Role of Nanomorphology and Interfacial Structure of Platinum Nanoparticles in Catalyzing the Hydrogen Oxidation Reaction

This work studies the hydrogen oxidation reaction using both single mesoporous platinum nanoparticles (r(np) = 23.1 +/- 2.1 nm) and low density random arrays of material. The activity of the platinum catalyst, toward the oxidation of hydrogen, is shown to be potential dependent and exhibits two peaks in activity. These peaks in activity are measured at both random arrays of platinum nanoparticles and at the single entity scale. This alteration in the particle activity is directly reflected in the variation of the electrochemical current. These peaks in current do not relate to a mass-transport limitation of the reaction, and at high overpotentials the oxidation reaction becomes fully inhibited. This potential dependency is revealed at high current densities and arises due to the sensitivity of the reaction rate to the platinum interfacial structure; the decrease in activity [at ca. -0.2 V vs Ag/AgCl (1 M KCl) in a nonbuffered condition] directly correlates with the potential at which underpotential deposited hydrogen is removed from the catalytic interface. The contribution of the internal mesoporous nanoparticle structure toward the total particle catalytic activity is further evidenced through comparison of the time-current transients recorded for individual nanoparticles of differing morphology (solid vs mesoporous) and by evidencing the sensitivity of the single particle catalytic activity to the used supporting electrolyte concentration.