Kinetic Behavior of Ti-Doped NaAlH₄ When Cocatalyzed with Carbon Nanostructures

Abstract

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.

Effect of Doped Transition Metal on Reversible Hydrogen Release/Uptake from NaAlH4

“…Great efforts have also been devoted to reduce the hydrogen release and recharging temperatures by improving the kinetics of the NaAlH 4 -based systems. [10][11][12][13][14][15][16][17] A recyclable hydrogen capacity of about 4 wt % in Ti-doped NaAlH 4 has been achieved routinely with reasonably good kinetics below the melting point. [18][19][20] Although the hydrogen capacity of the Ti-doped NaAlH 4 would not meet the target set by the US Department of Energy, the system serves as a useful prototype to understand the hydrogen interaction in similar complex metal hydrides.…”

Carbon Nanomaterials as Catalysts for Hydrogen Uptake and Release in NaAlH4

“…Several groups have investigated the use of carbon materials as possible catalysts for NaAlH 4 , and samples were almost exclusively ball milled (10)(11)(12)(13)(14). Four of these groups report that carbon materials are catalysts for the dehydrogenation and rehydrogenation of NaAlH 4 (10)(11)(12)(13).…”

Catalytic effect of fullerene and formation of nanocomposites with complex hydrides: NaAlH4 and LiAlH4

“…Several groups have investigated the use of carbon materials as possible catalysts for various complex hydrides (in particular NaAlH 4 ) and samples are prepared either by ball milling [7][8][9][10][11] or melt infiltration [12][13][14]. All these groups report that carbon materials act as catalysts for hydrogen sorption of NaAlH 4 .…”