Experimental Design for Voltage Driven Tracer Incorporation and Diffusion Studies on Oxide Thin Film Electrodes

Abstract

The effect of an applied overpotential on oxygen isotope incorporation and diffusion in oxide thin film electrodes is investigated by a novel experimental approach. A special electrode geometry leads to in-plane electron flow, perpendicular oxide ion flow and a well-defined laterally varying driving force. This design allows one to obtain a series of tracer depth profiles induced by a range of overpotentials on one and the same thin film. The approach was applied to La 0.8 Sr 0.2 MnO 3 (LSM) thin films deposited by pulsed laser deposition (PLD) on yttria stabilized zirconia (YSZ) single crystals. Tracer depth profiles were measured by secondary ion mass spectrometry (SIMS). These depth profiles include examples of pronounced apparent uphill diffusion that can be explained by considering an interplay of polarization-induced changes in stoichiometry within the LSM grains combined with fast oxygen transport along the grain boundaries.

Electrochemical Polarization Dependence of the Elastic and Electrostatic Driving Forces to Aliovalent Dopant Segregation on LaMnO3

“…The requirement for this condition is that the whole region of the electrode surface should be electrochemically active so that the ionic current is not drained solely through the near-WE region; this condition is met when the electronic current is far higher than the ionic current ( I elec ≫ I ion ). Huber et al showed that LSM had the appropriate electronic and ionic properties which satisfied such a condition. We have also confirmed the presence of a linear potential variation across the film surface, by in situ core-level photoemission measurements of LSM under polarization (Figures S2 and S3 in the Supporting Information).…”

“…The setup for the simultaneous probing of a range of polarization (Figure 1) is based on the recent design by Huber et al 57 The sample bias is applied to a Pt contact sputtered onto the electrode film, while the counter electrode (CE), the porous Pt layer on the back side of the YSZ electrolyte, is connected to ground. In contrast to a traditional CE, this model electrode is in electrical contact with a stripe of Pt on the working electrode (WE) side of the electrolyte crystal, connecting it to the thin-film electrode.…”

“…Illustration of the experimental setup designed for applying a continuous polarization gradient across the top electrode surface . Abbreviations: CE, counter electrode; WE, working electrode; LDM, La 0.8 D 0.2 MnO 3 (D = Ca, Sr, Ba); YSZ, Y 2 O 3 -stabilized ZrO 2 , 8 mol % Y 2 O 3 .…”

“…In the analysis, we establish a connection to the two reported driving forces behind segregation. We employ a recently developed electrochemical cell configuration utilizing a polarization gradient 57 across a thin-film electrode to obtain a large range of anodic or cathodic oxygen chemical potentials on one single sample. We obtain effective oxygen pressures spanning a range from 10 −16 to 10 15 atm.…”

Determination of Oxygen Diffusion and Surface Exchange Coefficients of Mixed Ionic-Electronic Conductors by Oxygen Semi-Permeation Methods

“…Additionally, two of these techniques could be used in combination 47,50 . More recently, the effect of applying an overpotential to the oxygen isotope exchange and diffusion in oxide thin film electrodes has been investigated 51 . An oxygen stoichiometry re-equilibration method under reducing conditions using solid electrolyte coulometry 52 or a thermogravimetric relaxation technique 53 has also been proposed.…”