Fuel cells are gaining in importance as an alternative to battery-operated electromobility in heavy traffic, especially since hydrogen is a CO2-neutral energy carrier if it is obtained from renewable sources. For efficient operation, fuel cells need an electrocatalyst that improves the electrochemical reaction in which electricity is generated. The platinum-cobalt nanoparticle catalysts used as standard today have good catalytic properties and require only as little as necessary rare and expensive platinum. In order for the catalyst to be used in the fuel cell, it must have a surface with very small platinum-cobalt particles in the nanometer range, which is applied to a conductive carbon carrier material. Since the small particles and also the carbon in the fuel cell are exposed to corrosion, the cell loses efficiency and stability over time.
A research team has developed an electrocatalyst for hydrogen fuel cells that, in contrast to the catalysts commonly used today, does not require a carbon carrier and is therefore much more stable. The new process is industrially applicable and can be used to further optimize fuel-cell-powered vehicles without CO2 emissions. The catalyst achieves high performance and promises stable fuel cell operation, even at higher temperatures and high current density.
In a hydrogen fuel cell, hydrogen atoms are split to generate electrical power directly from them. For this purpose, hydrogen is fed to an electrode where it is split into positively charged protons and negatively charged electrons. The electrons flow off via the electrode and generate electric current outside the cell, which drives a vehicle engine, for example. The protons pass through a membrane that is only permeable to protons and react on the other side on a second electrode coated with a catalyst (here, from a platinum-cobalt alloy network) with oxygen from the air, thus producing water vapor. This is discharged via the “exhaust.”
For the fuel cell to produce electricity, both electrodes must be coated with a catalyst. Without a catalyst, the chemical reactions would proceed very slowly. This applies in particular to the second electrode, the oxygen electrode; however, the platinum-cobalt nanoparticles of the catalyst can “melt together” during operation in a vehicle. This reduces the surface of the catalyst and therefore the efficiency of the cell. In addition, the carbon normally used to fix the catalyst can corrode when used in road traffic. This affects the service life of the fuel cell and consequently the vehicle. Previous similar catalysts without a carrier material always only had a reduced surface area. Since the size of the surface area is crucial for the catalyst’s activity and hence its performance, these were less suitable for industrial use.
The researchers incorporated a special process called cathode sputtering. With this method, a material’s individual components (here, platinum or cobalt) are dissolved (atomized) by bombardment with ions. The released gaseous atoms then condense as an adhesive layer. With the sputtering process and subsequent treatment, a very porous structure can be achieved, which gives the catalyst a high surface area and is self-supporting at the same time. A carbon carrier is therefore unnecessary.