# Probing Surface Changes in Fe–Ni Oxide Nanocatalysts with a ToF-SIMS-Coupled Electrochemistry Setup and Principal Component Analysis

## TL;DR

The paper introduces a new method combining electrochemistry and ToF-SIMS with PCA to study surface changes in Fe–Ni oxide nanocatalysts during the oxygen evolution reaction.

## Contribution

A novel contamination-free electrochemistry-ToF-SIMS setup with PCA is introduced to track catalyst surface dynamics during OER.

## Key findings

- PVP-related fragments dominate in early stages, while metal and electrolyte species emerge after activation.
- Cyclic voltammetry treatment leads to progressive ligand depletion and interface changes.
- Electrolyte deposition analysis confirms PVP and Fe–Ni fragment leaching during OER.

## Abstract

Understanding catalyst
surface dynamics under operating
conditions
is essential for improving electrocatalytic performance. Here, we
present a novel approach combining electrochemical treatment with
contamination-free transfer to Time-of-Flight Secondary Ion Mass Spectrometry
(ToF-SIMS), followed by principal component analysis (PCA), to probe
surface and interfacial changes in Ni–Fe oxide nanoparticles
stabilized by polyvinylpyrrolidone (PVP) during the oxygen evolution
reaction (OER). The surface analysis at three distinct treatment stages
revealed distinct chemical fingerprints across pristine nanoparticles,
after exposure to 1 M KOH electrolyte, and after cyclic voltammetry
treatment. The results highlight a progressive transition from ligand-rich
to ligand-depleted interfaces, with PVP-related fragments dominant
in the early stages and metal- and electrolyte-derived species emerging
after activation. Complementary ToF-SIMS analysis of electrolyte deposited
on Si wafers after each treatment step confirms the concurrent leaching
of PVP and Fe–Ni-based fragments during OER. These findings
underscore the dynamic nature of catalyst–electrolyte interfaces
and demonstrate a robust strategy for monitoring surface-sensitive
chemical changes associated with the nanoparticles, especially during
the initial cycles of the OER.