ANSTO's research capabilities, led by the OPAL nuclear research reactor and associated instruments provide access to users investigating areas as diverse as materials, life sciences, climate change and mining/engineering.
Fuel Cell Research
3.1 Solid-state Ionic Conductors for Solid-Oxide Fuel cells
Solid-state ionic conductors are ceramic materials through which specific ions (charged species) can move while leaving their frameworks essentially unchanged. They are critical components in solid-oxide fuel cells (SOFC's), which use hydrocarbons and other fuels more efficiently by bringing them into contact with oxide anions in a direct and controllable manner, rather than simply burning them in air.
This minimises pollution due to incomplete combustion and dramatically improves efficiency by producing electricity directly, rather than indirectly by using the heat of combustion to boil water to drive turbines to turn generators. Of particular interest is the use of fuel cells to "burn" pure hydrogen gas, with water as the only by-product.
The aim of this project is to obtain a better understanding of ionic-conduction mechanisms in materials used for SOFC's, both currently used and proposed for the future, and thereby contribute to optimising the performance of those materials and possibly discovering/developing new ones.
In-situ neutron-diffraction experiments under conditions close to those of SOFC operation (high temperature, gradient of partial oxygen pressure, atmosphere cycling) is the only way to establish direct connection between evolution of crystal structure of material with property response such as ionic conductivity and oxygen permeability.
Careful analysis of diffraction data provides additional information on sample microstructure evolution (degree of preferred orientation, crystallite size and/or microstrain) directly affecting mechanical stability of SOFC's.
A powerful technique to investigate these materials is in-situ single crystal neutron diffraction; however, this is rarely used because of the requirement for very large single crystals, which are difficult to grow. We will make use of the new floating-zone image furnace recently installed at the University of Sydney to grow the largest possible crystals, and investigate their structure using the unique capabilities of the quasi-Laue single-crystal neutron diffractometer KOALA to obtain structural data from crystals too small to be analysed by other neutron-diffraction instrumentation.
Investigations into the fundamentals of ionic transport are currently being pursued using model systems, such as the well-known mixed ionic-electronic conductors copper and silver chalcogenides, which have high-ionic conductivities.
See recent results
3.2 Polymer Electrolyte Fuel Cell Membranes
Soft polymer membranes that can exchange hydrated protons from the anode to the cathode of a fuel cell will is developed using plasma techniques. Present membranes are expensive (~AU$1000/m2), are easily poisoned (by hydrocarbon impurities), and their ability to conduct protons is strongly coupled to the hydration, making efficient operation over 100oC quite difficult.
The polymers containing sulfonic acid groups will be developed at the Space Plasma, Power and Propulsion group at the ANU by plasma polymerization from a gaseous mixture made up of styrene and trifluoromethane sulfonic (triflic) acid monomers. The role of the triflic acid is to bring the proton conductive functions (SO3-) while the styrene monomer constitutes the skeleton element of the carbonated polymer matrix.
A dry plasma process, similar to that presently used in the micro-electronics industry, has been used to deposit a low thickness membrane of a few micrometres where the morphology and chemical composition can be easily modified by changing the plasma parameters such as discharge power, gas pressures and flow rates and substrate temperature.
Using this approach it should be possible to obtain membranes with longer lifetime, increased chemical and thermal stability, higher conductivity, and operational temperatures greater than 100oC without the need for external humidification of the reactant gases.
A number of diagnostic systems such as Langmuir probes, energy selective ion energy analysers, network analysers, optical emission spectroscopy, FTIR spectrometers and ellipsometers, will be used for thin film diagnostics. The properties of the membranes will be characterized using scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and Fourier-transform infra-red spectroscopy (FTIR).
The conductivity will be determined by electrochemical impedance spectroscopy. Measurements of methanol sorption and methanol diffusion permeability will be determined using a quartz crystal microbalance and a Hittorf diffusion cell coupled to infra-red spectroscopy.
To give new insights into the proton dynamics in the picosecond time window and in the angstrom spatial scale, a neutron-scattering investigation of the water in these films will be performed. Specifically, quasielastic neutron scattering (QENS) will reveal the average dynamics of all the protons in the film. Quantitative information from QENS on the hydrogen atom motions relative to both space and time will allow a phenomenological picture of the H dynamics in the films to be developed.
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