Transparent conductive oxide type materials as the anode of solid oxide fuel cells at a reduced temperature

Abstract

Solid oxide fuel cells (SOFCs) can be used for the high-efficiency conversion of chemical energy into electricity. The exploration of new oxide anodes as alternatives to conventional Ni(O), aims to enhance coking resistance and the oxidation–reduction (redox) stability of the anode. An n-type semiconductor with electron charge carriers will be conducive to the electric conductivity, σ, under fuel conditions, but the research on n-type oxide electrodes is limited mostly to perovskite-type titanate that requires very high temperature and low oxygen partial pressure to provide a decent σ. Transparent conductive oxides (TCOs) with a superior σ even at room temperature are widely explored for electronic devices, but they have never been studied as an alternative oxide anode of an SOFC at a reduced temperature. An n-type TCO type material ZnGa2O4 (ZGO) that could be reduced at a temperature below 700 °C was used as the anode for the oxidation of H2 and hydrocarbon (ethanol and propane) at ≤650 °C. ZGO provided a high σ of 1.5 and 0.33 S cm−1 at 700 °C and 600 °C, respectively, and the cell with a ZGO anode and Sc0.18Ce0.01Zr0.81O2−δ electrolyte showed a high redox stability. The performance of the cell with a ZGO/GDC (Gd2O3 doped ceria) anode could be enhanced by the infiltration of 1% Ni, imparting a peak power of 574 mW cm−2 at 650 °C and a stable cell performance of 300 mW cm−2 at 600 °C for 300 hours. The cell was also found to be relatively stable under carbonaceous fuel, suppressing carbon deposition at 600 °C. This work provided a new avenue of designing an n-type oxide anode that could be reduced in situ under the fuel condition of a low-temperature SOFC.