Gadolinia Doped Ceria with Engineered Grain Boundaries as Potential Electrolyte Material for Thin-Film Solid Oxide Fuel Cells

Abstract

Thin-film solid oxide fuel cells are receiving increasing attention within the scientific community thanks to their high energy density and high efficiency in different temperature ranges. To be utilized as power supply systems for portable electronic devices, thin-film solid oxide fuel cells must demonstrate high power supply and low-temperature operation capabilities. Both capabilities are highly dependent on the function of the electrolyte layer, commonly comprised of ceramic mixed-ionic-electronic conductors [1]. The state-of-the-art thin-film solid oxide fuel cells utilize yttrium stabilized zirconia as an electrolyte material, despite its relatively low ionic conductivity within the typical working-temperature range of solid oxide fuel cells (up to 1000 °C). Moreover, the ionic conductivity of yttrium stabilized zirconia dramatically reduces with decreased temperature, limiting its performance as an electrolyte material for low-temperature (below 600 °C) solid oxide fuel cells [2].Gadolinia doped ceria is an alternative promising electrolyte material for low temperature solid oxide fuel cells. Its relatively high ionic conductivity below 600 °C makes it attractive as an electrolyte material although its partial electronic conductivity is a significant drawback [3]. This drawback is more pronounced in ultra-thin layers (sub-micron scale) solid oxide fuel cells devices. As a result, gadolinia doped ceria have been utilized only to a limited extent for thin-film solid oxide fuel cells.The issue of partial electronic conductivity might be resolved thanks to a non-conventional deposition technique of polycrystalline gadolinia doped ceria thin films. The proposed sputtering technique includes metallic alloy target and results in a granular morphology, as opposed to the columnar morphology obtained using the conventional sputtering method. As electrical conductivity of polycrystalline thin films is higher along the grain boundaries [4], gadolinia doped ceria layers with random crystallographic orientation are expected to be less electronically conductive. Here, we investigated the integration and the performance of granular gadolinia doped ceria as an electrolyte material for thin-film solid oxide fuel cells. The electronic-conduction properties along the grain boundaries of gadolinia doped ceria were studied, and a thin-film solid oxide fuel cell prototype was fabricated. Such devices with engineered grain boundaries hold the potential for low-temperature operation, high power output, and silicone-compatibility for novel integration opportunities and bulk-fabrication.