Oxide Research Articles

Microfluidic Synthesis of Multifunctional Micro-/Nanomaterials from Process Intensification: Structural Engineering to High Electrochemical Energy Storage.

Multifunctional micro-/nanomaterials featuring functional superiority and high value-added physicochemical nature have received immense attention in electrochemical energy storage. Microfluidic synthesis has become an emergent technology for massively producing multifunctional micro-/nanomaterials with tunable microstructure and morphology due to its rapid mass/heat transfer and precise fluid controllability. In this review, the latest progresses and achievements in microfluidic-synthesized multifunctional micro-/nanomaterials are summarized via reaction process intensification, multifunctional micro-/nanostructural engineering and electrochemical energy storage applications. The reaction process intensification mechanisms of various micro-/nanomaterials, including quantum dots (QDs), metal materials, conducting polymers, metallic oxides, polyanionic compounds, metal-organic frameworks (MOFs) and two-dimensional (2D) materials, are discussed. Especially, the multifunctional structural engineering principles of as-fabricated micro-/nanomaterials, such as vertically aligned structure, heterostructure, core-shell structure, and tunable microsphere, are introduced. Subsequently, the electrochemical energy storage application of as-prepared multifunctional micro-/nanomaterials is clarified in supercapacitors, lithium-ion batteries, sodium-ion batteries, all-vanadium redox flow batteries, and dielectric capacitors. Finally, the current problems and future forecasts are illustrated.

Stabilization of Organic Cations in Lead Halide Perovskite Solar Cells Using Phosphine Oxides Derivatives.

Preventing ion migration in perovskite photovoltaics is key to achieving stable and efficient devices. The activation energy for ion migration is affected by the chemical environment surrounding the ions. Thus, the migration of organic cations in lead halide perovskites can be mitigated by engineering their local interactions, for example through hydrogen bonding. Ion migration also leads to ionic losses via interfacial reactions. Undesirable reactivities of the organic cations can be eliminated by introducing protecting groups. In this work, we report bis(2-oxo-3-oxazolidinyl) phosphinic chloride (BOP-Cl) as a perovskite ink additive with the following benefits: (1) The phosphoryl and two oxo groups form six-membered intermolecular hydrogen-bonded rings with the formamidinium cation (FA), mitigating ion migrations. (2) The hydrogen bonding reduces the electrophilicity of the ammonium protons by donating electron density, therefore reducing its reactivity with the surface oxygen on the metal oxide. Furthermore, the molecule can react to form a protecting group on the nucleophilic oxygen at the tin oxide transport layer surface through the elimination of chlorine. As a result, we achieve perovskite solar cells with an efficiency of 25.0% and improved MPP stability T93 = 1200 h at 40-45 °C compared to a control device (T86 = 550 h). In addition, we show a negative correlation between the strength of hydrogen bonding of different phosphine oxide derivatives to the organic cations and the degree of metastable behavior (e.g., initial burn-in) of the device.

Catalytic Ozonation of Low Concentration Toluene over MnFeOx-USY Catalyst: Effects of Interactions between Catalytic Components and Introduction of Gas Phase NOx.

A series of Mn and Fe metal oxide catalysts loaded onto USY, as well as single metal oxides, were prepared and characterized. The effects of interactions between the catalytic components and the introduction of gas phase NO on the catalytic ozonation of toluene were investigated. Characterization showed that there existed strong interactions between MnOx, FeOx, and USY, which enhanced the content of oxygen vacancies and acid sites of the catalysts and thus boosted the generation of reactive oxygen species and the adsorption of toluene. The MnFeOx-USY catalyst with MnOx and FeOx dimetallic oxides exhibited the most excellent performance of catalytic ozonation of toluene. On the other hand, the presence of NOx in reaction gas mixtures significantly promoted both toluene conversion and mineralization, which was attributed to the formation of nitrate species on the catalysts surface and thus the increase of both acid sites and toluene oxidation sites. Meanwhile, the reaction mechanism between O3 and C7H8 was modified in which the strong interactions between MnOx, FeOx, and USY accelerated the reaction progress based on the L-H route. In addition, the formation of the surface nitrate species not only promoted reaction progress following the L-H route but also resulted in the occurrence of the reaction via the E-R route.

Wear Performance Evaluation of Polymer Overlays on Engine Bearings

Modern engine bearing materials encounter the challenge of functioning under conditions of mixed lubrication, low viscosity oils, downsizing, start–stop engines, potentially leading to metal-to-metal contact and, subsequently, premature bearing failure. In this work, two types of polymer overlays were applied to the bearing surface to compensate for extreme conditions, such as excessive loads and mixed lubrication. Two different polymer overlays, created through a curing process on a conventional engine bearing surface with an approximate thickness of 13 µm, were investigated for their friction and wear resistances under a 30 N load using a pin-on-disc setup. The results indicate that the newly developed polymer overlay (NDP, PAI-based coating) surface has a coefficient of friction (COF) of 0.155 and a wear volume loss of 0.010 cm3. In contrast, the currently used polymer overlay (CPO) in this field shows higher values with a COF of 0.378 and a wear volume loss of 0.024 cm3, which is significantly greater than that of the NDP. It was found that, in addition to accurately selecting the ratios of solid lubricants, polymer resins, and wear-resistant hard particle additives (metal powders, metal oxides, carbides, etc.) within the polymer coating, the effective presence of a transfer film providing low friction on the counter surface also played a crucial role.

Red mud and bismuth oxide based X-ray shielding tiles for upcoming hospitals: A comprehensive study on phase quantification and physical properties

Red mud (RM) is a solid alumina industry waste generated in millions of tonnes and is stockpiled across the globe. From the environmental perspective, research and innovation strategies are utmost necessary for the minimization and utilization of red mud. In an attempt to develop an environmentally friendly technology, RM was utilized with Bi2O3 for the development of radiation shielding tiles. RM is a source of many metal oxides, which react with Bi2O3 during sintering and form various high-dense phases. The Rietveld refinement of the tiles sintered from 600 to 1100°C confirms the formations and transformations of several high-dense phases like Bi24Ti2O40, BiFeO3, and Na0.5Bi0.5TiO3. The RM-Bi2O3 mixture sintered at 1100°C (RMBi1100) exhibited high density (3.64 ×103 kg m−3), less porosity (10 %), and flexural strength of 24 MPa. The results showed that the developed sample has a half-value layer (HVL) of 1.15 mm at 140 kV. The 15.5 mm, 13.5 mm, and 7 mm thick RMBi1100 tiles can effectively replace 2.3 mm, 2 mm, and 1 mm thick lead sheets respectively, that are used to establish radiation shielding structures in computed tomography, radiography & fluoroscopy, and dental infra oral radiography installations, respectively. It can promote the utilization of red mud and thereby reduce the environmental pollution associated with lead and red mud.

Waste plastics upcycled for high-efficiency H2O2 production and lithium recovery via Ni-Co/carbon nanotubes composites

The disposal and management of waste lithium-ion batteries (LIBs) and low-density polyethylene (LDPE) plastics pose significant environmental challenges. Here we show a synergistic pyrolysis approach that employs spent lithium transition metal oxides and waste LDPE plastics in one sealed reactor to achieve the separation of Li and transition metal. Additionally, we demonstrate the preparation of nanoscale NiCo alloy@carbon nanotubes (CNTs) through co-pyrolysis of LiNi0.6Co0.2Mn0.2O2 and LDPE. The NiCo alloy@CNTs exhibits excellent catalytic activity (Eonset = ~0.85 V) and the selectivity (~90%) for H2O2 production through the electrochemical reduction of oxygen. This can be attributed to the NiCo nanoalloy core and the presence of CNTs with abundant oxygen-containing functional groups (e.g., –COOH and C–O–C), as confirmed by density function theory calculations. Overall, this work presents a straightforward and green approach for valorizing and upcycling various waste LIBs and LDPE plastics.

Air-Stable High-Entropy Layered Oxide Cathode with Enhanced Cycling Stability for Sodium-Ion Batteries.

O3-type layered oxides have been extensively studied as cathode materials for sodium-ion batteries due to their high reversible capacity and high initial sodium content, but they suffer from complex phase transitions and an unstable structure during sodium intercalation/deintercalation. Herein, we synthesize a high-entropy O3-type layered transition metal oxide, NaNi0.3Cu0.05Fe0.1Mn0.3Mg0.05Ti0.2O2 (NCFMMT), by simultaneously doping Cu, Mg, and Ti into its transition metal layers, which greatly increase structural entropy, thereby reducing formation energy and enhancing structural stability. The high-entropy NCFMMT cathode exhibits significantly improved cycling stability (capacity retention of 81.4% at 1C after 250 cycles and 86.8% at 5C after 500 cycles) compared to pristine NaNi0.3Fe0.4Mn0.3O2 (71% after 100 cycles at 1C), as well as remarkable air stability. Finally, the NCFMMT//hard carbon full-cell batteries deliver a high initial capacity of 103 mAh g-1 at 1C, with 83.8 mAh g-1 maintained after 300 cycles (capacity retention of 81.4%).

Ultra-low-power super class-AB adaptive biasing operational transconductance amplifier with enhanced gain for biomedical applications

The operational transconductance amplifier (OTA) proposed in this article is a bulk-driven (BD), single-stage, super-class-AB, adaptive biasing, functioning in the subthreshold region (ST) with an enormously low power supply of ± 0.25 V, providing high-gain. The input core of the OTA circuit is composed of adaptively biased BD differential input pairs based on flipped voltage follower (FVF), which drive in class-AB mode with a partial positive feedback (PPF) approach. The circuit additionally employs FVF and self-cascode (SC)-based low-power current mirror loads at its output to obtain significantly high gain and unity gain frequency. In addition, using adaptive loads based on source-degenerated metal oxide semiconductor (MOS) resistors raises dynamic current more efficiently, consequently improving the slew rate and unity gain frequency (UGF) without drawing additional power. Employing the cadence spectre tool and the UMC 0.18 μm complementary metal oxide semiconductor (CMOS) process technology, the designed OTA has been simulated. The simulation outcomes substantiate that the amplifier provides high open loop DC gain of 75 dB, 18.75 kHz UGF with a phase margin of 63.93º, and input-referred noise (IRN) of 0.734 µV/Hz0.5 at 1 kHz frequency. The proposed OTA consumes just 60.15 nW of power. The performance results confirmed that the proposed OTA circuit is appropriate in biomedical applications.

2D nanosheet SnS2 solution-processed photoanodes: Unveiling enhanced visible light absorption for solar fuels applications

The scale-up of photoelectrochemical water splitting and CO2 reduction is currently hindered by the excessive band gap of metal oxide photoanodes. Metal sulfides 2D nanostructured morphology offer improved optoelectronic properties and catalytic capabilities in the oxygen evolution reaction (OER). This study demonstrates for the first time visible spectra absorption capabilities of SnxSy photoanodes, fabricated by facile non-vacuum techniques and post-annealed in a sulfur atmosphere, yielding SnS2 multilayer nanosheets with visible-light absorption down to 900 nm wavelengths. Optimal annealing (500 °C) resulted in >1 V photovoltages, photocurrents surpassing 1.6 mA/cm2 at 1.23VRHE, incident photon-to-current conversion efficiency (IPCE) of 75% at 330 nm. Photon conversion in the 500–900 nm range (down to 1.37 eV) is correlated with phase transformation from orthorhombic α-SnS to Sn2S3 and further hexagonal SnS2. IPCE is key for describing effective phase transformation and photon conversion at wavelengths below the dominant direct band gap for the SnS2, suggesting potential indirect transitions or confinement in the low-dimensional nanosheets. SnS2 nanosheets fabricated by solution-processed means, hold great potential for large-scale, cost-effective, and efficient photoelectrochemical devices.

NiOx Passivation in Perovskite Solar Cells: From Surface Reactivity to Device Performance.

Nonstoichiometric nickel oxide (NiOx) is one of the very few metal oxides successfully used as hole extraction layer in p-i-n type perovskite solar cells (PSCs). Its favorable optoelectronic properties and facile large-scale preparation methods are potentially relevant for future commercialization of PSCs, though currently low operational stability of PSCs is reported when a NiOx hole extraction layer is used in direct contact with the perovskite absorber. Poorly understood degradation reactions at this interface are seen as cause for the inferior stability, and a variety of interface passivation approaches have been shown to be effective in improving the overall solar cell performance. To gain a better understanding of the processes happening at this interface, we systematically passivated specific defects on NiOx with three different categories of organic/inorganic compounds. The effects on NiOx and the perovskite (MAPbI3) deposited on top were investigated using X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and scanning electron microscopy (SEM). Here, we find that the perovskite's structural stability and film formation can be significantly affected by the passivation treatment of the NiOx surface. In combination with density functional theory (DFT) calculations, a likely origin of NiOx-perovskite degradation interactions is proposed. The surface passivated NiOx layers were incorporated into MAPbI3-based PSCs, and the influence on device performance and operational stability was investigated by current-voltage (J-V) characterization, impedance spectroscopy (IS), and open circuit voltage decay (OCVD) measurements. Interestingly, we find that a superior structural stability due to interface passivation must not relate to high operational stability. The discrepancy comes from the formation of excess ions at the interface, which negatively impacts all solar cell parameters.

Analysis of an operational trans-conductance amplifier with positive feedback

In this paper, we present an analysis of an operational trans-conductance amplifier (OTA) with two positive feedback. The direct current (DC) transfer function is obtained by analyzing the OTA using the drain current in the weak inversion region. The analysis results were verified through comparison with SPICE simulations, and the characteristics of the DC transfer function analysis for the OTA design are well matched with the simulation results. The designed OTA dissipates a low power of 41.4 nW, and features the slew rate is improved by 436% compared to a conventional OTA without two positive feedback. Additionally, a DC gain and a unity-gain bandwidth is improved by 36 dB and 6.7 times, respectively. The OTAs are designed for the 0.18 μm complementary metal–oxide–semiconductor (CMOS) process.

Heteroatom doping enables hydrogen spillover via H+/e− diffusion pathways on a non-reducible metal oxide

Hydrogen spillover, the simultaneous diffusion of protons (H+) and electrons (e−) is considered to be applicable to ubiquitous technologies related to hydrogen but limited to over reducible metal oxides. The present work demonstrates that a non-reducible MgO with heteroatom Al dopants (Al–MgO) allows hydrogen spillover in the same way as reducible metal oxides. Furthermore, a H+ storage capacity of this material owing to hydrogen spillover is more than three times greater than those of various standard metal oxides based on H+ transport channels within its bulk region. Atomic hydrogen diffuses over the non-reducible Al–MgO produces active H+-e− pairs, as also occurs on reducible metal oxides, to enhance the catalytic performance of Ni during CO2 hydrogenation. The H+ and e− diffusion pathways generated by the heteroatom Al doping are disentangled based on systematic characterizations and calculations. This work provides a new strategy for designing functional materials intended to hydrogen spillover for diverse applications in a future hydrogen-based society.

Plasma‐assisted Surface Engineering to Stabilize Mn3+ in Electrodeposited Manganese Oxide Films for Water Oxidation

Manganese oxide is a unique type of transition metal oxide that effectively functions as a catalyst for the oxygen evolution reaction (OER). Here, manganese oxide (MnOx) polymorphs are synthesized through electrochemical deposition and treated with an atmospheric pressure plasma jet (APPJ). The APPJ surface treatment can generate numerous oxygen vacancies and modify the crystallinity of the MnOx films, which can enhance the long‐term stability of the MnOx films by stabilizing the Mn3+ content in the highly oxidizing environment. The increase in Mn3+ content and concentration of oxygen vacancies in the material synergistically increase the adsorption capacity of OH* and the electron‐transferring capacity of MnOx films in the OER process, making them more stable and effective for OER. MnOx films treated with APPJ exhibit significantly higher activity, better stability, and lower Tafel slopes for OER than untreated MnOx films. The MnOx films treated with APPJ can remain stable for up to 92 hours during OER with a current density of 10 mA cm‐2, with an onset overpotential of 310 mV. This strategy, which combines APPJ surface treatment techniques with electrodeposition methods, is innovative in the surface modification of manganese oxides with mixed valences to create OER catalysts with stable Mn3+ content.

Preparation and Optimization of Polyaniline/ Titanium Dioxide/ Carboxymethyl Cellulose Powder for Effective Nickel Adsorption

Hexanoic acid-doped polyaniline (PAni) is a great potential candidate to replace conventional adsorbent towards the removal of heavy metal waste from electroplating industry, especially nickel (Ni). In this study, different weight % (wt %) of titanium dioxide (TiO2) and carboxymethyl cellulose (CMC) are added to form PAni composites with enhanced Ni removal efficiency. All the synthesized samples were examined with FTIR, UV-Vis, conductivity measurement, XRD, TGA, and FESEM to confirm their chemical structures, oxidation states, electrical conductivity, crystallinity and incorporation of metal oxide, thermal stability, and surface morphology, respectively. Among the different samples, PAni / TiO2 20 % exhibited the highest Ni removal efficiency of 37.5 %. Upon further addition of CMC, PAni / TiO2 / CMC 5 % showed the highest Ni removal efficiency of 89.08 %. Optimization of the experimental parameters were conducted and a maximum Ni removal efficiency of 97.88 % was achieved at pH 10, 30 min contact time at a temperature of 30 °C, and with an adsorbent dosage of 0.01 g. This study shows that the composite of PAni / TiO2 / CMC 5 % shows good potential to be applied as adsorbent of the removal of Ni ions.

Flame made low Pt loading catalysts supported on different metal oxides for catalytic combustion of CO and CH4

Catalytic combustion is an effective approach to remove air pollutants from various emission sources. For this purpose, supported noble metal catalysts are preferred in commercial applications due to their outstanding catalytic activity for eliminating CO, hydrocarbon compounds and NOx. In this paper, we employ the flame spray pyrolysis method to prepare a series of Pt-based catalysts with four different supports (TiO2, ZrO2, MgO and ZnO) and variable low Pt loadings for catalytic combustion of CO and CH4. The performance of 0.5 Pt/TiO2 is the best in all samples, in which the T90 temperatures are 107 and 500 °C for 90% conversion of CO and CH4, respectively. To examine its thermal stability, a time-on-stream test at 700 °C for 420 min is carried out, resulting in a decrease of about 5% in the final conversion of CH4. The X-ray diffraction results show that TiO2 support is a mixed phase with a major amount of anatase and a small amount of rutile other than a pure phase of ZrO2, MgO and ZnO. Furthermore, X-ray photoelectron spectroscopy analysis and high-angle annular dark-field scanning transmission electron microscopy observation show that when the Pt loading is low, the Pt species exist as highly dispersed single atoms on the surface of the TiO2 support. As the Pt loading gradually increases, the state of the Pt species transitions from single atoms to Pt clusters, resulting in a decrease in dispersion. Ultimately, the Pt can successfully accumulate on the surface of the TiO2 nanoparticles, providing abundant active sites for efficient catalytic combustion reactions.

Photodegradation of Methylene Blue Using ZnO/Perlite under Ultraviolet Light

The disposal of waste in the continuously growing industries leads to pollution caused by pollutants. One of them is liquid waste originating from the textile industry, which contains toxic coloring agents such as methylene blue that are difficult to decompose in the environment. Therefore, an effort is needed to tackle this issue using photocatalysis. A frequently used photocatalyst material is a semiconductor metal oxide like ZnO. However, ZnO semiconductors still have limitations in their applications. To overcome these limitations, ZnO catalysts will be modified with a supporting material like perlite, which is a lightweight and porous material. This study aims to examine the effectiveness of ZnO/Perlite in degrading methylene blue. The ZnO/Perlite composite with a 20% composition shows the highest photocatalytic activity compared to the ZnO/Perlite composites with 10% and 30% compositions. The optimum condition for ZnO/Perlite 20% in degrading methylene blue is achieved with a mass of 0.3 grams, at pH 11, with 2 hours of stirring under ultraviolet light irradiation, resulting in a photocatalytic activity of 47.59% and a combined adsorption and photocatalytic activity of 78.1%.

Influence of Ni-doping on CuCo2O4 electrode for enhanced supercapacitor performance and sustainable energy storage

This work provides a revolutionary strategy for creating high-performance supercapacitors by designing and fabricating a unique nanostructured bimetallic oxide electrode. The proposed electrode leveraged the synergistic effects of metal oxides to enhance both energy density and charge-discharge kinetics. Ni-doped CuCo2O4 nanostructures (Cu1-xNixCo2O4) were synthesized in incremental order (x = 0.0, 0.05, 0.10, and 0.15) by facile sol-gel auto-combustion route. The nanostructures analyzed through x-ray diffraction, FTIR spectroscopy, Micro-Raman spectroscopy, x-ray photoelectron spectroscopy (XPS) and Scanning electron microscopy revealed the single phase and polycrystalline nature of CuCo2O4, with some impurity phases of CuO. The surface morphology studies showed numerous pores among the grains of Cu1-xNixCo2O4. Cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy (EIS) were used to investigate the electrochemical performance of synthesized Cu1-xNixCo2O4 samples. In a 3 M KOH electrolyte solution, the Cu1-xNixCo2O4 electrodes with x = 0.05 exhibited 2340 Fg−1 specific capacitance at 5 mVs−1, demonstrating superior electrochemical performance with excellent rate capability. Furthermore, it exhibited 35.88 Whkg−1 energy density, an exceptional 2484.74 Wkg−1 power density, and retained 99.9 % capacitance after 5000 cycles, demonstrating good stability. The results suggest that porous bimetallic oxide nanostructures can be promising candidates for the development of high-performance, environmentally friendly supercapacitors.

Lorentz Force-Actuated Bidirectional Nanoelectromechanical Switch with an Ultralow Operation Voltage.

The high operating voltage of conventional nanoelectromechanical switches, typically tens of volts, is much higher than the driving voltage of the complementary metal oxide semiconductor integrated circuit (∼1 V). Though the operating voltage can be reduced by adopting a narrow air gap, down to several nanometers, this leads to formidable manufacturing challenges and occasionally irreversible switch failures due to the surface adhesive force. Here, we demonstrate a new nanowire-morphed nanoelectromechanical (NW-NEM) switch structure with ultralow operation voltages. In contrast to conventional nanoelectromechanical switches actuated by unidirectional electrostatic attraction, the NW-NEM switch is bidirectionally driven by Lorentz force to allow the use of a large air gap for excellent electrical isolation, while achieving a record-low driving voltage of <0.2 V. Furthermore, the introduction of the Lorentz force allows the NW-NEM switch to effectively overcome the adhesion force to recover to the turn-off state.

Nanoarchitectonics and applications of two-dimensional materials as anodes for lithium-ion capacitors

Lithium-ion capacitors (LICs) represent an innovative hybridization in the energy storage field, effectively combining the best features of supercapacitors and lithium-ion batteries. However, the theoretical advantage of LICs is impeded by the low reaction efficiency of the negative electrode material and significant volume expansion. Two-dimensional (2D) materials, due to their unique morphology, abundant pores, rich active centers, and adjustable composition, have been widely studied and developed as negative electrodes for LICs. Therefore, it is imperative to provide a timely review of the latest advancements in the field. The review initiates with a detailed exploration of the infrastructure, key performance evaluation parameters, and the underlying energy storage mechanisms that define LICs. Subsequently, the focus shifts towards the cutting-edge research surrounding 2D materials, including graphene, MXene, transition-metal dichalcogenides, and transition-metal oxides. The review further elaborates on the typical applications of these 2D materials within LIC frameworks, highlighting their unique properties and contributions to enhanced energy storage solutions. In conclusion, the discussion addresses the significant challenges these materials encounter within LIC applications, such as scalability, cost, and integration issues, while also projecting future development prospects. It outlines both the current limitations and the potential breakthroughs that could pave the way for more advanced and efficient LIC technologies.

Boosting energy storage via the strong interaction between Cu2O clusters and carbon rich framework

Metal oxides have attracted tremendous attention because of their easy fabrication, high reversible voltage, and decent electrochemical capacity in lithium ion batteries. However, the conversion of their structure and the low electric conductivity always lead to a high polarization and poor cyclic stability. Herein, the strong interaction between Cu2O and porous carbon-rich framework is constructed through an in-situ synthesis method. Benefit from the synergistic effect derived from this interaction, the confined size and the high reversibility in chemical reaction of Cu2O are realized. In the hybrid system, the conjugated carbon skeleton with acetylene bond plays crucial role not only in building strong interactions, but also in interconnecting numerous Cu2O clusters for the transport of charge and storing of ions in a homogeneous solid. Hence, the composite material of porous carbon-rich material and Cu2O electrode delivers a decent capacity of 804 and 305 mAh g–1 in lithium and sodium ion batteries, respectively. These results suggest the great potential of such carbon framework/metal oxides composite material applied for high performance battery.