The role of ionic-electronic ratio in dual-phase catalytic layers for oxygen transport permeation membranes

Oxygen transport membrane (OTM) is an appealing technology for contributing to the decarbonization of the industry via oxy-combustion processes. Dual-phase composite materials are promising membrane candidates for this kind of processes due to their stability under CO2 atmospheres. Even so, the oxygen permeation through this kind of membranes is still limiting for practical application. A key well-studied membrane performance parameter is the ratio between composite crystalline phases since the percolative channels for each phase determine the final oxygen permeation flux. Here, we investigate the influence of the phase ratio on the surface-exchange reactions in catalytically-activated composite membranes composed of NiFe2O4 (NFO) and Ce0.8Tb0.2O2-delta (CTO). Electrical impedance spectroscopy (EIS) and oxygen permeation studies revealed a decrease in polarization resistance and an increase in oxygen flux as the ionic-phase proportion in the catalytic layers increases. At 850 degrees C, the 20NFO80CTO catalytic layer on a 650 mu m-thick 50NFO50CTO membrane reaches an oxygen flux of 0.2 mL min- 1 center dot cm- 2. That permeation was improved by a factor of 2.5 regarding the opposite phase ratio (80NFO20CTO) and 1.3 regarding a balanced phase ratio (50NFO50CTO) in the catalytic layer. The 20NFO80CTO electrodes showed the lowest resistances compared to the electrodes with higher NFO content, confirming that the O2 surface exchange is controlled by ionic-phase mechanisms rather than electronic phase ones.