Role of Geometric Relaxation in Oxygen Binding to Metal Nanoparticles.

Better oxygen reduction catalysts are needed to improve the efficiency and lower the cost of fuel cells. Metal nanoparticles are good candidates because their catalytic properties can differ from bulk metals. Using density functional theory calculations, we studied the geometric relaxation of metal nanoparticles upon oxygen binding. Because bound oxygen species are intermediates in the oxygen reduction reaction, the binding of oxygen can be correlated to catalytic activity. Our results show that Pt and Au are unique in that they exhibit a larger structural deformation than other metals, which is pronounced for particles with fewer than 100 atoms. The structural deformation induced by atomic oxygen binding stabilizes the oxidized state and thus reduces the catalytic activity of Pt-based random alloys. We show that the catalytic activity of Pt can be improved by forming alloys with less deformable metals.