Kinetic behavior of Ti-doped NaAlH4 when cocatalyzed with carbon nanostructures

The effects of SWNTs, MWNTs, AC, C(60), and G when used as a cocatalyst with Ti on the dehydrogenation and hydrogenation kinetics of NaAlH(4) were investigated for the first time in the important temperature range of 90 to 250 degrees C. All five carbons exhibited significant, sustaining, and synergistic cocatalytic effects on the dehydrogenation and hydrogenation kinetics of Ti-doped NaAlH(4) that persisted through charge and discharge cycling. SWNTs were the best cocatalyst, G was the worst cocatalyst, and all five carbons were inactive as a catalyst unless Ti was present. The carbon most likely was imparting an electronic contribution through the interaction of its facile pi-electrons with Ti through a hydrogen spillover mechanism, which explained why one carbon was better than another one in terms of optimal aromatic character, out-of-plane exposure of pi-electrons, and interaction of pi-bonds with neighboring sheets.