Metal Oxide Coatings Research Articles

A novel approach to the role of iridium and titanium oxide in deactivation mechanisms of a Ti/(36 RuO2-x IrO2-(64-x) TiO2) coating in sodium chloride solution

Iridium and Titanium oxide are known as the corrosion-resistant and bonding agents for mixed metal oxide coatings. Based on this fact, this study aims to investigate the effect of these oxides on the deactivation mechanisms of a typical Ti/(36RuO2-xIrO2-(64-x)TiO2) in sodium chloride solution. The coating with quantities of 16, 26, and 36 wt. % titanium oxide is applied by thermal decomposition method. Then, a comprehensive analysis is carried out on the coating's morphology and microstructure by electron microscopy, energy dispersive spectroscopy, and grazing incidence X-Ray diffraction analysis. Additionally, cyclic voltammetry, accelerated lifetime test, and electrochemical impedance spectroscopy is performed to investigate the coating's electrochemical properties and corrosion behavior. The results show that the anode with the coating of nominal composition Ti/(36RuO2-38IrO2-26TiO2) provides a nanostructured morphology, solid solutions of (Ru, Ir)O2 and (Ru, Ir, Ti)O2, with maximum lifetime and optimum electrocatalytic activity. This composition results in an improved bonding of the coating components, which delays pitting corrosion of the coating in sodium chloride solution. Ultimately, the predominant corrosion and deactivation mechanism is changed into the general dissolution of the electrocatalytic component which has enhanced durability of the coating.

Atomically-thin Schottky-like photo-electrocatalytic cross-flow membrane reactors for ultrafast remediation of persistent organic pollutants

The remediation of persistent organic pollutants in surface and ground water represents a major environmental challenge worldwide. Conventional physico-chemical techniques do not efficiently remove such persistent organic pollutants and new remediation techniques are therefore required. Photo-electro catalytic membranes represent an emerging solution that can combine photocatalytic and electrocatalytic degradation of contaminants along with molecular sieving. Herein, macro-porous photo-electro catalytic membranes were prepared using conductive and porous stainless steel metal membranes decorated with nano coatings of semiconductor photocatalytic metal oxides (TiO2 and ZnO) via atomic layer deposition, producing highly conformal and stable coatings. The metal - semiconductor junction between the stainless steel membranes and photocatalysts provides Schottky - like characteristics to the coated membranes. The PEC membranes showed induced hydrophilicity from the nano-coatings and enhanced electro-chemical properties due to the Schottky junction. A high electron transfer rate was also induced in the coated membranes as the photocurrent efficiency increased by 4 times. The photo-electrocatalytic efficiency of the TiO2 and ZnO coated membranes were demonstrated in batch and cross flow filtration reactors for the degradation of persistent organic pollutant solution, offering increased degradation kinetic factors by 2.9 and 2.3 compared to photocatalysis and electrocatalysis, respectively. The recombination of photo-induced electron and hole pairs is mitigated during the photo-electrocatalytic process, resulting in an enhanced catalytic performance. The strategy offers outstanding perspectives to design stimuli-responsive membrane materials able to sieve and degrade simultaneously toxic contaminants towards greater process integration and self-cleaning operations.

Transparent, hard-wearing and bio-based organic/silica hybrid coating for bamboo with enhanced flame retardant and antifungal properties

As an abundant natural resource, bamboo with enhanced flame retardancy and mildew resistance after surface treatment has a wider range of applications. Although several organic or metal oxide coatings have been used on bamboo, their basic properties such as transparency and durability are neglected, which limits their practical application. Herein, we prepared a new organic–inorganic coating by thermal curing between vanillin-derived epoxy (VEP) and hyperbranched siloxane (HPSi). The curing process of VEP/HPSi coating was analyzed with FTIR. When the mass ratio of VEP and HPSi was 20:28, the obtained Schiff base hybrid coating exhibited visible light transmittance over 90% and the highest pencil hardness of 9H. The mechanical properties of the coating were investigated by nanoindentation (hardness: 0.208 GPa, elastic modulus: 2.677 Gpa) and impact test. Impressively, the fabricated coating showed remarkable solvent wipe resistance (Xylene and ethanol: 1000 cycles) and continuous abrasion (cheesecloth test: 5000 cycles). In addition, the hydrophobic and dense coating endowed the coated bamboo excellent mildew resistance even in high humidity (97%). Due to the high thermal stability, the coated bamboo presented a significant enhanced flame resistance with a limiting oxygen index value of 29.1%. From a broader perspective, the Schiff base hybrid coating with excellent comprehensive performance and facile preparation process display great potential for practical application for bamboo or other substrates.

Formation of functional metal oxide coatings by metal carboxylates pyrolysis

Formation of functional metal oxide coatings by metal carboxylates pyrolysis

Effects of coating precursor states on performance of titanium-based metal oxide coating anode for Mn electrowinning

In this paper, the effects of different coating precursor states and concentrations on the properties of titanium-based metal oxide coatings were investigated. The excess water in the precursor were removed by two methods. The molar ratio of Sn:Sb:Ru:Co in the precursor was 6:1:1:0.8; 0.006–0.024 mol Sn4+ were made into same volume for next experiments. The physical phases of the coatings were analyzed by SEM and XRD. Based on the electrochemical tests and accelerated life tests, we concluding that the precursor prepared through 1PS liquid-phase filtering paper was more homogeneous and had a longer service life. The optimum molar mass of the coating solute was 0.9 mol/L Sn4+ which need 6 times of sintering, and the preparation efficiency was 43% higher than before. Meanwhile, the chlorine evolution potential was reduced by 22 mV and the service life was increased to nearly 2.6 times because of the better coating state and better bonding force with titanium substrate.

Efficient Catalysts for VO2 +/VO2+ Redox Couples in Vanadium Redox Flow Batteries

The Vanadium Redox Flow Battery (VRFB) is an efficient energy storage technology for large scale stationary applications. One of the main challenges of VRFB with conventional non-activated graphite felt electrodes (GFE) is slow kinetics of redox reactions V2+/V3+ on the negative electrode and VO2 + /VO2+ reaction on positive electrodes. The activation of GFE with catalytic coatings may enhance the rate of redox reactions due to the decrease of the charge transfer resistance and increase of wettability and specific surface area.In this work, we report on activation of positive GFEs with supported/unsupported metal and metal oxide coatings (metal loading 0.5-1mg/cm2). The electrochemical study was conducted by 1) cyclic voltammetry (CV) measurements at 1 mV/s, 20oC in 0.2M VOSO4/2M H2SO4, cycling tests of commercial VRFBs (9 cm2) with positive activated GFEs and negative thermally treated GFE at 500oC in air (GFE500) at i=80 mA/cm2, 20oC in a commercial vanadium electrolyte 1.6M [V]/2M H2SO4, and 2) electrochemcial impedance spectroscopy (EIS) (solution (Rs) and charge trasfer resistance(Rct)).Analysis of the peak current ratio (Jpa/Jpc= 1.43-1.55) of CVs measured on supported catalysts (samples 2,3, Table 1) of positive activated GFE demonstrates that they have the similar reversibility for VO2 + /VO2+ redox reactions compared to baseline elecrodes GFE500 (Jpa/Jpc= 1.36, sample 1). However, these catalysts have better electrochemical activity for redox reactions VO2 + /VO2+ than GFE500 as their peaks potential separation ΔEp of 0.15-0.17V are significantly less than that on GFE500 (ΔEp=0.345V). It is important to note, they have significantly lower charge transfer resistance of 0.46-0.57 Ohm.cm2 than that of baseline GFE500In-situ cycling tests of VRFBs with a positive activated GFE by 40% (50%Ir40%Ru10%Se)/5Sb-SnO2 (rGO) and negative GFE500 (sample 2, Table 1) demonstrate the higher energy efficiency (EE) of 86.4 than that of VRFBs with baseline electrodes GFE500 (EE-85.4%) (Table 1). Table 1. Electrochemical characterization of activated positive graphite felt electrodes in half cells and VRFB # Catalyst Jpa/Jpc ΔE (V) Rct (Ohm.cm2) EE*,% CE*,% VE*,% 1 GFE500 1.36 0.345 5 85.4 96.4 87.5 2 [40% (50%Ir40%Ru10%Se/5%Sb-SnO2)]/GFE500 1.43 0.172 0.46 86.4 95.9 90.2 3 [75% (Ta0.6Nb0.4TiO2)/C]/GFE500 1.55 0.15 0.63 86.2 95.6 89.9 *EE- Energy efficiency, CE- Coulombic efficiency, VE - Voltage efficiency Fig.1 Electrochemical performance of VRFB (energy,Coulombic, voltage efficiency, and charge/discharge capacity) with positive activated GFE500 (40% (70%Ir20%Ru10%Se)/C (rGO) and negative GFE500 at i=80mA/cm2, T=20oC , 25 ml/min in the commercial vanadium electrolyte (1.6M [V]/2M H2SO4) Figure 1

Use of Different Metal Oxide Coatings in Stainless Steel Based ECDs for Smart Textiles

Electrochromism is the ability of a material to selectively change its coloration under the influence of an external electric current/potential and maintain it even after the power source has been disconnected. Devices that use such a mechanism are known as electrochromic devices (ECDs). Over the years, significant effort has been invested into the development of flexible ECDs. Such electrochromic tapes or fibers can be used as smart textiles. Recently, we utilized a novel geometrical approach in assembling electrochromic tapes which does not require the use of optically transparent electrodes. The so-called inverted sandwich ECD configuration can employ various color-changing mechanisms, e.g., intercalation, redox reactions of electrolytes or reactions on electrode surfaces. One of the most frequently used electrochromic metal oxides is WO3. However, other metal oxides with different coloration responses also exist. In this paper, we explore the use of V2O5 and TiO2 in metal-tape-based ECDs in the inverted sandwich configuration and compare their performance with WO3-based devices. Morphological features of metal oxide thin layers were investigated with scanning electron microscopy (SEM), and the performance of the tapes was investigated electrochemically and spectroscopically. We demonstrate that well-established preparation techniques (e.g., sol–gel synthesis) along with coating approaches (e.g., dipping) are adequate to prepare optically nontransparent fiber electrodes. Depending on the metal oxide, flexible electrochromic fiber devices exhibiting different coloration patterns can be assembled. Devices with TiO2 showed little coloration response, while much better performance was achieved in the case of V2O5 and WO3 ECDs.

Application of ALD Thin Films on the Surface of the Surgical Scalpel Blade

The article describes biomaterials and surgical instruments, in particular surgical cutting tools. In addition, the functions of coatings and the layer vapor deposition methods are described. In the experimental component of the study, zinc oxide thin film was deposited on the surgical knife blades by the atomic layer deposition (ALD) method with a varying number of cycles. The structures of the deposited thin films were investigated using a Raman spectrometer and the surface topography of the samples was examined using atomic force microscopy and scanning electron microscopy. The adhesion of the thin films was tested using the micro-scratch method. The corrosion resistance was also tested. Surgical instruments coated with non-allergenic metal oxide coatings, containing metal structures that reduce the growth of bacteria, could significantly decrease the risk of undesirable reactions of the body during and after surgery.

Recent Progress on Synthesis, Characterization, and Applications of Metal Halide Perovskites@Metal Oxide

AbstractMetal halide perovskites (MHPs) have become a promising candidate in a myriad of applications, such as light‐emitting diodes, solar cells, lasing, photodetectors, photocatalysis, transistors, etc. This is related to the synergy of their excellent features, including high photoluminescence quantum yields, narrow and tunable emission, long charge carrier lifetimes, broad absorption spectrum along with high extinction absorptions coefficients, among others. However, the main bottleneck is the poor stability of the MHPs under ambient conditions. This is imposing severe restrictions with respect to their industrialized applications and commercialization. In this context, metal oxide (MOx) coatings have recently emerged as an efficient strategy toward overcoming the stabilities issues as well as retaining the excellent properties of the MHPs, and therefore facilitate the development of the related devices’ stabilities and performances. This review provides a summary of the recent progress on synthetic methods, enhanced features, the techniques to assess the MHPs@MOx composites, and applications of the MHPs@MOx. Specially, novel approaches to fabricate the composites and new applications of the composites are also reported in this review for the first time. This is rounded by a critical outlook about the current MHPs’ stability issues and the further direction to ensure a bright future of MHPs@MOx.

Understanding the Stabilizing Effects of Nanoscale Metal Oxide and Li-Metal Oxide Coatings on Lithium-Ion Battery Positive Electrode Materials.

Nickel-rich layered oxides, such as LiNi0.6Co0.2Mn0.2O2 (NMC622), are high-capacity electrode materials for lithium-ion batteries. However, this material faces issues, such as poor durability at high cut-off voltages (>4.4 V vs Li/Li+), which mainly originate from an unstable electrode-electrolyte interface. To reduce the side reactions at the interfacial zone and increase the structural stability of the NMC622 materials, nanoscale (<5 nm) coatings of TiOx (TO) and LixTiyOz (LTO) were deposited over NMC622 composite electrodes using atomic layer deposition. It was found that these coatings provided a protective surface and also reinforced the electrode structure. Under high-voltage range (3.0-4.6 V) cycling, the coatings enhance the NMC electrochemical behavior, enabling longer cycle life and higher capacity. Cyclic voltammetry, X-ray photoelectron spectroscopy, and X-ray diffraction analyses of the coated NMC electrodes suggest that the enhanced electrochemical performance originates from reduced side reactions. In situ dilatometry analysis shows reversible volume change for NMC-LTO during the cycling. It revealed that the dilation behavior of the electrode, resulting in crack formation and consequent particle degradation, is significantly suppressed for the coated sample. The ability of the coatings to mitigate the electrode degradation mechanisms, illustrated in this report, provides insight into a method to enhance the performance of Ni-rich positive electrode materials under high-voltage ranges.

A Comparative Review of Metal Oxide Surface Coatings on Three Families of Cathode Materials for Lithium Ion Batteries

In the recent years, lithium-ion batteries have prevailed and dominated as the primary power sources for mobile electronic applications. Equally, their use in electric resources of transportation and other high-level applications is hindered to some certain extent. As a result, innovative fabrication of lithium-ion batteries based on best performing cathode materials should be developed as electrochemical performances of batteries depends largely on the electrode materials. Elemental doping and coating of cathode materials as a way of upgrading Li-ion batteries have gained interest and have modified most of the commonly used cathode materials. This has resulted in enhanced penetration of Li-ions, ionic mobility, electric conductivity and cyclability, with lesser capacity fading compared to traditional parent materials. The current paper reviews the role and effect of metal oxides as coatings for improvement of cathode materials in Li-ion batteries. For layered cathode materials, a clear evaluation of how metal oxide coatings sweep of metal ion dissolution, phase transitions and hydrofluoric acid attacks is detailed. Whereas the effective ways in which metal oxides suppress metal ion dissolution and capacity fading related to spinel cathode materials are explained. Lastly, challenges faced by olivine-type cathode materials, namely; low electronic conductivity and diffusion coefficient of Li+ ion, are discussed and recent findings on how metal oxide coatings could curb such limitations are outlined.

Plasma Electrolytic Oxidation (PEO) Process-Processing, Properties, and Applications.

Plasma electrolytic oxidation (PEO) is a novel surface treatment process to produce thick, dense metal oxide coatings, especially on light metals, primarily to improve their wear and corrosion resistance. The coating manufactured from the PEO process is relatively superior to normal anodic oxidation. It is widely employed in the fields of mechanical, petrochemical, and biomedical industries, to name a few. Several investigations have been carried out to study the coating performance developed through the PEO process in the past. This review attempts to summarize and explain some of the fundamental aspects of the PEO process, mechanism of coating formation, the processing conditions that impact the process, the main characteristics of the process, the microstructures evolved in the coating, the mechanical and tribological properties of the coating, and the influence of environmental conditions on the coating process. Recently, the PEO process has also been employed to produce nanocomposite coatings by incorporating nanoparticles in the electrolyte. This review also narrates some of the recent developments in the field of nanocomposite coatings with examples and their applications. Additionally, some of the applications of the PEO coatings have been demonstrated. Moreover, the significance of the PEO process, its current trends, and its scope of future work are highlighted.

Enhanced Cycling and Rate Capability by Epitaxially Matched Conductive Cubic TiO Coating on LiCoO2 Cathode Films.

Layered lithium transition-metal oxides, such as LiCoO2 and its doped and lithium-rich analogues, have become the most attractive cathode material for current lithium-ion batteries due to their excellent power and energy densities. However, parasitic reactions at the cathode–electrolyte interface, such as metal-ion dissolution and electrolyte degradation, instigate major safety and performance issues. Although metal oxide coatings can enhance the chemical and structural stability, their insulating nature and lattice mismatch with the adjacent cathode material can act as a physical barrier for ion transport, which increases the charge-transfer resistance across the interface and impedes cell performance at high rates. Here, epitaxial engineering is applied to stabilize a cubic (100)-oriented TiO layer on top of single (104)-oriented LiCoO2 thin films to study the effect of a conductive coating on the electrochemical performance. Lattice matching between the (104) LiCoO2 surface facets and the (100) TiO plane enables the formation of the titanium mono-oxide phase, which dramatically enhances the cycling stability as well as the rate capability of LiCoO2. This cubic TiO coating enhances the preservation of the phase and structural stability across the (104) LiCoO2 surface. The results suggest a more stable Co3+ oxidation state, which not only limits the cobalt-ion dissolution into the electrolyte but also suppresses the catalytic degradation of the liquid electrolyte. Furthermore, the high c-rate performance combined with high Columbic efficiency indicates that interstitial sites in the cubic TiO lattice offer facile pathways for fast lithium-ion transport.

Контактна взаємодія частинок з поверхнею основи при газотермічному напиленні

Показана роль контактної взаємодії частинок, що напилюються, з основою у формуванні міцних газотермічних покриттів. В якості основних структуроутворюючих елементів в покриттях прийняті сплети – поодинокі напилені частинки. Проаналізовано основні фактори, що визначають структуру і властивості газотермічних покриттів в процесі напилення, причому найважливішу роль відіграє утворення контакту частинка – основа і процеси, що протікають на ньому. Проаналізовано основні фактори, що визначають взаємодію матеріалів частинки та основи. Розглянуто основні роботи, присвячені проблемі схоплювання частинок з основою при напиленні. Запропоновано при аналізі утворення фізичного контакту розглядати площу контакту, що утворюється, з урахуванням розмірів напилюваних частинок і наявності на поверхні основи мікро- і наношорсткості чотирьох рівнів: номінальної, контурної, фактичної і фізичної. Фізична площа контакту на кілька порядків менше контурної площі та на її площадках формуються найбільш міцні адгезійні зв'язки. Запропоновано рівняння для оцінки фізичної площі контакту в зоні дії напірного тиску.

Study of the Effects of Pretreatment Processing on the Properties of Metal Oxide Coatings on Ti-Based Sheet

Proper pretreatment of titanium sheets is conducive to uniform attachment of an oxide coating and makes electrode performance more stable and reliable. Four kinds of pretreated titanium sheets were prepared using different methods. The physical appearance of the Ti sheets after etching was observed by scanning electron microscopy (SEM), and the corrosion mechanism of two different pretreated titanium plates were proposed. Based on the test results of the electrochemical performance and SEM/X-ray diffraction of the coatings, their influence on the electrode performance was analyzed. The results showed that on the Ti sheets etched at 90℃ for 2 h in 20% HCl after polishing, the corrosion pits were conducive to the bonding of coatings with matrix, showed excellent coating conditions, and superior electrochemical performance. A service life of 2772 h was achieved according to the empirical formula of accelerated-life-test.

A Review on the Processing Technologies for Corrosion Resistant Thermoelectric Oxide Coatings

Oxide coatings are corrosion resistant at elevated temperatures. They also show intensive phonon scattering and strong quantum confinement behavior. Such features allow them to be used as new materials for thermoelectric energy conversion and temperature measurement in harsh environments. This paper provides an overview on processing thermoelectric oxide coatings via various technologies. The first part deals with the thermoelectricity of materials. A comparison on the thermoelectric behavior between oxides and other materials will be made to show the advantages of oxide materials. In the second part of the paper, various processing technologies for thermoelectric metal oxide coatings in forms of thin film, superlattice, and nanograin powder will be presented. Vapor deposition, liquid phase deposition, nanocasting, solid state approach, and energy beam techniques will be described. The structure and thermoelectric property of the processed metal oxide coatings will be discussed. In addition, the device concept and applications of oxide coatings for thermoelectric energy conversion and temperature sensing will be mentioned. Perspectives for future research will be provided as well.

Plasma spraying of transition metal oxide coatings

ABSTRACTThe rapid increase in the world population has drastically increased the generation of organic solid waste. Currently, this is disposed of mainly in landfills, leading to environmental pollution that necessitates the development of new treatment technologies. Catalytic wet oxidation has been proven to be an effective technology for solid waste destruction and the elimination of hazardous organic compounds. The aim of this work is to explore the production of NiO, MnO2, Fe2O3 and CuO as transition metal oxide catalyst coatings using plasma spraying. Little, if any, literature has been presented on the plasma spray deposition of these materials, so this work provides the first proof of concept and benchmark for future development. The coating compositions were quantified from XRD patterns and the coating thickness measured from cross-sectional optical images. The optimal coating from each composition was analysed by scanning electron microscopy to determine the coating microstructure and phase distribution.

Solar selective reflector materials: Another option for enhancing the efficiency of the high-temperature solar receivers/reactors

The cavity wall is an important part of a cavity receiver in determining the receiver efficiency. Using solar selective reflector (SSR) materials with low solar absorptivity and high thermal emissivity for the cavity wall design is one efficient way to improve the receiver efficiency. In this work, we present a systematic study of the optical and high-temperature stability performances of six different SSR materials: one refractory ceramic fiber based substrate material (Fiberfrax 140) and five metallic oxide coatings which are prepared by mixing metallic oxide powders of alumina, magnesium oxide and titanium dioxide with commercial inorganic adhesives. The thermal stability was studied by heating up and keeping the six candidate materials in atmospheric conditions at a temperature of 1250 °C for 200 h. The spectrum of hemispherical reflectance in the spectrum band 0.25–25 μm was measured for analyzing the optical performance of the candidate materials. The obtained results show that all the six materials studied have good solar selective reflection characteristics, i.e, low solar absorptivity and relatively high thermal emissivity. Especially, the alumina coated substrate material shows excellent performances both for thermal stability and solar selective reflection. The solar reflectivity can reach 94.6%.

Low‐Cost Regulating Lithium Deposition Behaviors by Transition Metal Oxide Coating on Separator

AbstractThe application of lithium metal anode, despite being of the highest capacity, is hindered by low Coulombic efficiency (CE) and serious lithium dendrites formation. A strategy of transition metal oxides (TMOs) particles coated porous polypropylene (PP) separator is developed to regulate lithium deposition behaviors through in situ forming artificial solid electrolyte interface (SEI) passivating layers. By virtue of quite low solubilities of TMOs in the electrolyte, the concentration of TMOs in the electrolyte can be maintained at a constant and the dissolved TMOs can be reduced to produce Li2O and Mn particles, which not only function as lithium nucleating seeds but are also involved in the formation of the SEI layer. The sustainably existed trace of TMOs ensures the artificial SEI layer can be re‐healed once damaged by the volume expansion of lithium. With the help of one typical TMO of MnO coating on PP, an interesting dendrite‐free dual layer Li deposition is observed, which significantly improves the CE of Li||Cu cells and cycling life of Li||Li cells. Using MnO coated PP, ultra‐thin lithium films are deposited on copper foils with an in situ constructed SEI passivating layer, which exhibits a much improved cycling performance in liquid ether electrolyte and even better performance in gel polymer electrolyte.

Non-Hydrolytic Synthesis of Visible Light Active Stable Metal Oxides and Metal Oxide Coatings for Fuel Forming Reactions

Non-Hydrolytic Synthesis of Visible Light Active Stable Metal Oxides and Metal Oxide Coatings for Fuel Forming Reactions