Fast Oxygen Separation Through SO₂- and CO₂‑Stable Dual-Phase Membrane Based on NiFe₂O₄–Ce_0.8Tb_0.2O_2‑δ

Abstract

Composite membranes with enhanced oxygen permeability and unprecedented stability in <i>oxyfuel</i>-like gas environments are reported. Specifically, 60 vol% NiFe₂O₄ - 40 vol% Ce_0.8Tb_0.2O_2‑δ (NFO-CTO) composite has been successfully obtained by one-pot fabrication method showing both spinel and fluorite pure phases. Narrow grain size distribution centered around 1 μm and homogeneous distribution of grains is attained, as well as percolative pathways from side to side of the dual-phase membranes. The composite resisted a stability test in wet SO₂ and CO₂ containing gas at 800 °C for 170 h, which represents a step forward toward its use in <i>oxyfuel</i> power plants. The conductivity of both phases is investigated as a function of temperature and oxygen partial pressure (<i>pO</i>_<i>2</i>). Oxygen separation in this kind of NFO-doped-ceria composite membranes occurs via the separate ambipolar transport through the two distinct percolating networks. Oxygen permeation flux values of 0.17 mL·min^–1·cm^–2 and 0.20 mL·min^–1·cm^–2 are achieved at 1000 °C when argon and pure CO₂ are used as sweep gas, respectively, through a 0.68 mm-thick membrane. Experiments at 900 °C showed that the material is stable and effective in pure CO₂ atmospheres and the oxygen permeation is even improved after 76 h on CO₂ stream