The optimization of MmNi5-xAlx hydrogen storage alloy for sea or lagoon navigation and transportation

Among hydrogen storage materials, the MmNi(5) (Mm = mischmetal, a mixture of rare earth elements) family of alloys has good properties for transportation technologies due to their ability to react reversibly with hydrogen at moderate pressures-and temperatures. It is also known that different composition of Mm or partial substitution of Ni by other elements modifies the hydride stability and induces a wide range of plateau pressures, giving them an excellent versatility. This work investigates a set of MmNi(5-x)Al(x) materials exploring different kinds of Mm and Al content (x = 0.15,0.20,0.25), in order to determine which composition best satisfies specific working conditions for possible employment in transportation by sea or lagoon where the water of the lagoon is used as a coolant. In the specific case of a public transportation ship (the classical vaporetto) on the Venice Lagoon, hard restrictions are required for these conditions since hydrogen sorption pressures are a key factor when considering the lagoon average temperature variations between winter and summer seasons. Experimental results of the present study led to a map of Vant'Hoff that let select the best material according to the required conditions. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.