Electrocatalysis under Conditions of High Mass Transport: Investigation of Hydrogen Oxidation on Single Submicron Pt Particles Supported on Carbon

The mechanism and kinetics of the hydrogen oxidation reaction (hor) has been investigated using carbon-supported single particles of Pt electrocatalyst with radii as small as 40 nm. The high mass transport rates on such small particles enable us to investigate the rapid kinetics of the hor in the absence of diffusion limitations. Surface kinetic controlled polarization curves during the electrochemical oxidation of hydrogen molecules in acid solution have been obtained in the entire H UPD region, showing features obviously different from those obtained on normal micrometer electrodes or in RDE experiments. For instance, two current plateaus rather than one are seen during the steady-state polarization of the hor on electrodes made of small particles. Upon decreasing the size of the Pt particles, the two current plateaus show greater separation and become better defined. A theoretical model for the steady-state polarization of the hor has been developed in which UPD H atoms of various states are considered...