Thomas H. Etsell

Sol-gel processing of ZnS

Abstract A sol-gel process has been developed for the chemical synthesis of ZnS at room temperature using zinc tert-butoxide and H2S as precursors in a toluene solution. The obtained reaction product was a yellow semi-transparent gel which dried to a reddish-orange solid. Characterization of the dried gel by XRD, IR and EDS confirmed that the product is ZnS with a Zn 5 atomic ratio ≈ 1:1.

Polarized electrochemical vapor deposition for cermet anodes in solid oxide fuel cells

Abstract A new process originally developed for sensors shows promise for coating porous nickel substrates with a layer of yttria stabilized zirconia (YSZ) for cermet anodes in solid oxide fuel cells (SOFCs). Traditionally, the cermets are deposited using randomly interspersed nickel and stabilized zirconia powders. However, the conducting nickel is a mostly discontinuous phase and thus the conductivity is impeded. With this new polarized electrochemical vapor deposition (PEVD) technique, the deposition of a uniform layer of YSZ was demonstrated using a platinum substrate, which had previously been sintered to a continuous layer over the fuel cell electrolyte. Films deposited over a 24 h period with a −0.300 V applied potential were on average 1–3 μm thick. After 5 days, the film becomes fully dense with few large blocked pores. Preliminary EDX testing indicates that the amount of deposition product decreases away from the substrate, indicating that deposition and film growth commence at the triple phase boundary.

Novel layered solid oxide fuel cells with multiple-twinned Ni0.8Co0.2 nanoparticles: the key to thermally independent CO2 utilization and power-chemical cogeneration

To energy-efficiently offset our carbon footprint, we herein developed a novel CH4–CO2 dry reforming process to co-produce electricity and CO-concentrated syngas, which takes advantage of the selective oxidation of H2 in high performance proton-conducting solid oxide fuel cells (SOFCs). In these cells, an additional functional layer, consisting of a Ni0.8Co0.2–La0.2Ce0.8O1.9 (NiCo–LDC) composite, was successfully incorporated into the anode support, forming a layered SOFC configuration. The multiple-twinned bimetallic nanoparticles were then proven to have superior activity towards in situ dry reforming. In comparison to the conventional design, this layered SOFC demonstrated drastically improved CO2 resistance as well as internal reforming efficiency (CO2 conversion reached 91.5% at 700 °C), and up to 100 h galvanostatic stability in a CH4–CO2 feedstream at 1 A cm−2. More importantly, H2 was effectively and exclusively converted by electrochemical oxidation, yielding no CO2 but CO concentrated syngas in the anode effluent. The maximum power density exceeded 910 mW cm−2 at 700 °C with a polarization resistance as low as 0.121 Ω cm2. Consequently, the heat released by H2 electrochemical oxidation fully compensated for that required by the extremely endothermic dry reforming reaction, making the entire process thermally self-sufficient. We also showed that the layered design was beneficial in terms of decreasing coking and increasing CO2 resistance of the SOFC in the mixed CO2 and CH4 feedstock. This novel process promises to play a pivotal role in future CO2 conversion and utilization.

High performance of microtubular solid oxide fuel cells using Nd2NiO4+δ-based composite cathodes

Nd2NiO4+δ infiltrated into porous yttria stabilized zirconia (YSZ) is proposed in this work as a cathode for solid oxide fuel cells (SOFCs). In order to obtain nickelate single phase, calcination times and temperatures of the salt precursors are studied. Anode supported microtubular cells using this cathode are fabricated and characterized, showing power densities of about 0.76 W cm−2 at 800 °C and a voltage as high as 0.8 V. No degradation is detected after 24 hours under current load, assuring reasonable stability of the cell. Preliminary solid oxide electrolysis cell (SOEC) results show slightly better performances in comparison with SOFC operation. It is believed that infiltration of nickelate salt precursors followed by calcination proposed in this work avoids high temperature sintering of the nickelate phase with the electrolyte and as a consequence, prevents their reaction. For this reason, infiltrated nickelates are very attractive for their use as intermediate temperature (IT) SOFC cathodes.

Magnetic properties of ilmenite, hematite and oilsand minerals after roasting

To recover heavy minerals from the Athabasca oil sands tailings, a roasting step is necessary to burn off the residual bitumen. However, most of the previous researchers, using a roasting step, did not seem to be able to separate the Fe-bearing titanium minerals (ilmenite and leucoxene) from the Fe-free titanium minerals (rutile and anatase). An investigation was therefore carried out to study the changes in magnetic properties after roasting to the types of minerals contained in the oil sands tailings. Ilmenite, hematite, and a rutile concentrate (LR Rutile) produced from the oil sands tailings (containing mainly leucoxene and rutile), were used in the study. It was observed that the magnetic susceptibility of ilmenite increased after either oxidation or reduction roasting at some intermediate temperatures and roasting time. For hematite, reduction roasting increased its magnetic susceptibility and oxidation roasting did not seem to have any effect. Reduction roasting of the LR Rutile resulted in an increase in its magnetic susceptibility, and this increase was mainly due to the contaminating Fe-bearing minerals (leucoxene). Upgrading of the LR Rutile was possible either by using low intensity magnetic separation following reduction roasting, or by using high intensity magnetic separation directly.

Electrochemical Study of a Polarized Electrochemical Vapor Deposition Process

The interfacing of modern vapor deposition technology and solid-state ionic technology has led to the recent development of polarized electrochemical vapor deposition (PEVD). Due to the unique electrocrystallization behavior of its products and easy process control through a solid electrochemical cell, PEVD holds promise for a wide range of potential applications. However, the migration of charged ionic and electronic carriers during PEVD is a kinetic process. The task related to studying PEVD working electrode kinetics in this investigation is to explain the sequence of partial reactions constituting the overall PEVD electrochemical reaction for product formation at the working electrode. The PEVD process for Na 2 CO 3 auxiliary phase deposition at the working electrode of a potentiometric CO 2 sensor was selected for the current electrochemical studies. The dependence of current density, or of reaction rate, upon various working electrode overpotentials and temperatures (500-550°C) was studied by a steady-state potentiostatic method. The PEVD reaction rate-limiting steps are solved for samples undergoing second-stage growth. The results from this investigation help in understanding the kinetics of the PEVD reaction and subsequent product formation in a PEVD system, improve knowledge of PEVD kinetics, and elucidate the possibility of further process control in PEVD.

Anode-Engineered Protonic Ceramic Fuel Cell with Excellent Performance and Fuel Compatibility

Directly utilizing hydrocarbon fuels, particularly methane, is advantageous yet challenging in high-performance protonic ceramic fuel cells. In this work, this technological hurdle is well addressed by selective deposition of secondary electrocatalysts within the porous Ni-cermet anode. This novel strategy sheds light on the development of multifunctional porous structures for energy and catalysis applications.

Preparation of tungsten sulfides by sol—gel processing

Abstract Tungsten sulfides were synthesized by reaction of different tungsten alkoxides and hydrogen sulfide in toluene. The reaction was performed in toluene solution at room temperature. Tungsten ethoxide yielded a brown black gel, while tungsten dichloride ethoxide produced a brown—black colloidal powder. The W/S at% ratios were 1:2.7 and 1:1.4 in the gel and powder, respectively. Both sol—gel products were amorphous materials. The gel appeared to be highly viscous liquid formed from spherical colloidal particles connected into a three-dimensional network. However, the powder consisted of loose colloidal particles whose radii were in the range 0.5 to 1 μm.

Spatial Modeling of Geometallurgical Properties: Techniques and a Case Study

High-resolution spatial numerical models of metallurgical properties constrained by geological controls and more extensively by measured grade and geomechanical properties constitute an important part of geometallurgy. Geostatistical and other numerical techniques are adapted and developed to construct these high-resolution models accounting for all available data. Important issues that must be addressed include unequal sampling of the metallurgical properties versus grade assays, measurements at different scale, and complex nonlinear averaging of many metallurgical parameters. This paper establishes techniques to address each of these issues with the required implementation details and also demonstrates geometallurgical mineral deposit characterization for a copper–molybdenum deposit in South America. High-resolution models of grades and comminution indices are constructed, checked, and are rigorously validated. The workflow demonstrated in this case study is applicable to many other deposit types.

Mechanisms involved in the formation and growth of Al–Cu–Ni hydrotalcite-like precipitates using the urea hydrolysis scheme

Urea hydrolysis was used to generate carbonate and hydroxide anions required to coprecipitate Al–Cu–Ni hydrotalcite-like compounds (HTlcs) as the precursors for alumina supported Cu–Ni catalysts. The factors influencing the urea hydrolysis and the morphology of the precipitates are discussed. It was found that the ratio of urea to metal salts (PTR), reaction time and temperature are three important parameters in the synthesis of HTlcs using urea hydrolysis. Among these, PTR and temperature are the most important factors in the formation of monodisperse precipitates. The results also indicate that the pH curves of precipitation tests are the best indicators of precipitation sequences. A reaction scheme for the formation of the Al–Cu–Ni HTl structure was also predicted.