Firing Up Fuel Cells with Nanotechnology
Nanotechnology can improve the efficiency of fuel cells in several ways. Fuel cells require the movement of ions through membranes. By using nanopores, you can limit what gets through the membranes and better control the reaction that occurs.
Researchers have capped the ends of nanopores to trap the acidic solution inside the membrane, thus improving the transport of hydrogen ions through the membrane in low humidity. This capability opens up the possibility of making fuel cells that operate in a wide range of humidity conditions.
A catalyst, usually platinum, makes fuel cell reactions at lower temperatures occur more easily. A second way that nanotechnology can improve the efficiency of fuel cells involves improving the catalyst. Researchers use nanoparticles to increase the surface area available for reactions, thus making the reaction more efficient — and less costly because less platinum is needed.
Finally, nano may produce hydrogen storage tanks small and lightweight enough to use in cars. Hydrogen bonds easily to carbon, so researchers have investigated the storage of hydrogen in graphene. 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 carbon’s high surface area exposure make graphene a good candidate for storing hydrogen.
Several groups are exploring the use of nanotechnology to improve the efficiency of fuel cells.
Researchers at the SLAC National Accelerator Laboratory have developed a way to use 80 percent less platinum for the cathode in fuel cells, which could significantly reduce their cost. The researchers alloyed platinum with copper in nanoparticles and then removed the copper from the surface of the nanoparticles, causing the platinum atoms to move closer to each other.
The reduced spacing between atoms (called lattice spacing) changes the electronic structure of the platinum atoms so that the separated oxygen ions are more easily released, making the catalyst more effective. A more effective catalyst means that less catalyst is required.
Another way to reduce the use of platinum 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 tests, they found that a fuel cell using a catalyst made with these nanoparticles generated 12 times more current than one containing a catalyst using pure platinum. The fuel cell also lasted ten times longer. The researchers believe this improvement is due to a more efficient transfer of electrons.
Hydrogen produced from hydrocarbons, such as oil or natural gas, contains carbon monoxide. To use this hydrogen in fuel cells, carbon monoxide must be removed, which increases the cost.
Researchers at Cornell University have found a way to reduce the amount of platinum used in the fuel cell and to increase the tolerance of the fuel cell for some contaminates in the hydrogen fuel, which decreases the cost of producing the hydrogen.
Researchers at the University of Illinois have developed a proton exchange membrane using a silicon layer with pores that are about 5 nanometers in diameter and capped by a layer of porous silica. The silica layer ensures 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.
This membrane had much better conductivity of hydrogen ions (100 times better) in low-humidity conditions than the membrane normally used in fuel cells. This approach could result in the creation of fuel cells that operate in environments with a wide range of humidity.