Phase-Assisted Tailored Conductivity of Doped Ceria Electrolytes to Boost SOFC Performance.

Efforts to lower the operating temperature of solid oxide fuel cells include producing electrolytes that are sufficiently conductive and stable below 600 °C. Doped ceria is one such electrolyte being considered. During this study, codoped ceria powders (Ce0.8Sm0.2-xMxO2-δ, M = Bi3+, Zn2+ and x = 0, 0.05, 0.1, 0.15, 0.2) were prepared via coprecipitation by the addition of sodium carbonate and annealed at 800 and 1200 °C, respectively. Poor solubility of the codopants in the ceria was observed for samples annealed at 800 °C, resulting in a mixed-phase product including stable phases of the oxides of these codopants. A second-stage partial incorporation of these codopants into the ceria lattice was observed when the annealing temperature was increased to 1200 °C, with both codopants forming cubic-type phases of their respective oxides. Materials were characterized using X-ray diffraction (XRD), Raman spectroscopy, and Fourier transform infrared spectroscopy (FTIR), as well as scanning electron microscopy (SEM) for structural and morphological investigations. The oxide ion conductivity was evaluated using electrochemical impedance spectroscopy between 550 and 750 °C. Fuel cell performance tests of selected samples (annealed at 1200 °C) showed remarkable improvement in peak power densities when the test temperature was increased from 500 to 600 °C (∼720 mW/cm2 for Ce0.8Sm0.15Bi0.05O2-δ and ∼1230 mW/cm2 for Ce0.8Sm0.15Zn0.05O2-δ), indicating possible contribution from the distinct cubic-type oxide phases of the codopants in performance enhancement.

Robust Arduino controlled spin coater using a novel and simple gravity chuck design.

Spin coaters offer an invaluable method of thin film fabrication. Various implementations, both proprietary and open-source exist, offering vacuum and gravity samples chucks. These implementations vary in their reliability, ease-of-use, cost, and versatility. Here we present a novel easy-to-use open-source gravity-chuck type spin coater with minimal points of failure at a material cost of around 100 USD (1500 ZAR). The unique chuck design makes use of interchangeable brass plate sample masks, each specific to a sample size, these can be made with basic skills and common hand tools. In comparison, replacement chucks for commercial alternatives can cost as much as the entire spin coater we present. Open-source hardware such as this provides an example for individuals in the field on the design and development of hardware where reliability, cost, and flexibility are most important, as is the case for many institutions in developing countries.

A New Hydrometallurgical Process for Metal Extraction from Electric Arc Furnace Dust Using Ionic Liquids.

This research proposes a new hydrometallurgical method for Zn, In, and Ga extraction, along with Fe as a common impurity, from electric arc furnace dust (EAFD), using ionic liquids. EAFD is a metal-containing waste fraction generated in significant amounts during the process of steelmaking from scrap material in an electric arc furnace. With valuable metal recovery as the main goal, two ionic liquids, [Bmim+HSO4-] and [Bmim+Cl-], were studied in conjunction with three oxidants: Fe2(SO4)3, KMnO4, and H2O2. The results indicated that the best combination was [Bmim+HSO4-] with [Fe2(SO4)3]. An experimental series subsequently demonstrated that the combination of 30% v/v [Bmim+HSO4-], 1 g of [Fe2(SO4)3], S/L ratio = 1/20, a 240 min leaching time, and a temperature of 85 °C was optimal, resulting in maximum extractions of 92.7% Zn, 97.4% In, and 17.03% Ga. In addition, 80.2% of the impurity metal Fe was dissolved. The dissolution kinetics of these four elements over a temperature range of 55-85 °C was found to be diffusion controlled. The remaining phases present in the leached residue were low amounts of ZnO, Fe3O4, ZnFe2O4, and traces of Ca(OH)2 and MnO2, and additional sharp peaks indicative of PbSO4 and CaSO4 appeared within the XRD pattern. The intensity of the peaks related to ZnO and Fe3O4 were observed to have decreased considerably during leaching, whereas some of the refractory ZnFe2O4 phase remained. SEM-EDS analysis revealed that the initial EAFD morphology was composed of spherical-shaped fine-grained particle agglomerates, whereas the leached residue was dominated by calcium sulphate (Ca(SO4))-rich needle-shaped crystals. The results clearly demonstrate that [Bmim+HSO4-] is able to extract the target metals due to its acidic properties.

The influence of the Li+ addition rate during the hydrothermal synthesis of LiFePO4 on the average and local structure.

A hydrothermal method was used to synthesize LiFePO4 to explore the effect of the rate of addition of the Li+ precursor to a mixture of the Fe2+ and PO43- precursors. Both the average and local structures were investigated using powder X-ray diffraction, Mössbauer spectroscopy and X-ray absorption spectroscopy. Slower addition rates led to increased oxidation of Fe2+ to Fe3+ despite purging all solutions constantly, as well as increased defects. The local structure as determined by extended X-ray absorption fine structure displayed far less variation between the samples. The formation of a Li3PO4 impurity appeared to be independent of the Li+ addition rate.

The Kinetics of Pyrite Dissolution in Nitric Acid Solution.

Refractory sulphidic ore with gold captured in pyrite has motivated researchers to find efficient means to break down pyrite to make gold accessible and, ultimately, improve gold extraction. Thus, the dissolution of pyrite was investigated to understand the mechanism and find the corresponding kinetics in a nitric acid solution. To carry this out, the temperature (25 to 85 °C), nitric acid concentration (1 to 4 M), the particle size of pyrite from 53 to 212 µm, and different stirring speeds were examined to observe their effect on pyrite dissolution. An increase in temperature and nitric acid concentration were influential parameters to obtaining a substantial improvement in pyrite dissolution (95% Fe extraction achieved). The new shrinking core equation (1/3ln (1 - X) + [(1 - X)-1/3 - 1)]) = kt) fit the measured rates of dissolution well. Thus, the mixed-controlled kinetics model describing the interfacial transfer and diffusion governed the reaction kinetics of pyrite. The activation energies (Ea) were 145.2 kJ/mol at 25-45 °C and 44.3 kJ/mol at higher temperatures (55-85 °C). A semiempirical expression describing the reaction of pyrite dissolution under the conditions studied was proposed: 1/3ln(1 - X) + [(1 - X)-1/3 - 1)] = 88.3 [HNO3]2.6 r0-1.3 e-44280/RT t. The solid residue was analysed using SEM, XRD, and Raman spectrometry, which all identified sulphur formation as the pyrite dissolved. Interestingly, two sulphur species, i.e., S8 and S6, formed during the dissolution process, which were detected using XRD Rietveld refinement.

Probing the stoichiometry dependent catalytic activity of nickel selenide counter electrodes in the redox reaction of iodide/triiodide electrolyte in dye sensitized solar cells.

Nickel selenide (Ni x Se y ) systems have received much attention in recent years as potential low cost counter electrodes (CEs) in dye sensitized solar cells (DSSCs). Their electrocatalytic activities are comparable to that of the conventional platinum CE. Despite their achievements, the effect of stoichiometry on their catalytic performance as CEs in DSSCs still remains unclear, hence the motivation for this work. Different stoichiometries of Ni x Se y were synthesized via a colloidal method in oleylamine or oleylamine/oleic acid mixture at the appropriate synthetic temperature and Ni to Se precursor ratio. X-ray diffraction revealed that different stoichiometries of nickel selenide were formed namely, NiSe2, Ni3Se4, Ni0.85Se, NiSe and Ni3Se2. Scanning electron microscopy showed that all the stoichiometries had predominantly spherical-like morphologies. Cyclic voltammetry, electrochemical impedance spectroscopy analysis and the photovoltaic performances of the DSSCs fabricated using the different Ni x Se y CEs revealed that selenium rich stoichiometries performed better than the nickel rich ones. Consequently, the catalytic activity towards the redox reaction of the triiodide/iodide electrolyte and hence the power conversion efficiency (PCE) followed the order of NiSe2 > Ni3Se4 > Ni0.85Se > NiSe > Ni3Se2 with PCE values of 3.31%, 3.25%, 3.17%, 2.35% and 1.52% respectively under ambient conditions.

Application of Protocols Devised to Study Bi(III) Complex Formation by Voltammetry: The Bi(III)-Picolinic Acid System.

Bi(III) coordination chemistry has been largely neglected due to the difficulties faced when studying these systems even though Bi(III) is used in various medicinal applications. This study of the Bi(III)-picolinic acid system by voltammetry applies the rigorous methodologies already developed to enable the study of Bi(III) systems starting in very acidic solutions to prevent precipitation. This includes calibrating the glass electrode accurately at these low pHs, compensating for the diffusion junction potential below pH 2 and determining the reduction potential of uncomplexed Bi(III) which cannot be directly measured. The importance of including nitrate from the background electrolyte as a competing species is highlighted, especially for data acquired below pH ∼ 2. From analysis of the voltammetric data, it was not clear whether a ML3OH species formed in solution or whether it was a combination of ML4 and ML4OH. Information from crystal structures and electrospray ionization-mass spectrometry measurements was thus used to propose the most probable species model. The log ß values determined were 7.77 ± 0.07 for ML, 13.89 ± 0.07 for ML2, 18.61 ± 0.01 for ML3, 22.7 ± 0.2 for ML4, and 31.4 ± 0.2 for ML4OH. Application of these methodologies thus opens the door to broaden our understanding of Bi(III) complexation.

Measurements and Modeling To Determine the Reduction Potential of Uncomplexed Bi(III) in Nitrate Solutions for Application in Bi(III)-Ligand Equilibria Studies by Voltammetry.

The free metal ion potential, E(M), is a critical parameter in the calculation of formation constants when using voltammetry. When studying complex formation of Bi(III), however, E(Bi) cannot be directly measured. In this work a nitrate background electrolyte was employed to obtain reversible reduction waves. To determine E(Bi), measurements have to be made below pH ∼ 2 before the bismuth-oxy-nitrate species precipitates and thus corrections for the diffusion junction potential (monitored using Tl(I) as an internal reference ion) must be made. Additionally shifts in potential due to both Bi(III) hydrolysis and Bi(III) nitrate formation must also be compensated for before E(Bi) can be evaluated. The value of E(Bi) was determined relative to E(Tl) so that in an experiments where ligand is added to determine formation constants, E(Bi) can be determined as accurately as possible (since E(Tl) can generally still be measured). The value of E(Bi) - E(Tl) was found to be 495.6 ± 1.4 mV for the conditions employed.