Preparation and Electrochemical Applications of Magnéli Phase Titanium Suboxides: A Review.

Magnéli phase titanium suboxides (M-TSOs) belong to a type of sub-stoichiometric titanium oxides based on the crystal structure of rutile TiO2. They possess a unique shear structure, granting them exceptional electrical conductivity and corrosion resistance. These two advantages are crucial for electrode materials in electrochemistry, hence the significant interest from numerous researchers. However, the preparation of M-TSOs is uneconomic due to high temperature reduction and other complex synthesis process, thus limiting their practical application in electrochemical fields. This review delves into the crystal structure, properties, and synthesis methods of M-TSOs, and touches on their applications as electrocatalysts in wastewater treatment and electrochemical water splitting. Furthermore, it highlights the research challenges and potential future research directions in M-TSOs.

In situfabrication of Cu-Mn-O nanostructure catalysts on Ti mesh and their catalytic property optimization for low-temperature and stable CO oxidation.

A series of interlaced 'tripe-shaped' nanoflake catalysts made of CuMn2O4werein situprepared on Ti mesh substrate through the associated methods of plasma electrolyte oxidation and hydrothermal technique. The surface morphology, elemental distribution and chemical state, phase composition and microstructure of CuMn2O4nanostructures prepared under different conditions were systemically investigated. To evaluate the catalytic activity, the CO oxidation as a probe reaction was used, and the results showed that 12h-Cu1Mn2-300 (hydrothermal reaction at 150 °C for 12 h, Cu/Mn = 1/2 in initial precursor, heat treatment temperature at 300 °C) exhibited the best CO oxidation capability withT100= 150 °C owe to the formation of uniform CuMn2O4nanosheet layersin situgrown on flexible Ti mesh and the synergistic effect of Cu and Mn species in spinel CuMn2O4, which makes it more active towards CO oxidation than pure copper/manganese oxides.

NH4F-Induced Morphology Control of CoP Nanostructures to Enhance the Hydrogen Evolution Reaction.

Developing non-noble metal catalysts with superior catalytic activity and excellent durability is critically essential to promote electrochemical water splitting for hydrogen production. Morphology control as a promising and effective strategy is widely implemented to change the surface atomic coordination and thus enhance the intrinsic catalytic performance of current electrocatalysts. Herein, a series of cobalt phosphide (CoP) electrocatalysts with tunable morphologies of nanosheets, nanowires, nanorods, and nanoblocks have been prepared for the enhanced hydrogen evolution reaction (HER) by only adjusting the amount of ammonium fluoride (NH4F) in the hydrothermal process. Benefiting from the large active area, high surface activity, and favorable ion and gas diffusion channels, the clustered CoP nanorods obtained at a concentration of 0.15 M NH4F show the best HER performance with only an overpotential of 71 mV at a current density of 10 mA cm-2 and a low Tafel slope of 60.75 mV dec-1 in 1 M KOH. After 3000 CV cycles and 24 h durability tests, there is only a very slight degradation of performance owing to its outstanding stability and robust substrate adhesion.

Catalyst-assisted heteroepitaxial strategy for highly orderedß-Ga2O3nanoarrays and their optical property investigation.

In this work, we demonstrate the growth of highly orderedß-Ga2O3nanoarrays with (001) preferred growth plane for the first time through a facile heteroepitaxial strategy using metal Ga and c-sapphire as Ga precursor and monocrystalline substrate. The (001) preferred growth plane means that theß-Ga2O3nanowires grow along the normal direction of the (001) plane. Theß-Ga2O3nanoarrays along (001) preferential plane exhibit inclined six equivalent directions that correspond to the six crystallographic symmetry of (0001)α-Al2O3. High-resolution transmission electron microscopy analyses confirm the good crystallinity and the existence of unusual epitaxial relationship of {310}ß-Ga2O3ǁ (0001)α-Al2O3and <001>ß-Ga2O3or <132>ß-Ga2O3ǁ [11¯00]α-Al2O3. UV-vis and cathodoluminescence measurements reveal the wide band gap of 4.8 eV and the strong UV-blue luminescence (300-500 nm) centered at ∼388 nm. Finally, the luminescence mechanism is further investigated with the assistance of x-ray photoelectron spectroscopy. The heteroepitaxial strategy of highly orderedß-Ga2O3nanoarrays in this work will undoubtedly pave a solid way toward the fundamental research and the applications of Ga2O3nanodevices in optoelectronic, gas sensor, photocatalyst and next-generation power electronics.

Hydrothermal Approach to Spinel-Type 2D Metal Oxide Nanosheets.

The peculiar physical and chemical properties of 2D nanostructures have aroused global research interest in developing new members, synthetic technology, and exploring their potential applications in functional nanodevices. However, it is extremely challenging to directly obtain the 2D nanosheets for these extrinsic layered structures using conventional routines. In this work, we demonstrate the facile and general synthesis of 2D spinel-type metal oxides nanosheets through a simple hydrothermal reaction. Using this method, cubic γ-Ga2O3, ZnGa2O4 and MnGa2O4 nanosheets with triangular/hexagonal configuration and ultrathin thickness have been synthesized, and all these nanosheets show preferential growth along (111) plane with the minimum formation energy. Microstructural and composition analyses using HRTEM, EDS, XPS, and so on reveal that the as-synthesized 2D nanosheets are well-crystallized in cubic fcc-phase and show high purity in composition, and the formation process of MGa2O4 nanosheets can be regarded as the competition of M2+ and Ga3+ in tetrahedral site. Spatially resolved cathodoluminescence measurement of individual 2D nanosheet shows that the γ-Ga2O3, ZnGa2O4, and MnGa2O4 nanosheets exhibit distinct luminescence behavior, and ZnGa2O4 nanosheets show the strongest emission in visible region. It is expected that the facile synthesis of spinel-type metal oxides of γ-Ga2O3, ZnGa2O4, and MnGa2O4 nanosheets will further promote the exploration of a variety of semiconductor nanostructures that could not be achieved using conventional technology suitable for layered structures and will also open up some opportunities for the integration of advanced functional nanodevices such as photodetectors, phosphors on the basis of them.

Cu3P-Ni2P Hybrid Hexagonal Nanosheet Arrays for Efficient Hydrogen Evolution Reaction in Alkaline Solution.

The development of efficient and low-cost hydrogen evolution reaction electrocatalysts has been regarded as a promising approach to produce sustainable and clean fuels to solve the energy crisis and environmental problems. Herein, 3D hybrid Cu3P-Ni2P hexagonal nanosheet arrays are successfully prepared on nickel foam (Cu3P-Ni2P/NF). Benefiting from synergistic effects and strong chemical coupling existing at the interface, the Cu3P-Ni2P/NF electrode exhibits a low overpotential of 103 mV at a current density of 10 mA cm-2, which is 47 and 100 mV less than that for Ni2P/NF and Cu3P/NF, respectively. It also shows excellent electrochemical durability for long-term reaction in alkaline medium. The excellent electrocatalytic activity makes the Cu3P-Ni2P/NF as a promising cathode toward efficient hydrogen evolution via electrochemical water splitting.

Composition and Band Gap Tailoring of Crystalline (GaN)1- x(ZnO) x Solid Solution Nanowires for Enhanced Photoelectrochemical Performance.

Photoelectrochemical water splitting has emerged as an effective artificial photosynthesis technology to generate clean energy of H2 from sunlight. The core issue in this reaction system is to develop a highly efficient photoanode with a large fraction of solar light absorption and greater active surface area. In this work, we take advantage of energy band engineering to synthesize (GaN)1- x(ZnO) x solid solution nanowires with ZnO contents ranging from 10.3% to 47.6% and corresponding band gap tailoring from 3.08 to 2.77 eV on the basis of the Au-assisted VLS mechanism. The morphology of nanowires directly grown on the conductive substrate facilitates the charge transfer and simultaneously improves the surface reaction sites. As a result, a photocurrent approximately 10 times larger than that for a conventional powder-based photoanode is obtained, which indicates the potential of (GaN)1- x(ZnO) x nanowires in the preparation of superior photoanodes for enhanced water splitting. It is anticipated that the water-splitting capability of (GaN)1- x(ZnO) x nanowire can be further increased through alignment control for enhanced visible light absorption and reduction of charge transfer resistance.

Template Approach to Crystalline GaN Nanosheets.

Crystalline GaN nanosheets hold great challenge in growth and promising application in optoelectronic nanodevices. In this work, we reported an accessible template approach toward the rational synthesis of GaN nanosheets through the nitridation of metastable γ-Ga2O3 nanosheets synthesized from a hydrothermal reaction. The cubic γ-Ga2O3 nanosheets with smooth surface and decent crystallinity can be directly converted into hexagonal GaN nanosheets with similar morphology framework and comparable crystal quality in NH3 at 850 °C. UV-vis spectrum measurement reveals that the GaN nanosheets show a band gap of 3.30 eV with strong visible absorption in the range of 370-500 nm. The template synthetic strategy proposed in this work will open up more opportunities for the achievement of a variety of sheetlike nanostructures that can not be obtained through conventional routines and will undoubtedly further promote the fundamental research of newly emerging sheetlike nanostructures and nanotechnology.

Semiconductor Solid-Solution Nanostructures: Synthesis, Property Tailoring, and Applications.

The innovation of band-gap engineering in advanced materials caused by the alloying of different semiconductors into solid-solution nanostructures provides numerous opportunities and advantages in optoelectronic property tailoring. The semiconductor solid-solution nanostructures have multifarious emission wavelength, adjustability of absorption edge, tunable electrical resistivity, and cutting-edge photoredox capability, and these advantages can be rationalized by the assorted synthesis strategies such as, binary, ternary, and quaternary solid-solutions. In addition, the abundance of elements in groups IIB, IIIA, VA, VIA, and VIIA provides sufficient room to tailor-make the semiconductor solid-solution nanostructures with the desired properties. Recent progress of semiconductor solid-solution nanostructures including synthesis strategies, structure and composition design, band-gap engineering related to the optical and electrical properties, and their applications in different fields is comprehensively reviewed. The classification, formation principle, synthesis routes, and the advantage of semiconductor solid-solution nanostructures are systematically reviewed. Moreover, the challenges faced in this area and the future prospects are discussed. By combining the information together, it is strongly anticipated that this Review may shed new light on understanding semiconductor solid-solution nanostructures while expected to have continuous breakthroughs in band-gap engineering and advanced optoelectronic nanodevices.

Photochemical Modification of Single Crystalline GaN Film Using n-Alkene with Different Carbon Chain Lengths as Biolinker.

As a potential material for biosensing applications, gallium nitride (GaN) films have attracted remarkable attention. In order to construct GaN biosensors, a corresponding immobilization of biolinkers is of great importance in order to render a surface bioactive. In this work, two kinds of n-alkenes with different carbon chain lengths, namely allylamine protected with trifluoroacetamide (TFAAA) and 10-aminodec-1-ene protected with trifluoroacetamide (TFAAD), were used to photochemically functionalize single crystalline GaN films. The successful linkage of both TFAAA and TFAAD to the GaN films is confirmed by time-of-flight secondary ion mass spectrometry (ToF-SIMS) measurement. With increased UV illumination time, the intensity of the secondary ions corresponding to the linker molecules initially increases and subsequently decreases in both cases. Based on the SIMS measurements, the maximum coverage of TFAAA is achieved after 14 h of UV illumination, while only 2 h is required in the case of TFAAD to reach the situation of a fully covered GaN surface. This finding leads to the conclusion that the reaction rate of TFAAD is significantly higher compared to TFAAA. Measurements by atomic force microscopy (AFM) indicate that the coverage of GaN films by a TFAAA layer leads to an increased surface roughness. The atomic terraces, which are clearly observable for the pristine GaN films, disappear once the surface is fully covered by a TFAAA layer. Such TFAAA layers will feature a homogeneous surface topography even for reaction times of 24 h. In contrast to this, TFAAD shows strong cross-polymerization on the surface, this is confirmed by optical microscopy. These results demonstrate that TFAAA is a more suitable candidate as biolinker in context of the GaN surfaces due to its improved controllability.

Morphology-controlled syntheses of α-MnO2 for electrochemical energy storage.

Manganese dioxide (MnO2) nanoarchitectures including microspheres assembled by nanosheets and hollow urchins assembled by nanorods have been successfully synthesized using a facile and efficient hydrothermal method at 150 °C. The effects of concentrations of the reactants and reaction time on the structures and morphologies of MnO2 were systematically investigated. The experimental results showed that the morphologies of MnO2 transformed into nanosheet-assembled microspheres (10 min) from nanorod-assembled hollow urchins (5 min) by tuning the suitable reaction time. The nanorod-assembled hollow urchins experienced the morphology transformation cycle from urchin to a disordered structure to urchin with the extension of the reaction time. Furthermore, the nanorods with different diameters and lengths were formed with different concentrations of reactants at the same reaction time (8 h). The MnO2 nanorods fabricated with 0.59 g KMnO4 showed a maximum specific capacitance (198 F g(-1)) with a good rate capability and excellent cycling stability (maintained 94% after 2000 cycles). Furthermore, the nanosheet-assembled microspheres exhibited the higher specific capacitance of 131 F g(-1) at 1 A g(-1) with a long-term cycling stability for the samples at different reaction times. These results indicated their promising applications as high-performance supercapacitor electrodes and provided a generic guideline in developing different nanostructured electrode materials for electrochemical energy storage.

Defect-Induced Nucleation and Epitaxy: A New Strategy toward the Rational Synthesis of WZ-GaN/3C-SiC Core-Shell Heterostructures.

In this work, we demonstrate a new strategy to create WZ-GaN/3C-SiC heterostructure nanowires, which feature controllable morphologies. The latter is realized by exploiting the stacking faults in 3C-SiC as preferential nucleation sites for the growth of WZ-GaN. Initially, cubic SiC nanowires with an average diameter of ∼100 nm, which display periodic stacking fault sections, are synthesized in a chemical vapor deposition (CVD) process to serve as the core of the heterostructure. Subsequently, hexagonal wurtzite-type GaN shells with different shapes are grown on the surface of 3C-SiC wire core. In this context, it is possible to obtain two types of WZ-GaN/3C-SiC heterostructure nanowires by means of carefully controlling the corresponding CVD reactions. Here, the stacking faults, initially formed in 3C-SiC nanowires, play a key role in guiding the epitaxial growth of WZ-GaN as they represent surface areas of the 3C-SiC nanowires that feature a higher surface energy. A dedicated structural analysis of the interfacial region by means of high-resolution transmission electron microscopy (HRTEM) revealed that the disordering of the atom arrangements in the SiC defect area promotes a lattice-matching with respect to the WZ-GaN phase, which results in a preferential nucleation. All WZ-GaN crystal domains exhibit an epitaxial growth on 3C-SiC featuring a crystallographic relationship of [12̅10](WZ-GaN) //[011̅](3C-SiC), (0001)(WZ-GaN)//(111)(3C-SiC), and d(WZ-GaN(0001)) ≈ 2d(3C-SiC(111)). The approach to utilize structural defects of a nanowire core to induce a preferential nucleation of foreign shells generally opens up a number of opportunities for the epitaxial growth of a wide range of semiconductor nanostructures which are otherwise impossible to acquire. Consequently, this concept possesses tremendous potential for the applications of semiconductor heterostructures in various fields such as optics, electrics, electronics, and photocatalysis for energy harvesting and environment processing.

Solid-solution semiconductor nanowires in pseudobinary systems.

Pseudobinary solid-solution semiconductor nanowires made of (GaP)(1-x)(ZnS)(x), (ZnS)(1-x)(GaP)(x) and (GaN)(1-x)(ZnO)(x) were synthesized based on an elaborative compositional, structural, and synthetic designs. Using analytical high-resolution transmission electron microscopy (HRTEM) and energy dispersive X-ray spectroscopy (EDS), we confirmed that the structure uniformity and a lattice match between the two constituting binary components play the key roles in the formation of quaternary solid-solution nanostructures. Electrical transport measurements on individual GaP and (GaP)(1-x)(ZnS)(x) nanowires indicated that a slight invasion of ZnS in the GaP host could lead to the abrupt resistance increase, resulting in the semiconductor-to-insulator transition. The method proposed here may be extended to the rational synthesis of many other multicomponent nanosystems with tunable and intriguing optoelectronic properties for specific applications.

Green growth path dependence momentum under the prism of COP26: the role of financial deepening, ICT development, and export diversification.

Financial deepening is important in resource allocation for more productive enterprises, leading to sustainable green growth. Moreover, rapid development in the digital economy and export diversification significantly affect green growth. From this perspective, our study explores the impact of financial deepening, ICT development, and export diversification on green growth in China's economies from 1996 to 2021. The study explores the linkage between financial deepening, ICT development, export diversification, and green growth by employing the nonlinear autoregressive distributed lag (NARDL) approach. The results obtained in the long run are as follows: positive shock in financial deepening brings positive change in green growth, whereas negative shock in financial deepening reduces green growth. In the long run, positive shock in ICT enhances green growth, but negative shock in ICT does not impact green growth. Moreover, positive shock in export diversification brings positive change in green growth, whereas negative shock in export diversification reports an insignificant impact on green growth. Based on findings, it is suggested that financial deepening, ICT development, and export diversification are conducive to sustainable green growth.

Triangular ZnO nanosheets: synthesis, crystallography and cathodoluminescence.

ZnO nanosheets with triangular morphology have been synthesized on an Au-coated silicon substrate through a facile thermal evaporation process. The morphologies and microstructures of the nanosheets were studied by a scanning electron microscope (SEM) and a high-resolution transmission electron microscope (HR-TEM). These studies show that a nanosheet is commonly composed of two parts: a triangular ZnO sheet and an Au nanoparticle attached on its tip-end. Detailed crystallography analyses conclude that the formation of the highly crystalline nanostructures can be assigned to a combination of a vapor-liquid-solid (VLS) process that is believed to be responsible for its initial nucleation and subsequent crystallization along the growth direction, and a vapor-solid (VS) process that is responsible for its further radial growth. The spatially-resolved cathodoluminescence (CL) spectra exhibit a sharp strong near-band-edge (NBE) emission in the ultraviolet range and a negligible green emission.

Energy technology innovation through the lens of the financial deepening: Financial institutions and markets perspective.

This paper examines the impact of financial deepening on energy technology green innovation over the period 1996 to 2020. Utilizing the nonlinear QARDL technique, we assess the asymmetric short and long-term impacts across various quantiles. The research employs two measures of financial deepening, namely financial institution deepening (FID) and financial market deepening (FMD). The findings reveal that a positive change in the FID causes energy green innovation to rise, while a negative change in the FID causes energy green innovation to fall in the long run at most quantiles. Further, we find that the rise in the FMD help improves energy green innovation; however, the fall in the FMD does not significantly impact energy green innovation at all quantiles. Based on the findings, our research will help policymakers to develop valuable policies for financial deepening to enhance energy green innovation.

Dual-Mode Conversion of Photodetector and Neuromorphic Vision Sensor via Bias Voltage Regulation on a Single Device.

Simultaneous implementation of photodetector and neuromorphic vision sensor (NVS) on a single device faces a great challenge, due to the inherent speed discrepancy in their photoresponse characteristics. In this work, a trench-bridged GaN/Ga2 O3 /GaN back-to-back double heterojunction array device is fabricated to enable the advanced functionalities of both devices on a single device. Interestingly, the device shows fast photoresponse and persistent photoconductivity behavior at low and high voltages, respectively, through the modulation of oxygen vacancy ionization and de-ionization processes in Ga2 O3 . Consequently, the role of the optoelectronic device can be altered between the photodetector and NVS by simply adjusting the magnitude of bias voltage. As a photodetector, the device is able to realize fast optical imaging and optical communication functions. On the other hand, the device exhibits outstanding image sensing, image memory, and neuromorphic visual pre-processing as an NVS. The utilization of NVS for image pre-processing leads to a noticeable enhancement in both recognition accuracy and efficiency. The results presented in this work not only offer a new avenue to obtain complex functionality on a single optoelectronic device but also provide opportunities to implement advanced robotic vision systems and neuromorphic computing.

Probing the role of surface activated oxygen species of CeO2 nanocatalyst during the redox cycle in CO oxidation.

The oxygen species of CeO2 nanocatalysts plays a key role in the CO oxidation. In this work, nanocrystalline CeO2 with infrared spectroscopy detectable surface superoxide (O2 -) species at room temperature is fabricated and CO oxidation is used as a probe reaction for the exploration of the characteristics of surface O2 - species on the CeO2 surface. We discover that the surface O2 - species have ignorable influences on the overall reaction rate of CO oxidation on pure ceria by comparing P-CeO2 (CeO2 prepared by precipitation method) with HT-CeO2 (CeO2 prepared by hydrothermal method). It is concluded that the reaction between CO molecules and surface O2 - species is the first and the fast step in the whole redox cycle, while the release of surface lattice oxygen is the second and the rate determining step of the catalysts. This work gives an intuitionistic exploration on the redox properties of pure nanocrystalline CeO2 with surface O2 - species and reveals the influences of these species in the whole redox circle of CO oxidation.

Wearable biosensors for real-time sweat analysis and body motion capture based on stretchable fiber-based triboelectric nanogenerators.

Carbon neutrality is a global green energy revolution meaning that the carbon dioxide can make ends meet. However, with the mushroom of the fifth generation wireless systems (5G) and the Internet of Things (IoT), it is a great challenge for powering the ubiquitous distributed devices, because the battery production and high overhead maintenance may bring more carbon emissions. Here, we present wearable biosensors for real-time sweat analysis and body motion capture based on stretchable fiber-based triboelectric nanogenerators (F-TENG). The F-TENG is made of stretchable conductive fiber (Ecoflex coating with polyaniline (PANI)) and varnished wires. Based on the coupling effect of triboelectric effect and enzymatic reaction (surface-triboelectric coupling effect), the wearable biosensors can not only precisely sense the motion states, but also detect glucose, creatinine and lactate acid in sweat in real-time. Importantly, the wearable devices can self-drive without any external power source and the response against glucose, creatinine and lactate acid can be up to 103%, 125% and 38%, respectively. On this basis, applications in biosensing and wireless communication have been demonstrated. This work exhibits a prospective potential application of F-TENG in IoT for diverse use.

Homogeneous and well-aligned GaN nanowire arrays via a modified HVPE process and their cathodoluminescence properties.

In this work, we demonstrate the growth of homogeneous and well-aligned [0001]-oriented 1-D GaN nanoarrays via a modified hydride vapor phase epitaxy (HVPE) process using GaCl3 and NH3 as precursors. The density and length of the grown nanowires can be easily controlled by the process parameters. It was found that the growth technique provides Cl-rich growth conditions, which lead to special morphology and optical properties of the GaN nanoarrays. Different from reported GaN nanowires, the as-synthesized GaN nanoarrays in this study exhibit a hollow bamboo-like structure. Also, the cathodoluminescence spectrum shows strong visible luminescence between 400 and 600 nm wavelengths centered at 450 nm, and the disappearance of an intrinsic emission peak, which has been investigated in detail with the assistance of first-principles calculations. The strategy proposed in this work will pave a solid way for the controlled nucleation and growth of well-aligned GaN nanowire arrays which are significant for applications in large-scale integrated optoelectronic nanodevices, functionalized sensors and photoelectrocatalysis.