Oct 7 2008
A team of scientists from the Universidad Complutense de Madrid (UCM) has designed a material with such high ion conductivity that it allows the use of hydrogen as a clean fuel. The research work has been published in the prestigious journal "Science".
Fuel cells are the foundation of this technology which, if it becomes industrially viable, would represent the beginning of an energy revolution that would replace the current fossil fuel based system by a model based on hydrogen. This would be an energy source that is practically endless and since it only generates water as a combustion by-product, it is ecologically friendly.
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 a temperature of up to 800 degrees Celsius is needed to achieve a high enough ionic conductivity. Therefore the challenge they must overcome is how to reduce the working temperature of this technology to an acceptable range.
Colossal ionic conductivity
Towards this end, a research group at the Complutense University has produced a material with a new structure 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.
The image of the molecular structure of this material has been obtained 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. This characteristic could allow their use at room temperature, permitting extensive use of hydrogen as an alternative energy source.