Enhanced Hydrogen Generation Properties of MgH2-Based Hydrides by Breaking the Magnesium Hydroxide Passivation Layer

Abstract

Due to its relatively low cost, high hydrogen yield, and environmentally friendly hydrolysis byproducts, magnesium hydride (MgH2) appears to be an attractive candidate for hydrogen generation. However, the hydrolysis reaction of MgH2 is rapidly inhibited by the formation of a magnesium hydroxide passivation layer. To improve the hydrolysis properties of MgH2-based hydrides we investigated three different approaches: ball milling, synthesis of MgH2-based composites, and tuning of the solution composition. We demonstrate that the formation of a composite system, such as the MgH2/LaH3 composite, through ball milling and in situ synthesis, can improve the hydrolysis properties of MgH2 in pure water. Furthermore, the addition of Ni to the MgH2/LaH3 composite resulted in the synthesis of LaH3/MgH2/Ni composites. The LaH3/MgH2/Ni composites exhibited a higher hydrolysis rate-120 mL/(g·min) of H2 in the first 5 min-than the MgH2/LaH3 composite-95 mL/(g·min)-without the formation of the magnesium hydroxide passivation layer. Moreover, the yield rate was controlled by manipulation of the particle size via ball milling. OPEN ACCESSEnergies 2015, 8 4238The hydrolysis of MgH2 was also improved by optimizing the solution. The MgH2 produced 1711.2 mL/g of H2 in 10 min at 298 K in the 27.1% ammonium chloride solution, and the hydrolytic conversion rate reached the value of 99.5%.

Controllable Hydrolysis Performance of MgLi Alloys and Their Hydrides

“…Each time about 0.1 g of the powder was placed in a 50 ml flask for hydrolysis test and 10 ml of solution was injected into the reactor as previous work. [27] Each hydrolysis experiment was done at least three times; the storage and loading of the samples were carried out in an Arfilled glove box.…”

“…Mg-based raw material is focused more because of the inferior hydrolysis kinetics of Al, and ball milling has been considered as a feasible way to solve the kinetic problem. [22,26] During ball milling process, adding metal hydride/salt composite/metal oxide can refine samples [27] to improve kinetic. [12,28,29] During hydrolysis reaction, the dissolved hydroxides product [30] can weaken the continuity of the Mg(OH) 2 passivation layer; catalysts can lower the activation energy and form a microgalvanic cell with magnesium to accelerate corrosion; [13,31] the introduction of solution ions may destroy the formation of Mg (OH) 2 passivation layer.…”

Fuel Production from Seawater and Fuel Cells Using Seawater

“…Hydrogen productionf rom the hydrolysis of active metals, such as Mg and Al, hasa ttracted much attention because of their abundance and nontoxicity. [65][66][67][68][69][70] Although Mg has al ow H 2 storage density (3.3 wt %) in water comparedt ot hat of Al (3.7 wt %), it is capable of generating hydrogen in an eutral aqueous solutioni nstead of the alkaline solutiont hat is requiredf or the hydrolysis of Al. [71][72][73][74] The Mg alloy can be fully recycled by electrical system with the efficiency of 41 %.…”

A Recycling Hydrogen Supply System of NaBH4 Based on a Facile Regeneration Process: A Review

“…Hydrolysis of hydrides, such as MgH 2 , ammonia borane (AB), and NaBH 4 , generating hydrogen with relatively high capacity at room temperature, is attracting increasing interest for hydrogen supply on demand [24][25][26]. Due to the low cost of Mg and the high capacity of MgH 2 (7.6 wt %) [27][28][29], much attention has been paid to MgH 2 hydrolysis [30][31][32]. However, the reaction is interrupted easily by the formation Inorganics 2018, 6, 10 2 of 12 of a magnesium hydroxide layer [33,34].…”