Ru Oxidation Research Articles

Synergistic Engineering of Dopant and Support of Ru Oxide Catalyst Enables Ultrahigh Performance for Acidic Oxygen Evolution

AbstractActive and robust electrocatalysts for acidic oxygen evolution reaction (OER) are of crucial importance for efficient proton exchange membrane water electrolyzer (PEM‐WE). Ruthenium (Ru) oxide has attracted considerable attention due to its high activity. However, the unsatisfying stability of Ru oxide in acidic OER environments hinders the application. Here, Ce‐doped RuO2 nanoparticles are designed and supported on Co─N─C material (Ce@RuO2/CoNC) for acidic OER. It is demonstrated that Ce@RuO2/CoNC delivers a super low overpotential of 150 mV and an excellent stability of 1000 h at 10 mA cm−2, outperforming most previously reported Ru‐based catalysts. The mass activity is estimated as 2365.5 AgRu−1 at 1.5 V (vs RHE), representing ≈2× advance compared to the best prior study. Furthermore, applied in a single‐cell PEM‐WE device, it can steadily operate for 1000 h at 200 mA cm−2. The studies show that Ce‐doping and Co─N─C support synergistically enhance the activity and stability of Ru oxide by optimizing the free energies of OER intermediates and suppressing the dissolution of Ru.

Ruthenium Single-Atom Modulated Protonated Iridium Oxide for Acidic Water Oxidation in Proton Exchange Membrane Electrolysers.

Proton exchange membrane water electrolysers promise to usher in a new era of clean energy, but they remain a formidable obstacle in designing active and durable electrocatalysts for the acidic oxygen evolution reaction (OER). In this study, a protonated iridium oxide embedded with single-atom dispersed ruthenium atoms (H3.8Ir1- xRuxO4) that demonstrates exceptional activity and stability in acidic water oxidation is introduced. The single Ru dopants favorably induce localized oxygen vacancies in the Ir─O lattice, synergistically strengthening the adsorption of OOH* intermediates and enhancing the intrinsic OER activity. In addition, the preferential oxidation of Ru and the electronegativity of the oxygen vacancies significantly stabilize the Ir─O active sites, improving the OER stability. Consequently, the H3.8Ir1─ xRuxO4 catalyst shows an overpotential of 255mV at 10mA cm-2 and displays exceptional catalytic endurance in acidic electrolytes, surpassing 1100 h, representing a remarkable one-order-of-magnitude increase in stability compared to that of pristine H3.8IrO4. A proton exchange membrane electrolyser utilizing the H3.8Ir1- xRuxO4 catalyst as an anode exhibits stable performance for more than 1280 h under a high current density of 2 A cm-2.

Structural development on Ru and RuO2 electrodes during oxygen evolution – a soft X-ray absorption spectroscopy approach

Time resolved in-situ X-ray absorption spectroscopy (XAS) in soft X-ray region was used to characterize polarized interphase on Ru and Ru oxide based electrodes under oxygen evolution reaction (OER) conditions. XAS spectra were used to align the type and population of oxygen-containing species formed at electrodes at anodic potentials with local electronic structure of the OER catalyst. The soft XAS data do not identify a single rate limiting process for OER at potentials negative to 1.7 V vs. RHE. Individual intermediates of the oxygen evolution process coexist at the surface at potentials preceding the actual OER onset. The OER is accompanied with redistribution of the electron density resulting for a start of the catalytic cycle reflecting the transfer of the electrons from water to the external circuit during catalyzed water oxidation. The observed spectral behavior indicates a confinement of the OER to the coordination unsaturated sites (cus) at the surface.

N‐heterocyclic carbene complexes RuII(arene) and their application as ROMP catalysts, antioxidant and anticancer agents

N‐Heterocyclic carbenes (NHCs) play an important role in metal complex catalysis and stabilisation, providing stability under non‐inert conditions and a high σ‐donor capacity. They are crucial ligands for the synthesis of organometallic compounds like RuII‐complexes, which can operate as very active catalysts for a variety of chemical transformations and functionalizations. RA(Ruthenium‐arene)NHC complexes, known for their piano‐stool structure, stabilise Ru(II) oxidation by occupying three ruthenium coordination sites with a η6‐coordinated arene ligand. The development of dual‐acting RuII‐arene complexes has sparked increased interest in their catalytic and biological properties. Because of their broad spectrum, metal complexes can give distinct mechanisms of pharmacological action than organic drugs. This study aimed to explore the impact of ligand amphiphilicity and counterion on bioactivity, designing a family of compounds with the NHC ligand bearing an ester moiety and switching the wingtip substituent from methyl to benzyl units. All synthesized compounds were tested in norbornene ROMP, a benchmark reaction for RuII potential catalysts and as anticancer and antioxidant compounds.

Photoacoustic Spectroscopy of Titanium Dioxide, Niobium Pentoxide, Titanium:Niobium, and Ruthenium-Modified Oxides Synthesized Using Sol-Gel Methodology.

The aim of this work was the development and morphological/chemical, spectroscopic, and structural characterization of titanium dioxide, niobium pentoxide, and titanium:niobium (Ti:Nb) oxides, as well as materials modified with ruthenium (Ru) with the purpose of providing improvement in photoactivation capacity with visible sunlight radiation. The new materials synthesized using the sol-gel methodology were characterized using the following techniques: scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), photoacoustic spectroscopy (PAS), and X-ray diffraction (XRD). The SEM-EDS analyses showed the high purity of the bases, and the modified samples showed the adsorption of ruthenium on the surface with the crystals' formation and visible agglomerates for higher calcination temperature. The nondestructive characterization of PAS in the ultraviolet visible region suggested that increasing calcination temperature promoted changes in chemical structures and an apparent decrease in gap energy. The separation of superimposed absorption bands referring to charge transfers from the ligand to the metal and the nanodomains of the transition metals suggested the possible absorption centers present at the absorption threshold of the analyzed oxides. Through the XRD analysis, the formation of stable phases such as T-Nb16.8O42, o-Nb12O29, and rutile was observed at a lower temperature level, suggesting pore induction and an increase in surface area for the oxides studied, at a calcination temperature below that expected by the related literature. In addition, the synthesis with a higher temperature level altered the previously existing morphologies of the Ti:Nb, base and modified with Ru, forming the new mixed crystallographic phases Ti2Nb10O29 and TiNb2O7, respectively. As several semiconductor oxide applications aim to reduce costs with photoexcitation under visible light, the modified Ti:Ru oxide calcined at a temperature of 800 °C and synthesized according to the sol-gel methodology used in this work is suggested as the optimum preparation point. This study presented the formation of a stable crystallographic phase (rutile), a significant decrease in gap energy (2.01 eV), and a visible absorption threshold (620 nm).

The surface chemistry of the atomic layer deposition of ruthenium on aluminum and tantalum oxide surfaces

The surface chemistry of Ru atomic layer deposition (ALD) processes based on the use of tris(2,2,6,6-tetramethyl-3,5-heptanedionato)ruthenium(III) (Ru(tmhd)3) and either molecular oxygen or atomic hydrogen on aluminum oxide films was characterized by a combination of surface-sensitive techniques. The thermal decomposition of the Ru metalorganic precursor was determined, by using a combination of reflection-absorption infrared spectroscopy (RAIRS), temperature programmed desorption (TPD), and X-ray photoelectron spectroscopy (XPS), to start below 400 K and to take place in a stepwise fashion over a wide range of temperatures. Gas-phase products from this chemistry include 2,2,6,6-tetramethyl-3,5-heptanedione (the protonated ligand, Htmhd; in a TPD peak at 520 K), isobutene (540 K; indicating the fragmentation of the organic ligands), and other products from isomerization and/or aldol condensation (650 and 730 K). This chemistry is accompanied by the reduction of the Ru3+ ions in two stages, involving the loss of some of their ligands and their direct bonding to the substrate first (between 500 and 600 K) and a full reduction to a metallic state later on (600–700 K). ALD cycles using either molecular oxygen or atomic hydrogen resulted in the slow build-up of Ru on the surface, but the co-deposition of carbon could not be avoided, at least in the initial cycles, while the alumina surface was still exposed. With O2, the Ru atoms alternate between partially-oxidized (after the O2 exposures) and zero-valent (after the Ru(tmhd)3 doses) states, and some Ru loss in the form of the volatile RuO4 oxide was seen after the second half of the ALD cycles; neither the Ru oxidation state alternation nor the elimination of some Ru from the surface were observed when using H·. The deposited Ru was determined, by combining results from angle-resolved XPS (ARXPS) and low-energy ion scattering (LEIS) experiments, to grow as 3D nanoparticles rather than as a layer-by-layer 2D film, presumably because the Ru precursor preferentially adsorbs (and decomposes more cleanly) on the metal surface. A discussion is provided of the implications of these results for the design of ALD processes.

Stereoscopic Imaging of Single Molecules at Plasma Membrane of Single Cell Using Photoreduction-Assisted Electrochemistry.

Stereoscopic imaging of single molecules at the plasma membrane of single cell requires spatial resolutions in 3 dimensions (x-y-z) at 10-nm level, which is rarely achieved using most optical super-resolution microscopies. Here, electrochemical stereoscopic microscopy with a detection limit down to a single molecule is achieved using a photoreduction-assisted cycle inside a 20-nm gel electrolyte nanoball at the tip of a nanopipette. On the basis of the electrochemical oxidation of Ru(bpy)3 2+ into Ru(bpy)3 3+ followed by the reduction of Ru(bpy)3 3+ into Ru(bpy)3 2+ by photogenerated isopropanol radicals, a charge of 1.5 fC is obtained from the cycling electron transfers involving one Ru(bpy)3 2+/3+ molecule. By using the nanopipette to scan the cellular membrane modified with Ru(bpy)3 2+-tagged antibody, the morphology of the cell membrane and the distribution of carcinoembryonic antigen (CEA) on the membrane are electrochemically visualized with a spatial resolution of 14 nm. The resultant stereoscopic image reveals more CEA on membrane protrusions, providing direct evidence to support easy access of membrane CEA to intravenous antibodies. The breakthrough in single-molecule electrochemistry at the cellular level leads to the establishment of high-resolution 3-dimensional single-cell electrochemical microscopy, offering an alternative strategy to remedy the imperfection of stereoscopic visualization in optical microscopes.

Plasma atomic layer etching of ruthenium by oxygen adsorption-removal cyclic process

Ruthenium (Ru) is a next-generation metal interconnect material, and the demand for precise etching is on the rise. This study explores anisotropic atomic layer etching (ALE) of Ru, utilizing various oxygen adsorption methods (O radical, oxygen plasma, or O2 molecule) and two types of plasma sources: inductively coupled plasma (ICP) and ion beam source. Through ICP ALE, an etch per cycle (EPC) of ∼ 1.5 Å/cycle was achieved using oxygen plasma for adsorption. For ion beam ALE, EPC values of ∼ 0.8 Å/cycle were obtained using oxygen radical, and ∼ 0.4 Å/cycle through physisorption using oxygen molecule without plasma generation. The higher EPC with the ICP ALE was attributed to spontaneous etching during oxygen adsorption during the oxygen plasma generation. Conversely, the lower EPC with ion beam ALE during oxygen adsorption using O2 molecule without plasma generation resulted from nonuniform oxidation of Ru during the adsorption step. Among the three ALE methods, optimal Ru ALE with 100 % ALE synergy was achieved with ion beam ALE, likely due to the absence of ion bombardment during oxygen adsorption and the precise Ar+ ion energy for removing RuOx formed on the surface.

Role of alumina particles in chemical-mechanical synergies in ruthenium polishing

Abrasive particles are usually considered to only play a "mechanical wear" role in the metal chemical mechanical polishing (CMP) process, neglecting their influence on chemical reactions. This study reveals the chemical role of Al2O3 particles in ruthenium (Ru) CMP by comparing the properties and polishing performance of Al2O3-SiO2 mixed slurry and pure SiO2 slurry. Several testing methods are used to investigate the mechanical and chemical actions of Al2O3 particles, including particle size distribution, Zeta potential, electrochemical reaction kinetics, oxide layer property and hydroxyl radical detection test. The results indicate that Al2O3 particles enhance the mechanical action by reducing the Zeta potential, and promote the chemical action by catalyzing hydrogen peroxide to produce hydroxyl radical (Fenton-like reaction) on Ru surface. These increase the material removal rate of Ru CMP with mixed slurry by nearly 5 times, while the surface roughness decreases by 60 %. The mechanism of chemical reaction promoted by increasing the hydroxyl radical concentration on Ru surface is confirmed from the aspects of increased corrosion current, oxide layer thickness and proportion of higher-valence Ru oxide (RuO2) in the oxide layer. Among them, the thickened oxide layer is a significant factor contributing to the substantial improvement in the material removal rate of Ru and the reduction in surface roughness. This study enhances the understanding of the chemical-mechanical synergistic mechanism of abrasive particles in metal polishing and elucidates the principle of this mechanism on promoting material removal and surface quality. It also provides new research ideas and theoretical guidance for efficient and high-quality metal polishing.

Defect Engineering in Composition and Valence Band Center of Y2(YxRu1-x)2O7-δ Pyrochlore Electrocatalysts for Oxygen Evolution Reaction.

Oxygen evolution reaction (OER) takes place in various types of electrochemical devices that are pivotal for the conversion and storage of renewable energy. This paper describes a strategy in the design of solid-state structures of OER electrocatalysts through controlling the cation substitution on the active metal site and consequently valence band center position of site-mixed Y2(YxRu1-x)2O7-δ pyrochlore to achieve high catalytic activity. We found that partially replacing the B-site Ru4+ cation with A-site Y3+ in pyrochlore-structured Y2Ru2O7-δ modifies the oxidation state of B-site Ru from 4+ to 5+, as observed by electron paramagnetic resonance (EPR) spectroscopy but does not continuously increase the oxygen vacancy concentration in these oxygen substoichiometric compositions, as quantified by thermogravimetric analysis (TGA) decomposition studies. We found the increased Ru oxidation state leads to a downshift in valence band center. X-ray photoelectron spectroscopy (XPS) analysis was performed to quantitatively determine the optimal band center to be ∼1.27 eV below the Fermi energy level based on the analysis of the valence band edge of these Ru-based Y2(YxRu1-x)2O7-δ OER electrocatalysts. This work highlights that defect engineering can be a practical, effective approach to the optimization of oxidation state and electronic band center for high OER catalytic performance in a quantitative manner.

Ultra‐Dense Supported Ruthenium Oxide Clusters via Directed Ion Exchange for Efficient Valorization of 5‐Hydroxymethylfurfural

AbstractMaximizing the loadings of active centers without aggregation for a supported catalyst is a grand challenge but essential for achieving high gravimetric catalytic activity, especially toward multi‐step reactions. The oxidation of 5‐hydroxymethylfurfural (HMF), a key biomass‐derived platform molecule, into 2,5‐furandicarboxylic acid (FDCA), a promising alternative to polyester monomer, is such a multi‐step reaction that involves 6 proton and electron transfers. This process often demands strong alkaline environment but also suffers from the alkali‐driven polymerization side‐reaction. Meanwhile, neutral media ameliorates the polymerization, but lacks efficient catalyst toward deep oxidation. Herein, we devised a strategy of creating ultra‐dense supported Ru oxide clusters via directed ion exchange in a Co hydroxyanion (CoHA) support material. Pyrimidine ligands were first incorporated into the CoHA interlayers, and the subsequent evacuation of pyrimidines created porous channels for the directed ion exchange with the built‐in anions in CoHA, which allowed the dense and mono‐disperse functionalization of RuCl62− anions and their resulting Ru oxide clusters. These ultra‐dense Ru oxide clusters not only enable high HMF electrooxidation currents under neutral conditions but also create microscopic channels in‐between the clusters for the expedited re‐adsorption and oxidation of intermediates toward highly oxidized product, such as 5‐formyl‐2‐furoic acid (FFCA) and FDCA. A two‐stage HMF oxidation process, consisting of ambient conversion of HMF into FFCA and FFCA oxidation into FDCA under 60 °C, was eventually developed to first achieve a high FDCA yield of 92.1 % under neutral media with significantly reduced polymerization.

Ultra-Dense Supported Ruthenium Oxide Clusters via Directed Ion Exchange for Efficient Valorization of 5-Hydroxymethylfurfural.

Maximizing the loadings of active centers without aggregation for a supported catalyst is a grand challenge but essential for achieving high gravimetric catalytic activity, especially toward multi-step reactions. The oxidation of 5-hydroxymethylfurfural (HMF), a key biomass-derived platform molecule, into 2,5-furandicarboxylic acid (FDCA), a promising alternative to polyester monomer, is such a multi-step reaction that involves 6 proton and electron transfers. This process often demands strong alkaline environment but also suffers from the alkali-driven polymerization side-reaction. Meanwhile, neutral media ameliorates the polymerization, but lacks efficient catalyst toward deep oxidation. Herein, we devised a strategy of creating ultra-dense supported Ru oxide clusters via directed ion exchange in a Co hydroxyanion (CoHA) support material. Pyrimidine ligands were first incorporated into the CoHA interlayers, and the subsequent evacuation of pyrimidines created porous channels for the directed ion exchange with the built-in anions in CoHA, which allowed the dense and mono-disperse functionalization of RuCl6 2- anions and their resulting Ru oxide clusters. These ultra-dense Ru oxide clusters not only enable high HMF electrooxidation currents under neutral conditions but also create microscopic channels in-between the clusters for the expedited re-adsorption and oxidation of intermediates toward highly oxidized product, such as 5-formyl-2-furoic acid (FFCA) and FDCA. A two-stage HMF oxidation process, consisting of ambient conversion of HMF into FFCA and FFCA oxidation into FDCA under 60 °C, was eventually developed to first achieve a high FDCA yield of 92.1 % under neutral media with significantly reduced polymerization.

Wafer-scale development, characterization, and high temperature stabilization of epitaxial Cr2O3 films grown on Ru(0001).

This work outlines conditions suitable for the heteroepitaxial growth of Cr2O3(0001) films (1.5-20nm thick) on a Ru(0001)-terminated substrate. Optimized growth is achieved by sputter deposition of Cr within a 4mTorr Ar/O2 20% ambient at Ru temperatures ranging from 450 to 600 °C. The Cr2O3 film adopts a 30° rotated honeycomb configuration with respect to the underlying Ru(0001) substrate and exhibits a hexagonal lattice parameter consistent with that for bulk Cr2O3(0001). Heating to 700 °C within the same environment during film preparation leads to Ru oxidation. Exposure to temperatures at or above 400 °C in a vacuum, Ar, or Ar/H2 3% leads to chromia film degradation characterized by increased Ru 3d XPS intensity coupled with concomitant Cr 2p and O 1s peak attenuations when compared to data collected from unannealed films. An ill-defined but hexagonally well-ordered RuxCryOz surface structure is noted after heating the film in this manner. Heating within a wet Ar/H2 3% environment preserves the Cr2O3(0001)/Ru(0001) heterolayer structure to temperatures of at least 950 °C. Heating an Ru-Cr2O3-Ru heterostacked film to 950 °C within this environment is shown by cross-sectional scanning/transmission electron microscopy (S/TEM) to provide clear evidence of retained epitaxial bicrystalline oxide interlayer structure, interlayer immiscibility, and epitaxial registry between the top and bottom Ru layers. Subtle effects marked by O enrichment and O 1s and Cr 2p shifts to increased binding energies are noted by XPS in the near-Ru regions of Cr2O3(0001)/Ru(0001) and Ru(0001)/Cr2O3(0001)/Ru(0001) films after annealing to different temperatures in different sets of environmental conditions.

NdMn1.5Ru0.5O5, a high-performance electrocatalyst with low Ru content for acidic oxygen evolution reaction

A mixed oxide with the crystal structure of the DyMn2O5 family, namely NdMn1.5Ru0.5O5, is reported active for the oxygen evolution reaction (OER) in acidic media. NdMn1.5Ru0.5O5 displays high OER activity of 500 A gRu−1 at 1.5 V. Moreover, is more stable than most Ru oxides reported to date, remaining active for more than 500 cycles between 1.1. and 1.7 V at low scan rate of 10 mV s−1. The high activity and stability are attributed to the Ru cations, as NdMn2O5 exhibits very low OER activity. NdMn1.5Ru0.5O5 has particularly short Ru–Ru distances of 2.60 Å, a value close to the Ru–Ru metallic distances around 2.642 Å. The high activity and durability of NdMn1.5Ru0.5O5 for the OER are also demonstrated in a proton exchange membrane water electrolysis cell by producing a low-loaded anode electrode with 0.5 mgRucm−2. The cell achieves 1.97 V at 0.5 A cm−2, consistent with the performances reported for Ru-based catalysts but with lower Ru loading. This performance is maintained during 100 h of operation. Additionally, NdMn1.5Ru0.5O5 displays visible ORR activity in acidic media, recording an onset potential of 0.85 V at 0.1 mA cm−2. It is noteworthy to highlight the extreme rarity of bifunctional ORR/OER catalysts acidic media.

Inhibiting effect of graphdiyne on Ru(bpy)32+ ECL and its application in drug detection based on the host–guest interaction of cucurbit[8]uril

Graphdiyne (GDY) is considered as another promising carbon material in biosensing field. However, the application of GDY in ECL sensing is in its infancy stage, and different roles of GDY are urgent to be discovered. In this work, strong anodic Ru(bpy)32+ electrochemiluminescence (ECL) was obtained at a cucurbit[8]uril (Q[8]) modified electrode. Although GDY exhibited electrocatalytic effect on the oxidation of Ru(bpy)32+, an apparent inhibiting effect of GDY on the ECL signal was observed due to the energy transfer. An “on-off-on” mode ECL sensor was fabricated to detect pancuronium (PMD) based on the competitive host–guest interaction between ferrocene (Fc), PMD and Q[8]. Fc modified single-stranded DNA was immobilized onto the surface of GDY, which could be attached onto the electrode through the interaction between Fc and Q[8]. The quenching effect of GDY could apparently decrease ECL signal. PMD exhibited stronger combining ability with Q[8] than Fc, and could replace Fc from the cavity of Q[8], leading to the recovery of ECL signal. The variation of ECL intensity changed linearly with the PMD concentration in the range of 10 nM to 50 μM with a detection limit of 5 nM (3σ). The proposed sensor has high sensitivity, outstanding specificity and accuracy, indicating that GDY has promising potential application in ECL sensing field based on its inhibiting effect.

The Promising Seesaw Relationship Between Activity and Stability of Ru-Based Electrocatalysts for Acid Oxygen Evolution and Proton Exchange Membrane Water Electrolysis.

The development of electrocatalysts that are not reliant on iridium for efficient acid-oxygen evolution is a critical step towards the proton exchange membrane water electrolysis (PEMWE) and green hydrogen industry. Ruthenium-based electrocatalysts have garnered widespread attention due to their remarkable catalytic activity and lower commercial price. However, the challenge lies in balancing the seesaw relationship between activity and stability of these electrocatalysts during the acid-oxygen evolution reaction (OER). This review delves into the progress made in Ru-based electrocatalysts with regards to acid OER and PEMWE applications. It highlights the significance of customizing the acidic OER mechanism of Ru-based electrocatalysts through the coordination of adsorption evolution mechanism (AEM) and lattice oxygen oxidation mechanism (LOM) to attain the ideal activity and stability relationship. The promising tradeoffs between the activity and stability of different Ru-based electrocatalysts, including Ru metals and alloys, Ru single-atomic materials, Ru oxides, and derived complexes, and Ru-based heterojunctions, as well as their applicability to PEMWE systems, are discussed in detail. Furthermore, this paper offers insights on in situ control of Ru active sites, dynamic catalytic mechanism, and commercial application of PEMWE. Based on three-way relationship between cost, activity, and stability, the perspectives and development are provided.

Chemical mechanism of oxidative etching of ruthenium: Insights into continuous versus self-limiting conditions

Ruthenium (Ru) has emerged as a promising material for microelectronic applications that require precise modification and patterning of thin films at the nanoscale. However, the susceptibility of Ru to oxidative etching has raised challenges in achieving the desired profile of Ru thin films. In this study, we investigated the mechanisms and conditions required for oxidative etching of Ru using density functional theory (DFT) calculations. Our calculations examined the thermodynamics and kinetics of several pathways toward the formation of gaseous RuO4, including oxidations of bulk Ru and RuO2, from both surfaces of which surface reactions were considered. Our findings suggest that etching reactions under O3 exposure are more favored on a Ru surface than on RuO2. Experimental results obtained from etching of Ru using O3 further support our computational predictions, indicating that oxide formation leads to a reduction in the etching rate and that quasi-self-limiting etching conditions can be achieved towards oxidative ALE of Ru. Our study may contribute to the fundamental understanding of Ru surface phenomena and provides insights into the development of effective ALE techniques for Ru.

A disordered oxide as an active phase during CO catalytic oxidation on Ru(0001)

The identification of the active phase of a catalyst under operando conditions is probably the most relevant task in basic catalysis research. In this respect, the Ru(0001) surface during CO oxidation is a traditional studied model, for both its importance in applied catalysis and for its peculiar behavior. In this work, we study the CO catalytic oxidation reaction on flat and defective Ru(0001) surfaces, concluding that the highest activity is achieved in oxidizing conditions when a disordered and thin Ru oxide is formed at the surface. Also, we find that in defective surfaces, with a high density of surface steps, this reaction is enhanced, related to the facile sub-surface incorporation of atomic oxygen and to the easier formation of the oxide. Thus, the CO catalytic oxidation on Ru(0001) is a structure-sensitive reaction, being active on the surface of the oxide formed in reaction conditions.

An effective strategy to boost lattice-oxygen-mediated acidic oxygen evolution

Designing electrocatalysts with high activity and stability for acidic oxygen evolution is pivotal to the development of proton-exchange membrane water electrolyzers. In this issue of Chem, Luo and co-workers found that anchoring RuO2 into robust metal-organic frameworks is an effective way to boost lattice-oxygen-mediated acidic oxygen evolution. Designing electrocatalysts with high activity and stability for acidic oxygen evolution is pivotal to the development of proton-exchange membrane water electrolyzers. In this issue of Chem, Luo and co-workers found that anchoring RuO2 into robust metal-organic frameworks is an effective way to boost lattice-oxygen-mediated acidic oxygen evolution. Atomically dispersed Ru oxide catalyst with lattice oxygen participation for efficient acidic water oxidationYao et al.ChemApril 5, 2023In BriefAn atomically dispersed Ru oxide catalyst strategy is reported to anchor Ru oxide on UiO-67-bpydc through Ru–N bonds for the OER under acidic electrolytes. The strong Ru–N bonds between Ru oxide and UiO-67-bpydc could not only accelerate the participation of lattice oxygen but also stabilize the soluble ∗Vo-RuO42− intermediates, leading to outstanding performance and long-term stability of the obtained Ru-UiO-67-bpydc catalyst toward the acidic OER. Full-Text PDF

Engineering metal oxidation using epitaxial strain.

The oxides of platinum group metals are promising for future electronics and spintronics due to the delicate interplay of spin-orbit coupling and electron correlation energies. However, their synthesis as thin films remains challenging due to their low vapour pressures and low oxidation potentials. Here we show how epitaxial strain can be used as a control knob to enhance metal oxidation. Using Ir as an example, we demonstrate the use of epitaxial strain in engineering its oxidation chemistry, enabling phase-pure Ir or IrO2 films despite using identical growth conditions. The observations are explained using a density-functional-theory-based modified formation enthalpy framework, which highlights the important role of metal-substrate epitaxial strain in governing the oxide formation enthalpy. We also validate the generality of this principle by demonstrating epitaxial strain effect on Ru oxidation. The IrO2 films studied in our work further revealed quantum oscillations, attesting to the excellent film quality. The epitaxial strain approach we present could enable growth of oxide films of hard-to-oxidize elements using strain engineering.