Reduction and Oxidation Study of Anode Supported Solid Oxide Fuel Cell
Solid Oxide Fuel Cells (SOFC) are an efficient energy technology for converting different types of fuels to electricity and heat. An important material limitation, especially for (planar) Ni-based anode supported cells, is their redox stability. The nickel volume change between its metallic and oxide state is destroying the thin electrolyte. Thereby it is crucial to understand mechanisms of nickel reduction, oxidation and coarsening in this system. Reduction parameters are also important from an electrochemical point of view because any change in microstructure will influence the anode reactions. On the other hand, it is observed that establishment of open circuit voltage during anode reduction is slow, and that stack performance often increases at first polarization; it is of interest to try and correlate these observations with a microstructural study. This study will focus on state-of-the-art Ni-YSZ Anode Supported Cells (ASC, supplied by HTceramix SA, Switzerland). Reduction and oxidation are carried out under different conditions. Outlet gases from a flow-through reactor containing the anode sample are analyzed by Mass Spectrometry (MS) to follow the chemical reaction. A Scanning Electron Microscopy (SEM) preparation and detection technique is used to analyze the cermets microstructure after different reduction and oxidation cycles. A Mathematica® code is developed to analyze and quantify SEM images. ThermoGravimetric Analysis (TGA) is used to confirm the MS measurements.