The increasing demand for clean energy sources that do not add more carbon dioxide and other pollutants to the environment has resulted in increased attention worldwide to the possibilities of a "hydrogen economy" as a long-term solution for a secure energy future based on potentially renewable resources. [1][2][3] Some of the greatest challenges are the discovery and development of new on-board hydrogen-storage materials and catalysts for fuel-cell-powered vehicles. New materials that store both high gravimetric (! 90 gm H 2 kg À1 ) and high volumetric (! 82 gm H 2 L À1 ) densities of hydrogen that can be delivered at temperatures between À20 and 85 8C are needed by the year 2015. [4] The volumetric constraints eliminate from consideration pressurized hydrogen systems and guide towards the development of solid storage materials. [5] There are several broad classes of solid hydrogenstorage materials that are currently being investigated as potential on-board storage materials: 1) metal materials, hydrides (e.g., MgH 2 ), [6] imides (e.g., LiNH 2 ), [7] and organic frameworks (e.g., Zn 4 O(1,4-benezenedicarboxylate)), [8] 2) complex hydrides (e.g., NaAlH 4 ), [9] and 3) carbon materials (e.g., carbon nanofibers, [10] single-wall carbon nanotubes). [11] The most thoroughly studied complex hydride, NaAlH 4 , has been shown to release hydrogen at 110 8C when doped with Ti; [12] however, the kinetics are very slow and hydrogen-storage densities are too low (56 gm H 2 kg À1 ) to meet long-term targets. The temperatures for H 2 release from carbon materials are too low, and the reported storage densities are controversial. [13] The hydrolysis of metal hydrides is being explored, but the unfavorable thermodynamics for regeneration of the spent material prevents their widespread application. For example, the reaction NaBH 4 +4 H 2 O!NaB(OH) 4 +4 H 2 is exothermic by À250 kJ mol À1 . Reaction enthalpy for hydrogen loss is an important property since near-thermoneutral thermodynamics will be critical for materials for reversible H 2 storage. To date, few of these materials meet the long-term gravimetric requirements and provide rapid hydrogen release at temperatures between À20 and 85 8C; thus, new materials and novel approaches are needed. Herein we show that the kinetics of hydrogen release are significantly enhanced at low temperatures for a new hybrid material, ammonia borane infused in nanoporous silica, and that the hydrogen purity is increased. These findings suggest that hydrogen-rich materials infused in nanoscaffolds offer a most promising approach to on-board hydrogen storage.Chemical hydrogen-storage materials that release H 2 by thermolysis without generating CO 2 may offer an attractive alternative to other systems studied. For example, the NH x BH x family of compounds [14] should provide favorable gravimetric densities of 245, 196, 140, and 75 gm H 2 kg À1 for x = 4, 3, 2, and 1, respectively. As the NB unit is isoelectronic with CC, these materials are viewed as inorganic analogues of hydrocarbons. Howeve...

No abstract

Aqueous rechargeable batteries are desirable for energy storage because of their low cost and high safety. However, low capacity and short cyclic life are significant obstacles to their practical applications. Here, we demonstrate a highly reversible aqueous zinc–iodine battery using encapsulated iodine in microporous carbon as the cathode material by controlling solid–liquid conversion reactions. We identified the factors influencing solid–liquid conversion reactions, e.g., the pore size, surface chemistry of carbon host, and solvent effect. Rational manipulation of the competition between the adsorption in carbon and solvation in electrolytes for iodine species is responsible for the high reversibility and cyclic stability. The zinc–iodine battery delivers a high capacity of 174.4 mAh g–1 at 1C, stable cyclic life over 3000 cycles with ∼90% capacity retention, and negligible self-discharge. We believe that the principles for stabilizing the zinc–iodine system could provide new insight for other conversion systems such as lithium–sulfur systems.

The increasing demand for clean energy sources that do not add more carbon dioxide and other pollutants to the environment has resulted in increased attention worldwide to the possibilities of a "hydrogen economy" as a long-term solution for a secure energy future based on potentially renewable resources. [1][2][3] Some of the greatest challenges are the discovery and development of new on-board hydrogen-storage materials and catalysts for fuel-cell-powered vehicles. New materials that store both high gravimetric (! 90 gm H 2 kg À1 ) and high volumetric (! 82 gm H 2 L À1 ) densities of hydrogen that can be delivered at temperatures between À20 and 85 8C are needed by the year 2015.[4] The volumetric constraints eliminate from consideration pressurized hydrogen systems and guide towards the development of solid storage materials.[5] There are several broad classes of solid hydrogenstorage materials that are currently being investigated as potential on-board storage materials: 1) metal materials, hydrides (e.g., MgH 2 ), [6] imides (e.g., LiNH 2 ), [7] and organic frameworks (e.g., Zn 4 O(1,4-benezenedicarboxylate)), [8] 2) complex hydrides (e.g., NaAlH 4 ), [9] and 3) carbon materials (e.g., carbon nanofibers, [10] single-wall carbon nanotubes).[11] The most thoroughly studied complex hydride, NaAlH 4 , has been shown to release hydrogen at 110 8C when doped with Ti; [12] however, the kinetics are very slow and hydrogen-storage densities are too low (56 gm H 2 kg À1 ) to meet long-term targets. The temperatures for H 2 release from carbon materials are too low, and the reported storage densities are controversial.[13] The hydrolysis of metal hydrides is being explored, but the unfavorable thermodynamics for regeneration of the spent material prevents their widespread application. For example, the reaction NaBH 4 +4 H 2 O!NaB(OH) 4 +4 H 2 is exothermic by À250 kJ mol À1 . Reaction enthalpy for hydrogen loss is an important property since near-thermoneutral thermodynamics will be critical for materials for reversible H 2 storage. To date, few of these materials meet the long-term gravimetric requirements and provide rapid hydrogen release at temperatures between À20 and 85 8C; thus, new materials and novel approaches are needed. Herein we show that the kinetics of hydrogen release are significantly enhanced at low temperatures for a new hybrid material, ammonia borane infused in nanoporous silica, and that the hydrogen purity is increased. These findings suggest that hydrogen-rich materials infused in nanoscaffolds offer a most promising approach to on-board hydrogen storage.Chemical hydrogen-storage materials that release H 2 by thermolysis without generating CO 2 may offer an attractive alternative to other systems studied. For example, the NH x BH x family of compounds [14] should provide favorable gravimetric densities of 245, 196, 140, and 75 gm H 2 kg À1 for x = 4, 3, 2, and 1, respectively. As the NB unit is isoelectronic with CC, these materials are viewed as inorganic analogues of hydrocarbons. However, NH ...

No abstract