Mixed ionic-electronic conducting (MIEC) membranes for thermochemical reduction of CO2: A review

Intermediate temperature membrane-supported CO2 thermochemical reduction using renewable energy is a clean approach for reusing CO2. To implement this technology at scale, stable catalytic membrane materials with fast kinetics should be developed, and reactor designs and system integrations should be optimized. In this review, we highlight major advancements in experimental and numerical efforts on mixed ionic-electronic conducting (MIEC) membrane-supported CO2 thermochemical reduction, and discuss the connection among materials, kinetics, membranes and reactor design. First, we discuss the thermodynamics and kinetics of CO2 reduction and the working principles of membrane reactors. Two methods are compared: chemical looping (redox) and membrane supported CO2 reduction. Next, we compare CO2 conversion rates on various membrane materials and their stability. Strontium based perovskites, e.g., Nb2O5-doped SrCo0.8Fe0.2O3-δ (SCoF-82) show the highest CO2 reduction rates so far, but they suffer degradation mainly from carbonate formation. Mixed-phase membranes are promising, with high reduction rates and good stability. Surface modification can enhance the reduction rates and increase membrane stabilities. In order to accelerate the development in materials and membranes, kinetic parameters, e.g., conductivity and reaction rate constants should be obtained from high throughput benchtop reactors complemented by reduced physical models. The mechanisms and transport models for surface kinetics and bulk diffusion are summarized. Using these results, changes in membrane morphology and surface chemistry are proposed. Finally, we summarize methods and system-scaled analysis to integrate this membrane technology with renewable or waste heat sources for fuel production and energy storage.