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...

The all-vanadium redox fl ow battery is a promising technology for large-scale renewable and grid energy storage, but is limited by the low energy density and poor stability of the vanadium electrolyte solutions. A new vanadium redox fl ow battery with a signifi cant improvement over the current technology is reported in this paper. This battery uses sulfate-chloride mixed electrolytes, which are capable of dissolving 2.5 M vanadium, representing about a 70% increase in energy capacity over the current sulfate system. More importantly, the new electrolyte remains stable over a wide temperature range of − 5 to 50 ° C, potentially eliminating the need for electrolyte temperature control in practical applications. This development would lead to a signifi cant reduction in the cost of energy storage, thus accelerating its market penetration.

Large‐scale electrical energy storage has become more important than ever for reducing fossil energy consumption in transportation and for the widespread deployment of intermittent renewable energy in electric grid. However, significant challenges exist for its applications. Here, the status and challenges are reviewed from the perspective of materials science and materials chemistry in electrochemical energy storage technologies, such as Li‐ion batteries, sodium (sulfur and metal halide) batteries, Pb‐acid battery, redox flow batteries, and supercapacitors. Perspectives and approaches are introduced for emerging battery designs and new chemistry combinations to reduce the cost of energy storage devices.

Large-scale energy storage has become the main bottleneck for increasing the percentage of renewable energy in our electricity grids. Redox flow batteries are considered to be among the best options for electricity storage in the megawatt range and large demonstration systems have already been installed. Although the full technological potential of these systems has not been reached yet, currently the main problem hindering more widespread commercialization is the high cost of redox flow batteries. Nafion, as the preferred membrane material, is responsible for about 11% of the overall cost of a 1 MW/8 MWh system. Therefore, in recent years two main membrane related research threads have emerged: 1) chemical and physical modification of Nafion membranes to optimize their properties with regard to vanadium redox flow battery (VRFB) application; and 2) replacement of the Nafion membranes with different, less expensive materials. This review summarizes the underlying basic scientific issues associated with membrane use in VRFBs and presents an overview of membrane-related research approaches aimed at improving the efficiency of VRFBs and making the technology cost-competitive. Promising research strategies and materials are identified and suggestions are provided on how materials issues could be overcome.