Impact of electrically formed interfacial layer and improved memory characteristics of IrOx/high-κx/W structures containing AlOx,GdOx, HfOx,and TaOx switching materials

Improved switching characteristics were obtained from high-κ oxides AlO_x, GdO_x, HfO_x, and TaO_x in IrO_x/high-κ_x/W structures because of a layer that formed at the IrO_x/high-κ_x interface under external positive bias. The surface roughness and morphology of the bottom electrode in these devices were observed by atomic force microscopy. Device size was investigated using high-resolution transmission electron microscopy. More than 100 repeatable consecutive switching cycles were observed for positive-formatted memory devices compared with that of the negative-formatted devices (only five unstable cycles) because it contained an electrically formed interfacial layer that controlled ‘SET/RESET’ current overshoot. This phenomenon was independent of the switching material in the device. The electrically formed oxygen-rich interfacial layer at the IrO_x/high-κ_x interface improved switching in both via-hole and cross-point structures. The switching mechanism was attributed to filamentary conduction and oxygen ion migration. Using the positive-formatted design approach, cross-point memory in an IrO_x/AlO_x/W structure was fabricated. This cross-point memory exhibited forming-free, uniform switching for >1,000 consecutive dc cycles with a small voltage/current operation of ±2 V/200 μA and high yield of >95% switchable with a large resistance ratio of >100. These properties make this cross-point memory particularly promising for high-density applications. Furthermore, this memory device also showed multilevel capability with a switching current as low as 10 μA and a RESET current of 137 μA, good pulse read endurance of each level (>10⁵ cycles), and data retention of >10⁴ s at a low current compliance of 50 μA at 85°C. Our improvement of the switching characteristics of this resistive memory device will aid in the design of memory stacks for practical applications.     

Quantified mass transfer and superior antiflooding performance of ordered macro‐mesoporous electrocatalysts

For oxygen reduction reaction (ORR), constructing porous catalysts are highly important for mass transfer inside. However, the various porous structures usually possess significantly different water buffer efficiency, that is, the antiflooding capability, for which one is still difficult to give a quantitative evaluation. In this work, we designed a special “rattle‐drum” like working electrode, by which an exactly quantitative assessment on the mass transfer efficiencies can be conducted. Particularly, ordered macro‐mesoporous Pt/C shows quantified mass transfer and antiflooding efficiency to be four times high as that of the commercial one. This observation should be attributed to their different pore characteristics, as the dual‐porosity Pt/C has 3.4 times the pore volume of the commercial one, together with regular pore arrangement. Simultaneously, it also demonstrated excellent durability, indicating that the macro‐mesoporous Pt/C indeed owns high stability in both antiflooding and durability. © 2018 American Institute of Chemical Engineers AIChE J, 64: 2881–2889, 2018     

Electrodepositing Pt on a Nafion-bonded carbon electrode as a catalyzed electrode for oxygen reduction reaction

The research aims to increase the utilization of platinum (Pt) catalysts and thus to lower the catalyst loadings in the electrode for oxygen reduction reaction (ORR). The electrodeposition of Pt was performed on a rotation disk electrode (RDE) of glass carbon (GC), on which a layer of Nafion-bonded carbon of Vulcan XC 72R was dispersed in advance. The behaviors of Pt RDE and GC RDE in an aqueous solution containing HCl and H₂PtCl₆ were firstly studied. It was found that Pt deposition could be achieved if the electrode potential is controlled below −0.20 V versus (saturated-potassium-chloride silver chloride electrode) SSCE. However, quite a high overpotential is necessary if a quick and apparent deposition were required. Unfortunately, at a high overpotential, the hydrogen evolution would be unavoidable and even accelerated by the formation of nanometer size of Pt particles on the RDE. It was found that it is futile to increase platinum deposits just through extending the deposition time. It was also found that too large deposition current is not helpful for increase of platinum deposition because most of the current was consumed on hydrogen evolution in this case. It has been confirmed that it is conducive to richen Pt ions, present in the form of anionic complex in solution, onto the working electrode to be deposited. It is also helpful to eliminate the hydrogen bubbles formed on the working electrode, i.e., uncatalyzed carbon electrode (UCE), by imposing a positive current on the UCE for a length of time in advance of each cathodic deposition. The potential changes during deposition were recorded. Cyclic voltammograms (CV) of electrodes in 0.5 M H₂SO₄ before and after the deposition were used to assess loading of metal catalysts in a wide range of potential from −0.20 to 1.1 V versus SSCE. The results have shown that the performance of such an electrode with loadings estimated to be 50 μg Pt/cm² is much better than those of a conventional electrode with loadings of 100 μg Pt/cm².     

Effect of Al2Cu precipitates size and mass transport on the polarisation behaviour of age-hardened Al–Si–Cu–Mg alloys in 0.05 M NaCl

The electrochemical behaviour of age-hardened Al–Si–Cu–Mg alloys was investigated in a 0.05 M NaCl solution under controlled mass transport conditions using a rotating disk electrode. This work aimed at getting better understanding of the effect of the alloy microstructure, in particular the size distribution of Al₂Cu phase, on the corrosion behaviour of the alloy. Three different size distributions of the Al₂Cu phase were obtained through appropriate heat treatments. The cathodic reduction of oxygen was found to occur mainly on the Al₂Cu phases acting as preferential cathodes. Small sized Al₂Cu phases were found to promote at high rotation rates a transition from a 4 electron to a 2 electron dominated oxygen reduction mechanisms.     

Effect of Fe substitution on the structure and properties of LnBaCo2−xFexO5+δ (Ln = Nd and Gd) cathodes

The effect of Fe substitution for Co on the crystal chemistry, thermal and electrical properties, and catalytic activity for oxygen reduction reaction of the layered LnBaCo_2−xFe_xO_5+δ (Ln = Nd and Gd) perovskite has been investigated. The air-synthesized LnBaCo_2−xFe_xO_5+δ samples exhibit structural change with increasing Fe content from tetragonal (0 ≤ x ≤ 1) to cubic (1.5 ≤ x ≤ 2) for the Ln = Nd system and from orthorhombic (x = 0) to tetragonal (0.5 ≤ x ≤ 1) for the Ln = Gd system. The thermal expansion coefficient (TEC) and electrical conductivity decrease with increasing Fe content in LnBaCo_2−xFe_xO_5+δ. While the substitution of a small amount of Fe (x = 0.5) for Co leads to slightly improved performance in solid oxide fuel cells (SOFC), larger Fe contents (x ≥ 1.0) deteriorate the fuel cell performance. In the Ln = Gd system, the better performance of the x = 0.5 sample is partly due to the improved chemical stability with the LSGM electrolyte at high temperatures. With an acceptable electrical conductivity of >100 S cm⁻¹ at 800 °C, the x = 0.5 sample in the LnBaCo_2−xFe_xO_5+δ (Ln = Nd and Gd) system offers promising mixed oxide-ion and electronic conducting (MIEC) properties.     

Application of bacteria involved in the biological sulfur cycle for paper mill effluent purification

In anaerobic wastewater treatment, the occurrence of biological sulfate reduction results in the formation of unwanted hydrogen sulfide, which is odorous, corrosive and toxic. In this paper, the role and application of bacteria in anaerobic and aerobic sulfur transformations are described and exemplified for the treatment of a paper mill wastewater. The sulfate containing wastewater first passes an anaerobic UASB reactor for bulk COD removal which is accompanied by the formation of biogas and hydrogen sulfide. In an aeration pond, the residual COD_organic and the formed dissolved hydrogen sulfide are removed. The biogas, consisting of CH₄ (80-90 vol.%), CO₂ (10-20 vol.%) and H₂S (0.8-1.2 vol.%), is desulfurised prior to its combustion in a power generator thereby using a new biological process for H₂S removal. This process will be described in more detail in this paper. Biomass from the anaerobic bioreactor has a compact granular structure and contains a diverse microbial community. Therefore, other anaerobic bioreactors throughout the world are inoculated with biomass from this UASB reactor. The sludge was also successfully used in investigation on sulfate reduction with carbon monoxide as the electron donor and the conversion of methanethiol. This shows the biotechnological potential of this complex reactor biomass.     

岛津TOC-4100型总有机碳测量仪及其在水质监测中的应用

针对TOC的“燃烧氧化—红外线分析”测定方法，重点介绍了日本岛津公司生产的TOC—4100型总有机碳测量仪的工作原理、性能特点及其在水质监测中的应用。     

SIRO2固体电解质氧探测器

介绍了固体电解质氧探测器的应用范围、探头的制作、发展水平和发展趋势,推广应用前景。     

Ketjen black carbon supported CoO@Co−N−C nanochains as an efficient electrocatalyst for oxygen evolution

We demonstrate an extremely facile in-situ pyrolysis followed by the reduction of partial Co²⁺ route to synthesize novel Ketjen black carbon (KB) supported CoO@Co?N?C (denoted as CoO@Co?NC/KB) nanochains using KB, urea and cobalt (Ⅱ) acetate as co-precursors. The as-prepared CoO@Co-NC/KB displays higher electrocatalytic activity, smaller Tafel slope and better durability for the oxygen evolution reaction than those of the benchmark commercial RuO₂ catalyst in 1.0 M KOH solution, far outperforming the control groups (i.e. CoO@Co?g-C₃N₄/KB, Co?NC/KB, CoO?NC/KB, CoO@Co/KB, CoO@Co?NC and Co₃O₄?NC/KB). The remarkable electrocatalytic performance of CoO@Co?NC/KB is primarily credited to the synergistic effect between Co and CoO species with a core-shell structure, increased active sites and considerably enhanced electronic conductivity.     

Alkaline direct alcohol fuel cells

The faster kinetics of the alcohol oxidation and oxygen reduction reactions in alkaline direct alcohol fuel cells (ADAFCs), opening up the possibility of using less expensive metal catalysts, as silver, nickel and palladium, makes the alkaline direct alcohol fuel cell a potentially low cost technology compared to acid direct alcohol fuel cell technology, which employs platinum catalysts. A boost in the research regarding alkaline fuel cells, fuelled with hydrogen or alcohols, was due to the development of alkaline anion-exchange membranes, which allows the overcoming of the problem of the progressive carbonation of the alkaline electrolyte. This paper presents an overview of catalysts and membranes for ADAFCs, and of testing of ADAFCs, fuelled with methanol, ethanol and ethylene glycol, formed by these materials.