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Mobile Electrical Energy Storage and the Challenge for Chemistry
- Posted on March 30, 2011
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As debates about alternative methods of propulsion on land continue, the commercial marine sector has gained access to a modernized form of old alternative propulsive energy. A company from Germany and another in the SW USA offer kite-sails that use the kinetic energy of high-altitude winds to provide a portion of the propulsive power required by boats and ships. In times past, many of the old clipper ships sailed parallel to the trade winds that carried them to trading ports around the world. The modern day kite-sail technology achieves the same end with larger boats and taps into winds that blow at higher velocity and higher frequency that winds that blow at lower elevations.
There has been ongoing interest in competitively priced, plug-in electric vehicles for the consumer market. Private companies have answered the call by offering plug-in electrically assisted bicycles that can travel for up to 40-miles at up to 25-miles per hour. Thousands of such units that are powered by a motor of 500-watts (0.67-Hp) output have been sold across North America and the world. Political unrest in oil producing nations usually results in higher oil prices. Citizens in many nations now have an alternative mode of transportation that uses a different fuel.
The proliferation of electrically assisted bicycles has resulted in an epidemic of expired lead-acid batteries in several Asian nations. In North America, these units carry the more expensive lithium batteries that can endure some 5000-deep-cycle discharges and recharges, 10-times the number of the lead-acid counterparts. The rate of expiry of the batteries prompts discussion as to whether new-generation super capacitors could become a viable alternative form of electrical energy storage. Such devices are being used to store electrical energy that is used to start commercial-duty diesel engines on large trucks and railway locomotives.
Government funded researchers in the USA have indicated the possibility of developing a super capacitor technology that could propel an automobile for up to 500-miles at freeway speeds. However, the appearance of a cost-competitive carbon nano-tube super capacitor may be many years into the future. There is a need for a cost-competitive super capacitor technology that can be a viable alternative form of energy storage, independently of government subsidy or special tax incentives. One option would be for entrepreneurs to seek to construct super capacitors using readily available energy storage materials.
That option may result in the appearance of super capacitors that may be suitable for forms of transportation other than the private automobile. BASF developed the barium titanate [BaTiO3] storage compound that can store up to 280 Watt-hours per kilogram in super capacitors. Their research suggests that bi-metallic oxides with semi-conductor properties may offer potential as energy storage material in competing super capacitors. Such devices may actually find market application despite offering lower energy storage is the same size of package.
A large super capacitor may use a commercially available material such as barium chromate [BaCrO4] to store energy, with market application in numerous sectors. The device may be built to a much larger scale than the batteries that power electrically assisted bicycles, offering operating range of 3-miles on an electrically assisted delivery vehicle. If most of the deliveries are within 1-mile of the point of origin and it takes 3-minutes to recharge the vehicle between each delivery, there may actually be commercial market application for such an energy storage system.
The low amount of power needed to recharge allows such vehicles to recharge from conventional power outlets. Entrepreneurs may develop coin operated recharging stations to recharge such vehicles from standard electrical outlets. Businesses that operate micro-power vehicles for delivery service, may install such units outside their premises to sell electric power to other users of micro-power vehicles. As the number of recharging stations increases in an urban area, so would the usage of super capacitor powered 2-wheeled micro-power vehicles.
Heavy Weight Vehicles:
A naturally occurring bi-metallic oxide ore or mineral called ilmenite [FeTiO3] is mined in remote locations such as Madagascar. Its chemical structure is very similar to that of barium titanate. Each molecule of ilmenite will store less energy than barium titanate. The low cost of the compound provides possible market application in some large-scale heavy weight, short-distance transportation applications such as railway operations and short-haul marine ferries.
A 4-axle locomotive that weighs some 240,000-lb may store electrical energy in multiple banks of super capacitors that contain some 45,000-lb (20,000 kg) of ilmenite. If the ilmenite can hold 50 watt-hours of energy per kilogram (very conservative estimate), the super capacitors could store 1000kW-hr (1340-Hp-hr) of energy. The locomotive could deliver some 3000-Hp for periods of up to 20-minutes, perhaps serving as an assistant to a diesel-powered locomotive on a multi-stop train, reducing diesel consumption in such operations.
It could also be coupled to an electric locomotive that would otherwise cause a major power swing on the distribution grid as is powers up to move a heavy train. The presence of the rechargeable locomotive on the train would reduce a sudden demand for electric power from the grid. It may be possible for a large rechargeable locomotive to operate commuter services, shunting and pull lightweight freight trains between inter-modal terminals.
The Search for a Polymer:
There are naturally occurring bi-metallic oxide molecules such as ilmenite [FeTiO3] and lithium aluminate [LiAlO2] with semi-conductive properties that allow them to store electrostatic energy in super capacitors. While barium titanate [BaTiO3] offers much greater energy storage density, there is potential market for a material that can greatly exceed its energy storage capacity. Much government-funded research has focused on developing carbon microstructures that are theoretically capable of storing immense amounts of electrostatic charge.
Such theoretical giant molecules or polymers of carbon may be several years to decades into the future. There may be the option of low-cost, privately funded research coming up with an intermediate form of polymer that may find market application until suitable carbon polymers appear in the distant future. The pharmaceutical industry has created many useful giant molecules using private funding and the list includes nylon, Teflon, polyester, nomex, kelvar and carbon fibers used to make various structures.
While it has been possible for many years to develop many bi-metallic oxides, the market application for such molecules was limited. Pure aluminum can chemically react with any of several metallic hydroxides and displace the hydrogen atoms. The list includes hydroxides of lithium, potassium, sodium [Na3AlO3], calcium [Ca3(AlO3)2], magnesium, nickel, iron (ferric and ferrous hydroxide) chrome [CrAlO3], manganese, barium and several other metals to produce a semi-conductive, bi-metallic oxide.
The challenge for chemists would involve modifying the reaction in a ways that produce a bi-metallic polymer of several hundred atoms. When incorporated into a super capacitor, the long chain of the polymer would be set at right angles (90-degrees) to the capacitor conductive plates. Such a layout may increase the spatial volume where the electrostatic charge is stored. However, the research challenge of producing a large bi-metallic oxide polymer may be daunting.
Organic-Metallic Oxide Polymers:
Private companies have long undertaken research into developing products based on long chains of carbon atoms. Variations include carbon fiber material and hydroxide molecules (-OH) being bonded to carbon atoms in glucose and carbohydrate molecules. There may be scope for chemical researchers to develop synthetic, extreme long chain carbohydrate molecules.
Aluminum can displace the hydrogen from metallic hydroxides and bond directly to the oxygen atoms. Researchers face the challenge of reacting aluminum with the hydroxide molecules in long-chain carbon polymers, to replace the hydrogen atoms with aluminum. Aluminum atoms may bond to pairs of adjacent oxygen atoms in some carbon chains and to alternate oxygen atoms in other chain, offering the possibly of linking 3 x parallel long carbon chains.
An alternate option would be to seek to replace pairs of hydrogen atoms with single barium atoms. The long chain of bonded carbon atoms would form the backbone of a polymer that would include a long string of barium atoms. The development of carbon fiber material may provide the precedent to develop parallel chains of carbon atoms, analogous to microscopic railway tracks with hydroxide molecules on both sides.
Researchers would need to develop a chemical reaction to replace the hydrogen atoms with a metal such as barium, to form metal-oxygen-carbon-carbon-oxygen-metal bonds perpendicular to the parallel carbon long chains. The result would be the carbon backbone carrying 2 x parallel long rows of barium atoms that may touch each other. The objective of such research would to develop semi-conductive polymers capable of storing substantial electrostatic charge in large-scale super capacitors.
Considerable progress has already occurred in the research to develop super capacitors that offer high-density energy storage. However, such devices presently have limited market application in the transportation sector, starting diesel engines. Private cars would constitute the major market for super capacitors capable of propelling such vehicles over extended distances (100-miles). A competitive energy storage compound for such application may be many years in the future. Chemical researchers face the challenge of developing a polymer capable of storing extreme electrostatic energy densities in lightweight and compact packages.
Commercially available materials such as barium chromate may be appropriate as super capacitor energy storage material for micro-power 2-wheel vehicles that would offer limited operating range. A proliferation of recharging stations appropriate to such technology in urban areas could help develop a market for super capacitor powered micro-power vehicles. Naturally occurring materials such as ilmenite would have application as super capacitor energy storage material in the commercial transportation sector (railway and marine).