Tungsten clusters derived from phosphotungstic acid to enhance hydrogen storage efficiency in MgH2

Abstract

MgH2 has a high hydrogen storage capacity but suffers from high operating temperature and slow dehydrogenation kinetics due to the strong Mg–H bond. Here, phosphotungstic acid are molecularly loaded on the surface of MgH2 submicron particles and then further reduced to tungsten clusters with size of ∼2 nm during hydrogen uptake/release operation. The tungsten clusters act as catalysts to reduce the dehydrogenation temperature and activation energy of MgH2 by 36 °C and 15 kJmol-1, respectively. W cluster-decorated MgH2 can release more than 6 wt% hydrogen in 30 min at 300 °C; even at 250 °C, the material can still absorb 6 wt% hydrogen in a few minutes and release 4 wt% hydrogen in 1 h, outperforming previously reported W-based catalysts (micro/submicron WO3 and WS2). In addition, this material also shows stable cycling performance. This study demonstrates promising prospects of polyoxometalates as efficient catalysts for hydrogen storage materials.