Hydrogen Evolution at a Single Supported Nanoparticle: A Kinetic Model

Abstract

A kinetic model of the processes during hydrogen evolution at a single Pd nanoparticle supported on an Au substrate is studied. It builds the theoretical framework for results of currently performed STM measurements on this system. The objective of the theory is to establish relations between measured transients and underlying processes. It, thereby, helps to implement the routines for the determination of kinetic parameters from transient currents and supplements the characterization of the Pd/Au system. The balance of hydrogen involves interfacial processes on the Pd/Au substrate surface, hydrogen diffusion in the bulk electrolyte and hydrogen oxidation at the tip. The key parameter of the model is the rate of hydrogen desorption from the Pd surface. If this rate is small hydrogen will spillover from the Pd particle and diffuse on the Au surface from where it will be subsequently released. Thereby, large amounts of hydrogen can be stored on the surface. It is demonstrated, that this mechanism complies with the high turnover rates at the smallest catalyst particles and characteristic time scales observed in experiment.