Bjoern Luerßen

Microspectroscopy at a moving reduction front in zirconia solid electrolyte

Employing photoelectron emission microscopy (PEEM) and scanning photoelectron microscopy (SPEM) the surface reduction of zirconia solid electrolyte under cathodic polarisation has been observed in situ. A microstructured platinum film and a porous platinum paste have been used as electrodes. Starting from the three phase boundary (tpb) between platinum, solid electrolyte and the gas phase, a reduction front was detected in PEEM by a significant local work function decrease. Local XPS shows that zirconia has been reduced behind the front, resulting in the presence of Zr atoms in a low oxidation state and Zr0.

Selforganization of alkali metal on a catalytic metal surface

The spatial distribution of potassium on an Rh(110) surface during the catalytic O2+H2 reaction is investigated employing photoelectron emission microscopy (PEEM) and scanning photoelectron microscopy (SPEM) as spatially resolving in situ methods. Depending on the reaction conditions, potassium condenses reversibly into macroscopic islands where it is coadsorbed with oxygen. Mass transport of potassium with the reaction fronts is observed. Differences in the mobility and in the bonding strength of potassium on the “reduced” and on the oxygen-covered surface areas are considered to be the key factors for the formation of the stationary concentration patterns.

Electrocatalysis on Pt/YSZ electrodes

Electrochemical polarization of porous metal electrodes on solid electrolytes often leads to an increase of their catalytic activity in heterogeneous reactions. Thin microstructured Pt films on single crystalline YSZ (yttria stabilized zirconia) are investigated as structurally and geometrically well-defined model systems in order to understand the origin of this effect. Photoelectron emission microscopy (PEEM) and scanning photoelectron microscopy (SPEM) have been applied as spatially resolving methods in situ to study the processes in the vicinity of the three-phase boundary (tpb). Measurements with SPEM show that atomic oxygen is created under anodic polarization and covers the Pt film homogeneously. A specific spillover species is not found, rather the formation of atomic oxygen is detected, which has the same O1s binding energy as chemisorbed oxygen from the gas phase.

Promotion of catalytic reactions by electrochemical polarization

Electrochemical polarization of metal electrodes on solid electrolytes may result in a pronounced promotion of their catalytic activity. A phenomenological analysis of this promotion effect is developed from simple thermodynamic and kinetic arguments and is compared with existing models. The strong modification of catalytic activity is related to the electrochemically controlled change of the chemical potential of a mobile component at the electrode interface within the (solid state) galvanic cell. Empirical relations reported in the literature are interpreted in terms of this chemical potential change.