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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Oxide-Encapsulated Ruthenium Oxide Catalysts for Selective Oxygen Evolution in Unbuffered pH-Neutral Seawater

Direct seawater electrolysis is a promising approach to producing green hydrogen in water-scarce environments using renewable energy. However, the undesirable chlorine evolution reaction and hypochlorite evolution reaction compete with the desired oxygen evolution reaction (OER) at the anode electrocatalyst. This issue is most pronounced in unbuffered pH-neutral solutions due to local acidification resulting from the OER. To overcome this challenge, this study provides a comprehensive evaluation of the use of silicon oxide (SiO x ) and titanium oxide (TiO x ) nanoscale overlayers coated on metallic ruthenium (Ru) and ruthenium oxide (RuO x ) thin film electrodes and their ability to block chloride ions from reaching active sites during operation in an unbuffered 0.6 M NaCl electrolyte. Using a combination of (electro)analytical techniques, encapsulated RuO x anodes are shown to effectively suppress Cl - transport to buried catalyst active sites while allowing for the desired OER to occur, leading to increases in OER faradaic efficiency at moderate overpotentials. Evidence for the ability of SiO x overlayers to block Cl - ions from reaching the active buried interface was obtained by monitoring the ν(O-H) stretching mode of OH adsorbates using in situ Raman spectroscopy. Here, this study also reports trade-offs between the activity, selectivity, and stability of bare and encapsulated Ru and RuO x electrocatalysts, finding that the magnitude of these trade-offs strongly depends on the complex interplay between electrode architecture, material properties, and catalytic performance, especially in unbuffered pH-neutral seawater.

58 GEOSCIENCES↗
DOE OSTI2026

Tantalum oxide stabilized molybdenum-doped ruthenium oxide electrocatalysts for PEM water electrolysis

Proton exchange membrane (PEM) water electrolysis offers key advantages, including high current density, high efficiency, and compact system architecture for hydrogen production. However, its widespread implementation is limited by the scarcity and high cost of Ir-based anodic catalysts. Herein, we report an Ir-free electrocatalyst for the acidic oxygen evolution reaction (OER): tantalum oxide (TaO x )–coated molybdenum-doped RuO 2 (TaO x -MoRuO 2 ). The catalyst exhibits a low overpotential of 180 mV at 10 mA cm -2 and excellent durability, with a degradation rate of 0.034 mV h -1 over a 150-hour test at 50 mA cm -2 —surpassing other Ru-based catalysts evaluated under similar conditions. A PEM electrolyzer employing TaO x -MoRuO 2 as the anode maintained stable operation for 100 hours at 500 mA cm -2 . In conclusion, the TaO x coating layer suppresses Ru and Mo dissolution, thus enhancing their stability likely via interfacial electronic reconfiguration of Ru and Mo mediated by bridging oxygen atoms.

Durability↗
DOE OSTI2021

A ruthenium oxide thermometer for dilution refrigerators operating down to 5 mK

At the lowest temperatures achieved in dilution refrigerators, ruthenium oxide resistance thermometers often saturate and therefore lose their sensitivity. In an effort to extend the range of such temperature sensors, we built a thermometer which maintains sensitivity to 5 mK. A key component of this thermometer is an in situ radio frequency filter which is based on a modern rf absorption material. Here, we show that the use of such a filter is only effective when it is encased in the same rf-tight enclosure as the ruthenium oxide sensor. Our design delivers an attenuation level that is necessary to mitigate the effects of parasitic heating of a fraction of pW present in our circuit. Furthermore, we show that the likely origin of this parasitic heating is the black body radiation present within the experimental space of the refrigerator. We found that the equilibration time of the thermometer increases rapidly as the temperature is lowered; below 5 mK this thermometer becomes impractical because of the prohibitively long equilibration times.

47 OTHER INSTRUMENTATION↗
DOE OSTI2023

On the Operando Structure of Ruthenium Oxides during the Oxygen Evolution Reaction in Acidic Media

In the search for rational design strategies for oxygen evolution reaction (OER) catalysts, linking the catalyst structure to activity and stability is key. However, highly active catalysts such as IrO x and RuO x undergo structural changes under OER conditions, and hence, structure–activity–stability relationships need to take into account the operando structure of the catalyst. Under the highly anodic conditions of the oxygen evolution reaction (OER), electrocatalysts are often converted into an active form. Here, we studied this activation for amorphous and crystalline ruthenium oxide using X-ray absorption spectroscopy (XAS) and electrochemical scanning electron microscopy (EC-SEM). We tracked the evolution of surface oxygen species in ruthenium oxides while in parallel mapping the oxidation state of the Ru atoms to draw a complete picture of the oxidation events that lead to the OER active structure. Our data show that a large fraction of the OH groups in the oxide are deprotonated under OER conditions, leading to a highly oxidized active material. The oxidation is centered not only on the Ru atoms but also on the oxygen lattice. This oxygen lattice activation is particularly strong for amorphous RuO x . We propose that this property is key for the high activity and low stability observed for amorphous ruthenium oxide.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Low-iridium stabilized ruthenium oxide anode catalyst for durable proton-exchange membrane water electrolysis

While mixing iridium (Ir) with ruthenium oxide (RuO 2 ) has proven to be an effective strategy for reducing Ir loading in anode catalysts for proton-exchange membrane (PEM) water electrolysers, achieving industrially relevant long-term stability typically requires an Ir-rich, Ru-lean combination. Here, in this study, by combining density functional theory with Metropolis Monte Carlo methods, we discovered that sufficient stabilization in the RuO 2 lattice could be achieved with less than 50 at.% of Ir, and that Ir in the first subsurface layer plays a critical role. By effectively dispersing Ir dopants within the RuO 2 lattice, we demonstrated an Ir:Ru atomic ratio of only 1:6 that exhibited exceptional stability for over 1,500 h of continuous water electrolysis at 2 A cm −2 . Our Ru 6 IrO x catalyst has the potential to reduce Ir loading by 80% compared with current commercial PEM water electrolysers, and its stability was further validated under industrial testing conditions in a 25-cm 2 PEM electrolyser.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Tantalum-stabilized ruthenium oxide electrocatalysts for industrial water electrolysis

The iridium oxide (IrO 2 ) catalyst for the oxygen evolution reaction used industrially (in proton exchange membrane water electrolyzers) is scarce and costly. Although ruthenium oxide (RuO 2 ) is a promising alternative, its poor stability has hindered practical application. Here, we used well-defined extended surface models to identify that RuO 2 undergoes structure-dependent corrosion that causes Ru dissolution. Tantalum (Ta) doping effectively stabilized RuO 2 against such corrosion and enhanced the intrinsic activity of RuO 2 . In an industrial demonstration, Ta-RuO 2 electrocatalyst exhibited stability near that of IrO 2 and had a performance decay rate of ~14 microvolts per hour in a 2800-hour test. At current densities of 1 ampere per square centimeter, it had an overpotential 330 millivolts less than that of IrO 2 .

Zhang, Jiahao [Sichuan Univ., Chengdu (China); Uni↗
DOE OSTI2021

Anode catalyst suitable for use in an electrolyzer

An anode catalyst suitable for use in an electrolyzer. The anode catalyst includes a support and a plurality of catalyst particles disposed on the support. The support may include a plurality of metal oxide or doped metal oxide particles. The catalyst particles, which may be iridium, iridium oxide, ruthenium, ruthenium oxide, platinum, and/or platinum black particles, may be arranged to form one or more aggregations of catalyst particles on the support. Each of the aggregations of catalyst particles may include at least 10 particles, wherein each of the at least 10 particles is in physical contact with at least one other particle. The support particles and their associated catalyst particles may be dispersed in a binder.

Xu, Hui↗
DOE OSTI2022

Non-noble metal based electro-catalyst compositions for proton exchange membrane based water electrolysis and methods of making

The invention provides electro-catalyst compositions for an anode electrode of an acid mediated proton exchange membrane-based water electrolysis system. The compositions include a noble metal component selected from the group consisting of iridium oxide, ruthenium oxide, rhenium oxide and mixtures thereof, and a non-noble metal component selected from the group consisting of tantalum oxide, tin oxide, niobium oxide, titanium oxide, tungsten oxide, molybdenum oxide, yttrium oxide, scandium oxide, cooper oxide, zirconium oxide, nickel oxide and mixtures thereof. Further, the non-noble metal component can include a dopant. The dopant can be at least one element selected from Groups III, V, VI and VII of the Periodic Table. The compositions can be prepared using any solution based methods involving a surfactant approach or a sol gel approach. Further, the compositions are prepared using noble metal and non-noble metal precursors. Furthermore, a thin film containing the compositions can be deposited onto a substrate to form the anode electrode.

Kumta, Prashant N.↗
DOE OSTI2026

Coupled Roles of Surface Chemistry and Hydrogen-Assisted Cycling in Ruthenium Atomic Layer Deposition on Silicon Oxides

Ruthenium (Ru) is a promising interconnect material for advanced semiconductor technologies due to its favorable scaling characteristics, including a short electron mean free path and strong electromigration resistance. In semiconductor integration, silicon oxide-based dielectrics serve as dominant insulating materials and constitute ubiquitous interfaces for metallization; however, their formation-dependent surface chemistry and its impact on Ru growth remain insufficiently explored. Here, we investigate Ru ALD on native oxide SiO x (N-SiO x ) and thermally grown SiO 2 (T-SiO 2 ) as model substrates using bis(ethylcyclopentadienyl)ruthenium(II) [Ru(EtCp) 2 ] under two distinct reactant-sequence environments: AB-type (Ru(EtCp) 2 /O 2 ) and hydrogenassisted ABC-type (Ru(EtCp) 2 /O 2 /H 2 ). Under the AB-type process, both N-SiO x and T-SiO 2 exhibit pronounced nucleation delay. N-SiO x shows earlier nucleation and higher nucleation density than T-SiO 2 , plausibly attributed to differences in surface hydroxyl populations. Similar temperature-dependent phase evolution is observed on both substrates, with mixed Ru and RuO 2 phases at 250 °C and predominantly metallic Ru at 300 °C accompanied by increased morphological roughening. In contrast, incorporating an H 2 subpulse (ABC-type) mitigates nucleation delay, particularly on hydroxyl-deficient T-SiO 2 , thereby reducing the substratedependent disparity observed under AB cycling. Moreover, RuO 2 formation is suppressed even at 250 °C on both substrates, shifting growth toward more metallic Ru with reduced resistivity (∼20 μΩ·cm at ∼ 20 nm on N-SiO x ). These trends suggest that H 2 influences the surface reaction pathway, contributing to enhanced metallic stabilization and altered early stage growth kinetics. Overall, this work clarifies the coupled roles of substrate chemistry and reactant-sequence design in governing Ru nucleation and early stage film evolution, providing insight relevant to next-generation interconnect integration and future area-selective deposition strategies.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Six-coordinate ruthenium water oxidation catalysts bearing equatorial polypyridinedicarboxylato and axial phosphine ligands

Ruthenium catalysts for water oxidation combining multidentate ligands [2,2':6',2"-terpyridine]-6,6"-dicarboxylato (tda) and 2,2'-bipyridine-6,6'-dicarboxylato (bda) with apical phosphine ligands have been prepared. Here, these new complexes were fully characterized by standard spectroscopic and single-crystal X-ray crystallography analyses, and their redox properties were evaluated by electrochemistry. Specifically, [Ru II (tda)(tris(2-furyl)phosphine) 2 ] displayed two reversible redox waves that were assigned to the Ru II/III and Ru III/IV transitions, respectively. The number of turnovers in Ce IV -driven water oxidation reached 258 for the bda analog, and for the tda analog, early reaction rates were first order in initial catalyst concentration. The effects of adding fractional equivalents of Ce IV were studied using UV–vis spectroscopy. Steric and electronic changes in the axial phosphine ligand can exert their effects on the properties and catalytic activity of the resulting complexes, which may be useful when exploring other chemistry of these complexes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Enabling Facile Anionic Kinetics through Cationic Redox Mediator in Li-Rich Layered Cathodes

Anionic oxygen redox has aroused great interests in developing high-capacity Li-ion battery cathode materials. The fundamental understanding of this concept, compared to cationic redox, has promoted extensive studies on lithium transition metal oxides including those of 4d and 5d transition metals. Lithium ruthenium oxide has been found to exhibit a reversible anionic redox upon cycling. However, lithium-rich layered oxide with anionic redox is still facing great challenges such as sluggish kinetics. Here we investigate the effect of cationic redox on the kinetics of anionic reaction when they are strongly coupled. We report the cobalt substituted lithium ruthenium oxide, where all Ru, Co and O redox participate in the charge compensation mechanism in relatively defined voltage regions. Additionally, the improved anionic kinetics is attributed to the fast cationic Co redox process that serves as a redox mediator. Our work sheds light into the potential direction to address the commonly believed sluggish anionic kinetics in high-capacity oxygen-redox cathode materials.

25 ENERGY STORAGE↗
DOE OSTI2025

Exploring Atomic-Scale Interactions at the Interface of Reducible Oxide and Ruthenium Nanocatalyst for Ammonia Decomposition

Restructuring atomic-scale interfaces between noble metal nanoparticles and metal oxides provides a promising approach to enhancing catalytic properties. In this study, Ru nanoparticles were supported on CeO 2 , ZrO 2 , and HfO 2 via pyrolysis of MOFs under oxygen-suppressed high-temperature conditions. Despite its nearly ideal particle size (∼2.3 nm), the Ru–CeO 2 /C catalyst exhibited the lowest ammonia decomposition activity. X-ray absorption spectroscopy and DFT calculations revealed that electron transfer from Ru to CeO 2 formed positively charged Ru and partially reduced Ce 4+ , weakening the catalytic performance. In contrast, oxygen-deficient ZrO 2 and HfO 2 support donated electrons to Ru, preserving its metallic state. These findings demonstrate that the reducibility of oxide supports governs the direction and magnitude of interfacial charge transfer, directly tuning catalytic behavior. This study provides insights into the design of oxide-supported Ru catalysts for ammonia decomposition.

Catalysts↗
DOE OSTI2026

A Mesopore-Confined and Graphene Oxide-Localized Ruthenium Catalyst Increases Rates of Mid-Chain Polyolefin Hydrogenolysis

A catalyst architecture with mesoporous silica coating Ru nanoparticles on reduced graphene oxide (mSiO 2 /Ru/rGO) localizes the 2 nm Ru solely at the closed bottoms of 2.9 nm diameter mesopores. mSiO 2 /Ru/rGO catalyzes the rapid, selective hydrogenolysis of polyolefins at wax formation rates (ν wax ) up to 1700 g wax ·g Ru –1 ·h –1 and a turnover frequency (TOF) for C–C bond cleavage of 130 ± 8 min –1 . The ν wax and TOF for mSiO 2 /Ru/rGO are 23× and 16× those of nonporous Ru/rGO, respectively, indicating that faster chain cleavage is also more selective inside mesopores. The methane yield from mSiO 2 /Ru/rGO is ca. 30% of the value obtained from Ru/rGO. Methane decreases, and wax selectivity improves with narrow-pore (2.3 nm) mSiO 2 /Ru/rGO. The reaction rate decreases at lower and higher H 2 pressures from its maximum at 37 bar. Log(TOF)-log(P H2 ) plots reveal rates ∝ [P H2 ] 2.8 or [P H2 ] −2.0 in the lower or higher pressure ranges, respectively. Corresponding plots for Ru/C give rates ∝ [P H2 ] 1 or [P H2 ] −2.4 . Ru is hydrocarbon-covered at low pressure; thus, the higher H 2 order for mSiO 2 /Ru/rGO indicates that mesopores increase the density of cleavable unsaturated moieties on the Ru surface. The lower H 2 order on Ru/C implies a lower density of cleavable groups because saturated segments occupy a larger fraction of the Ru surface. Higher surface occupancy by the hydrocarbon reactant correlates with more methane formation. Therefore, pore confinement, narrower pore diameter in mSiO 2 /Ru/rGO, or higher H 2 pressure leads to lower methane yields. Ru nanoparticles in mSiO 2 /Ru/rGO maintain equivalent activity and selectivity over five recycling tests.

Catalysts↗
DOE OSTI2024

Ruthenium-lead oxide for acidic oxygen evolution reaction in proton exchange membrane water electrolysis

Developing an active and stable anode catalyst for the proton exchange membrane water electrolyzer (PEM-WE) is a critical objective to enhance the economic viability of green hydrogen technology. However, the expensive iridium-based electrocatalyst remains the sole practical material with industrial-level stability for the acidic oxygen evolution reaction (OER) at the anode. Ruthenium-based catalysts have been proposed as more cost-effective alternatives with improved activity, though their stability requires enhancement. The current urgent goal is to reduce costs and noble metal loading of the OER catalyst while maintaining robust activity and stability. Here, in this study, we design a Ru-based OER catalyst incorporating Pb as a supporting element. This electrocatalyst exhibits an OER overpotential of 201 mV at 10 mA.cm -2 , simultaneously reducing Ru noble metal loading by similar to 40%. Normalization of the electrochemically active surface area unveils improved intrinsic activity compared to the pristine RuO 2 catalyst. During a practical stability test in a PEM-WE setup, our developed catalyst sustains stable performance over 300 h without notable degradation, underscoring its potential for future applications as a reliable anodic catalyst.

Electrocatalysis↗
DOE OSTI2026

Phase Transformation and Water Adsorption Behavior of As‐Deposited and Annealed Ru Metal Thin Films Prepared by Atomic Layer Deposition

ABSTRACT Surfaces play a central role in catalytic processes, and understanding the transformation of ruthenium metal into ruthenium oxide during annealing is essential for tailoring functional catalytic interfaces. In this study, we systematically investigate ≈22 nm thick Ru metal films deposited by atomic layer deposition (ALD) at 300°C, focusing on their chemical composition, structural evolution, and surface hydration behavior following post‐deposition annealing in air from 400 to 600°C. Lab‐based and synchrotron X‐ray photoelectron spectroscopy (XPS) reveal a gradual conversion from metallic Ru to fully oxidized Ru 4+ with increasing annealing temperature, accompanied by a corresponding increase in lattice oxygen. X‐ray diffraction (XRD) shows amorphous Ru oxide phases at 400°C and 500°C that evolve into crystalline RuO 2 at 600°C, while atomic force microscopy (AFM) indicates enhanced grain growth and surface roughening upon annealing. Ambient‐pressure XPS (AP‐XPS) under controlled H 2 O vapor environments (1–17 Torr) demonstrates that samples annealed at 400°C and 500°C exhibit initially high hydroxyl coverage that decreases with increasing water vapor pressure, concurrent with a rise in molecular H 2 O adsorption. In contrast, the crystalline RuO 2 surface formed at 600°C maintains stable hydroxylation and supports increased water uptake. Overall, this work provides fundamental insight into Ru oxide–H 2 O interactions and establishes design principles for engineering oxide surfaces optimized for electrocatalytic applications.

APXPS↗
DOE OSTI2021

Layered-rocksalt intergrown cathode for high-capacity zero-strain battery operation

Abstract The dependence on lithium-ion batteries leads to a pressing demand for advanced cathode materials. We demonstrate a new concept of layered-rocksalt intergrown structure that harnesses the combined figures of merit from each phase, including high capacity of layered and rocksalt phases, good kinetics of layered oxide and structural advantage of rocksalt. Based on this concept, lithium nickel ruthenium oxide of a main layered structure ( R $$\bar{3}$$ 3 ¯ m ) with intergrown rocksalt ( Fm $$\bar{3}$$ 3 ¯ m ) is developed, which delivers a high capacity with good rate performance. The interwoven rocksalt structure successfully prevents the anisotropic structural change that is typical for layered oxide, enabling a nearly zero-strain operation upon high-capacity cycling. Furthermore, a design principle is successfully extrapolated and experimentally verified in a series of compositions. Here, we show the success of such layered-rocksalt intergrown structure exemplifies a new battery electrode design concept and opens up a vast space of compositions to develop high-performance intergrown cathode materials.

25 ENERGY STORAGE↗
DOE OSTI2020

Metal-insulator and magnetic phase diagram of Ca 2 RuO 4 from auxiliary field quantum Monte Carlo and dynamical mean field theory

Layered perovskite ruthenium oxides exhibit a striking series of metal-insulator and magnetic-nonmagnetic phase transitions easily tuned by temperature, pressure, epitaxy, and nonlinear drive. In this work, we combine results from two complementary state-of-the-art many-body methods, auxiliary field quantum Monte Carlo and dynamical mean field theory, to determine the low-temperature phase diagram of Ca 2 RuO 4 . Both methods predict a low-temperature, pressure-driven metal-insulator transition accompanied by a ferromagnetic-antiferromagnetic transition. Further, the properties of the ferromagnetic state vary nonmonotonically with pressure and are dominated by the ruthenium $d_{xy}$ orbital, while the properties of the antiferromagnetic state are dominated by the $d_{xz}$ and $d_{yz}$ orbitals. Differences in the details of the predictions of the two methods are analyzed. This work is theoretically important as it presents the first application of the auxiliary field quantum Monte Carlo method to an orbitally degenerate system with both Mott and Hunds physics and provides an important comparison of the dynamical mean field and auxiliary field quantum Monte Carlo methods.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗