Does the oxide layer take part in the oxygen evolution reaction on platinum?: A DEMS study

Using ¹⁸O labelling together with differential electrochemical mass spectroscopy (DEMS) it was found that (i) an ¹⁸O containing Pt-oxide layer does not exchange oxygen with H₂¹⁶O; (ii) only ¹⁶O¹⁶O is evolved from H₂¹⁶O on an ¹⁸O containing oxide layer, both in acid and in alkaline solutions. Consequently, the oxide layer does not take part in the oxygen evolution reaction on Pt electrodes.     

Investigation of the oxygen evolution reaction on Ti/IrO2 electrodes using isotope labelling and on-line mass spectrometry

Oxygen evolution on Ti/IrO₂ anodes has been studied in 1M HClO₄ electrolyte using ¹⁸O labelling together with differential electrochemical mass spectrometry (DEMS) measurements.It has been shown that during successive cyclic voltammetric measurements in H₂ ¹⁸O containing electrolyte the amount of ¹⁶O₂ (m/z = 32) decreases, with a concomitant increase of ¹⁸O¹⁶O (m/z = 34) after each cycle before reaching a steady state after four cycles. The obtained higher ¹⁶O₂ concentration in the evolved oxygen during the first scans is because ¹⁶O from the IrO₂ film contribute in the oxygen evolution reaction.Analysis of the experimental data has shown that the amount of lattice oxygen, which is involved in the oxygen exchange reaction, is in the order of 1% of the total IrO₂ loading. This is an indication that only the outer surface of the oxide electrode participates in the oxygen evolution reaction.In a second series of experiments it has been demonstrated that oxygen evolution on Ir¹⁶O₂ in H₂¹⁸O containing electrolyte result in the formation of Ir¹⁸O₂.Consequently, we can conclude that the IrO₂ layers participate in the oxygen evolution reaction in acid media at least to a several monolayer extend.     

EQCM Study of Ru and RuO2 Surface Electrochemistry

The present study represents comparative analysis of voltammetric and microgravimetric behavior of active ruthenium (Ru), electrochemically passivated ruthenium (Ru/RuO₂) and thermally formed RuO₂ electrodes in the solutions of 0.5 M H₂SO₄ and 0.1 M KOH. It has been found that cycling the potential of active Ru electrode within E ranges 0 V–0.8 V and 0 V–1.2 V in 0.5 M H₂SO₄ and 0.1 M KOH solutions, respectively, leads to continuous electrode mass increase, while mass changes observed in alkaline medium are considerably smaller than those in acidic one. Microgravimetric response of active Ru electrode in 0.5 M H₂SO₄ within 0.2 V–0.8 V has revealed reversible character of anodic and cathodic processes. The experimentally found anodic mass gain and cathodic mass loss within 0.2–0.8 V make 2.2–2.7 g F^?1, instead of 17 g F^?1, which is the theoretically predicted value for Ru(OH)₃ formation according to equation: Ru+3H₂O?Ru(OH)₃+3H⁺+3e^?. In the case of Ru/RuO₂ electrode relatively small changes in mass have been found to accompany the anodic and cathodic processes within E range between 0.4 V and 1.2 V in the solution of 0.5 M H₂SO₄. Meanwhile cycling the potential of thermally formed RuO₂ electrode under the same conditions has lead to continuous decrease in electrode mass, which has been attributed to irreversible dehydration of RuO₂ layer. On the basis of microgravimetric and voltammetric study as well as the coulometric analysis of the results conclusions are presented regarding the nature of surface processes taking place on Ru and RuO₂ electrodes.     

High-performance supercapacitors of hydrous ruthenium oxide/mesoporous carbon composites

The amorphous hydrous ruthenium oxide/mesoporous carbon composites (denoted as RuO₂·xH₂O/MC), obtained by loading small amount of amorphous hydrous ruthenium oxide nanoparticles ranged from 0.9 to 5.4% by weight of Ru (denoted as RuO₂·xH₂O) on mesoporous carbon (MC), were investigated for the first time and were used for supercapacitors. Electrochemical measurements showed that RuO₂·xH₂O/MC composites not only have an enhanced specific capacitance but also retain the superior rate capability of MC. The RuO₂·xH₂O/MC composite with Ru loading of 3.6 wt% exhibited an increase of the specific capacitance of approximately 57% (from 115 to 181 F/g) at the scan rate of 25 mV s⁻¹ in 0.1 M H₂SO₄ aqueous electrolyte. The specific capacitance based on the mass of RuO₂ was estimated to be 1,527 F/g, by subtracting the contribution from MC in the composite. Cycle performance tests for RuO₂·xH₂O/MC composite (3.6 wt% Ru) showed that approximately 2.8% loss of the total capacitance was observed after 1,000 cycles.     

Electroanalytical Responses of Arsenic Oxide,Methanol, and Oxygen at the Ruthenium Oxide–Hexachloroiridate with Platinum Hybrid Film

Electrochemically active ruthenium oxide (RuO_x?nH₂O), ruthenium oxide/hexachloroiridate (RuO_x?nH₂O/IrCl₆^2?), and ruthenium oxide/hexachloroiridate/platinum (RuO_x?nH₂O/IrCl₆^2?/Pt) hybrid films have been prepared from the mixture of Ru³⁺, IrCl₆^2?, and PtCl₆^2? ions in an acidic aqueous solution. The repetitive cyclic voltammetry (CV) has been used for the film preparation process. The electrochemical properties and the growth mechanism of the above mentioned different kinds of hybrid films have been investigated using CV and electrochemical quartz crystal microbalance. The morphological and quantitative analyses have been carried out using scanning electron microscopy, atomic force microscopy and energy dispersive X‐ray. Among these above mentioned films, RuO_x?nH₂O/IrCl₆^2?/Pt hybrid film exhibits promising electrocatalytic activity towards the oxidation of arsenic oxide, methanol and reduction of oxygen. Further, detailed study of electrocatalysis using rotating ring disk electrodes and amperometric methods have been carried out for arsenic oxide oxidation and oxygen reduction reactions at the hybrid films. From the results, the sensitivity of RuO_x?nH₂O/IrCl₆^2?/Pt hybrid film has been calculated for arsenic oxide as 0.7 mA mM^?1; and for oxygen as 1.8 mA mM^?1.     

Reduction behavior of Ru/CeO2 catalysts and their activity for wet oxidation

Three kinds of Ru/CeO₂ catalysts were prepared. The mobility of the oxygen on Ru and their catalytic activity in the wet oxidation of acetic acid was investigated. Ru was present in the form of RuO₂, and TPR experiment showed that the reaction, RuO₂ + 2H₂ Ru + 2H₂O, took place in different temperature ranges depending upon the kind of the catalysts. The catalyst with easily reducible oxygen on Ru had high activity in wet oxidation, and the importance of the release of oxygen from Ru to the reactant was suggested.     

Fabrication of ruthenium-doped TiO2 electrodes by one-step anodization for electrolysis applications

Anodic TiO₂ films with a doping of Ru ions on the surface were coincidently prepared by facile one-step anodization for application of the electrode in electrolysis. We found that the amount of Ru ions on the surface of the oxide could be determined based on the applied potential in KRuO₄ electrolyte, which provided negative RuO₄^– ions through dissociation. Overpotentials for the evolution of both O₂ and Cl₂ were greatly reduced when the coincidently-Ru-doped TiO₂ was employed. The Ru-doped electrode prepared at 60 V showed the highest electrocatalytic activity due to the largest amount of Ru incorporation in the oxide.     

Surface analysis of a glass leached with stable isotopes

The distribution of oxygen and other elements within the leached layer of a soda-lime glass after a short-time treatment (15–60 min) in pure H₂ ¹⁸O and D₂ ¹⁸O was investigated by means of neutral primary beam secondary ion mass spectrometry (NPB-SIMS). The¹⁸O^– profiles resulting from the penetration of an oxygen containing species are not disturbed by interference of the species H₂ ¹⁶O^–, originating from the residual gas in the vacuum chamber. In agreement with previous results, no isotope effect could be detected. Hydration of the glass leads to a pronounced matrix effect which impedes oxygen analysis in the negative secondary ion mode. The ratio of the maximum¹⁸O^– intensity in the leached layer to the¹⁶O^– intensity in the bulk was recorded as a function of time for one series of experiments. The result is in accordance with the time-dependence of the Na₂O concentration in the leached layer.     

Thermal Activation of CH4 and H2 as Mediated by the Ruthenium Oxide Cluster Ions [RuOx]+ (x=1–3): On the Influence of Oxidation States

Thermal gas-phase reactions of the ruthenium-oxide clusters [RuO_x]⁺ (x=1–3) with methane and dihydrogen have been explored by using FT-ICR mass spectrometry complemented by high-level quantum chemical calculations. For methane activation, as compared to the previously studied [RuO]⁺/CH₄ couple, the higher oxidized Ru systems give rise to completely different product distributions. [RuO₂]⁺ brings about the generations of [Ru,O,C,H₂]⁺/H₂O, [Ru,O,C]⁺/H₂/H₂O, and [Ru,O,H₂]⁺/CH₂O, whereas [RuO₃]⁺ exhibits a higher selectivity and efficiency in producing formaldehyde and syngas (CO+H₂). Regarding the reactions with H₂, as compared to CH₄, both [RuO]⁺ and [RuO₂]⁺ react similarly inefficiently with oxygen-atom transfer being the main reaction channel; in contrast, [RuO₃]⁺ is inert toward dihydrogen. Theoretical analysis reveals that the reduction of the metal center drives the overall oxidation of methane, whereas the back-bonding orbital interactions between the cluster ions and dihydrogen control the H−H bond activation. Furthermore, the reactivity patterns of [RuO_x]⁺ (x=1–3) with CH₄ and H₂ have been compared with the previously reported results of Group 8 analogues [OsO_x]⁺/CH₄/H₂ (x=1–3) and the [FeO]⁺/H₂ system. The electronic origins for their distinctly different reaction behaviors have been addressed.     

Loading of Se/Ru/C electrocatalyst on a rotating ring-disk electrode and the loading impact on a H2O2 release during oxygen reduction reaction

The impact of the Se/Ru/C catalyst loading on the oxygen reduction reaction (ORR) was studied using the rotating disk (RDE) and rotating ring-disk electrode (RRDE) techniques. The catalyst was deposited on a glassy carbon tip and the catalyst loading varied from 5 to 200 μg cm⁻². Two catalysts with a different metal to carbon support ratios were studied. When the amount of the catalyst deposited on the electrode was decreased, a dramatic decrease in the ORR activity was found. Lowering the catalyst loading led, simultaneously, to a larger fraction of H₂O₂ released into the electrolyte. These observations suggest that the oxygen reduction to H₂O on the Se/Ru/C electrocatalyst occurs through a H₂O₂ intermediate. When the amount of the catalyst on the disk increases, H₂O₂ is efficiently reduced to H₂O before it can escape from the catalyst layer into the solution, or towards a membrane in a fuel cell.     

Detailed Description of Pulse Isotopic Exchange Method for Analyzing Oxygen Surface Exchange Behavior on Oxide Ion Conductors

A novel pulse ¹⁸O-¹⁶O isotopic exchange (PIE) technique for measurement of the rate of oxygen surface exchange of oxide ion conductors was presented. The technique employs a continuous flow packed-bed micro-reactor loaded with the oxide powder. The isothermal response to an ¹⁸O-enriched pulse passing through the reactor, thereby maintaining chemical equilibrium, is measured by on-line mass spectrometry. Evaluation of the apparent exchange rate follows from the uptake of ¹⁸O by the oxide at given reactor residence time and surface area available for exchange. The developed PIE technique is rapid, simple and highly suitable for screening and systematic studies. No rapid heating/quenching steps are required to facilitate ¹⁸O tracer anneal or analysis, as in other commonly used techniques based upon oxygen isotopic exchange. Moreover, the relative distribution of the oxygen isotopologues ¹⁸O₂, ¹⁶O¹⁸O, and ¹⁶O₂ in the effluent pulse provides insight into the mechanism of the oxygen exchange reaction. The PIE technique has been demonstrated by measuring the exchange rate of selected oxides with enhanced oxide ionic conductivity in the range of 350?900 oC. Analysis of the experimental data in terms of a model with two consecutive, lumped steps for the isotopic exchange reaction shows that for mixed conductors Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-δ(BSCF) and La₂NiO_4+δ the reaction is limited by the apparent rate of dissociative adsorption of O₂ molecules at the oxide surface. For yttria-stabilized zirconia (YSZ), a change-over takes place, from rate-limitations by oxygen incorporation below ∽800 oC to rate-limitations by O₂ dissociative adsorption above this temperature. Good agreement is obtained with exchange rates reported for these materials in literature.     

Oxygen evolution on SrFeO3 electrode

Oxygen evolution reactions on SrFeO₃ were investigated in alkaline and acidic solutions. It was found that the catalytic activity for the oxygen evolution reaction in the alkaline solution is high. The following reaction steps (V)+Fe+2H₂O→(O)+FeOH₂+2H⁺+2e^? in acidic solution and FeOH+OH^?→FeO^?+H₂O in alkaline solution are presumed to be rate-controlling in the anodic evolution of oxygen on SrFeO₃ electrode, where (V) denotes oxygen vacancy on the electrode surface. The reaction mechanism and the catalytic property are discussed in connection to the band structure of the oxide.     

Oxygen evolution on nanocrystalline RuO2 and Ru0.9Ni0.1O2−δ electrodes – DEMS approach to reaction mechanism determination

The mechanism of the oxygen evolution on RuO₂ and Ru_0.9Ni_0.1O_2−δ anodes was studied in 0.1 M HClO₄ using ¹⁸labeling combined with differential electrochemical mass spectrometry (DEMS). It was shown that the mechanism of the oxygen evolution is potential sensitive. At potentials negative to 1.12 V vs. SCE all the evolved oxygen originates from the electrolyte solution. At higher potentials an additional mechanism involving an exchange of the oxygen between electrolyte and electrocatalyst starts to apply. The extent of this oxygen exchange mechanism reflects the chemical composition of the electrocatalyst and is significantly higher at Ru_0.9Ni_0.1O_2−δ electrodes.     

焙烧气氛对Ru/Al2O3催化剂上甲烷部分氧化制合成气反应性能的影响

采用气相色谱、质谱和原位时间分辨红外光谱等技术对空气和Ar气氛中焙烧的Ru/Al2O3催化剂样品上甲烷部分氧化(POM)制合成气反应进行了跟踪,并采用化学吸附、X射线衍射、拉曼光谱和H2-程序升温还原等技术对催化剂进行了表征.结果表明,在Ru/Al2O3-Air上POM反应出现振荡现象,而在Ru/Al2O3-Ar上则可...     

Electrochemical and physical characterization of Pt–Ru alloy catalyst deposited onto microporous–mesoporous carbon support derived from Mo2C at 600 °C

The electrochemical reduction of oxygen on binary Pt–Ru alloy deposited onto microporous–mesoporous carbon support was studied in 0.5 M H₂SO₄ solution using cyclic voltammetry, rotating disk electrode (RDE), and impedance method. The microporous–mesoporous carbon support C(Mo₂C) with specific surface area of 1,990 m²?g^?1 was prepared from Mo₂C at 600 °C using the chlorination method. Analysis of X-ray diffraction, photoelectron spectroscopy, and high-resolution transmission electron microscopy data confirms that the Pt–Ru alloy has been formed and the atomic fraction of Ru in the alloy was ～0.5. High cathodic oxygen reduction current densities (?160 A?m^?2 at 3,000 rev?min^?1) have been measured by the RDE method. The O₂ diffusion constant (1.9?±?0.3?×?10^?5?cm²?s^?1) and the number of electrons transferred per electroreduction of one O₂ molecule (～4), calculated from the Levich and Koutecky–Levich plots, are in agreement with literature data. Similarly to the Ru/RuO₂ system in H₂SO₄ aqueous solution, nearly capacitive behavior was observed from impedance data at very low ac frequencies, explained by slow electrical double-layer formation limited by the adsorption of reaction intermediates and products into microporous–mesoporous Pt–Ru–C(Mo₂C) catalyst. All results obtained for C(Mo₂C) and Pt–Ru–C(Mo₂C) electrodes have been compared with corresponding data for commercial carbon VULCAN® XC72 (C(Vulcan)) and Pt–Ru–C(Vulcan) electrodes processed and measured in the same experimental conditions. Higher activity for C(Mo₂C) and Pt–Ru–C(Mo₂C) has been demonstrated.     

Connecting ruthenium substituted Keggin-type tungstophosphates by oxotungstic bridges: Evidence for the steric effect of {RuL3}2+ (L3 = η6-arene, (DMSO)3) fragments

The intrinsic reactivity of the organoruthenium-grafted tungstophosphates [α-PW₁₁O₃₉{Ru(η⁶-arene)(H₂O)}]^5? and [α-PW₁₁O₃₉{Ru(DMSO)₃(H₂O)}]^5? has been studied as a prerequisite for later catalytic studies. Upon reflux in aqueous solution, they partially transform into [{PW₁₁O₃₉Ru(η⁶-arene)}₂{WO₂}]^8? (when arene = benzene, toluene…) and [α-PW₁₁O₃₉{Ru(DMSO)}]^5?, respectively. In the former case, the conversion is markedly increased by deliberate addition of tungstate: through a solution NMR study, we show that [{PW₁₁O₃₉Ru(η⁶-p-cymene)}₂{WO₂}]^8? is quantitatively obtained by refluxing a 2:1:2 mixture of [α-PW₁₁O₃₉]^7?, [Ru(η⁶-p-cymene)Cl₂]₂ and [WO₄]^2? at pH 3. In contrast, a different type of complex, [{PW₁₁O₃₉Ru(DMSO)₃}₂{(WO₂(H₂O))₂O}]^8?, is formed by reaction of [α-PW₁₁O₃₉{Ru(DMSO)₃(H₂O)}]^5? with tungstate; it has been characterized by single crystal X-ray diffraction analysis of an acidic potassium salt, and by ¹⁸³W solution NMR. The more sterically demanding {Ru(DMSO)₃}²⁺ fragment probably does not allow the formation of [{PW₁₁O₃₉Ru(DMSO)₃}₂{WO₂}]^8?, while connection of {PW₁₁O₃₉Ru(DMSO)₃}^5? subunits is possible through the larger {(WO₂(H₂O))₂O}²⁺ bridge.     

氧化钌/石墨纳米片复合阵列电极的制备及其电容性能

通过电化学剥离法在石墨棒表面构筑了层数不等、彼此平行且垂直于基底的二维石墨纳米片(GNS)阵列, 而后采用阴极还原电沉积法在GNSs 表面均匀地包覆了一层氧化钌(RuO₂·xH₂O)薄膜, 形成了RuO₂·xH₂O/GNS 复合阵列电极. 电化学测试表明, RuO₂·xH₂O/GNS 复合阵列电极具有优良的超电容性能, 在0.5mol·L^-1 H₂SO₄电解质溶液中, 扫描速率为5 mV·s^-1, 电位窗口为0.9 V时, 其比电容高达4226 F·m^-2, 并且具有优异的循环性能, 经过20000圈充放电循环后, 电容保持率高达94.18%.     

Adsorption and desorption of different gases on Ru film in the dark and under UV irradiation

The adsorption and desorption of some vapors and gases (water, hydrogen, dinitrogen oxide, carbon monoxide, oxygen) on Ru film has been investigated at 305 K using a Tian-Calvet microcalorimeter. The initial heat of adsorption, the irreversible coverage and the temperature of maximum desorption rate indicate the following binding energy order: H₂>N₂O>H₂O>CO>O₂. The amount of photoadsorption (for H₂O, N₂O, H₂) and photodesorption (for CO and O₂) has also been determined by recording the pressure changes induced by UV irradiation of the Ru film.     

A Molecular Z-Scheme Artificial Photosynthetic System Under the Bias-Free Condition for CO2 Reduction Coupled with Two-electron Water Oxidation: Photocatalytic Production of CO/HCOOH and H2O2

Bio-inspired molecular-engineered systems have been extensively investigated for the half-reactions of H₂O oxidation or CO₂ reduction with sacrificial electron donors/acceptors. However, there has yet to be reported a device for dye-sensitized molecular photoanodes coupled with molecular photocathodes in an aqueous solution without the use of sacrificial reagents. Herein, we will report the integration of Sn^IV- or Al^III-tetrapyridylporphyrin (SnTPyP or AlTPyP) decorated tin oxide particles (SnTPyP/SnO₂ or AlTPyP/SnO₂) photoanode with the dye-sensitized molecular photocathode on nickel oxide particles containing [Ru(diimine)₃]²⁺ as the light-harvesting unit and [Ru(diimine)(CO)₂Cl₂] as the catalyst unit covalently connected and fixed within poly-pyrrole layer (RuCAT-RuC₂-PolyPyr-PRu/NiO). The simultaneous irradiation of the two photoelectrodes with visible light resulted in H₂O₂ on the anode and CO, HCOOH, and H₂ on the cathode with high Faradaic efficiencies in purely aqueous conditions without any applied bias is the first example of artificial photosynthesis with only two-electron redox reactions.