Ceria-yttria doped barium zirconate (BZCY) fabrication methods for greener energy devices
Elisabettamaria Schettino 1 , Chris Bowen 1 , Tom Fletcher 1 , Frank Marken 1 , James Roscow 1 , George Harrington 1 , Elena Madrid 2 , Joe Stonham 2 1 University of Bath, UK, 2 GKN Aerospace, UK
Solid oxide fuel cells (SOFC) are useful devices for clean conversion of energy and have been developed to facilitate their integration in the world of cleaner energy harvesting. This technology has exciting potential due to its high electrical efficiency and low operating costs. However, their high operating temperatures (800 – 900 ℃ ) have discouraged their use as propulsion systems, favoring devices operating at lower temperatures such as batteries or polymer electrolyte membrane (PEM) fuel cells. Recent advancements in materials development have allowed SOFC electrolytes to use proton conducting materials, thereby reducing their operating temperature range to 400 – 500 ℃ . A viable candidate electrolyte is ceria- and yttria-doped barium zirconate (termed BZCY). Despite this material performing well under laboratory conditions and promising a greener alternative to power generation, its methods of fabrication are far from being ready for mass production. Moreover, the high temperature and highly energy intensive manufacturing processes are not designed with the intent of being greener and energy efficient. The most conventional method for producing ceramics is called “solid state route (SSR)”. This is a synthesis method requiring temperatures above 1500 ℃ for several hours. The high temperature and extended time are necessary to achieve solid-state sintering and densification for the larger particle size of the material. Methods such as “sol-gel” synthesis are often used to reduce particle size dimensions and subsequently decrease the sintering temperature to ~ 1250 ℃ ; however, because of their nano-sized grains, BZCY fails to densify properly. Smaller grain size also increases reactivity with the surroundings, leading to degradation and loss of mechanical properties. A method that is more energy efficient and allows for adequate densification of nano-sized particles is therefore needed to allow for this technology to be truly competitive in the energy sector. Cold sintering proves to be the solution to the issues faced when manufacturing ceramic electrolytes. This method has been developed as a novel pathway to densification using a transient liquid phase, pressure, and heat to achieve dense ceramics. The procedure allows nano-sized particles to reach relative densities above 80 % at temperatures below 200 ℃ and pressures under 250 MPa. There is potential for the process to reduce the energy consumption related to the production of these electrolytes by 5 times compared to more conventional methods. Materials are fabricated by this novel route and characterised in terms of microstructure and electrical properties.
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