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

Abstract

A comprehensive theory for the adsorption of H2 and O2 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.

Hydrogen Oxidation on Stepped Rh Surfaces: µm-Scale versus Nanoscale

“…Field-modified binding energies of adsorbates influence the adsorption kinetics, shifting the adsorption equilibrium of coadsorbed species. In the case of the catalytic reaction this results in a significant field-induced shift of the kinetic phase diagram as was directly demonstrated for the CO oxidation [42] and for the H 2 oxidation [43,44] by in situ FIM of corresponding reactions. Moreover, in the case of positively charged tip, high electric field may even lead to the field-induced grains of the Rh foil and by FEM for the Rh tip apex, with the latter characterized at atomic resolution by FIM.…”

Nonlinear Dynamics of Reactive Nanosystems: Theory and Experiments

“…The bistability is made visible by FIM via abrupt and unpredictable modifications of the surface state of these quadrants flipping in an independent manner from the oxidized to the metallic states, and vice-versa. A kinetic phase diagram has been established earlier for this system [13,14]. For high temperatures, i.e.…”

“…Although the probability is indeed bimodal as expected, one should make sure that it is indeed the chemistry of the reaction that is responsible for the bistability and the transition between the states. To show this, we consider here a "backbone" model for the reaction, which is a simplification of the complex, realistic model developed in [13,14]. We first take into account the fact that oxygen adsorbs dissociatively on the surface: (6.18) an equation in which * stands for an available active site on the surface of the metal.…”

Field Ion and Field Desorption Microscopy: Surface Chemistry Applications

“…Of course, CO oxidation is not a sole reaction that can be studied in FIM. Other reactions like H 2 oxidation 48,56,57 and NO reduction with H 2 58-60 were also studied using FIM/FEM, often in combination with AP techniques to get an insight into the chemical composition of the surface and intermediate species. Mostly, the Pt, Rh, and Pd tips were used as specimens in these studies due to the importance of these metals in automotive exhaust converters.…”