Design of Mg-Ni alloys for fast hydrogen generation from seawater and their application in polymer electrolyte membrane fuel cells

Mg and its alloys are very attractive for hydrogen generation via hydrolysis because their hydrolysis reaction occurs in neutral seawater instead of the alkaline water necessary for the hydrolysis of Al and its alloys. The hydrogen generation rate from the hydrolysis of Mg is proportional to the corrosion rate of Mg to Mg²⁺. Mg powder, though producing a high reaction rate in the hydrolysis, causes explosive dangers when in contact with air or moisture. However, Bulk Mg such as plate and sheet exhibits an extremely low hydrogen generation rate. To overcome the disadvantage, Mg-Ni alloys were designed to form an electrochemically noble phase (Mg₂Ni) along grain boundaries (G.B.), and hence to significantly accelerate the hydrolysis rate by causing a galvanic and intergranular corrosion between the noble Mg₂Ni and Mg matrix. In particular, the Mg-2.7Ni alloy among the designed Mg-Ni alloys exhibits the highest hydrogen generation rate (23.8 ml min^-1 g^-1) that is 1300 times faster than that of pure Mg. Furthermore, it was demonstrated that PEMFC stably produced 7.3 W for 20 min when it is operated by the hydrogen generated from the hydrolysis of 2 g Mg-2.7Ni alloy, that is, equivalent to 1.215 KWh/Kg-Mg-2.7Ni alloy.