# Nickel-Induced Lattice Defects Limit Proton Uptake in Barium Zirconate Electrolytes

## TL;DR

Nickel in a type of ceramic material reduces its ability to conduct protons by creating defects that trap oxygen and hinder hydration.

## Contribution

The study identifies two novel mechanisms by which nickel impairs proton conductivity in barium zirconate electrolytes.

## Key findings

- Nickel forms defect clusters with Yb acceptors, trapping oxygen vacancies and reducing hydration.
- Excess B-site cations from NiO addition create antiphase boundaries that deplete bulk acceptors.
- These mechanisms are quantitatively linked to reduced hydration as measured by thermogravimetric analysis.

## Abstract

Nickel provides essential
catalytic properties for hydrogen electrodes
in proton-conducting ceramic electrochemical cells. However, Ni diminishes
the hydration capability and proton conductivity when incorporated
into electrolyte materials including BaZr0.8Yb0.2O3−δ studied here. Through semiquantitative
atomic-resolution scanning transmission electron microscopy, density
functional theory simulations, X-ray total scattering, and absorption
spectroscopy, we reveal that Ni forms point defect clusters with the
Yb acceptors wherein oxygen vacancies are trapped and resist hydration.
The resulting effective acceptor concentration is described by point
defect reactions in quantitative agreement with thermogravimetric
measurements of hydration for samples substituted with 2–5
mol % Ni by BaNiO2 addition. Moreover, excess B-site cations
due to NiO addition induce the formation of antiphase boundaries (APBs)
that are enriched in Yb and thereby deplete the bulk of acceptors,
further suppressing hydration. The adverse effects of Ni are thereby
resolved into two novel mechanisms, opening new avenues in point defect
engineering for high-performance electrolytes.