Reversible redox reactions in an epitaxially stabilized SrCoOx oxygen sponge

TL;DR

This study demonstrates that epitaxial stabilization of SrCoOx phases enables fast, reversible redox reactions at low temperatures, enhancing energy material performance without structural degradation.

Contribution

It introduces a method to lower redox temperatures in SrCoOx by epitaxial stabilization, allowing rapid reversible phase switching at 200-300°C.

Findings

Redox reactions occur within 1 minute at 200-300°C.

Epitaxial stabilization enables reversible phase switching.

Low Gibbs free energy difference facilitates fast redox activity.

Abstract

Fast, reversible redox reactions in solids at low temperatures without thermomechanical degradation are a promising strategy for enhancing the overall performance and lifetime of many energy materials and devices. However, the robust nature of the cation's oxidation state and the high thermodynamic barrier have hindered the realization of fast catalysis and bulk diffusion at low temperatures. Here, we report a significant lowering of the redox temperature by epitaxial stabilization of strontium cobaltites (SrCoOx) grown directly as one of two distinct crystalline phases, either the perovskite SrCoO3-{\delta} or the brownmillerite SrCoO2.5. Importantly, these two phases can be reversibly switched at a remarkably reduced temperature (200~300 {\deg}C) in a considerably short time (< 1 min) without destroying the parent framework. The fast, low temperature redox activity in SrCoO3-{\delta} is attributed to a small Gibbs free energy difference between two topotatic phases. Our findings thus provide useful information for developing highly sensitive electrochemical sensors and low temperature cathode materials.