Experimental study of ammonia fuel cells

The purpose of this thesis was to carry out the experimental study of direct ammonia fuel cells. The use of hydrogen in fuel cells poses a lot of problems. There is a lot of safety, technical and economic issues to be overcome to make its use as a fuel widespread. Ammonia is being considered as a very promising source of hydrogen for fuel cells. However, until now its use in fuel cells has received very little attention. Ammonia presents many advantages over hydrogen and other potential sources of hydrogen such as an easy storage and a world-wide distribution network. Ammonia is a suitable hydrogen carrier and can be easily cracked at high temperatures such as those used in solid oxide fuel cells. The present study was conducting using ammonia as fuel and argon as carrier gas in different solid oxide fuel cell systems: an annular design, a planar design and a micro laminated reactor. The electrolyte materials were calcia stabilized zirconia and yttria stabilized zirconia. As far as the electrodes are concerned, silver, platinum and nickel cermet were used as anode/materials and silver was employed as cathode material. The cell yoltage was measured as function of reactor configuration, space time, ammonia flow rate and ammonia concentration. The results demonstrate the high potential of ammonia over hydrogen when nickel is used as anode material. Solid proton conducting fuel cells operating on ammonia fuel were also studied. The electrolyte materials were fabricated from neodymium and gadolinium doped barium and strontium cerates. The dopant fraction ranged from 1 to 20 wt%. Silver was employed as cathode and anode material and was spray deposited. The application of proton conducting electrolytes results in higher current densities for a given voltage than the using typical oxide ion conductors such as 8mol % yttria stabilized zirconia. The potential of the proton conducting materials for application in ammonia synthesis at atmospheric pressure was also studied. They demonstrated promising results and could prove to be an alternative to the common ammonia synthesis processes.