CAREER: Tuning Kinetics and Stability of Membrane-Catalyst Systems for Hydrogen Production from Ammonia

About This Grant

Hydrogen can be used as a fuel or chemical feedstock to generate energy. However, hydrogen is difficult to store and transport. Ammonia has the chemical formula NH3, and is more convenient to store and transport. Accordingly there is great interest in temporarily converting hydrogen into ammonia, and then decomposing ammonia to recover hydrogen as a fuel. This project develops a membrane-based process for recovering hydrogen from ammonia. It combines the ammonia decomposition reaction, and the subsequent separation of hydrogen from ammonia and nitrogen, into a single operation. The process does not use expensive rare metals as catalysts. It is expected to be more energy-efficient compared with existing processes. The project benefits society by diversifying energy sources. Additional benefits to national interests come from training students in energy technology, outreach programs to engage pre-college students in STEM fields, and strengthening partnerships with industry. This project uses a mixed ionic-electronic conducting (MIEC) membrane with catalyst to convert ammonia and steam at the two sides of the membrane. The overall reaction is the redox-driven decomposition of ammonia. Oxygen permeability and long term durability of the membrane are critical for this technology. The overall research objective is to tune the kinetics and stability of the oxygen-permeable membrane-catalyst system. This will enable ammonia conversion to exceed its single-step decomposition limit and prevent formation of nitrogen oxides (NOx compounds). The project elucidates the coupled mass transport, charge transfer, and chemical kinetics occurring at membrane surface and interfaces. First, kinetic parameters of NH3 conversion and oxygen permeation will be analyzed to elucidate the reaction kinetics model for the proposed membrane-catalyst system. Next, the fundamental mechanisms influencing bulk and surface properties of the membrane-catalyst system will be investigated. For bulk properties, grain boundary chemistry, cation site distribution, and microstructural uniformity and defects will be characterized to discover their relationship with membrane bulk diffusion and stability. For surface properties, chemical bonding, redox state, and secondary phase(s) of catalyst and membrane will be correlated with surface kinetics and stability. Finally, the materials and system knowledge will be combined to construct a model that achieves ammonia conversion above the single-step NH3 decomposition limit and avoids NOx formation. Furthermore, the findings will extend beyond ammonia decomposition to inform other membrane-catalyst systems such as hydrocarbon reforming. Education and outreach activities in the project will include hands-on experiments, field visits, course development, and fireside chats to increase student and public interest in energy technologies and STEM careers, and to facilitate exchange between the students and industrial employers about career opportunities in energy fields. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.