Catalysts are used with fuels such as hydrogen or methanol to produce hydrogen ions. Platinum, which is very expensive, is the catalyst typically used in this process. Companies are using nanoparticles of platinum to reduce the amount of platinum needed, or using nanoparticles of other materials to replace platinum entirely and thereby lower costs.
Fuel cells contain membranes that allow hydrogen ions to pass through the cell but do not allow other atoms or ions, such as oxygen, to pass through. Companies are using nanotechnology to create more efficient membranes; this will allow them to build lighter weight and longer lasting fuel cells.
Small fuel cells are being developed that can be used to replace batteries in handheld devices such as PDAs or laptop computers. Most companies working on this type of fuel cell are using methanol as a fuel and are calling them DMFC's, which stands for direct methanol fuel cell. DMFC's are designed to last longer than conventional batteries. In addition, rather than plugging your device into an electrical outlet and waiting for the battery to recharge, with a DMFC you simply insert a new cartridge of methanol into the device and you're ready to go.
Fuel cells that can replace batteries in electric cars are also under development. Hydrogen is the fuel most researchers propose for use in fuel cell powered cars. In addition to the improvements to catalysts and membranes discussed above, it is necessary to develop a lightweight and safe hydrogen fuel tank to hold the fuel and build a network of refueling stations. To build these tanks, researchers are trying to develop lightweight nanomaterials that will absorb the hydrogen and only release it when needed. The Department of Energy is estimating that widespread usage of hydrogen powered cars will not occur until approximately 2020.
Researchers at the University of Copenhagen have demonstrated the ability to significantly reduce the amount of platinum needed as a catalyst in fuel cells. The researchers found that the spacing between platinum nanoparticles affected the catalytic behavior, and that by controlling the packing density of the platinum nanoparticles they could reduce the amount of platinum needed.
Researchers at Brown University are developing a catalyst that uses no platinum. The catalyst is made from a sheet of graphene coated with cobalt nanoparticles. If this catalyst works out for production use with fuel cells it should be much less expensive than platinum based catalysts.
Researchers at Ulsan National Institute of Science and Technology have demonstrated how to produce edge-halogenated graphene nanoplatelets that have good catalytic properties. The researchers prepared the nanoplatelets by ball-milling graphene flakes in the presence of chlorine, bromine or iodine. They believe these halogenated nanoplatelets could be used as a replacement for expensive platinum catalystic material in fuel cells.
Researchers at Cornell University have developed a catalyst using platinum-cobalt nanoparticles that produces 12 times more catalytic activity than pure platinum. In order to achieve this performance the researchers annealed the nanoparticles so they formed a crystalline lattice which reduced the spacing between platinum atoms on the surface, increasing their reactivity.
Researchers at the University of Illinois have developed a proton exchange membrane using a silicon layer with pores of about 5 nanometers in diameter capped by a layer of porous silica. The silica layer is designed to insure that water stays in the nanopores. The water combines with the acid molecules along the wall of the nanopores to form an acidic solution, providing an easy pathway for hydrogen ions through the membrane. Evaluation of this membrane showed it to have much better conductivity of hydrogen ions (100 times better conductivity was reported) in low humidity conditions than the membrane normally used in fuel cells.
Researchers at Rensselaer Polytechnic Institute have investigated the storage of hydrogen in graphene (single atom thick carbon sheets). Hydrogen has a high bonding energy to carbon, and the researchers used annealing and plasma treatment to increase this bonding energy. Because graphene is only one atom thick it has the highest surface area exposure of carbon per weight of any material. High hydrogen to carbon bonding energy and high surface area exposure of carbon gives graphene has a good chance of storing hydrogen. The researchers found that they could store14% by weight of hydrogen in graphene.
Researchers at Stony Brook University have demonstrated that gold nanoparticles can be very effective at using solar energy to generate hydrogen from water. The key is making the nanoparticles very small. They found that nanoparticles containing less than a dozen gold atoms are very effective photocatalysts for the generation of hydrogen.
Researchers at the SLAC National Accelerator Laboratory have developed a way to use less platinum for the cathode in a fuel cell, which could significantly reduce the cost of fuel cells. They alloyed platinum with copper and then removed the copper from the surface of the film, which caused the platinum atoms to move closer to each other (reducing the lattice space). It turns out that platinum with reduced lattice spacing is more a more effective catalyst for breaking up oxygen molecules into oxygen ion. The difference is that the reduced spacing changes the electronic structure of the platinum atoms so that the separated oxygen ions more easily released, and allowed to react with the hydrogen ions passing through the proton exchange membrane.
Another way to reduce the use of platinum for catalyst in fuel cell cathodes is being developed by researchers at Brown University. They deposited a one nanometer thick layer of platinum and iron on spherical nanoparticles of palladium. In laboratory scale testing they found that an catalyst made with these nanoparticles generated 12 times more current than a catalyst using pure platinum, and lasted ten times longer. The researchers believe that the improvement is due to a more efficient transfer of electrons than in standard catalysts.
Increasing catalyst surface area and efficiency by depositing platinum on porous alumina
Allowing the use of lower purity, and therefore less expensive, hydrogen with an anode made made of platinum nanoparticles deposited on titanium oxide.
Replacing platinum catalysts with less expensive nanomaterials
Using nanostructured vanadium oxide in the anode of solid oxide fuel cells. The structure forms a battery, as well a fuel cell, therefore the cell can continue to provide electric current after the hydrogen fuel runs out.
|QuantumSphere||Non-platinum catalyst||Reduces cost|
|MTI Micro||DMFC's||Minimizes moving parts, reduces cost, size and weight|
|UltraCell||DMFC's that uses an extra catalyst to convert methanol to hydrogen before reaching the core of the fuel cell||Increases power density and cell voltage|
|EDC Ovonics||Hydrogen fuel tanks using metal hydrides as the storage media||Reduce size, weight and pressure for storing hydrogen|
|Unidym||Carbon nanotube based electrodes||Improve efficiency of fuel cells by reducing resistive and mass transfer losses|
|GridShift||Hydrogen generation using nanoparticle coated electrodes||Improve efficiency of hydrogen generation by electrolysis|
|Aerogel Composite||Catalyst with platinum nanoparticles embedded in a carbon aerogel||Reduces platinum usage|
California Fuel Cell Partnership
Department of Energy Hydrogen Permitting Web site
Listing of Hydrogen Fueling Station Location Worldwide
Compiled by Earl Boysen of Hawk's Perch Technical Writing, LLC and UnderstandingNano.com. You can find him on Google+.