# Revealing Progressive Degradation of Cobalt Oxide Nanoparticles During Thermochemical Redox Cycling via Operando STEM-EELS

## TL;DR

Researchers used advanced imaging to study how cobalt oxide nanoparticles degrade during energy storage cycles, finding that their performance drops after the first cycle due to structural changes.

## Contribution

A novel method using operando STEM-EELS is introduced to observe cobalt oxide nanoparticle degradation during thermochemical cycling at high resolution.

## Key findings

- Reaction kinetics of cobalt oxide nanoparticles decrease after the first cycle due to sintering and nanostructural densification.
- Atmospheric conditions affect reaction transition temperatures but have limited impact on sintering over multiple cycles.
- Long-term durability of cobalt oxide nanoparticles depends on synthetic or nanostructural modifications rather than environmental factors.

## Abstract

Metal oxides are promising materials for long-duration
thermochemical
energy storage. Efforts to characterize their reaction kinetics, conversion
rate, and morphological evolution during thermochemical cycling have
largely focused on bulk and microscale measurements. However, the
design of nanostructured metal oxides could improve the reaction reversibility
and kinetics, warranting the development of platforms to investigate
how these materials behave at the nanoscale. Here, we demonstrate
the use of correlative, time-resolved electron energy loss spectroscopy
and imaging in an environmental transmission electron microscope for
studying the thermochemical cyclability of cobalt oxide nanoparticles
with high spatial and temporal resolution. The spectroscopic data
reveal a striking decrease in reaction kinetics after the first cycle,
resulting from sintering-driven nanostructural densification. Comparison
between cycling in humid and dry air shows that atmospheric conditions
can modulate reaction transition temperatures but have limited effects
on sintering over multiple cycles, suggesting long-term durability
will instead rely on synthetic and/or nanostructural modifications.