Stable ceria-based electrolytes for intermediate temperature-solid oxide fuel cells via hafnium oxide blocking layer

Abstract The electronic loss of ceria-based electrolytes is caused by the reduction of ceria at low oxygen partial pressure for intermediate temperature-solid oxide fuel cells. To address this issue, a thin hafnium oxide layer is deposited at the interface between the anode and electrolyte using a magnetron sputtering system, based on the hypothesis that the stability of ceria electrolytes in the anode side can be controlled as a function of the reducibility of the ceria surface. The performance of ceria-based cells (Nd 0.1 Ce 0.9 O 2-δ ; NDC, Sm 0.2 Ce 0.8 O 2-δ ; SDC) is investigated by varying the HfO 2 film thickness on the same ceria-based substrate. The range of thickness of the HfO 2 film is 121–686 A for 6–30 min with the deposition rate of 0.38 A‧S −1 . The open-circuit voltages and power densities of NDC- and SDC-based cells are measured at 600–700 °C as a function of HfO 2 film thickness. It is clearly observed that open-circuit voltages and the maximum power densities of both cells increase with the increasing of thickness of HfO 2 film until a film thickness of 600 A is reached. This indicates that the HfO 2 layer effectively prevents the electron transfer through the electrolytes by the reduction of ceria. Furthermore, the NDC-cell with the HfO 2 film shows a stable performance under a constant current density operation of 130 h at 650 °C.