# Nanoionics Drastically Accelerating Mass Transfer at Elevated Temperatures over 750 °C

## TL;DR

This paper shows that nanoionics can be stable and highly conductive at very high temperatures, enabling new applications in energy devices.

## Contribution

A novel design principle for stable nanoionics using ALD films at temperatures over 750 °C is introduced.

## Key findings

- Nanoionics achieved 7 orders of magnitude higher conductivity than bulk materials.
- ALD films remained stable after 500 h at 750 °C and 1000 h at 850 °C.
- Nanoionics formed conformal layers with uniform grain sizes of ~15 nm.

## Abstract

Nanoionics were previously considered thermally unstable
and infeasible
for devices operating above 500 °C. Here, we elucidate the design
principle for establishing stable nanoionics from various oxides.
We utilized reversible solid oxide cells (SOCs) as the test bed and
implemented nanoionics using atomic layer deposition (ALD). We demonstrate
a straightforward, interface-controlled, practical approach to render
a conformal, ∼15 nm thick ALD film, which initially thermodynamically
favors the formation of a solid solution with the substrate into surface
nanoionics with single or double layers of nanograins with random
crystal orientations. The nanoionics exhibited conductivity estimated
to be 7 orders of magnitude higher than that of their bulk-scale counterpart.
They demonstrated conformability with uniform grain sizes of ∼15
nm, even after electrochemical operation for ∼500 h at 750
°C and 1000 h at 850 °C. The thermal stability and conductivity
of such nanoionics represent a conceptual and technological framework
in nanoionics.