Direct Ammonia Fuel Cells: A General Overview, Current Technologies and Future Directions

Abstract

Ammonia will be utilized as a key energy vector for storage and long-distance transport in the developing hydrogen economy. Direct ammonia fuel cells have the potential to decrease the process complexity of current fuel cell technology and therefore increases overall efficiency and unit footprint where implemented. In this paper, current direct ammonia fuel cell technologies are explored, such as SOFC-O, SOFC-H, alkaline, and ammonia borane fuel cells. From this, it is shown that SOFC-O have high experimental power outputs of 1100 mW/cm2 but has disadvantages of high NOx production, lower fuel utilisation and low efficiency. Alkaline and ammonia borane fuel cells have lesser interest due to complex ammonia pre-treatment, high NOx production and lower power outputs of 450 mW/cm2 and 110 mW/cm2 respectfully. SOFC-H seem to have the most potential due to high theoretical power outputs, high efficiency, increased fuel utilisation and low NOx production. DAFC technology has yet to reach full commercialisation, but as the hydrogen economy develops the potential benefits of DAFCs in complexity and footprint reduction will drive further investment and development, particularly in the shipping sector.