Naixiong Jiang

A higher conductivity Bi2O3-based electrolyte

Abstract We have developed a Bi 2 O 3 electrolyte doped with Dy 2 O 3 and WO 3 (DyWSB) that exhibits a higher conductivity than that of 20 mol% erbia stabilized bismuth oxide (20ESB), thus, giving it the highest conductivity of any known solid oxide electrolyte. Electrical conductivity results of the Dy–W stabilized bismuth oxide system are presented. The dopants were selected based on their polarizability and its effect on structural stability and conductivity. At 800 °C, the conductivity of (BiO 1.5 ) 0.88 (DyO 1.5 ) 0.08 (WO 3 ) 0.04 is 0.57 S/cm (1.5 times as high as that of 20ESB), and at 500 °C, the conductivity is 0.043 S/cm (2 times as high as that of 20ESB).

Effect of oxygen sublattice ordering on interstitial transport mechanism and conductivity activation energies in phase-stabilized cubic bismuth oxides

Abstract Bismuth oxide doped with isovalent rare earth cations retains the high temperature defective fluorite structure upon cooling down to room temperature. However, these doped materials undergo an order–disorder transition of the oxygen sublattice at about 600°C. When annealed at temperatures less than the transition temperature, the oxygen sublattice continues to order, and consequently oxygen ion conductivity undergoes a decay. However, the conductivity activation energies of the ordered structures after extended aging at 500°C were observed to be lower than those of the structures prior to aging. Modeling of ordered structures based on TEM diffraction patterns indicates a 〈111〉 vacancy ordering in the anion sublattice. Neutron diffraction studies show additional structural changes in the oxygen sublattice due to ordering. These studies indicate that the ionic conductivity is dependent on the distribution of oxygen ions between the regular 8c sites and the interstitial 32f sites in the fluorite structure. Based on the TEM and neutron diffraction studies and conductivity activation energies of the ordered and disordered structures, a transport mechanism for oxygen ions through interstitial positions is proposed.

Stable High Conductivity Ceria/Bismuth Oxide Bilayered Electrolytes

The authors have developed a high conductivity bilayered ceria/bismuth oxide anolyte/electrolyte that uses the Po{sub 2} gradient to obtain stability at the anolyte-electrolyte interface and reduced electronic conduction due to the electrolyte region. Results in terms of solid oxide fuel cell (SOFC) performance and stability are presented. These results include a 90 to 160 mV increase in open-circuit potential, depending on temperature, with the bilayered structure as compared to SOFCs fabricated from a single ceria layer. An open-circuit potential of >1.0 V was obtained at 500 C with the bilayered structure. This increase in open-circuit potential is obtained without any measurable increase in cell resistance and is stable for over 1,400 h of testing, under both open-circuit and maximum power conditions. Moreover, SOFCs fabricated from the bilayered structure result in a 33% greater power density as compared to cells with a single ceria electrolyte layer.

Effect of Dopant Polarizability on Oxygen Sublattice Order in Phase-Stabilized Cubic Bismuth Oxides

Bismuth oxide doped with isovalent rare earth cations retains the high temperature defective fluorite structure upon cooling down to room temperature. However, these doped materials undergo an order-disorder transition of the oxygen sublattice at about 600 °C. When annealed at temperatures less than the transition temperature the oxygen sublattice continues to order, and consequently oxygen ion conductivity undergoes a decay.Modeling of ordered structures based on TEM diffraction patterns indicates a 〈111〉 vacancy ordering in the anion sublattice. Neutron diffraction studies show additional structural changes in the oxygen sublattice due to ordering. These studies indicate that the ionic conductivity is dependent on the distribution of oxygen ions between the regular 8c sites and the interstitial 32f sites in the fluorite structure.Earlier neutron diffraction studies indicate that short range ordering of the anion sublattice is related to the polarizability of the cations. In this study we relate the stability of the disordered structure and the formation of long range order to the polarizability of the dopant cations, in terms of the time constant for conductivity decay and the dielectric constant.

Structural stability and conductivity of cubic (WO3)x - (Dy2O3)y-(Bi2O3)1−x−y

Isovalent rare earth oxide cubic stabilized bismuth oxides undergo an order-disorder transition of the oxygen sublattice ∼600 °C. Annealing below this temperature leads to a decay in conductivity due to ordering. We recently discovered a high conductivity Bi2O3 electrolyte doped with both Dy2O3 and WO3 (DyWSB). The dopants were selected based on their polarizability and its effect on both structural stability and conductivity. Electrical conductivity results of the stabilized bismuth oxide system as function of temperature and time are presented. By manipulating the composition ratio of the dopants, the structural stability was enhanced resulting in a more stable conductivity.