The hydrogen economy is a priority for the EU’s post-COVID-19 economic recovery package guided by the European Green Deal. Hydrogen is in fact expected to play a pivotal role in a future climate-neutral economy, enabling emission-free transport, heating and industrial processes as well as energy storage as renewable carrier. However, the so called “green hydrogen” produced by zero-emission water electrolysis exploiting renewable electricity, represents only 5 % of the global hydrogen, being not yet as cost competitive as the one produced from natural gas/fossil fuels. “Grey” and “blue hydrogen” obtained from the classical processes (i.e. hydrocarbon reforming and pyrolysis) contains inevitably CO2, CO, H2O, and other contaminants. Thus, differently from H2 produced by water electrolysis, the gases separation is a mandatory step to obtaining pure hydrogen through conventional technologies involving fossil fuels and C-based materials.
In this context, ceramic-ceramic composite membranes, constituted by proton conducting perovskite (BCZY) and a suitable electron conductor (GDC), have received increasing attention for their capability to separate hydrogen at high temperature (500-1000°C) with full selectivity, highly chemical and thermal stability and intrinsic lower cost respect the Pd–based technology. These characteristics make these systems promising candidates for their integration into membrane reactors or existing plant. For practical uses, however, these membranes must ensure long-term performances and good mechanical resistance under operating conditions. Structural and chemical degradation may in fact occur at high temperatures in long time exposure of operational atmospheres (CO2, CO, H2, etc.) affecting permeability and mechanical stability. In this study, mechanical properties and composition changes of BCZY-GDC membranes after H2 and CO2-rich atmosphere exposure at high temperature (750°C) and operation were accurately investigated.

Acknowledgement
This work has been funded by the agreement between the Italian Ministry of Economic Development and the Italian National Research Council ‘‘Ricerca di sistema elettrico nazionale’’.