Oscillations and Bistability in the Catalytic Formation of Water on Rhodium in High Electric Fields

A comprehensive theory for the adsorption of H(2) and O(2) on a nanometric rhodium field emitter tip is developed to describe the equilibrium properties, the adsorption-desorption kinetics, as well as its observed nonlinear reaction behavior and oscillatory states. The basis is a kinetic mean-field model for hydrogen, oxygen, and subsurface oxygen which takes into account the anisotropy of the tip's surface. The resulting model reproduces the correct anisotropy, period and form of the oscillations, as well as the bistability diagram for a varying temperature, hydrogen pressure, and external electric field as observed in a field ion microscope.