Engineering topics

Coyle, Christopher A.

Publications and source records attributed to Coyle, Christopher A..

5 records

DOE OSTI2021

Sr and Co Vapor-Phase Transport from LSCF Cathodes

A series of tests were performed to differentiate between surface diffusion and vapor-phase diffusion of chemical species from LSCF cathode material at typical sintering temperatures (up to 1100°C) in SOFC production. A GDC source substrate was printed with LSCF and separated by an air gap from a YSZ target substrate. Various geometries with long surface paths were employed to reduce the possibility of surface transport. Sr and Co were detected on the target substrates via energy dispersive spectroscopy (EDS) and x-ray photoelectron spectroscopy (XPS), including spatially resolved XPS. These results support a vapor-phase transport mechanism for Sr and Co. Sintering conditions and barrier layer requirements may need to be revisited to prevent the formation of undesired strontium zirconate at cathode/electrolyte interface due to vapor-phase transport.

vapor phase transport, SOFC cathode, Sr transport↗

DOE OSTI2019

Mechanofusion for Improved Control of Cermet TPBAR Pellet Microstructure

Mechanofusion is an alternative fabrication technique that has the potential to advance cermet TPBAR pellets by producing LiAlO 2 -Zr core-shell powders that will provide tighter control of targeted microstructural characteristics such as the presence and thickness of Zr surrounding every LiAlO 2 particle in the cermet. Significantly enhanced microstructural control will translate to improved control of material properties and characteristics that affect the in-reactor performance of cermet TPBAR pellets. It was the intention of this work to demonstrate the efficacy of mechanofusion for producing precursor powders for TPBAR pellets, however materials procurement issues prevented this objective from being fully realized. In spite of these issues, in the short amount of time during which appropriate materials were available, it was demonstrated that mechanofusion does indeed have promise for producing the desired structures although the process yet requires optimization.

36 MATERIALS SCIENCE↗

DOE OSTI2019

Tailored Syngas via High Temperature H2O-CO2 Co-Electrolysis

This project has developed a new testing capability at PNNL and has evaluated solid oxide electrolysis cell (SOEC) materials for the ability to co-electrolyze carbon dioxide and steam to produce synthesis gas. CO 2 -H 2 O co-electrolysis, the simultaneous electrochemical reduction of carbon dioxide and steam, was performed on the porous Ni-based electrodes in high temperature SOECs. Experiments were conducted using small button cells and the rate of the electrochemical reactions was measured at 750°C for varied reactant compositions: 10-98%CO 2 and 5-50% H 2 O, also in the presence of some H 2 and CO to ensure reducing environment and avoid Ni oxidation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2018

Evaluation of Cation Migration in Lanthanum Strontium Cobalt Ferrite Solid Oxide Fuel Cell Cathodes via In-Operando X-ray Diffraction

Anode-supported SOFC button cells with LSCF-6428 cathodes were operated at various temperatures under constant current conditions for hundreds of hours in dry or humid (~3% water) cathode air while continuously collecting 1 hour XRD scans throughout the test duration. Additionally, one cell in dry air was held at OCV, and 12% CO2 was added to the humid air for another cell. Long cumulative XRD count times allowed minor phases in concentrations of less than 0.1 wt% to be identified. In humid air, cell performance increased during the first couple of hundred hours. XRD measured a gradual shift of Fe-rich Fe,Co spinel peaks to lower angles while post-mortem SEM discovered nano-nodules on the LSCF surfaces. When 12% CO2 was added to humid air, performance degradation was observed after the initial conditioning response, unlike in tests without CO2, which were stable after conditioning. XRD also measured a shift in the peaks of the major LSCF phase in the test with CO2 indicative of some degree of gradual decomposition. Cells tested at constant current in dry air exhibited fast initial degradation that decelerated over time, while the cell held at OCV maintained a stable voltage. XRD of the cathodes held at OCV at 750 °C and operated at constant current at 700 °C in dry air measured a slower shift of the Fe-rich spinel peaks to lower angles than was seen in tests in humid air, along with a shift in the peaks of a Co-rich Fe,Co spinel to higher angles. Post-mortem SEM of cells exposed to dry air discovered smaller nano-nodules on the LSCF surfaces than had been present in cells tested in humid air. Cells tested at constant current in dry air at 750 °C and 800 °C did not exhibit any gradual changes in the XRD patterns nor were nano-nodules discovered.

Hardy, John S.↗

DOE OSTI2017

Developing Cost-Effective Dense Continuous SDC Barrier Layers for SOFCs

Significantly improved performance during electrochemical testing of a cell with a dense continuous pulsed laser deposited (PLD) samarium doped ceria (SDC) layer spurred investigations into the fabrication of dense continuous SDC barrier layers by means of cost-effective deposition using screen printing which is amenable to industrial production of SOFCs. Many approaches to improve the SDC density have been explored including the use of powder with reduced particle sizes, inks with increased solids loading, and doping with sintering aids (1). In terms of sintering aids, dopants like Mo or binary systems of Mo+Cu or Fe+Co greatly enhance SDC sinterability. In fact, adding dopants to a screen printed, prefired, porous SDC layer made it possible to achieve a dense continuous barrier layer atop the YSZ electrolyte without sintering above 1200°C. Although the objective of fabricating a dense continuous layer was achieved, additional studies have been initiated to improve the cell performance. Underlying issues with constrained sintering and dopant-enhanced ceria-zirconia solid solubility are also addressed in this paper.

Nguyen, Hoang Viet P.↗