From the catalysts employed the Co/SiO2 catalyst displayed the highest energy yield of 3.2 and 5.3 g NH 3 . kW -1 . h -1 for ammonia synthesis over the N2/sea water vapor and N2/H2 systems respectively at a power of 2 W (Fig. &). The Ag/SiO2 and Cu/SiO2 delivered energy yields of 2.7 and 5.0 g NH 3 . kW -1 . h -1 obtained from the N2/sea water vapor and N2/H2 systems, respectively. These results confirmed the important role of the catalysts in the synthesis of ammonia and the possible need of different catalysts when switching the hydrogen source for this reaction due to the added presence of oxygen.