Metal-oxide Interface Research Articles

First-principle studies of oxidation effects on grain boundary strength in nickel

Nickel-base alloys are susceptible to stress corrosion cracking (SCC), in which the fracture mainly propagates along oxidized grain boundaries (GBs). To understand how oxidation degrades GB strength, first-principle-based density functional theory (DFT) calculations are conducted to study three types of interfaces: partially oxidized GBs, fully oxidized GBs, and metal-oxide interface, using Ni as a model system. For partially oxidized GBs, both substitutional and interstitial oxygen atoms of different coverages are inserted at three Ni GBs: Σ3(111) coherent twin, Σ3(112) incoherent twin, and Σ5(210) high-angle GB. The results show that the GB strength decreases almost monotonically with the increasing oxygen coverage at all GBs. Typically, substitutional oxygen causes a stronger embrittlement effect than interstitial oxygen, except at the Σ3(111). In addition, the oxygen-induced mechanical distortion has a smaller contribution to the embrittlement than its chemical effect except for high-coverage oxygen interstitials at the Σ3(111). For the fully oxidized GBs, three NiO GBs of the same types as in Ni are studied. Although the strengths of Σ3(112) and Σ5(210) NiO GBs are much weaker than the Ni counterparts, the Σ3(111) NiO GB has a higher strength than that in Ni. Finally, the strength of a Ni/NiO metal-oxide interface is calculated, which is found to be the weakest one among all interfaces studied in this work, suggesting that metal-oxide interfaces could be favorable crack initiation sites.

In situ formation of stable solid electrolyte interphase with high ionic conductivity for long lifespan all-solid-state lithium metal batteries

Parasitic reactions inevitably occur at the interface of lithium (Li) metal and polymer electrolytes due to ultrahigh Li reducibility coupled with poor interfacial stability or ionic conductivity. This leads to significant capacity loss and inferior lifespan of Li metal batteries (LMBs). Herein, we engineered a stable solid electrolyte interphase (SEI) layer at the interface of Li metal and polyethylene oxide (PEO) electrolyte via incorporation of phosphazene molecules. The phosphazene-solid polymer electrolyte (P-SPE) shows a significantly higher long-term stability against Li metal anode when compared with non-modified SPE. Using cryogenic transmission electron microscopy (cryo-TEM) and X-ray photon spectroscopy (XPS), Li3N, LiF, Li3P and Li3PO4 nanocrystals were identified in the SEI layer. The Li|Li cell with P-SPE cycle for 1800 cycles at 0.2 mA cm‒2. The Li||LFP cells with P-SPE deliver a specific capacity of ∼150 mAh g−1 and ∼120 mAh g−1 at 1C and 2C charge/discharge rates, respectively, with up to 80% capacity retention after 500 and 1000 cycles, respectively. Critical role of phosphazene-modified SEI in improving electrochemical performance is further investigated by density function theory (DFT) and ab-initio molecular dynamic (AIMD) calculations. This study offers a promising approach for engineering a stable and ion-conductive Li|polymer electrolyte interface for long lifespan LMBs.

Role of the Support Oxidation State on the Catalytic Activity of Two-Dimensional Pt/TiOx Catalysts

The interaction between metal and support is known to substantially enhance catalytic activity. Herein, we investigate the effect of the support’s oxidation state on the metal–support interaction (MSI) with two-dimensional Pt/TiOx catalysts. Using titanium oxide supports with five different oxidation states and Pt nanoparticles deposited on the supports via arc plasma deposition, we accurately performed the CO oxidation reaction in a batch reactor. We confirmed that the catalyst whose support has the highest oxidation state exhibits the best catalytic activity. The catalysts’ turnover frequency value varied sequentially from 4.0 to 19.4 at 513 K, and the activation energy also varied sequentially from 23.90 to 19.13 kcal/mol depending on the oxidation states of the supports. Kinetic studies have shown that the additional reaction pathway following the Mars–van Krevelen mechanism formed at the metal–oxide interface, which was affected by the oxidation states of the supports. The compositional effects of the support were confirmed by X-ray photoelectron spectroscopy analysis: the MSI effect was maintained even after the surface of the titanium oxides completely oxidized.

Insights into the interfacial speciation of Ni in the corrosion layer of high burnup Zircaloy-2 cladding: A combined XRD, XAS, and LFDFT study

This work reports atomic-scale experimental and modeling studies of the zirconium oxide microstructure formed at the metal-oxide (M/O) interface, and the crystallography as well as the redox chemistry of alloying element nickel in the corrosion layer found on a serviced boiling water reactor Zircaloy-2 fuel rod cladding. Complying with radioprotection aspects a small-sized sample with only limited radioactivity, taken from a very high burnup (∼ 79 MWd/kgU) cladding tube material, was prepared for the investigation using synchrotron-based X-ray microprobe techniques such as X-ray fluorescence (μXRF), X-ray diffraction (μXRD) and X-ray absorption spectroscopy (μXAS). The patterns of Ni K-edge XAS of solute Ni, probed at several location within the corrosion layer, have been recorded and analyzed. Close to the metal-oxide interface both the allotropic forms of zirconium oxide, monoclinic and tetragonal phases, have been identified by XRD analyses. XAS results of the barrier layer at the metal-oxide interface reveal that the oxides contain Ni atoms as divalent cations located in the proximity of oxygen vacancies. Near the M/O interface regions, all oxidized nickel atoms have a Ni2+ homogeneous distribution and no trace or even evidence of any metallic Ni is found in the oxide matrix. The experimental results, also supported by first-principles ligand field DFT calculations, are interpreted in term of energetics, stability, chemical and structural specificity of divalent Ni ions in zirconium oxide microstructure. The present investigation on the basis of a combined experimental and theoretical approach shows that the oxidized nickel ions being situated in the neighborhood of oxygen defects is influential on the hydrogen evolution reaction including the hydrogen intake behavior accompanied with the oxidation reaction in irradiated Zircaloy-2.

Voltage-driven reduction method to optimize in-situ exsolution of Fe nanoparticles at Sr2Fe1.5+xMo0.5O6-δ interface

Improving the catalytic activity of perovskite electrodes by loading metal nanoparticles through interface engineering is one of the research hotspots in the field of CO2 electrolysis in solid oxide electrolytic cell (SOEC). The challenge is to improve the stability and carbon resistance of the metal-oxide interface while reducing time costs and improving scalability. We used applied voltage-driven reduction and non-stoichiometric doping to make Fe nanoparticles uniformly and firmly anchored on the surface of Sr2Fe1.5+xMo0.5O6-δ (SF1.5+xM, x = 0, 0.025, 0.05, 0.075, 0.1) within 180 s, optimized the distribution of Fe nanoparticles on the surface of SF1.5+xM, and thus constructed a metal-oxide interface with high activity and high stability, effectively preventing the sintering and carbon deposition of metal particles. When the electrode composition is SF1.575 M, the CO yield is 4.0 mL·min-1·cm-2, while the polarization impedance is 0.155 Ω·cm-2, at 850 °C, 1.6 V. It can be said that voltage-driven reduction is an effective and efficient method applied to interface engineering.

Nanoscale chemical and structural investigation of solid solution polyelemental transition metal oxide nanoparticles

Although it has been shown that configurational entropy can improve the structural stability in transition metal oxides (TMOs), little is known about the oxidation state of transition metals under random mixing of alloys. Such information is essential in understanding the chemical reactivity and properties of TMOs stabilized by configurational entropy. Herein, utilizing electron energy loss spectroscopy (EELS) technique in an aberration-corrected scanning transmission electron microscope (STEM), we systematically studied the oxidation state of binary (Mn,Fe)3O4, ternary (Mn, Fe, Ni)3O4, and quinary (Mn, Fe, Ni, Cu, Zn)3O4 solid solution polyelemental transition metal oxides (SSP-TMOs) nanoparticles. Our findings show that the random mixing of multiple elements in the form of solid solution phase not only promotes the entropy stabilization but also results in stable oxidation state in transition metals spanning from binary to quinary transition metal oxide nanoparticles.

A comparison of dry and wet condition CO oxidation activity of a supported silver catalyst at low temperature

Economizing low-temperature CO oxidation using Ag/TiO2 catalyst to achieve complete conversion with and without water vapor through the activation of CO, initiated by the highly abundant reducible oxidic-Ag species at the metal–oxide interface.

Resistive switching characteristics of W/TiO2/ITO devices

Materials with resistance-switching properties are proving to be promising for the novel non-volatile memories-resistive random-access memory (ReRAM). Despite extensive research on electric field-induced resistance switching, there are diverse opinions about its reliability and working mechanism. In this work, we analysed the impact of SET and RESET voltages on the switching characteristics and the possible current conduction mechanism of W/TiO2/ITO devices. By simple solution processing and spin coating, titanium dioxide thin films were grown on ITO, glass, silicon, and quartz substrates. The precursor and solvent used for the synthesis of the active layer were titanium isopropoxide and ethanol, respectively. Polycrystalline films with an anatase structure were formed after annealing at 400 °C with a 20 nm average crystallite size, as evidenced by X-ray diffraction patterns. The crystalline nature of the fabricated film has been found to improve on annealing. Using Raman spectroscopy, the chemical bonding states of the film were studied. A UV–visible spectrometer study confirms that anatase TiO2 possesses an indirect band gap transition with a 3.42 eV band gap. The device shows reversible, reproducible, stable, and bipolar resistance-switching behaviour as indicated by current–voltage (I-V) measurements, and it was found that there exists a minimum voltage (∼-4 V) to set the device into an ON state. Compared to crystalline TiO2, theamorphous active layer offers much better switching characteristics, such as good cyclic endurance with a Roff-Ronratio ∼ 10.The current–voltage characteristics were fitted to various carrier transport mechanismssuch as Ohmic conduction, Schottky emission (SE), Space-charge-limited conduction (SCLC), and Poole-Frenkel emission (PF). Among these, the ohmic and SE mechanisms were detected at low and high fields, respectively. Schottky barrier modulation at the metal-oxide interface has been identified as the motive for switching.

Implications of Ga promotion and metal-oxide interface from tailored PtGa propane dehydrogenation catalysts supported on carbon.

Propane Dehydrogenation is a key technology, where Pt-based catalysts have widely been investigated in industry and academia, with development exploring the use of promoters (Sn, Zn, Ga, etc.) and additives (Na, K, Ca, Si, etc.) towards improved catalytic performances. Recent studies have focused on the role of Ga promotion: while computations suggest that Ga plays a key role in enhancing catalytic selectivity and stability of PtGa catalysts through Pt-site isolation as well as morphological changes, experimental evidence are lacking because of the use of oxide supports that prevent more detailed investigation. Here, we develop a methodology to generate Pt and PtGa nanoparticles with tailored interfaces on carbon supports by combining surface organometallic chemistry (SOMC) and specific thermolytic molecular precursors containing or not siloxide ligands. This approach enables the preparation of supported nanoparticles, exhibiting or not an oxide interface, suitable for state-of-the art electron microscopy and XANES characterization. We show that the introduction of Ga enables the formation of homogenously alloyed, amorphous PtGa nanoparticles, in sharp contrast to highly crystalline monometallic Pt nanoparticles. Furthermore, the presence of an oxide interface is shown to stabilize the formation of small particles, at the expense of propene selectivity loss (formation of cracking side-products, methane/ethene), explaining the use of additives such as Na, K and Ca in industrial catalysts.

Synergistic interface between metal Cu nanoparticles and CoO for highly efficient hydrogen production from ammonia borane.

The development of efficient non-noble metal catalysts for the dehydrogenation of hydrogen (H2) storage materials is highly desirable to enable the global production and storage of H2 energy. In this study, Cu x -(CoO)1-x /TiO2 catalysts with a Cu-CoO interface supported on TiO2 are shown to exhibit high catalytic efficiency for ammonia borane (NH3BH3) hydrolysis to generate H2. The best catalytic activity was observed for a catalyst with a Cu : Co molar ratio of 1 : 1. The highest dehydrogenation turnover frequency (TOF) of 104.0 molH2 molmetal -1 min-1 was observed in 0.2 M NaOH at room temperature, surpassing most of the TOFs reported for non-noble catalysts for NH3BH3 hydrolysis. Detailed characterisation of the catalysts revealed electronic interactions at the Cu-CoO heterostructured interface of the catalysts. This interface provides bifunctional synergetic sites for H2 generation, where activation and adsorption of NH3BH3 and H2O are accelerated on the surface of Cu and CoO, respectively. This study details an effective method of rationally designing non-noble metal catalysts for H2 generation via a metal and transition-metal oxide interface.

The role of chromium content in aqueous passivation of a non-equiatomic Ni38Fe20CrxMn21-0.5xCo21-0.5x multi-principal element alloy (x = 22, 14, 10, 6 at%) in acidic chloride solution

The effect of the Cr content on the corrosion behavior in a series of single-phase non-equiatomic Ni38Fe20CrxMn21-0.5xCo21-0.5x (6 < x < 22 at%) multi-principal element alloys (MPEAs) was investigated in acidified NaCl solutions. Comparisons were made with binary solid solution Co-Cr, Ni-Cr, and Fe-Cr alloys over a similar range of Cr contents. The corrosion behavior was evaluated using in-situ AC and DC electrochemical methods and ex-situ surface sensitive characterization techniques. Passivity and various levels of local corrosion resistance were obtained in the MPEA with 10 at% Cr or above. The binary Ni-Cr alloys with 12–30 at% Cr behaved similarly. The MPEA with 6 at% Cr and binary alloys with 5, 6, or 10 at% Cr were marginally passive or active and underwent localized corrosion during both linear sweep voltammetry and potentiostatic hold experiments. Passive films formed during potentiostatic hold experiments were characterized with X-ray photoelectron spectroscopy and atom probe tomography. Cr cation enrichment in the passive films was observed for all alloys and similar enrichment factors were obtained as a function of Cr content regardless of whether MPEA or binary alloy except for the Fe-Cr alloy. Moreover, passive current density was correlated with the Cr cation fraction in the passive film. The degree of Cr enrichment was attributed to a combination of thermodynamic and kinetic factors, such as selective chemical dissolution of alloying elements as well as limitation due to solute depletion at the metal oxide interface in alloys with a bulk Cr content ≤ 10 at%.

Enhanced Electrolysis of CO2 with Metal–Oxide Interfaces in Perovskite Cathode in Solid Oxide Electrolysis Cell

The application of solid oxide electrolysis cell in CO2 electroreduction is a hot research topic at present, but the development of low−cost catalysts with high catalytic activity has always been a challenge for this work. Herein, we use NiCu alloy nanoparticles to modify the perovskite LSCM electrode to build a metal–oxide active interface to obtain high catalytic performance. At 850 °C, 4.66 mL min−1 cm−2 CO productivity and 97.7% Faraday current efficiency were obtained. In addition, the current remained stable during the 100 h long−term test, indicating that the active interface has the dual effect of improving catalytic performance and maintaining cell durability.

A Proposed R-T Model for Atmospheric Corrosion of Metallized Film in AC Capacitors

Atmospheric corrosion is a significant issue affecting the storage quality of metallized film capacitors (MFCs). Oxygen and moisture in the atmosphere permeate among the layers in capacitor, initiating oxidation on the surface of metal layer, which increases the electrode resistance. In this work, a resistance–time model is proposed to study the atmospheric corrosion mechanism of nano-scaled Al–Zn metal layer. The analysis results point out that it is the barrier of metal–oxide interface that affects the anticorrosion ability. Moreover, the metal composition is studied as a factor influencing the anticorrosion ability, revealing that the enhancement gained by adjusting the composition tends to saturate once the Al content exceeds 10 wt.%. Therefore, in terms of MFCs for ac applications, the Al content in electrode should be controlled within 10 wt.% as a compromise between the atmospheric and electrochemical corrosion.

Intensified gas-phase hydrogenation of acetone to isopropanol catalyzed at metal-oxide interfacial sites

The gas-phase acetone hydrogenation to isopropanol is an environmentally benign process relevant to chemical, energy and medical fields, but the catalysts qualified at low temperature and pressure remain challenging. Herein, we show the intensified gas-phase hydrogenation of acetone to isopropanol at metal-oxide interface. The Pt/CeO2 catalyst with highly active and stable Pt-CeO2 interface delivers 92 % acetone conversion with 99 % isopropanol selectivity at 80 °C, weight hourly space velocity of 10 h−1, H2/acetone molar ratio of 2, and 0.1 MPa, and its catalytic performance is preserved during a single-running test of 200 h. A series of electron microscopic, thermal, and spectroscopic analyses testify that acetone could be efficiently adsorbed on oxygen vacancy at Pt-CeO2 interface. The H atoms dissociated by Pt spill over to the interface to hydrogenate the chemically-adsorbed acetone thereon to form isopropanol. Inspired by such observation, the Pt-CeO2 interface was extended to other metal-oxide interfaces (metal: Pt and Ni; oxide: CeO2, TiO2, ZrO2 and Fe3O4), all exhibiting excellent catalytic performance. For example, the Ni/CeO2 could offer 91 % acetone conversion and 99 % isopropanol selectivity, identical to that of Pt/CeO2 under the same conditions. This work particularly investigated the acetone adsorption at the metal-oxide interface, establishing the foundation for rational design of high cost performance catalysts for aldehydes/ketones hydrogenation and other reactions.

Effect of Reprocessing on Microstructure and Corrosion Resistance of Zr-Sn-Nb Alloy

To study the effect of reprocessing on the microstructure and corrosion resistance of Zr-Sn-Nb alloy, the original plates of Zr-Sn-Nb alloy were hot-rolled, cold-rolled and recrystallized to obtain the reprocessed plates. The microstructure of both plates was observed with a scanning electron microscope (SEM), a transmission electron microscope (TEM) and electron backscattering diffraction (EBSD). The original plates and reprocessed plates were put into a static autoclave for 300 days in 360 °C/18.6 MPa water. The relationship between the microstructure and corrosion resistance of the Zr-Sn-Nb alloy was discussed. The coarse deformation grains with twins and fine recrystallized grains were obtained, and grain sizes became smaller. The Ostwald ripening of second phase particles (SPPs) happened, and the average size of SPPs increased. Some SPPs changed from an HCP structure to an FCC structure. Reprocessing made the transition advance, which is related to the accelerated evolution of cracks in the oxide film and the increase in metal-oxide film interface roughness. The deterioration of corrosion resistance is closely related to the change of grain size, SPP size and SPP structure.

The effect of cross-linker structure on interfacial interactions, polymer dynamics and network composition in an epoxy-amine resin

Understanding interactions at the polymer / metal oxide interface is central to improving the performance lifetime of corrosion resistant coatings, where network polymers commonly form via step growth mechanisms in the presence of pigments. Here we employ a holistic analytical approach encompassing ATR-FTIR, DSC and molecular dynamics simulations to consider how crosslinker structure affects adsorption and incorporation into the network, using a stoichiometric mixture of diglycidylether of bisphenol-A (DGEBA) with m-xylylenediamine (MXDA) cured in the presence of hematite (Fe2O3) and goethite (FeOOH) powders. We find that the rigid MXDA molecule has two distinct binding modes on both hematite and goethite, and that synergistic hydrogen bonding modes observed on goethite limit interconversion between the two. Moreover, we find that binding persists in fully cured composite samples, determining the levels of residual amine. In contrast to previously reported results using triethylenetetramine (TETA) crosslinkers, however, we find that the Tg of composite specimens is independent of added hematite and goethite volumes. Molecular dynamics simulations demonstrate this is due to electrostatic binding between the cationic Fe sites and electronegative heteroatoms in MXDA. This renders both amine functionalities unavailable for incorporation into the network and hence, unlike TETA, MXDA adsorption does not determine polymer dynamics.

Multi-heterointerfaces for selective and efficient urea production.

A major impediment to industrial urea synthesis is the lack of catalysts with high selectivity and activity, which inhibits the efficient industrial production of urea. Here, we report a new catalyst system suitable for the highly selective synthesis of industrial urea by in situ growth of graphdiyne on the surface of cobalt-nickel mixed oxides. Such a catalyst is a multi-heterojunction interfacial structure resulting in the obvious incomplete charge-transfer phenomenon between a graphdiyne and metal oxide interface and multiple intermolecular interactions. These intrinsic characteristics are the origin of the high performance of the catalyst. Studies on the mechanism reveal that the catalyst could effectively optimize the adsorption/desorption capacities of the intermediate and promote direct C-N coupling by significantly suppressing by-product reactions toward the formation of H2, CO, N2 and NH3. The catalyst can selectively synthesize urea directly from nitrite and carbon dioxide in water at room temperature and pressure, and exhibits a record-high Faradaic efficiency of 64.3%, nitrogen selectivity (Nurea-selectivity) of 86.0%, carbon selectivity (Curea-selectivity) of ∼100%, as well as urea yield rates of 913.2μgh-1mgcat -1 and remarkable long-term stability.

Metal-oxide catalysts for CO TOX and PROX processes in the Pt–Cr/Mo/W systems

The properties of Pt-based catalysts could be modified by the addition of second metal and formation of an alloy or metal-oxide interface. In the present work we studied the effect of Cr, Mo and W doping on the Pt performance in CO TOX and PROX reactions. [Pt(NH3)4]MO4 (M = Mo, W) salts and solid solutions [Pt(NH3)4](M’O4)x(M″O4)1-x (M’ = Cr,Mo,W; M’‘ = Cr,Mo,W) were used as a single-source catalyst precursors. They were synthesized and characterized by a number of physicochemical methods of analysis. The thermal properties of obtained salts were studied in an oxidative atmosphere. The process of the decomposition is multistage and ends with a formation of platinum and the corresponding oxides of base metals (Cr/Mo/W).

Interface effect of Fe and Fe2O3 on the distributions of ion induced defects

The stability of structural materials in extreme nuclear reactor environments—with high temperature, high radiation, and corrosive media—directly affects the lifespan of the reactor. In such extreme environments, an oxide layer on the metal surface acts as a passive layer protecting the metal underneath from corrosion. To predict the irradiation effect on the metal layer in these metal/oxide bilayers, nondestructive depth-resolved positron annihilation lifetime spectroscopy (PALS) and complementary transmission electron microscopy (TEM) were used to investigate small-scale defects created by ion irradiation in an epitaxially grown (100) Fe film capped with a 50 nm Fe2O3 oxide layer. In this study, the evolution of induced vacancies was monitored, from individual vacancy formation at low doses—10−5 dpa—to larger vacancy cluster formation at increasing doses, showing the sensitivity of positron annihilation spectroscopy technique. Furthermore, PALS measurements reveal how the presence of a metal–oxide interface modifies the distribution of point defects induced by irradiation. TEM measurements show that irradiation induced dislocations at the interface is the mechanism behind the redistribution of point defects causing their accumulation close to the interface. This work demonstrates that the passive oxide layers formed during corrosion impact the distribution and accumulation of radiation induced defects in the metal underneath and emphasizes that the synergistic impact of radiation and corrosion will differ from their individual impacts.

Structure and Properties of Ultrathin SiOx Films on Cu(111).

The metal-oxide interface plays a crucial role in catalysis, and it has attracted increasing interest in recent years. Cu/SiO2, as a common copper-based catalyst, has been widely used in industrial catalysis. However, it is still a challenge to clarify the structures of the interface of Cu-SiOx and the effect on catalytic performance. Herein, we prepared ultrathin SiOx films by evaporating Si onto a Cu(111) surface followed by annealing in an O2 atmosphere, which were characterized by various surface science techniques. The results showed that a SiOx film could grow nearly layer-by-layer on the Cu(111) surface in the present condition. Both X-ray photoelectron spectroscopy (XPS) and high-resolution electron energy loss spectroscopy (HREELS) results confirmed the presence of Cu-O-Si and Si-O-Si species. Thermal stability experiments illustrated that the well-ordered silica films were stable under annealing in vacuum. The feature of CO adsorption suggested a CO-Cuδ+ species induced from the Cuδ+-O-Si. Low-energy ion scattering spectroscopy (LEIS) and XPS results demonstrated that some Cu2O appeared on the surface when the 1 ML SiOx/Cu(111) was exposed in O2 at 353 K.