular C-H···Ni anagostic interactions. The anion-sensing properties of 2 were studied with halide ions by cyclic voltammetry. It was observed that 2 acts as sensor for bromide. Complexes 1 , 2 , and 3 , were utilized to prepare nickel sulfide, nickel–iron sulfide-1, and nickel–iron sulfide-2, respectively. The composition, structure, morphology, and optical properties of nickel sulfide and nickel–iron sulfides were examined using powder X-ray diffraction, transmission electron microscopy, energy-dispersive X-ray spectroscopy, ultraviolet–visible, fluorescence, and infrared spectroscopy. Powder X-ray diffraction patterns of nickel sulfide, nickel–iron sulfide-1, and nickel–iron sulfide-2 indicate the formation of orthorhombic Ni₉S₈, cubic NiFeS₂, and cubic Ni₂FeS₄, respectively. The photocatalytic activities of as-prepared nickel sulfide and nickel–iron sulfide-1 nanoparticles were investigated for photodegradation of methylene blue and rhodamine-B under ultraviolet irradiation. Nickel–iron sulfide-1 nanoparticles show slightly higher photodegradation efficiency compared with the nickel sulfide nanoparticles.     

Carbon‐Supported Rh17S15‐Rh Electrocatalysts Applied in the Oxygen Reduction Reaction

Rh₁₇S₁₅‐Rh catalysts supported on acid‐treated carbon black were prepared from RhCl₃ by a facile method using sulfur source ((NH₄)₂S₂O₃) and reducing agent (NaBH₄), followed by an additional thermal treatment at 650 °C in argon. The prepared catalyst comprised an Rh₁₇S₁₅ single crystalline phase and a zero‐valent metal (Rh) phase supported on a conductive carbon. By XRD characterization, the constituent ratio of Rh₁₇S₁₅ to Rh in the electrocatalysts, ranging from 51–95 %, varied with the increase of amount of (NH₄)₂S₂O₃ or NaBH₄. Morphologies of the resulting catalysts were characterized by transmission electron microscopy (TEM) technique. Most of particles were found to have a distribution of agglomerates ranging in size from 10 to 50 nm. In studying the effect of the constituent phases of chalcogenide electrocatalysts on oxygen reduction reaction activity, it is paramount to understand and optimize the structure sensitivity of the reaction, which will aid in determining the optimal ratio of Rh₁₇S₁₅ to Rh of the electrocatalyst. Activity and stability of the prepared catalysts were addressed using a series of cyclic voltammetry (CV) experiments in 1 M HCl electrolyte, in which the electrocatalyst of 95 % of Rh₁₇S₁₅ was found to be the most stable. The rotating disk electrode (RDE) experiment indicated the sulfide catalyst with 82 % of Rh₁₇S₁₅ showed the better performance for the ORR, which was discussed based on the compromise between the stability for the constituent phase of Rh₁₇S₁₅ in 1 M HCl and enhanced activity found for Rh phase.     

Effects of thermal activation on the oxidation pathways of methanol at bulk Pt–Ru alloy electrodes

The competition between pathways that lead to adsorbed CO and CO₂ during the electrochemical oxidation of 1.0 M methanol in 0.1 M HClO₄ on two bulk Pt–Ru alloys (10 at.% Ru (X_Ru≈0.1) and 90 at.% Ru (X_Ru≈0.9)) was investigated for temperatures in the range of 25–80°C. On the high Ru content alloy studied (X_Ru≈0.9), the dissociative chemisorption of methanol was inhibited below 70°C; the faradaic current for methanol oxidation was low, and only small quantities of adsorbed CO and CO₂ were detected with infrared spectroscopy between 0.2–0.8 V (vs. RHE). At 80°C, strong infrared bands from CO₂ and adsorbed, atop coordinated CO were observed over the potential ranges of 0.4–0.8 V and 0.2–0.8 V, respectively. The infrared measurements are consistent with the observation that bulk, high Ru content alloy electrodes appear passivated toward methanol oxidation below 70°C. On the low Ru content alloy studied (X_Ru≈0.1), the methanol surface chemistry was similar to that of pure, polycrystalline Pt, but the electrode was more poison resistant than Pt. For both alloys, the persistence of strong adsorbed CO bands and rapid CO₂ production between 0.4–0.8 V suggests CO functions as a reactive species with high steady-state coverages at these potentials.     

Coordination compounds of 2-mercapto-1-methylimidazole with platinum(II), palladium(II), rhodium(III) and ruthenium(III)

Summary Complexes of 2-mercapto-1-methylimidazole (TMZ) with Pt^II, Pd^II, Rh^III and Ru^III of the general formulae Pt(TMZ)₂Cl₂, Pd(TMZ)₄Cl₂. Rh(TMZ)Cl₃ and Ru(TMZ)Cl₃ have been obtained. The thermal stabilities of the compounds were estimated by derivatographic measurements and the electron-donating atom of the measurements and the electron-donating atom of the ligand was identified from the i.r. absorbtion spectra. Lattice constants for the Pt^II and Pd^II complexes were estimated from their x-ray powder diffraction patterns.     

Nanoporous PtRu Alloys with Unique Catalytic Activity toward Hydrolytic Dehydrogenation of Ammonia Borane

Nanoporous (NP) PtRu alloys with three different bimetallic components were straightforwardly fabricated by dealloying PtRuAl ternary alloys in hydrochloric acid. Selective etching of aluminum from source alloys generates bicontinuous network nanostructures with uniform size and structure. The as‐made NP‐PtRu alloys exhibit superior catalytic activity toward the hydrolytic dehydrogenation of ammonia borane (AB) than pure NP‐Pt and NP‐Ru owing to alloying platinum with ruthenium. The NP‐Pt₇₀Ru₃₀ alloy exhibits much higher specific activity toward hydrolytic dehydrogenation of AB than NP‐Pt₃₀Ru₇₀ and NP‐Pt₅₀Ru₅₀. The hydrolysis activation energy of NP‐Pt₇₀Ru₃₀ was estimated to be about 38.9 kJ mol^?1, which was lower than most of the reported activation energy values in the literature. In addition, recycling tests show that the NP‐Pt₇₀Ru₃₀ is still highly active in the hydrolysis of AB even after five runs, which indicates that NP‐PtRu alloy accompanied by the network nanoarchitecture is beneficial to improve structural stability toward the dehydrogenation of AB.     

Metal complexes of ligands containing intercalating units. Synthesis of nickel(II), copper(II), rhodium(II), and platinum(II) complexes with diamine-substituted acridines and quinolines,and with mitonafide [N-(2,2-dimethylaminoethyl)-3-nitro-1, 8-naphthalimide] and related ligands

Summary The preparations and characterisation are reported of a range of complexes of Ni^II, Cu^II, Rh^II, and Pt^II with 6-chloro-2-methoxyacridine substituted in the 9-position with –NH(CH₂)_nNR₂ groups (where n=2 or 3, R=H or Me), and of complexes with 7-chloroquinoline analogously substituted in the 4-position. The preparations are also reported of complexes of the types [Rh(CH₃CO₂)₂L]₂, Cu(CH₃CO₂)₂L₂, PtL₂Cl₂, and (LH)₂[PtCl₄], where L=N-(2,2-dimethylaminoethyl)-3-nitro-1, 8-naphthalimide (mitonafide) and/or its 2,2-aminoethyl-, 2,2-aminopropyl-, or 2,2-dimethylaminopropyl analogues. Initial cytotoxicity studies are reported for some of the Pt compounds.     

Dimerization of bicyclo[2.2.1]hepta-2,5-diene in the presence of rhodium carboxylate complexes

Conclusions Bicyclo [2.2.1]hepta-2,5-diene (norborndiene) dimerizes in the presence of Rh (II) carboxylate complexes Rh₂(RCOO)₄ (R=CH₃, CF₃) at 25–100°C to form preferentially the products of (4+2) cycloaddition. The rate of the reaction in the presence of Rh₂ (CF₃COO)₄ is an order of magnitude higher than for Rh₂(CH₃COO)₄. Under the reaction conditions Rh(II) is reduced by norbornadiene to Rh(I).Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 635–639, March, 1982.     

Determination of Antimony in Environmental Samples by ETAAS Using Different Permanent Modifiers

Single noble metal permanent modifiers such as, Rh, Ir, and Ru, as well as mixed tungsten plus noble metal (W–Rh, W–Ru, W–Ir) permanent modifiers thermally deposited on the integrated platform of a transversally heated graphite atomizer (TGA) were employed for the determination of antimony in sludge, soil, sediment, coal, ash and water samples by electrothermal atomic absorption spectrometry (ETAAS).Microwave digests of solid samples and water samples were directly introduced into different pre-treated platforms of graphite tubes. The performance of the modifiers for accurate antimony determination in real samples depended strongly on the type of permanent modifier chosen. The single noble metal (Rh, Ir and Ru) permanent modifiers were suitable for analyte determinations in simpler matrices, such as waters (recoveries of certified values 95–105%), but the analyte recoveries of certified values in sludge, soil, sediment, coal, and ash samples were always lower than 90%. On the other hand, for the determination of antimony, using W–Rh, W–Ru, and W–Ir permanent modifiers presented recoveries of certified values within 95–105% for all the samples.Long-term stability curves obtained for the determination of antimony in environmental samples with different permanent modifiers (Rh, Ir, Ru, W–Rh, W–Ir, W–Ru) showed that the improvement in tube lifetime depends on the tungsten deposit onto the platform. The tungsten plus noble metal permanent modifier presents a tube lifetime of at least 40% longer compared to a single permanent modifier.     

Determination of Ultra-Trace Platinum,Palladium, Ruthenium,Rhodium, and Iridium in Rocks and Minerals by Inductively Coupled–Plasma Mass Spectrometry Following Nickel Sulfide Fire Assay Preconcentration and Open Mixed Acid Digestion

Platinum (Pt), palladium (Pd), ruthenium (Ru), rhodium (Rh), iridium (Ir), and osmiun (Os) are platinum-group elements with similar physic-chemical properties, and have important applications in geochemistry and environmental chemistry. However, due to their low abundance and inhomogeneous distribution in natural ores as well as the nugget effect, the accurate determination of the platinum-group elements has been a challenge for geological analysis. In this work, self-prepared and purified sodium carbonate (NiCO₃) instead of commercial nickel oxide (NiO) was used as the fire assay collector in order to greatly reduce the reagent blank and method detection limits. In addition, the fuming time of HClO₄ was strictly controlled at 10?min and a high sensitive method was developed for the simultaneous determination of ultra-trace Pt, Pd, Ru, Rh, and Ir in minerals by inductively coupled plasma-mass spectrometry (ICP-MS) following preconcentration with the nickel sulfide fire assay. Under the optimized conditions, the linear ranges of Pt, Pd, Ru, Rh, and Ir were between 0 and 100?ng mL^?1, with correlation coefficients exceeding 0.9997. The detection limits were 0.015, 0.056, 0.014, 0.004, 0.012?ng mL^?1 (for 10?g sample) for Pt, Pd, Ru, Rh and Ir, respectively. The developed method was successfully applied to analyze Chinese Certified Reference Materials (CRMs) GBW07288, GBW07289, GBW07290, GBW07291, GBW07292, GBW07293, GBW07294, GBW07101, GBW07102 and GBW07201 and the determined values were in good agreement with the certified values. The relative standard deviations (n?=?5) of Pt, Pd, Ru, Rh and Ir were between 3.42% and 6.87% for the determination of GBW07291.     

Analysis of the surface of PtxNi1?x alloys

Summary The surface composition of three polycrystalline Pt_xNi_1–x alloys (metal foils) was determined by ion scattering spectroscopy (ISS) with He ions of an energy of 1 keV. The targets have been pretreated by bombarding with rare-gas ions (He, Ar and Xe), by annealing at 500°C and by exposing them to increasing amounts of oxygen (up to 20 Langmuir). The results obtained from the polycrystalline alloys are compared to results from a Pt₁₀Ni₉₀ silica supported catalyst. The surface composition was also measured by ISS. The catalyst was pretreated by bombarding with He ions and by exposing it to 10 L oxygen.     

X-ray diffraction study of [Ru(NH3)5Cl][ReCl6] and [Ru(NH3)5Cl]2[ReCl6]Cl2 and their thermolysis products. Crystal-chemical analysis of the Ru-Re system

Binary complex salts [Ru(NH₃)₅Cl][ReCl₆] and [Ru(NH₃)₅Cl]₂[ReCl₆]Cl₂ were synthesized and characterized. An X-ray diffraction analysis showed that they were isostructural with the previously obtained isoformula salts [Rh(NH₃)₅Cl][OsCl₆] and [Ir(NH₃)₅Cl]₂[PtCl₆]Cl₂, respectively. Thermolysis of these compounds under hydrogen and helium was studied. According to X-ray phase analysis data, bimetallic solid solutions Ru_0.67Re_0.33 and Ru_0.50Re_0.50 were the final products of thermolysis. Their unit cell parameters correspond to the characteristics of alloys with similar compositions. Original Russian Text Copyright ? 2009 by S. A. Martynova, K. V. Yusenko, I. V. Korolkov, I. A. Baidina, and S. V. Korenev __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 50, No. 1, pp. 126–132, January–February, 2009.     

Study of silica supported PtxNi1-x catalysts by ion scattering spectroscopy

As supported Pt_xNi_1–x catalysts are used for hydrogenation reactions, it seemed necessary to assess the surface composition of the reduced samples. To approach the usual reduction conditions we applied in situ reduction in a reaction chamber (1 mbar H₂ up to 500 °C) placed in ultra high vacuum recipient (UHV: 10^–9 to 2.10^–10mbar). All ion scattering spectroscopy measurements were performed in UHV. Charging of the samples was avoided by electron bombardment (5 eV). The variation of the surface composition was determined after subsequent sputtering, thermal treatment at 500 °C and during oxygen adsorption. A comparison with previous results of surface compositions of binary alloys (polycrystalline foils [1, 2] and single crystals Pt_xNi_1–x [3]) is given.Dedicated to Professor Dr. rer. nat. Dr. h. c. Hubertus Nickel on the occasion of his 65th birthday     

Synthesis, properties, and thermal decomposition products of [Ru(NH3)5Cl][PtCl6] and [Ru(NH3)5Cl]2[PtCl6]Cl2

The double complex salts [Ru(NH₃)₅Cl][PtCl₆] (I) and [Ru(NH₃)₅Cl]₂[PtCl₆]Cl₂ (II) were synthesized and studied by X-ray diffraction. They were found to be isostructural to the previously synthesized [Rh(NH₃)₅Cl][OsCl₆] and [Ir(NH₃)₅Cl]₂[PtCl₆]Cl₂. The thermolysis of the complexes in the atmosphere of hydrogen and helium was studied by the powder X-ray diffraction analysis. The product of the salt I thermolysis is a single-phase solid solution Ru_0.5Pt_0.5 (a = 3.857(3) ?), the thermolysis of salt II results in a double-phase metallic powder. Original Russian Text ? S.A. Martynova, K.V. Yusenko, I.V. Korol’kov, S.A. Gromilov, 2007, published in Koordinatsionnaya Khimiya, 2007, Vol. 33, No. 7, pp. 541–545.     

Water‐Splitting Electrocatalysis in Acid Conditions Using Ruthenate‐Iridate Pyrochlores

The pyrochlore solid solution (Na_0.33Ce_0.67)₂(Ir_1?xRu_x)₂O₇ (0≤x≤1), containing B‐site Ru^IV and Ir^IV is prepared by hydrothermal synthesis and used as a catalyst layer for electrochemical oxygen evolution from water at pH<7. The materials have atomically mixed Ru and Ir and their nanocrystalline form allows effective fabrication of electrode coatings with improved charge densities over a typical (Ru,Ir)O₂ catalyst. An in situ study of the catalyst layers using XANES spectroscopy at the Ir L_III and Ru K edges shows that both Ru and Ir participate in redox chemistry at oxygen evolution conditions and that Ru is more active than Ir, being oxidized by almost one oxidation state at maximum applied potential, with no evidence for ruthenate or iridate in +6 or higher oxidation states.     

Thermodynamic parameters of liquid ternary Fe1−x(Ni5/6Cr1/6)x alloys

Summary Computer-aidedKnudsen cell mass spectrometry is used for thermodynamic investigations on liquid ternary Fe_1–x(Ni_5/6Cr_1/6)_x alloys. The thermodynamic excess properties have been determined by means of the Digital Intensity-Ratio (DIR) method. Liquid ternary Fe_1–x(Ni_5/6Cr_1/6)_x alloys are characterized by exothermic molar heats of mixingH ^E, negative molar excessGibbs energiesG ^E, and negative molar excess entropiesS ^E. At 1850 K, the minimumH ^E value is –3120 J/mol (42.3 at.% Fe), the minimumG ^E value is –2540 J/mol (30 at.% Fe), and the minimumS ^E value is –0.44 J/(mol K) (60 at.% Fe). At 1850 K, the thermodynamic activities of Fe show slight negative deviations from the ideal behaviour for alloys with a Fe-content of less than 75 at.%, and ideal behaviour for the Fe-rich alloys (x _Fe>0.75).

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Thermodynamische Parameter flüssiger ternärer Fe_1–x(Ni_5/6Cr_1/6)_x-Legierungen

Zusammenfassung Die Thermodynamik flüssiger ternärer Fe_1–x(Ni_5/6Cr_1/6)_x-Legierungen wurde mit Hilfe der computerunterstützten Knudsenzellen-Massenspektrometrie studiert. Die thermodynamische Auswertung der experimentellen Untersuchungen erfolgte nach der digitalen Intensitätsverhältnismethode (DIR). Flüssige ternäre Fe_1–x(Ni_5/6Cr_1/6)_x-Legierungen zeigen exotherme molare MischungswärmenH ^E, negative molareGibbssche ZusatzenergienG ^E, und negative molare ZusatzentropienS ^E. Bei 1850 K sind die Minimumswerte fürH ^E –3120 J/mol (42.3 At.% Fe), fürG ^E –2540 J/mol (30 At.% Fe) und fürS ^E –0.44 J/(mol K) (60 At.% Fe). Bei 1850 K zeigen die thermodynamischen Aktivitäten von Fe bei Legierungen mit einem Fe-Gehalt von höchstens 75 At.% leichte negative Abweichungen vom idealen Verhalten, die Fe-reichsten Legierungen (x _Fe>0.75) verhalten sich hingegen nahezu ideal.