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July 11, 2012

Cella Energy Researching Commercially Viable Microbeads for Revolutionary Hydrogen Storage

Hydrogen storage start-up Cella Energy’s US subsidiary has signed a contract with NASA Kennedy Space Center (KSC) for the further research, development and potential production of its micro-bead, polymer-encapsulated chemical hydride technology.

Although suitable for proof-of-concept work and potentially for initial demonstrator projects, the current microbeads are not commercially viable, Cella says. They are expensive to make and cannot be easily re-hydrided.

Cella is working on other hydride materials with slightly lower hydrogen contents but with the ability to cycle them into the hydride phase many hundreds of times. These are being encapsulated in hydrogen- permeable high-temperature polymers based on polyimide.

L2 Aerospace is partnering with Cella Energy, a company with patented technology in safe, low-cost hydrogen storage materials to produce longer duration unmanned systems (UAVs). The initial goal is to triple the duration that would be possible using lithium ion batteries.

Cella Energy is seeking to develop and to commercialize a way to nanostructure and encapsulate complex chemical hydride materials to improve their performance, in terms of temperature of operation, adsorption and desorption kinetics, and to render them safe to handle in air.

The final product is either a fine micro-fibrous polymer mat that resembles white tissue paper, or a fine polymer powder, micro-bead diameter ~ 0.5 - 5 μm, with the hydride material entrained in ~50 - 200nm pores within the polymer.

Although hydrogen is the most abundant element in the universe it does not occur naturally on our planet. Storing hydrogen up to now has required either high pressure storage cylinders at up to 700 times atmospheric pressure (700bar or 10,000psi) or super-cooled liquids at -253°C (-423°F). Neither is practical on a large scale as these hydrogen storage methods both require large amounts of energy to either pressurise or cool the hydrogen, and present significant safety risks.

Packaged in a regular shaped fuel tank or container

The Cella Energy hydrogen storage materials are stored at ambient temperatures and pressures, this means that the Cella Energy hydrogen storage materials can be packaged in a regular shaped fuel tank. They do not require the large heavy cylinders designed to withstand high pressures normally associated with hydrogen storage.

High hydrogen content – exceed DoE targets of 4.5%

Cella's materials are already performing at 6wt% weight percentage of hydrogen, but Cella is now working with complex hydrides that store hydrogen at up to 20wt%. These exceed the revised 2009 Department of Energy targets to produce hydrogen storage materials that would compete with gasoline
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Cella’s current composite material uses ammonia borane (NH3BH3) as the hydride and polystyrene as the polymer nano-scaffold. Ammonia borane in its normal state releases 12 wt% of hydrogen at temperatures between 110 °C and 150 °C, but with very slow kinetics. In the Cella materials, the accessible hydrogen content currently is reduced to 6 wt% but the temperature of operation is reduced so that it starts releasing hydrogen below 80 °C and the kinetics are an order of magnitude faster, according to the company.

Although suitable for proof-of-concept work and potentially for initial demonstrator projects, the current microbeads are not commercially viable, Cella says. They are expensive to make and cannot be easily re-hydrided.

Cella is working on other hydride materials with slightly lower hydrogen contents but with the ability to cycle them into the hydride phase many hundreds of times. These are being encapsulated in hydrogen- permeable high-temperature polymers based on polyimide.

The eventual goal is to use the pellets in fuel cells.






Cella Energy uses the benefits of nano-structuring to encase hydrides using coaxial electrospinning. Hydrides are materials that contain hydrogen. Electrospinning is a proven low-cost method of producing micro-fibres by wet-spinning polymers. Once produced the fibres can be 30x smaller than a human hair, and together resemble white tissue paper. The fibres have a core-shell structure, where the core is a hydride and the outer shell a polymer. The outer shell polymer safely encapsulates the hydride: it acts as a filter that only allows hydrogen to pass and stops other molecules like oxygen to traverse, making the materials 100% safe.

Today a billion drivers of internal combustion engine vehicles refuel by pumping liquid gasoline and diesel into fuel tanks. This refuelling takes a few minutes and provides ranges of 300 miles or ~500km. While there are risks associated with handling gasoline, these risks are accepted by most drivers.

Gasoline and diesel vehicles are well established and the internal combustion engine ICE efficiency is increasing year on year. However to meet new emission regulation legislation standards around the world and to off-set the rising cost of fuel, the automotive industry is introducing battery electric vehicles EVs and hybrid vehicles. These vehicles use lithium-ion batteries, the technology is new, and the charging infrastructure is yet to be established universally. EVs typically have ranges of up to 100 miles and can take several hours to recharge. Research shows that vehicles need ranges of 300 miles to overcome the phenomenon known as range anxiety or the fear of being stranded. EVs are expensive to develop because they require new electric drive trains, and so are likely to cost more than conventional ICE vehicles.

By contrast hydrogen vehicles can be refuelled in a few minutes and provide a 300 miles or ~500km range. Most conventional ICE vehicles can be converted to run on hydrogen with minor modifications and are known as H2-ICE, or the electric drive trains developed for EVs can be configured as fuel cell vehicles FCVs. Both H2-ICE and FCVs produce zero carbon emissions at the point of use.

Up to now neither H2-ICE or FCVs have seen widespread adoption because there are few places to refuel the vehicles with hydrogen. The early vehicles have used either liquid hydrogen at -253°C (-423°F) or compressed hydrogen cylinders at up to 10,000psi pressure or 700bar (700x atmospheric pressure). Refuelling requires a new high-cost specialist infrastructure of hydrogen refilling stations.

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