Show Abstract ▼

Abstract: Thermoelectric materials offer the possibility of enhanced energy efficiency due to waste heat scavenging. Based on their high-temperature stability and ease of synthesis, efficient oxide-based thermoelectrics remain a tantalizing research goal; however, their current performance is significantly lower than the industry standards such as Bi2Te3 and PbTe. Among the oxide thermoelectrics studied thus far, the development of n-type thermoelectric oxides has fallen behind that of p-type oxides, primarily due to limitations on the overall dimensionless figure of merit, or ZT, by large lattice thermal conductivities. In this article, we propose a simple strategy based on chemical intuition to discover enhanced n-type oxide thermoelectrics. Using state-of-the-art calculations, we demonstrate that the PbSb2O6-structured BaBi2O6 represents a novel structural motif for thermoelectric materials, with a predicted ZT of 0.17–0.19. We then suggest two methods to enhance the ZT up to 0.22, on par with the current best earth-abundant n-type thermoelectric at around 600 K, SrTiO3, which has been much more heavily researched. Our analysis of the factors that govern the electronic and phononic scattering in this system provides a blueprint for optimizing ZT beyond the perfect crystal approximation.

Show Abstract ▼

Abstract: Glauconite is an authigenic, iron-rich clay mineral that is abundant in greensands formations worldwide. Evidence from these formations suggests that glauconite is commonly diagenetically converted to carbonate minerals such as siderite, ankerite, and ferroan dolomite. This process represents a natural CO2 sink that may provide an effective mechanism for the engineered mineralization of anthropogenic CO2. To evaluate glauconite carbonation reactions and improve our understanding of glauconite diagenesis, we performed a detailed evaluation of the mechanisms through which carbonate minerals naturally replace glauconite during diagenesis of glauconitic sandstones from the Lower Cretaceous Upper Mannville Group in western Alberta, Canada. Using a combination of optical microscopy and scanning electron imaging, electron microprobe and bulk geochemical analyses, and X-ray fluorescence mapping, we show glauconite carbonation in the Mannville group is an reduction-facilitated, coupled glauconite recrystallization and siderite precipitation reaction. X-ray absorption near-edge spectroscopic mapping and spot analyses demonstrate that this reaction is accompanied by a significant shift in the oxidation state of Fe, from dominantly oxidized in glauconite to reduced in carbonate reaction products. Together, these results suggest that geochemical conditions - most importantly, temperature, partial pressure of CO2, and fluid redox state - were thermodynamically favorable for glauconite carbonation during burial diagenesis of Mannville Group sandstones. Results of thermodynamic models illustrate that, although K-feldspar is favored to precipitate during reductive glauconite dissolution and accompanying Fe-carbonate precipitation, its precipitation is likely kinetically limited, and that an Fe-impoverished glauconite is expected to recrystallize instead. Our findings show that glauconite carbonation is likely a common phenomenon in the subsurface, and thus that glauconite is potentially a significant cation source for mineralizing anthropogenic CO2.

Open Access

Show Abstract ▼

Abstract: Atomically dispersed transition metal-nitrogen-carbon catalysts are emerging as low-cost electrocatalysts for the oxygen reduction reaction in fuel cells. However, a cost-effective and scalable synthesis strategy for these catalysts is still required, as well as a greater understanding of their mechanisms. Herein, iron, nitrogen co-doped carbon spheres (Fe@NCS) have been prepared via hydrothermal carbonization and high-temperature post carbonization. It is determined that FeN4 is the main form of iron existing in the obtained Fe@NCS. Two different precursors containing Fe2+ and Fe3+ are compared. Both chemical and structural differences have been observed in catalysts starting from Fe2+ and Fe3+ precursors. Fe2+@NCS-A (starting with Fe2+ precursor) shows better catalytic activity for the oxygen reduction reaction. This catalyst is studied in an anion exchange membrane fuel cell. The high open-circuit voltage demonstrates the potential approach for developing high-performance, low-cost fuel cell catalysts.

Show Abstract ▼

Abstract: Climate change, and the need of recycling, are two interconnected topics that are gaining more and more relevance nowadays. In order to decrease the CO2 emissions and reduce, or contain, the pollution that is having devastating effects on our climate, recycling seems to be a necessity that can not be postpone or diminished anymore. In the effort of reducing pollution, the aluminium world (industry and Academia) is playing an important role. Recycling aluminium, in fact, require only 10% of the energy necessary to extract it form the bauxite ore, leading to a massive energy and cost saving, as well to a reduction on the CO2 emissions equivalent to take off the road 900000 cars for 12 months. Up to now, the only closed loop recycling process is the one for usage beverage cans (UBC): used cans are collected, molten together, and used again to create new cans without the addition of any other material. When it comes to the automotive industry things are a bit more complicated. There are two main ways, adopted by industries, to recycle Al alloys depending on their composition. Wrought alloys are recycled remelting the scrap with primary Al, and cast alloys are obtained remelting wrought alloys and adjusting their composition for the different purposes. Although these two methods meet the requirement so far, they will lead to a nonrecyclable scrap surplus in the near future, consequently, new possibilities are being explored. In this work, a method to recycle aluminium alloys based on fractional solidification is proposed. The technology developed is based on an idea proposed by A.L Lux and M.C Flemings in which a semisolid alloy is isothermally squeezed towards a filter. Lux and Flemings tested their method on Sn-Pb alloys and on a small scale (500 g). The technology developed in this thesis, has been tested first on model aluminium alloys, and once the optimised procedure was established, on real aluminium scrap alloys, and on a bigger scale (up to 3 kg). The effect of several parameters (temperature, squeezing procedure, ultrasound, and grain refinement) on the purification efficiency was investigated and a 60% purification efficiency was achieved. Along with the technology development, a more fundamental study was carried out focusing on the investigation of the semisolid deformation, the liquid migration through the mush and the role of morphology on the permeability of the semisolid alloy. Finally, through the use of a numerical model, the feasibility of the Scheil-Gulliver approach to our case study, was investigated.

Open Access

Show Abstract ▼

Abstract: The catalytic activity of the bimolecular reaction was affected by many parameters. Although many efforts have been dedicated to investigate the influence of secondary interactions in pre-organizing catalysts, the hydrophobic effect on Ru-bda-type water oxidation catalysts remains unclear as a result of the lack of an ideal catalytic model. In this work, four catalysts 1–4 with variable hydrophobicity have been synthesized, and cerium(IV)-driven water oxidation results showed that the hydrophobic complexes 3 and 4 outperformed the hydrophilic complex 2. Steric mapping, nuclear magnetic resonance, and differential pulse voltammogram studies indicated that the increase in activity has no correlation with electronic and steric effects but has correlation with hydrophobicity. Molecular dynamics have shown that the modifications of the hydrophobicity on the axial pyridine ligands of the Ru-bda type of catalysts can improve the water oxidation catalytic activity by stabilizing the pre-reactive catalyst dimer.