Influence of the chemical nature of Boron‐Doped diamond anodes on wastewater treatments

This review summarizes recent advances in wastewater treatment using BDD anodes, involving different aspects of the chemical nature of the anode that are important during the oxidation of organic compounds in water. Synthesis parameters such as the proportion of diamond (sp³) and graphite (sp²), boron doping level, substrate nature and BDD surface modifications are discussed in this work. The influence of the salts dissolved in water, such as sulphate, carbonate, phosphate and chloride, during the treatment was also described. In addition, a new cycle for the oxidation of pollutants using BDD is included.     

Anodic behaviour and passivation of a lead electrode in sodium carbonate solutions

Cyclic voltammograms of a lead electrode were obtained in Na₂CO₃ solution as a function of the starting potential, electrolyte concentration and voltage scanning rate. The shape of the voltammograms was found to depend on the starting potential as well as the sweep number. This is probably due to changes in the activation state of the electrode surface. The first anodic portion of the voltammograms is characterized by a shoulder and two peaks corresponding to the formation of PbCO₃, PbO and PbO₂, respectively. The cathodic portion shows the occurrence of two peaks corresponding to the reduction of PbO₂ to PbO and PbO to Pb, successively, followed by the formation of PbH₂. An increase in concentration of CO ₃ ^2– ions leads to a negative shift in the values of the peak potentials, E_p, accompanying the formation of PbO and PbO₂. In addition, the current density for both the anodic oxidation peaks showed marked dependence on the concentration of the electrolyte. An increase in the scanning rate was observed to lead an increase in the size of the voltammograms. The current density of both the anodic peaks and the anodic passivation region were proportional to v^1/2. Such behaviour is expected in a diffusion-controlled processes. In addition, the anodic peaks are shifted towards more positive values of potential, whereas the cathodic peaks are shifted in the negative direction, indicating irreversible formation of the passive film on the electrode surface.     

Electrochemical degradation of chlorobenzene on boron-doped diamond and platinum electrodes

In this paper the electrochemical degradation of chlorobenzene (CB) was investigated on boron-doped diamond (BDD) and platinum (Pt) anodes, and the degradation kinetics on these two electrodes was compared. Compared with the total mineralization with a total organic carbon (TOC) removal of 85.2% in 6 h on Pt electrode, the TOC removal reached 94.3% on BDD electrode under the same operate condition. Accordingly, the mineralization current efficiency (MCE) during the mineralization on BDD electrode was higher than that on the Pt electrode. Besides TOC, the conversion of CB, the productions and decay of intermediates were also monitored. Kinetic study indicated that the decay of CB on BDD and Pt electrodes were both pseudo-first-order reactions, and the reaction rate constant (k_s) on BDD electrode was higher than that on Pt electrode. The different reaction mechanisms on the two electrodes were investigated by the variation of intermediates concentrations. Two different reaction pathways for the degradation of CB on BDD electrode and Pt electrode involving all these intermediates were proposed.     

Effect of PbO<Subscript>2</Subscript> on the Formation of YBCO Films Fabricated Via Sedimentation Deposition and Partial Melting Technique

PbO₂ addition in sedimentation deposition prepared films was investigated by SEM, EDX, and RT measurements to determine its effect on the formation of YBCO films. YBCO films on SrTiO₃ (STO) (100) substrates of varying amounts of PbO₂ were partially melted at 980 ^°C, annealed, and oxygenated in flowing oxygen atmosphere. In addition, a YBCO sample partially melted at higher temperature was also done for comparison. From the SEM, EDX, and RT analyses, it was found that the film having 8 wt% PbO₂ produces a film with the highest superconducting transition temperature comparable to that of a YBCO sample partially melted at peritectic point. Moreover, it was observed that addition of PbO₂ enhances matter transport between Y123 particles and lowers the processing temperature for the fabrication of YBCO films via the sedimentation deposition method.     

Structure and superconductivity of Bi-(Pb)-Ca-Sr-Cu-O ceramics processed by arc melting

The Bi-(Pb)-Ca-Sr-Cu-O ceramics of typical cation composition 2 (0.4) 223, presintered at 800°C, are formed by arc melting and rapidly cooling the 2021 superconducting phase, CaO, and Cu₂O. The arc-melted samples sintered in air at 840°C exhibit a solid-state structural transformation of the components and a mixture of 2122 and 2223 superconducting phases, and small amounts of Ca₂CuO₃, Ca₂PbO₄, and CuO appear. When the arc melting is used as an intermediate stage in the preparation of the high-T _c superconductors in this system, a significant increase in density (from 3.7 to 5.7 g/cm³) and in critical current density (from 28 to 60 A/cm² in zero field and at liquid-nitrogen temperature) is observed, while the critical temperature remains practically unchanged (–104 K).     

Electrochemical production of hydrogen peroxide on Boron-Doped diamond (BDD) electrode

Hydrogen peroxide (H₂O₂) is a clean oxidizing reagent with many industrial, environmental, medical, and domestic applications. It has been frequently produced using the anthraquinone oxidation process. However, more recently, the electrochemical production of H₂O₂ has become a popular alternative, as this process is chemically green and sustainable since it employs abundant and inexpensive starting molecules (O₂ and H₂O). This review focuses on the electrochemical synthesis of H₂O₂ using the two-electron water oxidation reaction (2e^? WOR) and two-electron oxygen reduction reaction (2e^? ORR), both on boron-doped diamond (BDD) electrodes functioning as an anode or cathode, respectively. This review begins by identifying the important and fundamental characteristics of BDD electrodes, as well as the influence of their chemical and physical properties in the electrochemical production of H₂O₂. The principles and mechanism of the 2e^? WOR and 2e^? ORR are also discussed. In addition, various environmental applications of H₂O₂ electrochemical production (via the 2e^? ORR and 2e^? WOR) are addressed. Finally, the sustainability and costs of BDD electrodes and future strategies to improve BDD performance are considered.     

Preparation and characterization of regioregular poly(3-octylthiophene-2,5-diyl)/copper indium disenillide/titania heterojunction polymer solar cells

By optimizing the P3OT/CISe ratio, TiO₂ content in the P3OT/CISe active layer, annealing temperature and time, this study investigated hybrid Al/Ca/P3OT:CISe:TiO₂/PEDOT:PSS/ITO thin film solar cells with improved efficiency. Due to an increase in charge-carrier transport and a decrease of electron-hole recombination, it is possible to increase the efficiency of hybrid solar cells by adding TiO₂ nanoparticles to the P3OT:CISe active film. Also, performance enhancement of the solar cells can occur with an increase of CISe content in P3OT as well as the addition of a PEDOT:PSS layer to the cell structure. The optimum TiO₂ content in P3OT:CISe layer is 15 wt.%. The optimum annealing temperature and time are 125 °C and 30 min, respectively. The formation of large CISe and TiO₂ aggregates that reduce charge mobility may cause the decrease of efficiency. The rough surface may effectively reduce the charge-transport distance and provide nanoscale phase separation that further enhances internal light scattering and light absorption. The best results for the open circuit voltages (V_oc), short-circuit current density (J_sc), fill factor (FF), and efficiency (η_e) of Al/Ca/POCT15/PEDOT:PSS/ITO hybrid solar cells obtained at optimized conditions were V_oc = 0.49, J_sc = 3.20, FF = 42.96, and η_e = 0.674, respectively.     

Li2O–ZnO–Co3O4–TiO2 composite thin-film electrocatalyst for efficient water oxidation catalysis

Thin films of different Li₂O–ZnO–Co₃O₄–TiO₂ (LZCT) compositions were prepared and employed as electrocatalysts (i.e., anodes) to perform water oxidation reaction (WOR). The electrocatalytic activities of these thin films were compared with those exhibited by the sodium salt of cobalt phosphate (Na₂CoP₂O₇) (CP) thin-film electrocatalyst, which is a well-known water oxidation catalyst (WOC). These results suggest that the 10Li₂O–10ZnO–40Co₃O₄–40TiO₂ composition exhibits a better catalytic activity in terms of higher faradaic efficiency (>98%), lower over potentials (<400?mV), higher reaction stability (up to 30 continuous cyclic voltammetry (CV) cycles), and the rate of O₂ and H₂ gas evolution in terms of current density (about 1?mA/cm²) in comparison with those exhibited by CP thin-film electrocatalyst. Furthermore, these LZCT thin films exhibited very high specific surface area values and due to the unique microstructure of ZnCo₂O₄ phase evolved out of these LZCT compositions at a calcination temperature of 550°C for 30?min it has been found to be responsible for the higher specific surface area values measured for these thin-film compositions.     

SnO2 Anode Surface Passivation by Atomic Layer Deposited HfO2 Improves Li‐Ion Battery Performance

For the first time, it is demonstrated that nanoscale HfO₂ surface passivation layers formed by atomic layer deposition (ALD) significantly improve the performance of Li ion batteries with SnO₂‐based anodes. Specifically, the measured battery capacity at a current density of 150 mAg^?1 after 100 cycles is 548 and 853 mAhg^?1 for the uncoated and HfO₂‐coated anodes, respectively. Material analysis reveals that the HfO₂ layers are amorphous in nature and conformably coat the SnO₂‐based anodes. In addition, the analysis reveals that ALD HfO₂ not only protects the SnO₂‐based anodes from irreversible reactions with the electrolyte and buffers its volume change, but also chemically interacts with the SnO₂ anodes to increase battery capacity, despite the fact that HfO₂ is itself electrochemically inactive. The amorphous nature of HfO₂ is an important factor in explaining its behavior, as it still allows sufficient Li diffusion for an efficient anode lithiation/delithiation process to occur, leading to higher battery capacity.     

Removal of colour and COD from wastewater containing acid blue 22 by electrochemical oxidation

Electrochemical oxidation of synthetic wastewater containing acid blue 22 on a boron-doped diamond electrode (BDD) was studied, using cyclic voltammetry and bulk electrolysis. The influence of current density, dye concentration, flow rate, and temperature was investigated, in order to find the best conditions for COD and colour removal. It was found that, during oxidation, a polymeric film, causing BDD deactivation, was formed in the potential region of water stability, and that it was removed by anodic polarisation at high potentials in the region of O(2) evolution. Bulk electrolysis results showed that the electrochemical process was suitable for completely removing COD and effectively decolourising wastewaters, due to the production of hydroxyl radicals on the diamond surface. In particular, under optimal experimental conditions of flow rates (i.e. 300 dm(3) h(-1)) and current density (i.e. 20 mA cm(-2)), 97% of COD was removed in 12h electrolysis, with 70 kWh m(-3) energy consumption.     

Recent progress of NiCo2O4-based anodes for high-performance lithium-ion batteries

Lithium-ion batteries (LIBs) are deemed as the most promising energy storage devices due to their high power density, excellent safety performance and superior cyclability. However, traditional carbon-based anodes are incapable of satisfying the ever-growing demand for high energy density owing to their low intrinsic theoretical capacity. Therefore, the research of post-carbon anodes (such as transition metal) for LIBs has exponentially increased. Among them, NiCo₂O₄ together with its composites have been widely studied by academic workers due to their high theoretical capacity and excellent electronic conductivity. In this review, the electrochemical reaction mechanism and recent progress including the synthetic method, various nanostructures and the strategies for improving performance of NiCo₂O₄ are summarized and discussed here. Specially, the hollow porous nanostructured NiCo₂O₄-based materials composed of 2D structures usually exhibit excellent capacity and stable cyclability. This review also offers some rational understandings and new thinking of the relationship between the synthetic method, morphologies, blending, current collector and electrochemical performance of NiCo₂O₄-based anodes. We have reason to believe that the integration of NiCo₂O₄ materials in these clean energy devices provides important chances to address challenges driven by increasing world energy demand.     

Electrochemical degradation of a real textile effluent using boron-doped diamond or β-PbO2 as anode

Constant current electrolyses are carried out in a filter-press reactor using a boron-doped diamond (Nb/BDD) or a Ti-Pt/β-PbO₂ anode, varying current density (j) and temperature. The degradation of the real textile effluent is followed by its decolorization and chemical oxygen demand (COD) abatement. The effect of adding NaCl (1.5 g L⁻¹) on the degradation of the effluent is also investigated. The Nb/BDD anode yields much higher decolorization (attaining the DFZ limit) and COD-abatement rates than the Ti-Pt/β-PbO₂ anode, at any experimental condition. The best conditions are j = 5 mA cm⁻² and 55 °C, for the system's optimized hydrodynamic conditions. The addition of chloride ions significantly increases the decolorization rate; thus a decrease of more than 90% of the effluent relative absorbance is attained using an applied electric charge per unit volume of the electrolyzed effluent (Q_ap) of only about 2 kA h m⁻³. Practically total abatement of the effluent COD is attained with the Nb/BDD anode using a Q_ap value of only 7 kA h m⁻³, with an energy consumption of about 30 kW h m⁻³. This result allows to conclude that the Nb/BDD electrode might be an excellent option for the remediation of textile effluents.     

Nanoparticles of IrO<Subscript>2</Subscript> or Sb–SnO<Subscript>2</Subscript> increase the performance of iridium oxide DSA electrodes

Dimensionally stable anodes (DSAs) are widely used in electrochemical industries as gas evolution electrodes. In order to decrease the power consumption during gas evolution, the performance of the electrodes must be increased. In this study, IrO₂- or Sb-doped SnO₂ (ATO) nanoparticles were added to IrO₂ DSAs at a level of 5–40%. The anode surfaces were characterised with scanning electron microscopy (SEM) and X-ray diffraction (XRD). The performance of the anodes for the oxygen evolution reaction was measured in 0.5 mol L⁻¹ H₂SO₄ solution potentiostatically. The performance increased for both the IrO₂ and the ATO nanoparticles’ addition. The maximum performance with IrO₂ nanoparticles occurs when the electrode contains 40 wt% nanoparticles, with more than double the current density at 1.25 V, and for ATO, the maximum occurs at 10% nanoparticles with a 70% increase in current density. These both correspond to the maxima in electrochemically active surface area as determined by cyclic voltammetry. The improvement in performance appears therefore to be primarily caused by the increase in surface area. Addition of catalytically active nanoparticles is shown to be an effective method to increase DSA electrode performance towards the oxygen evolution reaction.     

Boron‐Doped Diamond for Hydroxyl Radical and Sulfate Radical Anion Electrogeneration,Transformation, and Voltage‐Free Sustainable Oxidation

Boron‐doped diamond‐based electrochemical advanced oxidation processes (BDD‐EAOPs) have attracted much attention. However, few systematic studies concerning the radical mechanism in BDD‐EAOPs have been published. In situ electron paramagnetic resonance spectrometry is used to confirm that SO₄^?? is directly electrogenerated from SO₄^2?. Then, excess SO₄^?? dimerizes to form S₂O₈^2? and accumulates in the BDD‐EAOP system. But no S₂O₈^2? accumulates at pH = 10 owing to the rapid transformation of SO₄^?? and S₂O₈^2?. Above the overpotential of water oxidation, ^?OH is electrogenerated and cooperated with SO₄^??. In the power‐off phase, the accumulated S₂O₈^2? can be reactivated to SO₄^?? via specific degradation intermediates to achieve sustainable degradation. Di‐n‐butyl phthalate (DnBP), a typical endocrine disruptor, is selected as a model contaminant. Surprisingly, 99.8% of DnBP (initial concentration of 1 mg L^?1) is removed, using an intermittent power supply strategy with a periodic 10 min power‐on phase at a duty ratio of 1:2, reducing the electrical energy consumption (1.8 kWh m^?3) by more than 30% compared with continuous power supply consumption. These radical electrogeneration transformation mechanisms reveal an important new strategy for sustainable oxidation, especially for in situ water restoration, and are expected to provide a theoretical basis for BDD applications.     

Effects of excess Pb on structural and electrical properties of Pb(Zr0.48Ti0.52)O3 thin films using MOD process

Pb(Zr_0.48Ti_0.52)O₃ thin films at 20% excess Pb were synthesized on Pt/Ti/SiO₂/Si(100) substrates at different annealing temperatures by a metal-organic decomposition process. The microstructure of the PZT films was investigated by x-ray diffraction and atomic force microscopy. The composition of the films was characterized by Rutherford Backscattering Spectroscopy (RBS). These results showed that The PZT films have perovskite phase coexisted with PbO₂ phase. The PbO₂ phase mainly was formed by excess Pb which congregate at boundaries of crystalline grains during the annealing process and may be absorbed part of oxygen ion at normal sites, thus leading to an increase of oxygen vacancies in the PZT film. PbO₂ phase and oxygen vacancies act as pinning centres, which has an effect on the ferroelectric domain switching. This eventually resulted in an increase of fatigue rate in PZT films.     

A soluble-lead redox flow battery with corrugated graphite sheet and reticulated vitreous carbon as positive and negative current collectors

A soluble-lead redox flow battery with corrugated-graphite sheet and reticulated-vitreous carbon as positive and negative current collectors is assembled and performance tested. In the cell, electrolyte comprising of 1·5 M lead (II) methanesulfonate and 0·9 M methanesulfonic acid with sodium salt of lignosulfonic acid as additive is circulated through the reaction chamber at a flow rate of 50 ml min^???1. During the charge cycle, pure lead (Pb) and lead dioxide (PbO₂) from the soluble lead (II) species are electrodeposited onto the surface of the negative and positive current collectors, respectively. Both the electrodeposited materials are characterized by XRD, XPS and SEM. Phase purity of synthesized lead (II) methanesulfonate is unequivocally established by single crystal X-ray diffraction followed by profile refinements using high resolution powder data. During the discharge cycle, electrodeposited Pb and PbO₂ are dissolved back into the electrolyte. Since lead ions are produced during oxidation and reduction at the negative and positive plates, respectively there is no risk of crossover during discharge cycle, preventing the possibility of lowering the overall efficiency of the cell. As the cell employs a common electrolyte, the need of employing a membrane is averted. It has been possible to achieve a capacity value of 114 mAh g^???1 at a load current-density of 20 mA cm^???2 with the cell at a faradaic efficiency of 95%. The cell is tested for 200 cycles with little loss in its capacity and efficiency.     

Room temperature plasma oxidation: A new process for preparation of ultrathin layers of silicon oxide, and high dielectric constant materials

In this paper we present basic features and oxidation law of the room temperature plasma oxidation, (RTPO), as a new process for preparation of less than 2 nm thick layers of SiO₂, and high-k layers of TiO₂. We show that oxidation rate follows a potential law dependence on oxidation time. The proportionality constant is function of pressure, plasma power, reagent gas and plasma density, while the exponent depends only on the reactive gas. These parameters are related to the physical phenomena occurring inside the plasma, during oxidation. Metal-Oxide-Semiconductor (MOS) capacitors fabricated with these layers are characterized by capacitance-voltage, current-voltage and current-voltage-temperature measurements. Less than 2.5 nm SiO₂ layers with surface roughness similar to thermal oxide films, surface state density below 3 × 10¹¹ cm^− 2 and current density in the expected range for each corresponding thickness, were obtained by RTPO in a parallel-plate reactor, at 180 mW/cm² and pressure range between 9.33 and 66.5 Pa (0.07 and 0.5 Torr) using O₂ and N₂O as reactive gases. MOS capacitors with TiO₂ layers formed by RTPO of sputtered Ti layers are also characterized. Finally, MOS capacitors with stacked layers of TiO₂ over SiO₂, both layers obtained by RTPO, were prepared and evaluated to determine the feasibility of the use of TiO₂ as a candidate for next technology nodes.     

Ex Situ Spark Plasma Sintering of Short Powder-in-Tube MgB<Subscript>2</Subscript> Tapes with Open and Closed Ends

Short powder-in-tube tapes of MgB₂ in the Fe sheath were fabricated by ex situ route from a commercial powder containing some free Mg and MgO impurity phases. The final heat treatment was performed by spark plasma sintering (SPS). Tapes were with open (OT) or closed (CT) endings. Closed endings were made by folding and pressing. The MgB₂ core of the OT sample has shown a higher low-field critical current density, a higher maximum pinning force, a slightly higher disorder, smaller average MgB₂ crystallite size, a weak contact between Fe and MgB₂ core, and more macro-flux jumps. The upper and irreversibility fields were similar for OT and CT samples. In the center of the MgB₂ cores, the detected impurity phase is MgO, while at the interface with Fe, MgB₄ also occurs. Impurity phases found at interface, MgO and MgB₄, are present in the center of the bulk SPSed samples. Reactions and pinning-force-related parameters are discussed with respect to Mg behavior influenced by condition of endings. It is inferred that the presence of free Mg in the raw MgB₂ powder has an important contribution to observed differences, and its removal or control is recommended.     

Monitoring phase formation of Pb-substituted Bi-Sr-Ca-Cu-O superconducting samples at different preparative stages using Raman spectroscopy and X-ray diffraction

Raman spectroscopy and X-ray diffraction were used to follow structure and phase formation at various stages in order to study the effect of Pb substitution in (Bi_1–x Pb _x Sr₃Ca₃Cu₄O _y samples. We found that major reactions involving Bi₂O₃ occurred at around 700°C and that reactions with Ca, Cu, and Pb started at a lower temperature. The amount of Ca₂PbO₄ formed increases as a function of lead concentration and annealing temperature (up to 800°C), but excess lead substitution (50%) destroys the superconductivity. The high-temperature superconducting phase (2223) is only observed in the 15% and 20% leaded samples. These two samples exhibit a higher amount of Ca₂PbO₄ during intermediate processing stages, which suggests that the presence of the Ca₂PbO₄ is important for the formation of the high-T _c phase. It was found that theT _c increases with lead concentration (up to 20% Pb).