Effects of thermal history on the performance of low-temperature solid oxide fuel cells with Sm0.2Ce0.8O2-δ electrolyte and LiNi0.81Co0.15Al0.04O2 electrodes

Abstract

In this study, low-temperature solid oxide fuel cells with an ∼560 μm thick Sm0.2Ce0.8O2−δ (SDC) electrolyte and ∼890 μm thick LiNi0.81Co0.15Al0.04O2−δ (NCAL) electrodes are constructed and characterized under three experimental conditions. The cell with an NCAL cathode pre-reduced under an H2 atmosphere at 550 °C presents the best electrochemical performance. This is ascribed to facts that the reduction reaction generating Ni–Co alloy particles on the NCAL surface and partial reoxidation of Ni–Co to Ni(Co)O under an air atmosphere during subsequent experiments increase the triple-phase-boundary area, improve the catalytic activity for the oxygen reduction reaction, and cause a low polarization resistance (0.186 Ω cm2). Also, the reduction of the Ni foam–NCAL anode triggers the formation of H+/O2− bi-ionic SDC–Li2CO3–LiOH composite electrolytes. The LiOH–Li2CO3 melt permeates and densifies the electrolyte layer; this significantly increases the electrical conductivity of the electrolyte layer to 0.291 S cm−1 and lowers the ohmic resistance of the cell (0.170 Ω cm2). The Li2CO3–LiOH phases serve as electron-blocking layers to limit the electronic conductivity of the electrolyte layer. This induces a high open-circuit voltage of 1.024 V and a high maximum power density of 611.3 mW·cm−2.