Solid oxide fuel cells (SOFCs) offer an efficient energy conversion technology for alleviating current energy problems. High temperature proton-conducting (HTPC) oxides are promising electrolytes for this technology, since their activation energy is lower than that of conventional oxygen-ion conductors, enabling the operating temperature reduction at 600 °C. Among HTPC oxides, doped BaZrO3 materials possess high chemical stability, needed for practical applications. Though, poor sinterability and the resulting large volume of highly resistive grain boundaries hindered their deployment for many years. Nonetheless, the recently demonstrated high proton conductivity of the bulk revived the attention on doped BaZrO3, stimulating research on solving the sintering issues. The proper selection of dopants and sintering aids was demonstrated to be successful for improving the BaZrO3 electrolyte sinterability. We here briefly review the synthesis strategies proposed for preparing BaZrO3-based nanostructured powders for electrolyte and electrodes, with the aim to improve the SOFC performance.

Photoelectrochemical cells offer a more elegant, clean, and sustainable way to store solar energy as chemical energy through the splitting of water into its primitive form (H2 and O2). Among many metal oxides pointed as candidates for this application, the fundamental characteristics of hematite (α-Fe2O3), such as abundance, excellent chemical stability in an aqueous environment, and favorable optical band gap, emerged as a promising photoanode. Although attractive, the poor optoelectronic properties necessitate a large application of overpotential for split water assisted by solar irradiation, limiting the high performance of this material. Since the electrode was built using materials in nanoscale, significant advances were achieved. This review highlights new insights and recent progress in the use of a purpose-built material process to build hematite electrodes for improving photocatalytic activity. In addition, reduction on the required overpotential by effective control-treatment of morphology and surface of vertically aligned hematite nanorods will be addressed. An interesting set of results were also discussed revisiting a novel strategy recently presented in the literature and complementary advances was illustrated. These latest efforts aid in pointing out the challenges or obstacles to be overcome using this morphology and in defining new opportunities.

Hematite has been considered as one of the most promising materials for solar water splitting, although its photoelectrochemical performance is still not very high and limited by its intrinsic properties. In the past few years, sizable advances in the development of hematite photoelectrodes for enhanced water splitting activities have been achieved by a variety of rational modification strategies, including nanostructure design for efficient charge collection, metal ion doping for promoted charge carrier transfer, heterojunctions for efficient charge separation, and surface and/or interface modification for retarded charge recombination and enhanced light absorption. In this article, research work and milestone achievement actually focused on hematite photoelectrodes for water splitting is reviewed in detail. A review on this topic by answering the key question, “how to modify or design hematite photoelectrode to improve its conductivity, enhance charge separation as well as catalyze surface water oxidation,” in authors' view, can be potentially helpful to enable hematite for further efficient solar energy conversion, which will be very inspiring and important to this field.

By combining high-resolution transmission electron microscopy and scanning transmission electron microscopy with analytical capability, we investigated the nanostructure of a textured hematite photoanode with columnar grains obtained by the colloidal deposition of magnetite nanocrystals. This initial report describes in detail the structure and chemistry of the α-Fe2O3/SnO2:F interface by identifying semicoherent and incoherent interfaces as well as a localized interdiffusion layer of Sn and Fe at the interface (∼100 nm in length). Our study indicates that unintentional doping by tin at a high sintering temperature is not significant in enhancing hematite photoanode performance for water oxidation. The correlation of nanoscale morphology with photoelectrochemical characterization facilitated the identification of the beneficial effect of a preferential growth direction of a hematite film along the [110] axis for water-splitting efficiency.

Confining light metal hydrides in micro- or mesoporous scaffolds is considered to be a promising way to overcome the existing challenges for these materials, e.g. their application in hydrogen storage. Different techniques exist which allow us to homogeneously fill pores of a host matrix with the respective hydride, thus yielding well defined composite materials. For this report, the ordered mesoporous carbon CMK-3 was taken as a support for LiAlH4 realized by a solution impregnation method to improve the hydrogen desorption behavior of LiAlH4 by nanoconfinement effects. It is shown that upon heating, LiAlH4 is unusually oxidized by coordinated tetrahydrofuran solvent molecules. The important result of the herein described work is the finding of a final composite containing nanoscale aluminum oxide inside the pores of the CMK-3 carbon host instead of a metal or alloy. This newly observed unusual oxidation behavior has major implications when applying these compounds for the targeted synthesis of homogeneous metal–carbon composite materials.

High rate of charge carrier recombination is a critical factor limiting the photocatalytic activity of g-C3N4. In this contribution, we demonstrate that this issue can be alleviated by constructing a plasmonic photocatalyst with tailored plasmonic-metal nanostructures, i.e., core–shell-typed Ag@SiO2 nanoparticles. Compared with pure g-C3N4, the photocatalytic hydrogen production activity was enhanced by 63% for Ag@SiO2/g-C3N4. As analysis from the photoluminescence results, the enhancement could be attributed to that plasmonic nanostructures favored the separation of electron–hole pairs in the semiconductor due to localized surface plasmons resonance effect. It was found that the silica shell between the Ag nanoparticles and g-C3N4 was essential for the better photocatalytic activity of Ag@SiO2/g-C3N4 than that of Ag/g-C3N4 by limiting the energy-loss Förster energy transfer process.

An in situ redox reaction was developed to synthesize bundled tungsten oxide (WO3@W18O49) ultrafine nanowires (BUNs) loaded with Ag nanoparticles using weakly reductive W18O49 and oxidative silver nitrate as precursor. However, due to the weak activation between the two reactants, redox just happened on the surface of W18O49, resulting in the formation of W18O49 coated with WO3 (here, we refer this structure to WOx simply), and the bulk phase of the composites retained the same pattern. Ag nanoparticles (<5 nm) with a narrow size distribution were obtained and immobilized onto WOx BUNs without any aggregation. The paper presented a systematic investigation on the Ag-WOx nanocomposite used as a catalyst for the reduction of p-nitrophenol and as an antibacterial agent against Escherichia coli. The remarkably enhanced performance may be ascribed to the moderate interaction of the small Ag-NPs and WOx BUNs with high specific surface area.

We have studied the magnetoresistance (MR) of hydrogen plasma-treated pure ZnO wires of tens of micrometer diameter at different temperatures. A negative MR of 1% at 8 T applied field is measured for all wires at 4 K, independent of the temperature (300 K … 773 K) used during the hydrogen treatment. However, a positive MR develops, the higher the treatment temperature. The MR can be explained with a semiempirical model taking into account local magnetic moments and the s–d exchange interaction. These results together with field anisotropy in the MR indicate the appearance of magnetic order due to the hydrogen treatment in agreement with recently published reports on the influence of hydrogen in bulk ZnO single crystals. Hydrogen doping may provide a way to trigger defect-induced magnetism in small oxide structures.

The effects of stearic acid on the high-energy ball milling of tin powder have been investigated. The mean crystallite sizes, microstrain, and phase transformations were examined using different techniques like x-ray diffraction (XRD), Rietveld refinement method, and differential scanning calorimetry (DSC). After 28 h of milling, the Rietveld analysis showed the stabilization of Sn mean crystallite sizes at around 50 nm. Due to the presence of oxygen in stearic acid, the milling process gradually produced an amorphous Sn oxide phase. The DSC thermogram of the sample milled for 28 h showed two exothermic peaks separated by an endothermic peak. Based on the DSC measurements, two samples were annealed at 240 and 350 °C for 20 min. The annealing at 240 °C confirmed the presence of an amorphous phase which crystallized in nanostructured tetragonal SnO phase. The annealing at 350 °C revealed the nucleation of nanostructured tetragonal SnO2 phase.

Novel water-soluble titanium complexes coordinated by hydroxycarboxylic acids or amines were developed, and the hydrothermal treatment of the new complexes was carried out to elucidate the formation mechanism of the titania polymorphs including rutile, anatase, and brookite. An empirical relationship among the crystal structure of TiO2, the ligand, and the complex structure was found. Anatase, rutile, or a mixture of both was obtained by the hydrothermal treatment of the complexes coordinated by hydroxycarboxylic acids. The structure of complexes prepared using hydroxycarboxylic acids, which have one hydroxyl and one carboxylic groups, seems to be preferable for the formation of rutile. It was also found that the hydrothermal treatment of titanium complexes coordinated by amine with NAc2 structure resulted in the formation of brookite. Thus, the effect of ligand and complex structure on the crystal structure of TiO2 synthesized by the hydrothermal treatment of the complexes was proposed.

Fe3O4@TiO2 magnetic photocatalysts containing sub-10-nm TiO2 nanocrystals with two different morphologies (nanoparticles and nanorods) were prepared via a facile straight dipping process. A series of comparative experiments on organic pollutant degradation demonstrated that Fe3O4@TiO2 nanorods show superior activity and faster degradation rates than Fe3O4@TiO2 nanoparticles. Combined with the study of high resolution transmission electron microscopy, crystal models are given to analyze the morphology effect of TiO2 nanocrystals on their photocatalytic activities for organic degradation. TiO2 nanorods with more (100) crystal planes, which have relatively higher surface energy and relative higher density of Ti atoms, showed a higher activity than that of TiO2 nanoparticles. Furthermore, both Fe3O4@TiO2 nanorods and Fe3O4@TiO2 nanoparticles show better photocatalytic activities than several comparison Fe3O4@TiO2 samples due to the strong size effect arising from the tiny size of TiO2 nanorods and nanoparticles. These magnetic photocatalysts also show advantages in separation and recycling utilization.

We present a simple and quick procedure for the one-pot synthesis of manganese oxides under a basic solvothermal condition in the presence of cationic surfactants acting as the template in a 2-butanol/water solution. Three-dimensional spinel-type MnO2 microspheres composed of small nanoparticles have been fabricated for the first time using our method. Their corresponding electrochemical performances in the applications of supercapacitor electrodes exhibit a good specific capacitance (SC) value of ∼190 F/g at 0.5 A/g and excellent SC retention and Coulombic efficiency of ∼100% and ∼95% after 1000 charge/discharge cycles at 1 A/g, respectively. This suggests its potential applications in energy storage devices. Further, we demonstrate that this solvothermal technique enables the morphological tuning of manganese oxides in various forms such as schists, rods, fibers, and nanoparticles. This work describes a rapid and low-cost technique to fabricate novel architectures of manganese oxides having the desired crystal phase, which will highly benefit various supercapacitor applications.

A facile inexpensive route has been developed to prepare ZnO hierarchical materials with microplate/nanohole structures based on the colloidal monolayer template by the precursor thermal decomposition. These hierarchical structured materials demonstrated an excellent superhydrophobicity with self-cleaning effect and an enhanced photocatalytic performance to organic molecules, which are attributed to big roughness and large surface area of such special hierarchical structures. The formation mechanism of such hierarchical structures was investigated in detail by tracing morphology changing at different precursor concentrations. At high precursor concentration, both incompletely restricted ZnO growth of colloidal templates and preferable growth of microplates take place at the same time, and hence, ZnO hierarchical materials with microplate/nanohole structures are formed. With increasing precursor concentration, the number density of ZnO microplates tends to be larger. The large number density of ZnO microplates and holes on the microplates render the sample a large surface area and surface roughness, leading to good superhydrophobicity and photocatalytic activity. Such hierarchical ZnO micro/nanostructured materials have important applications in environmental science, microfluidic devices, etc.

Homogenous strontium titanate (SrTiO3) nanofibers were prepared via the electrospinning of precursor solutions containing both strontium and titanium salts. Photocatalytic activities of these SrTiO3 nanofibers for hydrogen generation from water were examined and compared to that of SrTiO3 nanoparticles. The nanofibers calcined at 700 °C showed the highest photocatalytic activity of 167 μmol/h/g among the SrTiO3 samples tested. The high activity was attributed to the ideal stoichiometric ratio of Ti/Sr, small crystallite size, high crystallinity, mesoporous structure, large surface area, and appropriate energy gap. These were confirmed through field emission scanning electron microscopic with energy dispersive spectroscopic observations, x-ray diffraction patterns, N2 gas absorption–desorption isotherm measurements, photoelectron yield spectroscopy in air, and UV-visible spectrophotometry.

The oxidant peroxo method (OPM) exhibits several advantage and unique characteristics not found in the traditional methods for the synthesis of lead- and bismuth-based oxides. First of all, it is a clean method based on hydrogen peroxide that matches perfectly with the green chemistry approach. Second, the oxidizing local atmosphere provided by the precursor during its crystallization is unique among all the wet chemical techniques of synthesis, which usually result in reducing environment. Besides these advantages, only a few studies have focused on the use of the OPM to obtain better materials, which makes this field of study an excellent opportunity for the development of materials with higher purity and controlled morphologies.

Formaldehyde (HCHO) is widely used in construction, wood processing, furniture, textile, and carpeting industries. However, it is highly toxic. It strongly irritates human eyes and nose, and is a carcinogen. In this paper, the effects of gas concentration and operating temperature on the sensing properties of the nano-SnO2 flat-type coplanar gas sensor arrays to formaldehyde were studied. The results revealed that the nano-SnO2 flat-type coplanar gas sensor arrays exhibited good sensitivity such as a fast response, short recovery time, and low detection limit. In addition, the adsorption and surface reactions of formaldehyde on SnO2 films were also studied by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) at 200–300 °C. Molecularly adsorbed formaldehyde, formate, dioxymethylene, polyoxymethylene, H2O, and CO2 surface species were formed during formaldehyde adsorption at 200–300 °C. Moreover, a possible mechanism of the reaction process was given.

A Cu–Ni sectioned cathode made up of two hemicycles of each of the metals was used for reactive co-sputtering of a thin film combinatorial library of Cu–Ni oxides covering a total compositional spread of 63 at.%. The thickness profiling of the library showed a nonuniform film thickness with a maximum region shifted toward the Cu side of the cathode. The presence of CuO, Cu2O, NiO, and metallic Cu–Ni alloys was identified during the scanning x-ray diffraction investigations along the compositional spread. A distinct structural zone was defined between Cu–14 at.% Ni and Cu–19 at.% Ni, where the scanning electron microscopy investigations showed a higher surface porosity combined with smaller grain sizes. This zone corresponds to the maximum film thickness region and correlates well with the position of the maximum work function of the Cu–Ni oxide films as mapped using a scanning Kelvin probe. During local corrosion studies focused on Cu dissolution, an improved corrosion resistance was identified in the Ni rich side of the compositional spread.

In the present study, we report an activation and enhancement of room temperature ferromagnetism in pure ZnO and V-doped ZnO (Zn0.95V0.05O and Zn0.90V0.10O) thin films by trioctylphosphine (TOP) functionalization. X-ray diffraction patterns show a slight decrease in the intensity of the diffraction peak on TOP functionalization. Atomic force micrographs of pure and V-doped ZnO films reveal no disorder in the film surface on TOP functionalization. The chemical bond formation of TOP on ZnO film surface was examined by x-ray photoelectron spectroscopy measurements. Photoluminescence measurements of TOP-functionalized ZnO films show enhancements of UV emission and quenching of visible emission. TOP-functionalized ZnO films reveal enhanced ferromagnetic behavior as evidenced from vibrating sample magnetometer measurements.

Nanoporous tungsten oxide films were synthesized by an anodic oxidation process in aqueous NaF/HF electrolytes. The tungsten films were deposited by the radio frequency magnetron sputtering method on sapphire substrates, and the anodic oxidation process was conducted in a dual-electrode reaction chamber with graphite electrode. The effects of processing parameters (anodic voltage, time, temperature, and the operation distance) on the morphology and porosity of the synthesized films were investigated experimentally. The samples were characterized by x-ray diffraction and scanning electron microscopy. The results showed that the pore diameter and porosity increased gradually with increasing anodic voltage, whereas the “wall” of the pore was subjected to electric breakdown at 60 V, and the pore diameter and porosity decreased. The pore diameter and porosity showed an early increased and later decreased state as the operation time and distance are increased. The sensitive response in the resistive method is reaction-dominated type and is exhibited as a linear relationship as a function of hydrogen gas concentration. The response toward 500 ppm hydrogen in air is up to 15.1 with a response time of 10 min at 200 °C.