Rensselaer Polytechnic Institute (RPI)

Most liquid fuels used in transportation today are derived from petroleum and burned in internal combustion engines. This combination is attractive because of the high energy density of the fuels and current economics, but it remains partially reliant on imported petroleum and is highly carbon intensive. Alternatives to internal combustion engines, such as fuel cells that convert chemical energy to electricity, have shown promise in vehicle powertrains, but are hindered by inefficiencies in fuel transport and storage. Carbon-neutral liquid fuels (CNLFs), such as ammonia, used in conjunction with fuel cells, offer an alternative transportation system that addresses these challenges. These fuels can be produced by converting water and air using chemical or electrochemical processes powered by renewable electricity. The resulting CNLFs can be stored and transported using existing liquid fuels infrastructure to the point-of-use. However, there are technical challenges associated with converting CNLFs to hydrogen for use in conventional fuel cells or directly to electricity. Advanced materials such as membranes and catalysts and new electrochemical processes are required to efficiently generate hydrogen or electricity from energy-dense CNLFs at higher conversion rates and lower costs.

Rensselaer Polytechnic Institute (RPI) will develop an innovative, hollow fiber membrane reactor that can generate high purity hydrogen from ammonia. The project combines three key components: a low-cost ruthenium (Ru)-based catalyst, a hydrogen-selective membrane, and a catalytic hydrogen burner. Pressurized ammonia vapor is fed into the reactor for high-rate decomposition at the Ru-based catalyst and at a reaction temperature below 450°C. Ceramic hollow fibers at the reactor boundary will extract the high purity hydrogen from the reaction product. Residual hydrogen will be burned with air in the catalytic burner to provide heat for ammonia cracking. Both the high-purity hydrogen and the heated exhaust from the catalytic hydrogen combustion are fed past the ammonia vapor before it enters the reactor, increasing its temperature and improving the overall efficiency of the process. The team seeks to develop a compact and modular membrane reactor prototype that can deliver hydrogen at high rate per volume from ammonia decomposition at relatively low temperatures (<450°C) and high conversion (>99%).