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 degrees C absorbed gaseous hydrogen of similar to 4.5 mass% even at room temperature under lower pressure than I MPa within 15 s and finally its capacity reached more than 5 mass%. On the other hand, the catalyzed MgH2 after rehydrogenation desorbed similar to 6 mass% hydrogen at 160 degrees 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 similar to 71 kJ/mol H-2, indicating the product was significantly activated due to the catalytic effect of Nb2O5. (c) 2005 Elsevier B.V. All rights reserved.