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A dense inner layer is highly valued among the surface coatings created through plasma electrolytic oxidation (PEO) treatment, because the PEO coating has been troubled by inherent porosity since its conception. To produce the favored structure, a proven technique is to prompt a soft sparking transition, which involves a sudden decrease in light and acoustic emissions, and a drop in anodic voltage under controlled current mode. Typically these phenomena occur in an electrolyte of sodium silicate and potassium hydroxide, when an Al-based sample is oxidized with an AC or DC (alternating or direct current) pulse current preset with the cathodic current exceeding the anodic counterpart. The dense inner layer feature is pronounced if a sufficient amount of oxide has been amassed on the surface before the transition begins. Tremendous efforts have been devoted to understand soft sparking at the metal–oxide–electrolyte interface. Studies on aluminum alloys reveal that the dense inner layer requires plasma softening to avoid discharge damages while maintaining a sufficient growth rate, a porous top layer to retain heat for sintering the amassed oxide, and proper timing to initiate the transition and end the surface processing after transition. Despite our understanding, efforts to replicate this structural feature in Mg- and Ti-based alloys have not been very successful. The soft sparking phenomena can be reproduced, but the acquired structures are inferior to those on aluminum alloys. An analogous quality of the dense inner layer is only achieved on Mg- and Ti-based alloys with aluminate anion in the electrolytic solution and a suitable cathodic current. These facts point out that the current soft sparking knowledge on Mg- and Ti-based alloys is insufficient. The superior inner layer on the two alloys still relies on rectification and densification of aluminum oxide.

We demonstrate the applicability of LAMOX as an electrolyte for solid oxide fuel cells (SOFC) by preparing two anodesupported cells based on La0.9Dy0.1Mo2O9 and La0.9Dy0.1Mo1 W1O9, and operating at 625°-700°C under single chamber conditions. The two cells, supported by a composite of NiO and Gddoped ceria (GDC), are initialized with a porous Ni1GDC disk to catalyze the partial oxidation reaction of methane. The partially oxidized methane reduces NiO to Ni catalyst and activates the cell at 650°C. A typical membrane electrode assembly of the single chamber SOFC cell consists of a 60-lm-thick La0.9Dy0.1Mo2O9 electrolyte, an anode of Ni1GDC, and a cathode of lanthanum strontium cobalt ferrite. Its peak power measures 220 mW/cm² at 700°C in a tubular chamber of 15 mm in diameter, with the total methane/ air flow rate of 350 mL/min and CH4:O252:1. [ABSTRACT FROM AUTHOR]

Well-aligned anatase (A)–TiO2nanocrystals (NCs) were grown by cold-wall metalorganic chemical vapor deposition (MOCVD) on fused silica using titanium-tetraisopropoxide (Ti(OC3H7)4) as the source reagent. Field emission scanning electron microscopy (FESEM) micrographs showed the growth of vertically aligned NCs. X-ray diffractometry (XRD) pattern revealed the aligned A–TiO2with a preferential orientation of (220). Raman spectrum confirmed the deposition of pure anatase phase TiO2on fused silica. Luminescence of self-trapped excitons and oxygen vacancies were observed in anatase NCs. The indirect band gap of A–TiO2was determined to be 3.14 ± 0.01 eV by analyzing the surface photovoltage spectrum. Energy-dispersive X-ray spectroscopy (EDS) and X ray photoelectron spectroscopy (XPS) analyses showed oxygen vs.titanium ratio of 2.0 ± 0.1 for the as-deposited TiO2NCs. Further structural characterization of the well-aligned A–TiO2NCs was studied using transmission electron microscopy (TEM) technique. The formation of building units bonded along {112} facets with preferred (220) orientation of the well-aligned A–TiO2NCs on fused silica were presented and the probable growth mechanisms were discussed. [ABSTRACT FROM AUTHOR]

The electrochemical performance and structural features of (La1− yCa y)(Co xFe1− x)O3 cathode prepared via a citrate acid gel route are studied when it is interfaced with the (La1.8Dy0.2)(Mo2− zW z)O9 electrolyte. The resistance and chemical capacitance of a low-frequency arc are extracted from the impedance results to evaluate its catalytic activity in oxygen reduction reaction (ORR). (La0.75Ca0.25)(Co0.8Fe0.2)O3 cathode exhibits the minimum area-specific resistance of 0.9 Ω cm2 and maximum capacitance of 5.7 mF/cm2 at 800°C among the compositions of x=0.1–0.9 and y=0.25. As the Co content increases, the decrease in resistance outweighs the increase in capacitance so that the product of resistance and capacitance ( RC time constant) decreases. In contrast, when varying the Ca content of the A-site, the changes in resistance and the capacitance compensate each other; hence the RC time constant is virtually unchanged with respect to the calcium content. Thus, Co is a more influential element than Ca on the ORR catalytic activity. The pore structure study reveals a small amount of Mo diffuses from the electrolyte into the cathode, and its quantity is reduced when interfaced to an electrolyte of high W content. [ABSTRACT FROM AUTHOR]

The structural features and catalytic activities of PtIr electrocatalysts derived from vertical IrO2nanotubes (IrO2NT) of 1100 nm in height and 80−100 nm in diameter have been studied using scanning electron microscopy, transmission electron microscopy, X-ray powder diffraction, and cyclic voltammetry toward COadand methanol oxidation. Lattice oxygen of IrO2NT is removed under high-vacuum thermal annealing to facilitate nucleation of 3−5 nm Ir grains and subsequent synthesis of PtIr catalyst on the tube walls. Interestingly, the apparent dimensions and orientation of IrO2NT can be preserved via pore generation in the oxygen removal process. The tubular wall was transformed from a thin dense plate of IrO2(110) single crystal into a porous plate consisting of connected Ir grains that exhibit lattice fringes of the Ir110 spacing with preferential orientation of Ir10 parallel to the IrO2NT growth direction. The amount of Ir being reduced, the Ir grain size, and the deposited Pt size strongly influence the surface area and the catalytic activity. The Pt−Ir−IrO2NT catalyst reduced at 500 °C exhibits a significantly higher activity than Pt−IrO2NT and Pt−IrNT in methanol oxidation and also a higher current density than that of a Johnson−Matthey PtRu catalyst in the high potential region. [ABSTRACT FROM AUTHOR]

Synthesis of conducting oxide strontium ruthenate is carried out in a hot-wall tubular reactor, using Sr(C11H19O2)2/Ru(C5H5)2/O2 reaction system. Owing to a large difference in depositing efficiency between strontium and ruthenium precursors, the stoichiometric ratio of thin film is controlled in one cycle of two consecutive depositions at different temperatures. Thin films of SrRuO3 single phase are synthesized in the subsequent 700°C annealing. Thin films of SrRuO3 with extra ruthenium oxide can also be prepared by adjusting the molar ratio of RuO2 and SrO layers. The deposition sequence of ruthenium oxide first, strontium oxide later is preferred. If the deposition sequence is reverse, the thin film is plagued with unreacted oxides even when the annealing temperature is raised to 800°C. The relative ease of preparing SrRuO3 thin films, when RuO2 is under SrO, is attributed to evaporation of ruthenium oxide in O2 and diffusion in its open columnar microstructure. The sheet resistivity of thin film decreases with the ruthenium content. The room temperature resistivity of SrRuO3 film of Ru/(Sr + Ru) = 0.5 is around 910 μohm-cm. The room-temperature resistivity of Ru/(Ru + Sr) = 0.53 decreases to 470 μohm-cm. The root mean square surface roughness of 700°C synthesized SrRuO3 thin film is 22 nm, in a 2 × 2 μm2 area of film thickness 280 nm. [ABSTRACT FROM AUTHOR]

We report on the preparation and field-emission properties of vertically aligned conductive IrO[sub 2] nanorods. The unique geometrical features of IrO[sub 2] nanorods, including nanosized structure and self-assembled sharp tip, exhibit a strong effect on field enhancement (β∼40 000), which result in a low threshold field (E[sub th]∼0.7 V/μm) defined at the beginning of emission. A low turn-on field for driving a current of 10 μA/cm[sup 2] is about 5.6 V/μm, which is comparable with the carbon nanotube, diamond, and amorphous carbon. The potential of using IrO[sub 2] nanorods as an emitter material has been demonstrated. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Capacity degradation and ion insertion of a miniaturized electrochemical capacitor are studied using ionic liquid [EMI] [TFSI] as the electrolyte. This capacitor is featured with two comb-like electrodes of vertical carbon nanotubes, ∼70 μm in height and 20 μm in interelectrode gap. We quantify the levels of ion insertion damage with Raman spectroscopy after the electrode experiences 120 consecutive voltammetric cycles to various potential limits. Distinct structural damage emerges due to [EMI] when the negative potential reaches −1.7 V, and those due to [TFSI] arise when the positive potential reaches 1.7 V vs. RHE. Judging from the peak broadenings, [EMI] is more detrimental than [TFSI]. When the voltage window ΔU is set as less than or equal to 2.8 V, both electrode potentials are within the two intercalation limits, little or no decay is observed in 104 charge/discharge cycles. When ΔU is 3.4 V, the positive potential exceeds the upper limit, but the negative potential stays within the lower limit, the cell capacitance decreases moderately. When ΔU increases to 3.8 V, both electrodes suffer from damages because of exceeding the intercalation limits. And the cell capacitance decreases substantially, even leading to a premature failure. [ABSTRACT FROM AUTHOR]