Portable current sources utilizing aluminum-water hydrogen   generatorsfor use with cell phones and notebooks

Operating principle: insert the cartridge and start the charging

Activities are under way at the Joint Institute for High Temperatures of the Russian Academy of Sciences, which are aimed at developing prototypes of free-breathing hydrogen-air fuel cells (FB HAFC) with a solid polymer electrolyte of the Nafion type for compact power supplies (CPS) utilizing microgenerators of hydrogen (MGH). The use of HAFC as a basis for compact power supplies (CPS) is motivated by a number of factors, including the high energy density and the high energy-to-weight ratio inherent in these cells. Compared to large stacks with forced delivery of oxidizer to cathode, free-breathing fuel cells are more attractive from the standpoint of their cost and reliability.

These power supplies include a hydrogen generator, one or several two-section assemblies of FB HAFC, a dc/dc matching converter–and–voltage stabilizer, and an electromagnetic valve. A distinguishing feature of these CPS is the fact that the source of hydrogen is provided by MGH with replaceable aluminum-water cartridges.

The MGH is a device (Fig. 1) with an expendable replaceable cartridge placed in a hermetic casing provided with a pipe connection for the outlet of hydrogen directed to the fuel cell. The cartridge consists of two parts, namely, a container with water and the main part, i.e., a cell with hydrogen-generating substance (activated aluminum). Water is contained in special moisture-absorbing materials located in the container. Activated aluminum is present in the form of powder. The parts are separated by a membrane element of preassigned porous structure. Water-retaining separators are located in the path of hydrogen escape for retaining the condensate carried over from the cartridge along with hydrogen.

		Cartridges may differ in shape, size, volume, and energy capacity. However, the operating principle of MGH is the same and consists in the following. In storage, the reagents are placed in a sectional cartridge and are separated by a special moisture-proof partition to avoid the contact of aluminum with water or its vapors. For producing hydrogen, both parts of the cartridge must be brought into contact; as a result, water via membrane will start coming to the reagent at a certain velocity which defines the productive capacity of the MGH.
Fig. 1. Schematic of aluminum-water microgenerator of hydrogen: 1, casing of microgenerator of hydrogen; 2, pipe connection for the escape of hydrogen; 3, container for water; 4, cell with hydrogen-generating substance; 5, membrane element; 6, water-retaining separator.		.

If required, the capacity for self-regulation may be structurally realized in the MGH. In the absence of consumption of hydrogen, water is squeezed out from the active zone via separating membrane into the container with water because of increasing pressure of hydrogen. In so doing, hydrogen proper (given correct organization of porous structure of the membrane) partly squeezes water out from the pores, remains locked in the membrane, prevents the transfer of water to the active mass, and does not leave the hydrogen space. With depletion of remaining water in the active zone, the reaction stops, and the hydrogen pressure ceases to increase.
 

The advantages of MGH include:

– environmental safety,
– low cost,
– long-term storage of reagents,
– high specific parameters,
– possibility of miniaturization,
– possibility of automatic control of release of hydrogen,
– possibility of using ordinary water,
– capacity for operation at room temperature,
– purity of produced hydrogen (99.99 ignoring moisture content or better),
– energy capacity per unit volume: 300 W-h/liter,
– energy capacity per unit mass of article: 200 W-h/kg,
– hydrogen content in the cartridge in view of excess water: 1.6% by mass,
– the moisture content of hydrogen has a favorable effect on the operation of HAFC with a solid polymer electrolyte of the Nafion type in the case of operation in the “free-breathing” mode.

		External supply sources for cell phone (Fig. 2) are designed for ensuring the working capacity and charging of storage batteries of any type and the replacement of mains-operated charging devices in the absence of the mains, for example, in the field. Such devices may be used as power supplies for any portable instrument with the load characteristics similar to those of cell phone.
Fig. 2.  The universal charging device for cell phones

 

		Compact power supplies for notebooks (Fig. 3) include a microgenerator of hydrogen with several cartridges of two-section assemblies of FB FC, a dc/dc converter, an electromagnetic valve, and an air-delivery system with a fan. The air is delivered into the gaps between the free-breathing fuel cells with the aid of a fan whose rotation rate depends on the strength of current on the FC which defines (according to Faraday law) the consumption of reagents. All of the identified parts of CPS are combined in a single casing.
Fig. 3. External power supply for notebook