Metal-insulator transition of the reduced surface of yttria-stabilized zirconia near Pt electrodes

TL;DR

This study reveals that the reduced surface of yttria-stabilized zirconia (YSZ) near platinum electrodes undergoes a metal-insulator transition, creating an extended triple phase boundary that varies with environmental conditions.

Contribution

It demonstrates that the reduced YSZ surface exhibits a metal-insulator transition, expanding the traditional atomic-scale triple phase boundary to a micrometer-scale region.

Findings

YSZ surface undergoes a metal-insulator transition near Pt electrodes

The conducting region can extend several microns depending on conditions

Extended triple phase boundary influences electrochemical reactions

Abstract

The electrochemical reactions of solid oxide fuel cells occur in the region where gas-phase species, electrode, and electrolyte coincide. When the electrode is an ionic insulator and the electrolyte is an electronic insulator, this `triple phase boundary' is assumed to have atomic dimensions. Here we use photoemission electron microscopy to show that the reduced surface of the electrolyte yttria-stabilized zirconia (YSZ) undergoes a metal-insulator transition near Pt negative electrodes. YSZ's electron conducting region functions as an extended triple phase boundary that can be many microns in size, depending on oxygen pressure, temperature, applied voltage, and time.