Microwave Synthesis and Sintering Methods for Reversible Solid Oxide Fuel Cell Fabrication

Abstract

The primary focus of our work has been on the development of a stable mixed ionic and electronic conducting (MIEC) oxide electrode that is catalytic for application as an air electrode in reversible solid oxide fuel cells (RSOFCs). For this purpose, our recently developed La0.3Sr0.7Fe0.7Cr0.3O3-δ (LSFCr) material [1], shown to be active as both an anode and cathode material in symmetrical SOFCs, has been modified by replacing the Sr in the A site with Ca, producing La0.3Ca0.7Fe0.7Cr0.3O3- δ (LCFCr), which has been shown to be a very promising oxygen and fuel electrode for reversible SOFCs [2-4]. In the present work, we are working towards a solid oxide fuel cell/electrolysis cell that is fabricated entirely with the use of MW techniques, starting with the synthesis of the electrode/electrolyte powders and including the sintering of the full cell. We have already demonstrated that the LCFCr material can be produced from the precursor salts by microwave (MW) methods, showing that the pure phase can be obtained at a much lower synthesis temperature (300 oC) and that the synthesis time can be cut down by ca. 50% as compared to conventional solid-state processing methods [5]. Another outcome is that there is a significant increase in its surface area (10.4 m2 g-1) vs. what is obtained using standard methods, i.e., 0.89 m2 g-1 ) [5].More recently, we have developed an effective method for the MW co-sintering of the anode-electrolyte-cathode combination in one simple step. This approach, in which sintering temperatures as high as 1000 oC can be achieved in just a few minutes, would have a significant impact on both lowering material and cell manufacturing costs and on further enhancing the performance of these cells. In this work, the LCFCr perovskite powders were first formed using MW methods and were then screen-printed on both sides of a gadolinia-doped ceria (GDC) electrolyte, followed by MW-assisted sintering of the cell. It is worth noting that there were no MW susceptors added in any of the fabrication steps and the normal pre-sintering steps used in conventional furnaces were also not needed. We show that these LCFCr/GDC/LCFCr cells, sintered using only MW methods, gave performances that were very similar to cells fabricated using normal ceramic processing methods. However, the time required to achieve this was decreased by ca. ten times, thus translating to significant savings in manufacturing costs.