Electrical transport in a molten-solid V2O5-ZrV2O7 composite

Molten-solid composite oxides are candidates as oxygen transport membranes (OTMs) at intermediate temperatures (500-700 degrees C). Effects of the constituent phases and interphases on surface reactions and transport processes in these composites are elusive. Here we contribute fundamental insight to such materials systems, applying electrochemical impedance spectroscopy (EIS) and electromotive force (emf) measurements to investigate the electrical conductivity characteristics of a 30 mol% V2O5-ZrV2O7 composite with a eutectic melting point at similar to 670 degrees C. When V2O5 melts and increases the V2O5 volume percolation, the electrical conductivity increases by a factor of 10 and the activation energy increases from 0.21 to similar to 0.7 eV. The oxygen red-ox reaction at the surface changes from being rate limited by charge transfer processes to mass transfer processes as a consequence of fast oxygen exchange in molten V2O5 as compared to the all-solid composite. These effects coincide with the ionic transport number rising from essentially zero to similar to 0.4, reflecting a significant increase in the relative oxide ion conductivity. Oxygen permeation across a 30 mol% V2O5-ZrV2O7 membrane was estimated to be in the same order as for several dual-phase membranes, but one magnitude lower than for single-phase mixed conducting membranes at intermediate temperatures.

Automated summary

Research on molten-solid composite oxides as oxygen transport membranes at intermediate temperatures shows that the electrical conductivity increases significantly when V2O5 melts and the oxygen red-ox reaction shifts from being rate limited by charge transfer to mass transfer processes. The ionic transport number also sees a significant increase, indicating a rise in relative oxide ion conductivity. Oxygen permeation across the composite membrane is estimated to be lower than for single-phase mixed conducting membranes but comparable to several dual-phase membranes.