Remarkable improvement of hydrogen sorption kinetics in magnesium catalyzed with Nb₂O₅

Kinetics of hydrogen absorption and desorption reactions was investigated on the MgH₂ composite doped with 1 mol% Nb₂O₅ as a catalyst by ballmilling. The composite after dehydrogenation at 200 °C absorbed gaseous hydrogen of ∼4.5 mass% even at room temperature under lower pressure than 1 MPa within 15 s and finally its capacity reached more than 5 mass%. On the other hand, the catalyzed MgH₂ after rehydrogenation desorbed ∼6 mass% hydrogen at 160 °C under purified He flow, which followed the first order reaction. From the Kissinger plot, the activation energy for hydrogen desorption was estimated to be ∼71 kJ/mol H₂, indicating the product was significantly activated due to the catalytic effect of Nb₂O₅.