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

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 Sc_0.18Ce_0.01Zr_0.81O_2−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.