Revisiting the Origin of Low Work Function Areas in Pattern Forming Reaction Systems: Electropositive Contaminants or Subsurface Oxygen?

Abstract

In pattern-forming reaction systems, the conversion of macroscopic islands of chemisorbed oxygen into low work function (WF) areas has been attributed to formation of a subsurface oxygen species. We prepare micrometer-sized oxygen islands on Pt(100) and Pt(110) by reaction fronts in catalytic CO oxidation in the 10 −6 mbar range. By applying electron microscopy with chemical and structural sensitivity, we characterize their chemical composition upon annealing in vacuum. On Pt(100) we reproduce the previously reported transformation from high to low WF, estimating a relative change Δϕ ≈-0.8 eV with respect to the CO covered surface. We demonstrate that the change in WF is due to a strong enrichment of electropositive contaminants, namely Ca and Ti, in the oxygen islands. On Pt(110) predosed with Cs, we find that the alkali metal accumulates in the oxygen islands, producing Δϕ ≈ −0.4 eV relative to CO−adlayer. Our experiments suggest that the interpretation of the low WF areas as due to "subsurface oxygen" should be revised and attributed to the local enrichment of electropositive species.

Adsorption and Hydrogenation of CO2 on Rh Nanosized Crystals: Demonstration of the Role of Interfacet Oxygen Spillover and Comparative Studies with O2, N2O, and CO

“…More generally, the reactivity of CO 2 is important in the context of CO 2 revalorization, and a better understanding of the processes, at the molecular level, might lead to the design of a more efficient catalyst toward the conversion of CO 2 into, for example, methanol or higher alcohols. The question regarding the presence of O(sub) 80 and O(bulk) is important in the frame of catalyst aging and the evolution of catalytic properties 81 of Rh nanoparticles with time.…”

Oxygen Adsorption, Subsurface Oxygen Layer Formation and Reaction with Hydrogen on Surfaces of a Pt–Rh Alloy Nanocrystal

“…Oxygen adsorbed on the metal surface can as well diffuse under the surface. The existence of subsurface oxygen was observed for the platinum group metals, comprising Pt, Pd, Rh [44][45][46][47][48][49][50][51]. PEEM studies clearly attributed lowering of work function during oxygen adsorption on Pt(100) to subsurface oxygen diffusion [52].…”