The University of Tokyo, in collaboration with Toyota Motor Corporation, Toyota Central R & D Labs, and Quantum Science and Technology Research and Development Organization, promotes oxidation on the platinum nanoparticle positive electrode catalyst of polymer electrolyte fuel cells by the coexistence of oxygen and water. For the first time, it was clarified experimentally that the performance of the

　The polymer electrolyte fuel cell developed as a highly efficient and clean power source uses carbon in which platinum nanoparticles of the catalyst are dispersed in the positive electrode.However, when a platinum catalyst is used, there is a problem that an activation overvoltage is generated by humidification and the cell voltage is lowered.To solve this problem, first-principles calculations were carried out, and it was predicted that the promotion of oxidation of the platinum catalyst was caused by the co-adsorption of oxygen and water, but this has not yet been clarified experimentally.

　Therefore, the joint research group used high-resolution fluorescent X-ray absorption spectroscopy at the beamline BL8XU of the large-scale radiation facility SPring-11.Platinum nanoparticles with an average particle size of 2 to 3 nanometers used for the positive electrode were reacted with oxygen and water, and their oxidation state was analyzed.

　As a result, it was detected that the coexistence of oxygen and water promoted the oxidation of platinum, and the theoretical prediction was experimentally proved.It is also explained that the cause of this is that oxygen is co-adsorbed on platinum with water, which stabilizes the reaction and slows the progress of the reaction, resulting in more overvoltage.

　In addition, we also analyzed platinum-cobalt alloy nanoparticles with excellent catalytic properties.It was discovered that the co-adsorption of oxygen and water hardly promotes oxidation.It has also been found that as the particle size of the nanoparticle catalyst increases, the oxidation-promoting effect of water diminishes.

　Based on this result, the development of a method to reduce the amount of platinum used by alloying and to eliminate water on the surface of the platinum catalyst is progressing, and it is expected that the performance of the fuel cell will be improved and the cost will be reduced.

Paper Information: [Scientific Reports] Wetting Induced Oxidation of Pt-based Nano Catalysts Revealed by In Situ High Energy Resolution X-ray Absorption Spectroscopy