Improved Hydrogen Generation Performance via Hydrolysis of MgH₂ with Nb₂O₅ and CeO₂ Doping

Abstract

Rapid formation of magnesium hydroxide passivation layer during hydrolysis of MgH₂ seriously blocks its application as a hydrogen generation material. MgH₂ is also susceptible to oxidation. MgH₂ with Nb₂O₅ and/or CeO₂ doping has been prepared via high energy ball milling in this work with the aim of enhancing the hydrolysis performance and oxidation resistance. The phase compositions, microstructure and hydrogen evolution properties have been systematically investigated. Nb₂O₅ and CeO₂ particles with particle size in the range of ∼20–200 nm are uniformly dotted on the surface of MgH₂ matrix after ball milling. It is found that Nb₂O₅ shows better facilitating effects than CeO₂ on the hydrolysis performance of MgH₂. As-milled MgH₂+10%Nb₂O₅ and MgH₂+10%CeO₂ samples generate ∼705 and 474 mL g⁻¹ of hydrogen in distilled water within 60 min, respectively. Introducing MgCl₂ in water can also significantly enhance the hydrolysis reaction kinetics and conversion rate. As-milled MgH₂+10%Nb₂O₅ sample shows a hydrogen yield of 1222 mL g⁻¹ in 5% MgCl₂ solution, corresponding to a conversion rate of 74.6%. However, air exposed MgH₂+10%Nb₂O₅ sample hardly generates any hydrogen in MgCl₂ solution. CeO₂ can modify the oxidation resistance to some extent. MgH₂ with CeO₂ doping can still produce ∼250 mL g⁻¹ of hydrogen after 24 h air exposure.

Fig. 5 Kinetic curves of hydrogen production from hydrolysis of as-received MgH₂ and as-milled samples in (a) distilled water and (b) 5% MgCl₂ solution at 20°C. (c) is the corresponding conversion ratios in (a) and (b).