Planar ultracapacitors of miniature interdigital electrode loaded with hydrous RuO2 and RuO2 nanorods

Planar ultracapacitors of miniature interdigital electrode are prepared, using the standard technologies of photolithography and reactive sputtering. The ultracapacitor is denoted by its deposition sequence, for example, hRuO₂NRGT indicates pseudocapacitive hydrous RuO₂ (hRuO₂) and RuO₂ nanorods (NR) are grown on an interdigital stack layer of gold (G) and titania (T). The connection between structure and performance is studied through contrasting the hRuO₂NRGT capacitor with other capacitors built on a less conducting stack layer or without hydrous RuO₂ filling the gaps between the nanorods. The stack layer can be a major source of cell resistance. For instance, a buffer layer of titania could be utilized between the capacitive RuO₂ and the Au current collector to overcome the delamination problem. But the less conductive titania also makes its cyclic voltammograms (CV) elliptical and tilted, and causes a pronounced IR drop during the cell discharging. In contrast, CV of the hRuO₂NRGT capacitor on a conductive stack layer takes the shape of horizontal rectangle, and its discharge curve shows no sign of IR drop. Filling hydrous RuO₂ into the gap reduces the cell resistance between nanorods, improves the discharge performance as well. The power output of hRuO₂NRGT, with the two resistances minimized, is 30.6 μW at 75 μA and 1.23 μW at 5 μA.     

RuO2·xH2O/NiO composites as electrodes for electrochemical capacitors: Effect of the RuO2 content and the thermal treatment on the specific capacitance

RuO₂·xH₂O/NiO composites having RuO₂ contents in the range 0-100 wt.% have been prepared by a co-precipitation method. Structural, microstructural and textural transformations after heating the as-prepared composites at 200 and 600 °C have been followed by X-ray diffraction, scanning electron microscopy (SEM) and nitrogen adsorption/desorption isotherms. At 200 °C the composites are made of micrometric particles in which nanometric crystallites of the two oxides are aggregated. The composites show microporosity (0.02-0.10 cm³/g), mesoporosity (0.07-0.12 cm³/g) and relatively high specific surface area (62-309 m²/g). At 600 °C the composites are fully dehydrated and RuO₂ has crystallized and segregated. Microporosity and mesoporosity as well as specific surface area are strongly decreased. Specific capacitance and specific surface area of the composites heated at 200 and 600 °C have been measured and discussed on the basis of the RuO₂ content. For comparison the specific capacitance and specific surface area of mixtures of NiO and RuO₂·xH₂O (or RuO₂) have been taken as references. The higher specific capacitance of the 200 °C-heated composites compared to the 600 °C-heated ones is due to the higher specific surface area of the former and the higher pseudocapacitance of RuO₂·xH₂O compared to RuO₂. The discussion reported in this work can be applied to other composites such as RuO₂·xH₂O/carbon and RuO₂·xH₂O/other oxides.     

Cement composition and sulfate attack: Part I

Four cements were used to address the effect of tricalcium silicate content of cement on external sulfate attack in sodium sulfate solution. The selected cements had similar fineness and Bogue-calculated tricalcium aluminate content but variable tricalcium silicates. Durability was assessed using linear expansion and compressive strength. Phases associated with deterioration were examined using scanning electron microscopy and X-ray diffraction. Mineralogical phase content of the as-received cements was studied by X-ray diffraction using two methods: internal standard and Rietveld analysis.The results indicate that phase content of cements determined by X-ray mineralogical analysis correlates better with the mortar performance in sulfate environment than Bogue content. Additionally, it was found that in cements containing triclacium aluminate only in the cubic form, the observed deterioration is affected by tricalcium silicate content. Morphological similarities between hydration products of high tricalcium aluminate and high tricalcium silicate cements exposed to sodium sulfate environment were also observed.     

Electrochemical oxidation of polyvinyl alcohol using a RuO2/Ti anode

Polyvinyl alcohol (PVA), known as the dominant contributor of chemical oxygen demand (COD) in textile wastewater, is very difficult to decompose by conventional treatment technologies. In this study, electrochemical oxidation using a RuO₂/Ti anode was applied to treat a PVA solution. The mechanisms of PVA degradation and COD destruction were investigated, while the operating parameters affecting the mechanisms were also studied. The parameters investigated included current density, PVA concentration in waste stream, the rate of electrolyte consumption of sodium chloride, and the feed rate of wastewater. The overall mass transport behavior of electrochemical oxidation of PVA was explained by the mathematical relationship of dimensionless numbers such as the Reynolds, Schmidt and Sherwood numbers.     

The effect of foreign ions on the reactivity of the CaO-SiO2-Al2O3-Fe2O3 system: Part II: Cations

The subject of this paper is the effect of foreign cations on the reactivity of the CaO-SiO₂-Al₂O₃-Fe₂O₃ system. One reference mixture and eighteen modified mixtures, prepared by mixing the reference sample with 1% w/w of chemical grade MnO₂, CuO, V₂O₅, PbO, CdO, ZrO₂, Li₂O, MoO₃, Co₂O₃, NiO, WO₃, ZnO, Nb₂O₅, CrO₃, Ta₂O₅, TiO₂, BaO₂ and H₃BO₃ were studied. The effect on the reactivity is evaluated on the basis of the free lime content in samples sintered at 1200 and 1450 °C. At 1200 °C, the reactivity of the mixture is greatly increased in the presence of Cu and Li oxides. Based on their effect at 1450 °C, the added elements can be divided into three groups. W, Ta, Cu, Ti and Mo show the most positive effect, decreasing the free CaO (fCaO) content by 30-60%, compared with the pure sample. Cr and B cause an increase of fCaO content, while the rest of the elements exhibit a marginal positive effect. According to their volatility at 1450 °C, the added compounds can be subdivided into three groups of low (Ti⁴⁺, Cu²⁺, Mo⁶⁺, W⁺⁶, V⁵⁺, Zn²⁺, Zr⁴⁺), moderate (Cr⁶⁺, Co³⁺, Ni²⁺, Mn⁴⁺) and high volatility (Cd²⁺, Pb²⁺). All burned samples, analyzed by means of X-ray diffraction, have a final mineralogical composition, which corresponds to the structure of a typical clinker.     

Co (II) porphyrin adsorbed on SiO2/SnO2/phosphate prepared by the sol-gel method: Application in electroreduction of dissolved dioxygen

This paper describes the immobilization procedure of 5,10,15,20-tetrakis(1-methyl-4-pyridyl)-21-H,23-H-porphyrin ion on SiO₂/SnO₂/phosphate, obtained by the sol-gel processing method. P 2p X-ray photoelectron and the ³¹P MAS NMR spectra revealed that dihydrogen phosphate is the species present on the surface. The porphyrin was adsorbed on the surface of the modified material and furthermore metallized in situ with Co (II) ion. The porphyrin metallation process was followed with UV-vis spectroscopy by inspecting the Q bands of the free and metallated porphyrin. The free porphyrin presented four Q bands associated to a D_2h local symmetry and the metallated one, two bands related to a D_4h local symmetry. The amount of electroactive species adsorbed on the material was estimated by integrating the area under the peak of Co (II) → Co (I) reduction by using the pulse differential voltammetric technique. The amount of the metallated porphyrin was 2.3 × 10⁻¹⁰ mol cm⁻². A carbon paste electrode of the modified material containing metallated porphyrin was used to study the electrocatalytic reduction of dissolved dioxygen by means of cyclic voltammetry, chronoamperometry and linear sweeping voltammetry. The modified electrode was very stable and exhibited the electrocatalytic reduction of dissolved dioxygen at −180 mV versus SCE by a two-electron mechanism, producing hydrogen peroxide at pH 5.4. The electroactive species was strongly retained on the material surface, presumably inside the pores of the material, since in a test of various oxidation-reduction cycles no significant decrease of the current densities was detected, indicating that it was not leached off during the experiment.     

Electrocatalytic activity of amorphous RuO2 electrode for oxygen evolution in an aqueous solution

The electrocatalytic activity of amorphous and crystalline RuO₂ thin films for oxygen evolution in an aqueous solution was investigated. The RuO₂ films were prepared on FTO substrates by electrodeposition or RF magnetron sputtering technique. The obtained films were annealed at various temperatures. In both cases, the as-prepared films or the 200 °C annealed film had an amorphous structure, whereas the films annealed at 300 °C and over were crystallized to rutile structure. The analysis of the Tafel slope indicated that the rate-determining step in the oxygen evolution reaction on the amorphous RuO₂ was the combination of the adjacent Ru–OH groups, whereas that on crystalline RuO₂ was the dissociation of O–H bond in Ru–OH group. The onset potentials of the amorphous RuO₂ films for oxygen evolution were shifted toward the negative side by 0.06–0.03 V from those for the rutile crystalline samples. The shift of the onset potential is probably attributed to the structural flexibility which is characteristic of the amorphous surface. This result suggested that the electrocatalytic activity of amorphous RuO₂ for oxygen evolution was higher than that of rutile crystalline RuO₂.     

Study of carbon-supported IrO2 and RuO2 for use in the hydrogen evolution reaction in a solid polymer electrolyte electrolyzer

Carbon-supported IrO₂ and RuO₂ were prepared using an incipient wetness method and were then calcinated at various temperatures. IrO₂/C and RuO₂/C are less expensive than the conventional Pt/C material and more stable than metal Ni in an acidic electrolyte. Moreover, IrO₂/C and RuO₂/C are not influenced by under potential deposition (UPD) and show lower sensitivity to poisoning by Ni or Fe impurities. The physical properties of IrO₂/C and RuO₂/C were investigated via XRD and TEM. Cyclic voltammograms (CV) and Tafel plots were used to provide information regarding surface redox reaction and electrocatalytic activity. The activity and durability of IrO₂/C and RuO₂/C were studied after prolonged potential cycling between −0.3 and 0.3 V_SCE. After comparison of Tafel plots of Pt/C and IrO₂/C after activation, it was observed that they have similar electrocatalytic activities in a hydrogen evolution reaction (HER). A single cell test with solid polymer electrolyte (SPE) proved that the performance of IrO₂/C (0.5 mg cm⁻²) was similar to that of Pt/C (0.5 mg cm⁻²).     

Development of ceramic electrochemical sensor based on Bi2Ru2O7+x − RuO2 sub-micron oxide sensing electrode for water quality monitoring

Sub-micron Bi₂Ru₂O_7+x + RuO₂ oxide sensing electrodes (SE) for water quality sensors were prepared on platinised ceramic substrate of the sensor. Their morphology was analysed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray analysis (EDX). Sensing properties of the Bi₂Ru₂O_7+x + RuO₂-SE were investigated for potentiometric detection of pH and dissolved oxygen (DO) in water in the temperature range of 4–30 °C. Sensor was capable to measure DO from 0.5 to 8.0 ppm and pH from 2.0 to 13.0, respectively. The obtained results show acceptable linearity of the measuring characteristics. Long-term stability trial for Bi₂Ru₂O_7+x + RuO₂-SE revealed that bio-fouling can be one of the main destructive factors affecting the performance of the sensors in the long run. The screen-printing technology used in the multi-sensory implementation provides fundamental properties of miniaturization, reasonable accuracy and low cost.     

Photoelectrocatalytic degradation of rhodamine B using Ti/TiO2 electrode prepared by laser calcination method

The method of Ti/TiO₂ photoelectrode prepared by using laser calcination method instead of oven calcination process was introduced. The prepared TiO₂ film was observed with AFM and XRD. Photoelectrocatalytic degradation of rhodamine B (RB) using this electrode was investigated, and anodic potential and pH were optimized. The laser power applied in this electrode preparation was also discussed, and it indicated that TiO₂ particle prepared with high laser power was crystallized adequately and the photoelectrocatalytic ability was satisfactory. RB degradation was investigated under different conditions, and it showed that photoelectrocatalytic degradation could achieve efficient and complete mineralization of organic pollutant. The photoelectrocatalytic oxidation using the Ti/TiO₂ electrode calcinated by laser was compared with that of the electrode calcinated by furnace, and it showed that the reaction rate of RB degradation using the electrode by laser was faster than that by furnace. Additionally, electrochemical impedance spectroscopy (EIS) was performed at the two different photoelectrodes, which verified the higher photocatalytic activity of the laser-treated electrode further.     

Electrochemical degradation of Ibuprofen on Ti/Pt/PbO2 and Si/BDD electrodes

The electrochemical oxidation of Ibuprofen (Ibu) was performed using a Ti/Pt/PbO₂ electrode as the anode, prepared according to literature, and a boron doped diamond (BDD) electrode, commercially available at Adamant Technologies. Tests were performed with model solutions of Ibu, with concentrations ranging from 0.22 to 1.75 mM for the Ti/Pt/PbO₂ electrode and 1.75 mM for the BDD electrode, using 0.035 M Na₂SO₄ as the electrolyte, in a batch cell, at different current densities (10, 20 and 30 mA cm⁻²). Absorbance measurements, Chemical Oxygen Demand (COD) and Total Organic Carbon (TOC) tests were conducted for all samples. The results have shown a very good degradation of Ibu, with COD removals between 60 and 95% and TOC removals varying from 48 to 92%, in 6 h experiments, with higher values obtained with the BDD electrode. General Current Efficiency and Mineralization Current Efficiency, determined for both electrodes, show a similar behaviour for 20 mA cm⁻² but a very different one at 30 mA cm⁻². The combustion efficiency was also determined for both anodes, and found to be slightly higher with BDD at lower current density and equal to 100% for both anodes at 30 mA cm⁻².     

Al2O3-coated SnO2/TiO2 composite electrode for the dye-sensitized solar cell

A novel Al₂O₃-coated SnO₂/TiO₂ composite electrode has been applied to the dye-sensitized solar cell. In such an electrode, two kinds of energy barriers (SnO₂/TiO₂ and TiO₂/Al₂O₃) were designed to suppress the recombination processes of the photo-generated electrons and holes. After the SnO₂ was modified by colloid TiO₂, the photoelectric conversion efficiency of the SnO₂/TiO₂ composite cell increased to 2.08% by a factor of 2.8 comparing with that of the SnO₂ cell. The Al₂O₃ layer on the SnO₂/TiO₂ composite electrode further suppressed the generation of the dark current, resulting in 37% improvement in device performance comparing with the SnO₂/TiO₂ cell.     

Non-destructive characterisation of alumina/aluminium titanate composites using a micromechanical model and ultrasonic determinations: Part II. Evaluation of microcracking

A method for non-destructive detection of microcracks in ceramic composites is described. The method involves the combination of ultrasound characterisation with the application of a three-phase micromechanical model, which considers cracks and pores as void constituents. Four alumina-aluminium titanate materials with different levels of microcracking, from no cracks (monophase alumina) to severely cracked (alumina + 40 vol.% of aluminium titanate) including an alumina + 10 vol.% aluminium titanate material with incipient microcracking have been developed to test the validity of the method. Specimens have been fabricated by colloidal processing and the longitudinal and transverse ultrasound velocities have been determined by the ultrasonic pulse-echo and transmission ultrasound-immersion techniques, employing a digital signal processing. It has been demonstrated that it is possible to differentiate between pores and microcracks, both modelled as void constituents, in terms of the aspect ratio.     

The leaching of chlorine from hard coal: Part I. Relationship between the process parameters and its effectivity

In the study the research potential offered by the Scanning Electron Microscope to investigate into the surface of hard coal for mineral substances, especially of chlorine, was utilized. The identification of such substances - basing upon the resulting X-ray spectra and photographs - allowed one to corroborate the usefulness of further investigation step - viz. leaching. Variable parameters in those investigations were: grain size, leaching temperature, time and leaching cycles. Of great importance for the efficiency of the leaching process is granulation. The smaller the grain of coal, the more chlorine was removed because the opening of pores closed in the process of fragmentation increases the carbon surface available for water molecules.     

Microstructure refinement of alumina: Optimisation by gas pressure sintering process

This paper investigates densification and grain growth evolutions during gas pressure sintering of alumina. Isothermal sintering runs are performed under different nitrogen pressures: atmospheric pressure and 2 MPa. Experimental data are fitted thanks to constitutive laws in order to understand nitrogen pressure effect on densification and grain growth mechanisms of a fine-grained alumina. An optimal run of densification is proposed as an application of these results.     

Autogenous deformations of cement pastes: Part II. W/C effects, micro-macro correlations, and threshold values

A broad experimental study has been performed, from the end of mixing up to 2 years, on a set of plain cement pastes prepared with the same type I ordinary portland cement (OPC) and various water-to-cement ratios (W/C), and cured at various constant temperatures. Several parameters have been measured on the hydrating materials, such as chemical shrinkage, volumetric and one-dimensional autogenous deformations, degree of hydration of the cement, Ca(OH)₂ content and Vicat setting times. Drying shrinkage has also been measured on the mature materials. In this part II of the paper, the effects of W/C within the range 0.25-0.60 have in particular been analysed in relation to the microstructural characteristics of the materials. This micro-macro analysis has highlighted a W/C threshold value (located around 0.40) both at the macro-level (on autogenous, but also on drying deformations and durability-related properties) and at the micro-level (characteristics of the hydration products, MIP porosity and pore size distribution, etc.).In addition, volumetric and one-dimensional autogenous shrinkage deformations have been compared in the case of W/C=0.25 and T=20 °C. Finally, a critical twofold (chemical and structural) effect of calcium hydroxide has been found. When significant structural effects, generated by the formation and the growth of large-size Ca(OH)₂ crystals, take place, swelling can become prominent, as observed for one-dimensional autogenous deformations in the case of medium and high W/C, and deviations are recorded on linear relationships.     

Degradation of azo dye from aqueous solutions using nano-SnO2/Ti electrode prepared by electrophoretic deposition method: Experimental Design

In this work, degradation of C.I. Acid Red 33 (AR33) in aqueous solutions was investigated. The combined electrolysis–ozone (ECO) process optimized based on SnO₂ nanoparticles electrode (nano-SnO₂/Ti) as anode using response surface methodology (RSM) involving a five-level central composite design (CCD). The nano-SnO₂/Ti electrode was prepared using electrophoretic deposition (EPD) method. The electrode was characterized by field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD) and cyclic voltammetry (CV). The initial pH, current density, reaction time and electrolyte concentration were selected as independent variables in central composite design while color removal efficiency was considered as the response function. Based on analysis of variance (ANOVA), the coefficient of determination value (R² = 0.981) was high. In optimum conditions, maximum color removal efficiency (93.2%) was obtained after 16 min; and the removal of chemical oxygen demand (COD) was reduced to 57.1% after 60 min.     

Phase separation induced by hydration of the mixed Ca/Sr aluminates Ca3−xSrxAl2O6: A crystallographic study

The compounds formed by the hydration of single-phase samples of the mixed, solid solution, Ca/Sr aluminates, Ca_3−xSr_xAl₂O₆, 3≤x≤0 have been studied using high-resolution synchrotron powder diffraction. Hydration of these mixed metal aluminates generally resulted in the formation of at least two hydrogarnet phases, one Ca-rich and the other Sr-rich. The structures of these hydrogarnets have been refined from neutron or synchrotron powder X-ray diffraction (XRD) data. A simple solubility model to explain the phase separation is presented.