05/29/2015
Fuel cells with less platinum thanks to novel aerogel catalyst
Fuel cells are power sources based on direct conversion of hydrogen into electricity. Great advantage of the fuel cells is the fact, that neither carbon dioxide no other undesirable substances are generated in this process. Pure water is a solely by-product of the reaction. These so named low temperature polymer electrolyte fuel cells (PEFC) have been already successfully tested in cars and busses. More research is anyway necessary in order to improve their applicability and to reduce costs. Scientists from TU Dresden and from the Paul Scherrer Institute (PSI, Villigen, Switzerland) have designed, developed and characterized a new nanomaterial, which allows several time improvement of efficiency and durability of this kind of cells by simultaneous reduction of the material costs.
A typical PEFC electrochemically converts hydrogen (as fuel) and oxygen (taken from air) into water and electricity. One of the critical steps of the process is the reduction of oxygen on the positive electrode of the cell. The reaction is very slow at the normal conditions and can be sufficiently accelerated only in presence of suitable noble metal (e.g. platinum) catalysts. Platinum nanoparticles utilized for this purposes are normally immobilized on the surface of highly porous carbonaceous materials, which provide mechanical strength to the catalyst. Unfortunately, carbon-based materials undergo corrosion, which leads to reduced efficiency of whole process. This motivates a search for catalysts which can operate without substrate material, so named self-supported catalysts.
3-dimensional aerogels consisting of a self-supported nanostructure based solely on nanoparticles (platinum and palladium) are the materials developed by the international team from TU Dresden (Prof. Alexander Eychmüller's group) and PSI (Prof. Thomas J. Schmidt's group). The demonstrated efficiency of the oxygen reduction on these new aerogel-electrodes is about 5 times higher compared to that provided by comprehensive commercially available catalysts. This shows the dramatic potential of the aerogel materials for the reduction of the operational costs of fuel cells as only one fifth of the amount of noble metals is necessary for the conversion of the same amount of oxygen. Another advantage of the aerogel materials includes their surprisingly high durability, which is presently not enough understood and will be an object of further studies. Moreover, the approaches developed to create nanometallic aerogels are quite flexible and allow introduction of other nanomaterials and functional units in the 3-dimensional nanostructure which greatly extends potential impact of aerogel materials to other application directions, e.g. heterogeneous catalysis, waste treatment and sensors.
Source: TU Dresden