Metal Oxide Surfaces Research Articles

Elucidating the Surface Chemistry of Atomic Layer Deposition on Complex Metal Oxide Cathode Materials

Current research in the field of lithium-ion batteries (LIBs) is geared towards stabilizing the electrode-electrolyte interfaces to improve the LIB cycling stability and storage capacity. In particular, irreversible reactions between non-aqueous electrolytes and metal oxide cathode surfaces can corrode the active material and reduce LIB performance. Protective coatings on the cathode surface can mitigate these issues, and atomic layer deposition (ALD) is well-suited to prepare ultrathin, conformal, corrosion-resistant barrier layers on the surface of the electrodes. While there are reports that some metal oxide and metal fluoride barrier coatings on select cathodes can improve LIB performance, there is no general understanding of why certain ALD coating/cathode combinations are beneficial while others are not. This problem is complicated by the move towards complex LIB cathodes such as lithium nickel manganese cobalt oxide (NMC) materials that may have multiple phases present on the surface including hydroxides and carbonates. Understanding how the ALD precursors react on these materials to create protective coatings is challenging and requires a systematic study to elucidate the surface chemistry of the ALD precursors with each component of the complex oxide surface. Therefore, this work aims at understanding the effects of ALD precursor exposures and ALD coatings on the surface electronic structure of LIB cathode materials.Al2O3 and AlF3 were selected as prototypical metal oxide and metal fluoride surface coatings as they are widely reported in literature due to their ability to act as barrier coatings on cathodes. Additionally, the ALD precursor vapors used for these coatings, i.e., trimethyl aluminium (TMA) and hydrogen fluoride pyridine (HFpy), were adsorbed on the surfaces of these cathode materials under typical ALD conditions to observe their effect on the surface composition and electronic state. The cathode materials chosen for this study included all of the component oxides for NMC cathodes (i.e. Li, Ni, Mn, and Co) in all common oxidation states (e.g., MnO, MnO2, and Mn2O3) as well as selected ternary, quaternary, and quinary forms. In each case, the substrate surface was characterized using X-ray photoelectron spectroscopy (XPS) before and after surface treatment to elucidate changes in the surface composition and charge state induced by the individual ALD precursors and the ultrathin coating. Overall, this fundamental study will assist in the design and synthesis of novel ALD barrier coatings that demonstrate the highest sensitivity on multi-element cathode materials, ultimately leading to robust electrode-electrolyte interfaces for high-performance LIBs.

Controlling Heterogeneous Catalysis with Organic Monolayers on Metal Oxides.

ConspectusA key theme of heterogeneous catalysis research is achieving control of the environment surrounding the active site to precisely steer the reactivity toward desired reaction products. One method toward this goal has been the use of organic ligands or self-assembled monolayers (SAMs) on metal nanoparticles. Metal-bound SAMs are typically employed to improve catalyst selectivity but often decrease the reaction rate as a result of site blocking from the ligands. Recently, the use of metal oxide-bound organic modifiers such as organophosphonic acid (PA) SAMs has shown promise as an additional method for tuning reactions on metal oxide surfaces as well as modifying oxide-supported metal catalysts. In this Account, we summarize recent approaches to enhance catalyst performance with oxide-bound monolayers. These approaches include (1) modification of metal oxide catalysts to tune surface reactions, (2) formation of SAMs on the oxide component of supported metal catalysts to modify sites at the metal-support interface, and (3) enhancement of catalyst performance (e.g., stability) through modification of sites remote from the active sites.Both the headgroups and organic tail groups of PA SAMs or other ligands can influence reactions on metal oxide surfaces. Binding of the headgroup can selectively poison certain active sites, altering the selectivity in a manner analogous to metal-bound ligands (at the expense of active site quantity). Moreover, tail groups can be functionalized to interact favorably with reactants and intermediates, for instance through dipole-dipole interactions. On supported metal catalysts like Pt/Al2O3, PA SAMs can selectively form on the oxide support. This selective deposition allows for modification of the metal-support interface with minimal blockage of metal sites. PA headgroups were shown to provide tunable acid sites at the interface, dramatically improving hydrodeoxygenation rates of various alcohols. Additionally, organic tail functionality was used to activate or stabilize specific reactants at the interface, such as with the use of amine-functionalized PAs to stabilize chemisorption of CO2 during the reverse water gas shift reaction. PAs have also been found to affect the electronic properties of bulk metal sites through long-range electron withdrawal via the oxide, providing an additional avenue to tune catalytic behavior. Finally, organic modifiers were shown to enhance catalytic performance without directly modifying the active site. For instance, in biphasic liquid environments the modification of catalyst particles with hydrophobic or hydrophilic SAMs shifts the selectivity of multipath reactions on the basis of the hydrophobicities of different intermediates and products. As another "long-range" effect, the deposition of ligands on oxide supports improved catalyst stability through both improved resistance to sintering and suppression of active site poisoning. The recent contributions discussed in this Account demonstrate the versatility and significant potential for the approach of modifying catalysts with oxide-bound organic monolayers.

Mt-supported ZnO/TiO2 nanocomposite for agricultural antibacterial agent involving enhanced antibacterial activity and increased wettability

Nano-scale antibacterial agents have attracted enthusiastic attention due to their size-dependent qualities, effective antibacterial activity, and unique physiochemical properties, which showed great application potential in plant protection and nutrition. In this work, Mt-supported ZnO/TiO2 nanocomposite was prepared through sol-gel assisted impregnation method, and its antibacterial activity against gram-positive bacteria (S. aureus) and the wettability on cucumber leaves was investigated. The results suggested that the pillaring of Mt by TiO2 increased BET specific surface area, improved Zn-dispersion, enhanced adsorption capacity, forming an exfoliation structure of TiO2 pillared Mt nanocomposite. Besides, Mt-supported ZnO/TiO2 nanocomposite showed an obvious increase of antibacterial activity and wetting property over pure ZnO and Mt-supported ZnO composite due to the doping of zinc oxide by carbon atoms and the increase of exposed active sites caused by the effective dispersion of ZnO. In addition, the optimal performance was achieved for 15.04% Zn element content with the diameter of the inhibition zone was 48.53 ± 0.1 mm and the contact angle was 82.5 ± 0.2° attributed to the increased BET surface area (72.33 m2/g) and metal oxide interaction between TiO2 and Zn2+. The relatively low cost, green and environment friendly, high antibacterial activity, and wettability of Mt-supported ZnO/TiO2 nanocomposite offers new avenues for the antibacterial agent in the field of agriculture and crop protection.

Atomic Force Microscopy and Infrared Nanospectroscopy of COVID-19 Spike Protein for the Quantification of Adhesion to Common Surfaces.

The COVID-19 pandemic has claimed millions of lives worldwide, sickened many more, and has resulted in severe socioeconomic consequences. As society returns to normal, understanding the spread and persistence of SARS CoV-2 on commonplace surfaces can help to mitigate future outbreaks of coronaviruses and other pathogens. We hypothesize that such an understanding can be aided by studying the binding and interaction of viral proteins with nonbiological surfaces. Here, we propose a methodology for investigating the adhesion of the SARS CoV-2 spike glycoprotein on common inorganic surfaces such as aluminum, copper, iron, silica, and ceria oxides as well as metallic gold. Quantitative adhesion was obtained from the analysis of measured forces at the nanoscale using an atomic force microscope operated under ambient conditions. Without imposing further constraints on the measurement conditions, our preliminary findings suggest that spike glycoproteins interact with similar adhesion forces across the majority of the metal oxides tested with the exception to gold, for which attraction forces ∼10 times stronger than all other materials studied were observed. Ferritin, which was used as a reference protein, was found to exhibit similar adhesion forces as SARS CoV-2 spike protein. This study results show that glycoprotein adhesion forces for similar ambient humidity, tip shape, and contact surface are nonspecific to the properties of metal oxide surfaces, which are expected to be covered by a thin water film. The findings suggest that under ambient conditions, glycoprotein adhesion to metal oxides is primarily controlled by the water capillary forces, and they depend on the surface tension of the liquid water. We discuss further strategies warranted to decipher the intricate nanoscale forces for improved quantification of the adhesion.

Formation of Environmentally Persistent Free Radicals (EPFRs) on the Phenol-Dosed α-Fe2O3(0001) Surface.

Environmentally persistent free radicals (EPFRs) are a class of toxic air pollutants that are found to form by the chemisorption of substituted aromatic molecules on the surface of metal oxides. In this study, we employ X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS) to perform a temperature-dependent study of phenol adsorption on α-Fe2O3(0001) to probe the radical formation mechanism by monitoring changes in the electronic structure of both the adsorbed phenol and metal oxide substrate. Upon dosing at room temperature, new phenol-derived electronic states have been clearly observed in the UPS spectrum at saturation coverage. However, upon dosing at high temperature (>200 °C), both photoemission techniques have shown distinctive features that strongly suggest electron transfer from adsorbed phenol to Fe2O3 surface atoms and consequent formation of a surface radical. Consistent with the experiment, DFT calculations show that phenoxyl adsorption on the iron oxide surface at RT leads to a minor charge transfer to the adsorbed molecule. The experimental findings at high temperatures agree well with the EPFRs' proposed formation mechanism and can guide future experimental and computational studies.

High-Temperature Decomposition of Diisopropyl Methylphosphonate on Alumina: Mechanistic Predictions from Ab Initio Molecular Dynamics

The enhanced degradation of organophosphorous-based chemical warfare agents (CWAs) on metal-oxide surfaces holds immense promise for neutralization efforts; however, the underlying mechanisms in this process remain poorly understood. We utilize large-scale quantum calculations for the first time to probe the high-temperature degradation of diisopropyl methylphosphonate (DIMP), a nerve agent simulant. Our Born-Oppenheimer molecular dynamics (BOMD) calculations show that the $\gamma$-Al$_2$O$_3$ surface shows immense promise for quickly adsorbing and destroying CWAs. We find that the alumina surface quickly adsorbs DIMP at all temperatures, and subsequent decomposition of DIMP proceeds via a propene elimination. Our BOMD calculations are complemented with metadynamics simulations to produce free energy paths, which show that the activation barrier decreases with temperature and DIMP readily decomposes on $\gamma$-Al$_2$O$_3$. Our first-principle BOMD and metadynamics simulations provide crucial diagnostics for sarin decomposition models and mechanistic information for examining CWA decomposition reactions on other candidate metal oxide surfaces.

Influence of Surface and Structural Variations in Donor-Acceptor-Donor Sensitizers on Photoelectrocatalytic Water Splitting.

Conjugated organic chromophores composed of linked donor (D) and acceptor (A) moieties have attracted considerable attention for photoelectrochemical applications. In this work, we compare the optoelectronic properties and photoelectrochemical performance of two D-A-D structural isomers with thiophene-X-carboxylic acid (X denotes 3 and 2 positions) derivatives and 2,1,3-benzothiadiazole as the D and A moieties, respectively. 5,5'-(Benzo[c][1,2,5]thiadiazole-4,7-diyl)bis(thiophene-3-carboxylic acid), BTD1, and 5,5'-(benzo[c][1,2,5]thiadiazole-4,7-diyl)bis(thiophene-2-carboxylic acid), BTD2, were employed in the study to understand how structural isomers affect surface attachments within chromophore-catalyst assemblies and their influence on charge-transfer dynamics. Crystal structures revealed that varying the position of the -COOH anchoring group causes the molecules to either contort out of a plane (BTD1) or adopt a near-perfect planar conformation (BTD2). BTD1 and BTD2 were co-loaded with either a water oxidation catalyst, [Ru(2,6-bis(1-methylbenzimidazol-2-yl)pyridine)-(4,4'-((HO)2OPCH2)2-2,2'-bipyridine)(OH2)]2, RuCt2+, or proton reduction catalyst [Ni(P2PhN2C6H4CH2PO3H2)2]2+, NiCt2+, on oxide electrodes to facilitate photodriven water splitting reactions. Emission quenching measurements indicate that both BTD1 and BTD2 inject electrons into n-type SnO2|TiO2 electrodes and holes into p-type NiO semiconductors from their respective excited states at high efficiencies >60%. Photocurrent densities of chromophore-catalyst assemblies obtained using linear sweep voltammetry (LSV) show that BTD2-sensitized photoanodes generate significantly more photocurrent than BTD1-sensitized electrodes; however, both exhibit similar performances at the photocathode. Photoelectrocatyltic measurements demonstrate that both BTD1 and BTD2 performed similarly, generating Faradaic efficiencies of 39 and 38% at the anode or 61 and 79% at the cathode. Transient absorption measurements suggest that the differences between the LSV and photoelectrocatalytic measurements result from the differences in quantum yields of the photogenerated redox equivalents, which is also a reflection of the varying metal oxide surface conformation. Our findings suggest that BTD2 should be investigated further in photocathodic studies since it has the structural advantage of being incorporated into diverse types of chromophore-catalyst assemblies.

Coherent Acoustic Interferometry during the Photodriven Oxygen Evolution Reaction Associates Strain Fields with the Reactive Oxygen Intermediate (Ti-OH*).

The oxygen evolution reaction (OER) from water requires the formation of metastable, reactive oxygen intermediates to enable oxygen-oxygen bond formation. Conversely, such reactive intermediates could also structurally modify the catalyst. A descriptor for the overall catalytic activity, the first electron and proton transfer OER intermediate from water, (M-OH*), has been associated with significant distortions of the metal-oxygen bonds upon charge-trapping. Time-resolved spectroscopy of in situ, photodriven OER on transition metal oxide surfaces has characterized M-OH* for the charge trapping and the symmetry of the lattice distortions by optical and vibrational transitions, respectively, but had yet to detect an interfacial strain field arising from a surface coverage M-OH*. Here, we utilize picosecond, coherent acoustic interferometry to detect the uniaxial strain normal to the SrTiO3/aqueous interface directly caused by Ti-OH*. The spectral analysis applies a fairly general methodology for detecting a combination of the spatial extent, magnitude, and generation time of the interfacial strain through the coherent oscillations' phase. For lightly n-doped SrTiO3, we identify the strain generation time (1.31 ps), which occurs simultaneously with Ti-OH* formation, and a tensile strain of 0.06% (upper limit 0.6%). In addition to fully characterizing this intermediate across visible, mid-infrared, and now GHz-THz probes on SrTiO3, we show that strain fields occur with the creation of some M-OH*, which modifies design strategies for tuning catalytic activity and provides insight into photo-induced degradation so prevalent for OER. To that end, the work put forth here provides a unique methodology to characterize intermediate-induced interfacial strain across OER catalysts.

Structural Transformation of Heterogeneous Materials for Electrocatalytic Oxygen Evolution Reaction.

Electrochemical water splitting for hydrogen generation is a promising pathway for renewable energy conversion and storage. One of the most important issues for efficient water splitting is to develop cost-effective and highly efficient electrocatalysts to drive sluggish oxygen-evolution reaction (OER) at the anode side. Notably, structural transformation such as surface oxidation of metals or metal nonoxide compounds and surface amorphization of some metal oxides during OER have attracted growing attention in recent years. The investigation of structural transformation in OER will contribute to the in-depth understanding of accurate catalytic mechanisms and will finally benefit the rational design of catalytic materials with high activity. In this Review, we provide an overview of heterogeneous materials with obvious structural transformation during OER electrocatalysis. To gain insight into the essence of structural transformation, we summarize the driving forces and critical factors that affect the transformation process. In addition, advanced techniques that are used to probe chemical states and atomic structures of transformed surfaces are also introduced. We then discuss the structure of active species and the relationship between catalytic performance and structural properties of transformed materials. Finally, the challenges and prospects of heterogeneous OER electrocatalysis are presented.

Strain-age cracking in vacuum electron beam welded IN738LC alloy during post-weld heat treatment

IN738LC joint by vacuum electron beam welding (VEBW) exhibited high strain-age cracking (SAC) susceptibility and SAC mainly propagated along grain boundaries (GBs) of fusion zone (FZ) after post-weld heat treatment (PWHT). SAC occurred in the temperature range of 700 °C ∼1000 °C when IN738LC joints were subjected to PWHT with air atmosphere. The time to crack initiation decreased rapidly as the holding temperature rose. The investigation of influence factors of SAC indicated that the precipitation of γʹ particles, age hardening, oxidation-induced embrittlement and residual stress had a significant impact on the formation of SAC in FZ. Age-contraction stress induced by the precipitation of γʹ particles and residual stress acting on FZ were the essential factors to induce SAC. In addition, age hardening originating from the precipitation of γʹ particles and surface oxidation of weld metal exacerbated the formation of SAC during PWHT.

One‐Step Synthesis of Carbon‐Protected Co3O4 Nanoparticles toward Long‐Term Water Oxidation in Acidic Media

The design and development of highly efficient and stable oxygen evolution reaction (OER) electrocatalysts in acid media are important for various renewable technologies. Herein, an advanced Co3O4 electrocatalyst supported on a mesoporous hydrophobic carbon paper (Co/29BC) is formed via a simple one‐step thermal decomposition of cobalt nitrate. Through this novel approach, the amorphous carbon layer resulting from the thermal decomposition of carbon‐containing species in the mesoporous layer provides enhanced electronic conduction and protection against corrosion to the Co3O4 nanoparticles. Equally important, the OER performance is found to be correlated with the morphology and surface composition of Co3O4. With optimized Co3+ active sites and oxygen vacancies at the metal oxide surface, the Co3O4 catalyst shows superior OER performance and durability in a proton exchange membrane (PEM) water electrolyzer, with a small overpotential (350 mV) at a constant current density of 10 mA cm−1 for over 50 h. Accordingly, this work provides new insights toward the design of high‐performance and highly stable OER electrocatalysts in corrosive acidic environments.

Below-room-temperature solution-grown ZnO porous nanosheet arrays with ppb-level NO2 sensitivity under intermittent UV irradiation

It is difficult for a chemiresistive metal oxide gas sensor to operate at room temperature due to the poor desorption ability of the adsorbed gases during recovery. UV irradiation helps to clean the surface of metal oxides, but it is also unfavorable for gas adsorption. In this work, intermittent UV irradiation, i.e., UV on (off) before (after) exposure to a target gas, is found to remarkably enhance the sensitivity of ZnO toward NO2. Porous nanosheet arrays of ZnO have been in-situ grown on the sensor chip in an alkaline bath at a low temperature of 8 °C. Heterogeneous growth of nanosheet arrays and homogeneous growth of nanosheet-constructed spheres take place on the substrate and in the bulk solution, respectively. The as-grown ZnO nanosheet arrays contain not only macropores between nanosheets but also mesopores within the nanosheets, which endow them superior NO2 sensing properties under intermittent UV irradiation. The growth kinetics of ZnO porous nanosheet arrays and the mechanism of the NO2 sensing under intermittent UV irradiation have been elaborated.

First-Principles Studies of the Surface and Interface between/Among Metal Oxides Used in SOFCs

On the surface and interface, all materials change the property such as stability and electronic states from them on bulk. Human being continue to apply the phenomena to the key technologies from early times. For example, in solid oxide fuel cells (SOFCs), important phenomena such as fuel decomposition, charge transfer etc., occur at surface or triple phase boundary (TPB) that consists of catalyst, electrolyte, and gas phase. To solve remaining issues of SOFCs such as degradation or efficiency improvement, important is to know the detail of property changes of materials used in SOFCs on the surface and interface. Theoretical study is efficient approach to investigate material property, especially electronic states. Therefore, in this study, we have focused on surface and interface of metal oxides used as electrolytes in SOFCs and investigated theoretically their property using two calculation models with first-principles calculation. In concrete, one is density functional theory (DFT) calculations with the TPB model that consists of Ni catalyst cluster, YSZ electrolyte, and gas phase. In this case, we have tried to decide the reliable structure to discuss properties on TPB and evaluated adsorption reactivity etc. The other is DFT calculations with the hetero-structure interface model that consists of zirconia (ZrO2) and ceria (CeO2). In this case, we have tried to evaluated electronic states on that interface and discussed in terms of conductivity control. Here, only the results of optimized YSZ (111) surface model and density of state (DOS) change in ZrO2/CeO2 hetero-structure are shown as examples for word limitation. The CASTEP software was used for all calculations.Geometry optimization of YSZ (111) surface model have been performed with some arrangements of yttrium (Y) atoms and oxygen vacancy in order to identify the most stable structure. Our model consists of (111) three layers includes 2×2 or 2×4 ZrO2 unit cells, 15 Å vacuum layer, and 9.1 % substituted Y atoms. In the most stable YSZ 2×2 model, one Y atom is on the top Zr atoms layer and another Y atom is on the middle Zr atoms layer nearest to the top Y atom, and oxygen vacancy is on the 2nd O atoms layer nearest to the top Y atom. We have found the position of oxygen vacancy against Y atoms and surface is sensitive to the YSZ surface stability. Oxygen vacancy does not prefer to stick around two Y atoms. It indicates that improvement for the geometry unstability of cubic ZrO2 is more important than keeping local electroneutrality even near on the surface. By applying this finding, we have performed geometry optimization of YSZ 2×4 unit cell model with changing Y atom arrangements in the same layer and keeping the stable structure in 2×2 unit cell model. The most stable YSZ 2×4 surface model finally-obtained is shown in attached figure (A).Our 2nd topic is for the electronic states change on the interface of metal oxides. We have calculated DOS with pure ZrO2, pure CeO2, and several ZrO2/CeO2 models hetero-connected with (111) surfaces. DOS changes by hetero-connection are shown in attached figure (B). A new small peak not appeared in the cases of pure ZrO2 and pure CeO2 is observed in 01 eV near Fermi level. It is considered that the peak is caused by the interaction between 4f orbital shown in 13 eV of Ce atoms and 2p orbital shown in -50 eV of O atoms in ZrO2 on the interface. In addition, the peak height is influenced only by the thickness of CeO2 layers, not that of ZrO2 layers. Our results suggest that we can control electronic conductivity of these metal oxides with hetero-structuration in atomic level especially at low temperature. Other results and detailed discussion will be reported at our meeting publications (ECS Transactions) and presentation in this conference. Figure 1

Photoredox Catalysis Using Heterogenized Iridium Complexes*.

Heterogenized photoredox catalysts provide a path for sustainable chemical synthesis using highly tunable, reusable constructs. Here, heterogenized iridium complexes as photoredox catalysts were assembled via covalent attachment to metal oxide surfaces (ITO, ZrO2, Al2O3) in thin film or nanopowder constructs. The goal was to understand which materials provided the most promising constructs for catalysis. To do this, reductive dehalogenation of bromoacetophenone to acetophenone was studied as a test reaction for system optimization. All catalyst constructs produced acetophenone with high conversions and yields with the fastest reactions complete in fifteen minutes using Al2O3 supports. The nanopowder catalysts resulted in faster and more efficient catalysis, while the thin film catalysts were more robust and easily reused. Importantly, the thin film constructs show promise for future photoelectrochemical and electrochemical photoredox setups. Finally, all catalysts were reusable 2–3 times, performing at least 1000 turnovers (Al2O3), demonstrating that heterogenized catalysts are a sustainable catalyst alternative.

Microstructural basis for improved corrosion resistance of laser surface processed AZ31 Mg alloy

Despite their excellent strength-to-weight ratio, wider use of magnesium (Mg) alloys for light-weight applications is limited by their poor corrosion resistance, especially in chloride-containing environments. The present study shows improved corrosion resistance imparted by laser surface processing (LSP) of a commercial AZ31 (Mg-3Al-1Zn) alloy. Nanosecond laser processing at three different power settings was carried out on the surface of a 1-mm-thick rolled AZ31 sheet. Electrochemical studies and salt spray testing (ASTM B117) indicate substantial enhancement of corrosion resistance in LSP-treated AZ31. The underlying reasons behind improved corrosion resistance of the LSP-AZ31 surface have been studied through detailed microstructural characterization and chemical analysis by SEM, TEM, and XPS. Formation of a ∼0.5 μm thick mixed metal (Mg, Al) oxide surface film, together with refinement in the size and number density of Al-Mn intermetallic particles, are shown to play a major role toward improved corrosion resistance after LSP treatment of the AZ31 alloy.

Synthesis of Aminopropyltriethoxysilyl-Substituted Imines and Amides

A series of small molecules containing aminopropyltriethoxysilyl-substituted imines and amides were synthesized so that they could potentially be incorporated into self-assembled monolayers (SAMs) on metal oxide surfaces. Simple one-step imine preparations and two-step amide preparations are reported here.

Extension of the Linear Response Function of Electron Density to a Plane-wave Basis and the First Application to Periodic Surface Systems

Abstract This paper proposed using the linear response function (LRF) of Kohn-Sham orbitals for checking the convergence regarding thickness in periodic slab-and-vacuum model calculations. The effectiveness was demonstrated using the alkaline earth metal oxide (001) surface. The calculated LRF decreases and converges to zero toward the opposite side of a slab. The proposed LRF scheme can be used as a guide to judge convergence of the slab thickness.

Hydroxide melt induced corrosion of Ni at elevated temperatures under steam electrolysis conditions

Molten alkali electrolyte based high temperature water electrolysis (HTWE) process offers an efficient pathway to integrate renewable energy resources for large scale and economic hydrogen production. Long term and stable operation of these systems require an in-depth understanding of materials stability under anodic and cathodic exposure conditions of the cell and cell stacks. In the present study, we report our findings on the corrosion of Ni in the presence and absence of (Li–Na) hydroxide melt at 600 °C under oxidizing and reducing conditions representative of HTWE. While the Ni electrode was found to remain thermodynamically stable in metallic form under cathodic (reducing) exposure conditions, the corrosion rate in molten hydroxide under oxidizing conditions was found to be non-parabolic in nature. A cyclic voltammetry study provides the breakdown of the passive metal-oxide surface layer at the anodic overpotential region between 0.45 V and 2 V in molten hydroxide under oxidizing conditions. A thermochemical process for accelerated corrosion based on the oxide scale fluxing in hydroxide melt has been developed.

Chemistry of Oxygen Ionosorption on SnO2 Surfaces.

Ionosorbed oxygen is the key player in reactions on metal-oxide surfaces. This is particularly evident for chemiresistive gas sensors, which operate by modulating the conductivity of active materials through the formation/removal of surface O-related acceptors. Strikingly though, the exact type of species behind the sensing response remains obscure even for the most common material systems. The paradigm for ab initio modeling to date has been centered around charge-neutral surface species, ignoring the fact that molecular adsorbates are required to ionize to induce the sensing response. Herein, we resolve this inconsistency by carrying out a careful analysis of all charged O-related species on three naturally occurring surfaces of SnO2. We reveal that two types of surface acceptors can form spontaneously upon the adsorption of atmospheric oxygen: (i) superoxide O2– on the (110) and the (101) surfaces and (ii) doubly ionized O2– on the (100) facet, with the previous experimental evidence pointing to the latter as the source of sensing response. This species has a unique geometry involving a large displacement of surface Sn, forcing it to attain the coordination resembling that of Sn2+ in SnO, which seems necessary to stabilize O2– and activate metal-oxide surfaces for gas sensing.

Viscosity sensor with temperature measurement function based on multifunctional metal matrix composite

A temperature-compensated viscosity sensor was developed. The sensor consisted of a multifunctional metal matrix composite incorporating a metal-core piezoelectric fiber and a surface-oxidized metal fiber. This viscosity sensor was developed as a sensor that can withstand harsh environments, such as engine oil monitoring. In this case, viscosity is affected by oil deterioration, sludge mixing, and temperature changes. Therefore, a multifunctional metal matrix composite was fabricated using two metal-core piezoelectric fibers for viscosity measurements, and a surface-oxidized metal fiber for temperature. The metal oxide surface has a notch made by removing the oxide film, which forms a thermocouple when it comes into contact with the metal matrix. After evaluating the device's characteristics in standard room temperature, the viscosity was measured using glycerine solutions with different concentrations and varying temperatures. The temperature dependence of the sensor was measured and used for calibrating the results. This temperature dependence was present due to changes in dimensions due to thermal expansion of the matrix, and Young's modulus, piezoelectric constant, and relative dielectric constant of the piezoelectric ceramic fibers. A correction formula was calculated based on temperature dependence to demonstrate that temperature compensation was possible at range of from 2 to 25 Pa s kgm3.