Functional properties of highly stable SrTi0.95-xZr0.05NixO3-δ for use as oxygen transport membranes

Abstract

Mixed ionic-electronic conducting ceramics have the potential to serve as oxygen transport membranes, thereby facilitating the separation of pure oxygen from air for a variety of chemical conversion applications. Given that the majority of the membrane reactors are operated in a reducing atmosphere, the stability of the materials is of great importance. In this study, the SrTi_0.95-xZr_0.05Ni_xO_3-δ (x = 0.01, 0.03, 0.05, 0.10, 0.15) (STZN_x) powders were successfully synthesized and subsequently sintered into membranes. Ni substitution enhances oxygen permeability and catalytic activity via exsolution, while Zr improves structural stability by minimizing cation mismatch. XRD results indicate a Ni solubility limit below 15 %. An increase in the Ni content results in a corresponding enhancement in oxygen permeability, with STZN10 achieving the highest oxygen permeability while retaining a single phase. Thermochemical stability tests were conducted by annealing samples in a reducing atmosphere containing 2.9 % H₂ in Ar. The XRD and thermogravimetric analysis (TGA) demonstrate that STZN_x displays remarkable stability in reducing atmospheres. The presence of well-distributed Ni particles on the surface of STZN10 is observed after annealing in 2.9 % H₂/Ar at 900°C for 48 h, proving the successful exsolution phenomenon aiming for improved catalytic activity for applications such as partial oxidation of methane. It can therefore be concluded that 10 % Ni-doped STZN10 is a promising material for oxygen transport membranes in catalytic membrane reactors.