Thermo-chemical and -mechanical Stability of Materials in Membrane Reactors for Renewable Syngas Production

Kurzfassung

The urgency of decarbonizing energy systems has intensified interest in solar-thermochemical CO₂ and H₂O splitting as a promising route for renewable syngas (CO + H₂) production, with excess oxygen as a byproduct. Oxygen transport membranes (OTMs) offer an energy-efficient solution for in-situ oxygen separation, but their performance relies on mixed ionic-electronic conductors (MIECs) that retain stability and functionality under these harsh conditions.

While higher operating temperatures (>1000 °C) enhance the efficiency of CO₂/H₂O splitting, they also impose severe challenges for OTMs. Three leading material classes based on ceria, zirconia, and calcium titanate emerge as candidates, each balancing trade-offs in ionic/electronic conductivity, thermal stability, and mechanical resilience. Ceria and calcium titanate show superior conductivity but may sacrifice long-term stability, whereas zirconia-based materials exhibit greater mechanical robustness at the cost of performance.

This study investigates the thermodynamic and structural behavior of these materials under high-temperature, low-pressure, and low-oxygen partial pressure conditions, probing their intrinsic stability mechanisms. A second critical challenge is long-term mechanical integrity, particularly under creep deformation, a time-dependent, irreversible strain induced by sustained thermal and mechanical loading. Even sub-yield stresses can compromise membrane integrity over time, threatening operational lifespan.

We systematically assess the thermochemical and thermomechanical stability of pre-selected OTM materials, addressing both fundamental degradation pathways and applied stress resistance. By elucidating these failure modes, we aim to guide the development of high-performance, durable OTMs for scalable solar-thermochemical syngas production, accelerating the transition to a low-carbon energy future.