October 12, 2008 A team of scientists from the Universidad Complutense de Madrid (UCM) has designed a material with incredibly high ion conductivity properties that could lead to the development of more efficient fuel cells.
The function of fuel cells is similar to that of batteries, but while batteries only store energy in a closed chemical system, fuel cells produce energy by combusting hydrogen. To accomplish this, fuel cells require an electrolyte that permits the flow of ions between the electrodes. The problem that scientists currently face is that temperatures of up to 800 degrees Celsius are needed to achieve a high enough ionic conductivity.
Researchers say the new "super-lattice" material produced at the Complutense University maintains ionic conductivity near room temperatures. The material was created by alternating layers of an ion conductive material that is currently used in fuel cells (Yttria-stabilized zirconia) with a dielectric material (Strontium titanate). The combination of these two materials with very diverse crystalline structures has produced a rare atomic disposition full of gaps that act as a path for the flow of ions. This results in a ‘colossal ionic conductivity’ at the transition surface between the two materials at room temperature.
The molecular structure of this material has been analyzed at the Oak Ridge National Laboratory (USA) using a scanning transmission electron microscope with a resolution of less than 0,1 nanometres (the approximate size of an hydrogen atom). The researchers were very surprised to see in the images a perfectly structured growth at the atomic level, in spite of the very different structures of the materials. As a matter of fact, this result was absolutely unexpected according to the experience gathered from the analysis of this type of structures.
An even greater surprise was the high degree of ionic conductivity, measured at the Universidad Complutense in collaboration with the Universidad Politécnica de Madrid. It is about a hundred million times higher than that of materials used at present for the fabrication of fuel cells and it is this characteristic that could allow their use at room temperature, permitting extensive use of hydrogen as an alternative energy source.
The collaborative paper by researchers at the Universities of Madrid and ORNL has been published in the Journal Science.