Nanostructured ceramic proton conductors for hydrogen separation

Ceramic membranes operating at high-temperature are a key-technology for hydrogen separation processes including advanced chemical reactors, power generation, CO2 capture, and hydrogen separation/purification from gas mixtures. Thanks to their 100% selectivity, high proton-electron conductivity, intrinsic lower costs if compared with Pd-based technologies, and chemical and temperature stability, ceramic composites based on BaCe0.65Zr0.20Y0.15O3-δ-Gd0.2Ce0.8O2 (BCZY-GDC) have gained increasing attention as asymmetric membranes for H2 purification. Several efforts have been made to obtain planar and crack free asymmetric membranes by tape casting. However, the long processing times and the moderate hydrogen permeation fluxes obtained employing this technology are still not suitable for industrial applications. In order to improve the H2 permeation, a lot of research is currently focused on optimizing the microstructure of the porous support aiming to increase the gas access and transport through it. The obtainment of well oriented pore structures also facilitates the impregnation of washcoating and/or catalysts to enhance the membranes efficiency. Here different shaping techniques such as freeze casting and additive manufacturing (micro extrusion) were explored in order to obtain hierarchically-structured supports for proton-conducting ceramic membranes. Strategies to obtain nanostructured washcoats and catalytic layers are also presented and discussed. Moreover, preliminary studies on the low temperature compaction of BCZY-GDC specimens by the cold sintering process are provided.