Koichi Eguchi, professor at the Graduate School of Engineering, Kyoto University, announced the details of the research and development of ammonia fuel cells.
The research and development is conducted as part of the "Energy Carrier Project," which was launched by Japan's Ministry of Education, Culture, Sports, Science and Technology in fiscal 2013.
Ammonia (NH3) was chosen as a hydrogen source in the project because its hydrogen density is 12.1kg/100L, which is higher than that of liquefied hydrogen (7.06kg/100L). Also, ammonia liquefies at 25°C under atmospheric pressure and can be easily dealt with. On the other hand, liquefied hydrogen needs to be stored at an extremely low temperature because it liquefies at -242°C, causing a major technical problem.
Furthermore, if a widely-used hydrocarbon (CH)-based fuel is used to produce hydrogen, it also produces carbon monoxide (CO) and carbon dioxide (CO2), causing a carbon emission problem.
Eguchi plans to develop a polymer electrolyte fuel cell (PEFC) and solid-oxide fuel cell (SOFC) that use ammonia. But practically, he aims to develop an SOFC that operates at high temperatures.
PEFCs are commercially available for home use and have been widely adopted. To realize a PEFC using ammonia as a fuel, Eguchi plans to (1) decompose ammonia into hydrogen gas and nitrogen gas by using a molten salt catalyst at a temperature of 650°C or lower, (2) remove ammonia gas at a temperature of 400°C or lower so that the density of ammonia in the hydrogen gas becomes 0.1ppm or lower and (3) send the hydrogen gas into a fuel cell.
Because the polymer electrolyte film of PEFC is susceptible to ammonia gas, it is necessary to remove a considerable amount of ammonia gas. This is predicted to be a major technical problem.
SOFCs, which have been commercialized by Osaka Gas Co Ltd, JX Nippon Oil & Energy Corp, etc for home use, can operate at high temperatures (700 to 900°C). Therefore, Eguchi considers it possible to make ammonia directly react with oxygen gas and generate electricity. Of course, he is also considering an indirect method that decomposes ammonia into hydrogen gas and nitrogen gas.
For the development of an SOFC that uses ammonia as a fuel, Eguchi is considering using a nickel-based cermet for its positive electrode, partially-stabilized zirconia-based ceramics for its electrolyte film and manganese oxide containing a lanthanum strontium-based material for its negative electrode. He expects that its power generation efficiency will be higher than those of existing SOFCs (45%).
The key challenge lies in the selection of a catalyst material that decomposes ammonia, and he is considering using iron, cobalt, nickel or ruthenium.
In terms of the design, decisions have to be made on the placements and operations of the SOFC and its ammonia cracking reactor.