Improved activation and hydrogen storage properties of a Mg85Ni15 melt-spun alloy via surface treatment with NH4+ solution

An amorphous Mg85Ni15 melt-spun hydrogen storage alloy, processed by submersion in an aqueous solution of NH4+, is able to absorb nearly 5 mass% hydrogen at 473 K during the first hydrogenation cycle. The nanocrystalline microstructure formed during devitrification of the metallic glass is preserved by the lower required activation temperature of the NH4+-treated material compared to the as-spun material; and the kinetics of subsequent absorption/desorption cycles at 573 K are dramatically improved. The material activated at 473 K exhibits a decrease in hydride decomposition temperature by 30 K, observed via DSC and TPD experiments, compared to a sample activated at 573 K. The NH4+-treatment of a glassy alloy presented here provides a practical alternative to ball milling for forming a nanocrystalline material and facilitating activation, requiring much less time and a more commercially scalable option.

► A Mg85Ni15 alloy is processed for hydrogen storage using aqueous solution of NH4+. ► NH4+-treatment allows the material to be activated at 473 K, absorbing 5 mass% H. ► Improvements in activation kinetics are comparable to those achieved by ball milling. ► DSC and calculations demonstrate improved thermodynamics due to capillarity effects.