# Oxygen Bridge Governs OER via Deep Self-Reconstruction in Fe–Co Oxyhydroxides

## TL;DR

This paper shows how iron-rich catalysts can be designed to efficiently split water by optimizing oxygen bridge structures, improving the oxygen evolution reaction's performance and stability.

## Contribution

The study introduces a self-reconstruction strategy for Fe–Co oxyhydroxides that enhances OER activity and stability through oxygen bridge geometry optimization.

## Key findings

- The Fe0.42Co0.58OOH/NF catalyst achieved an overpotential of 220 mV at 10 mA·cm−2 and a Tafel slope of 31.9 mV·dec−1.
- Dynamic oxygen bridge transitions during reconstruction improved structural robustness and active-site density.
- Fe3+–O–Fe3+ units synergized with Co4+ species to activate the lattice oxygen mechanism, enhancing OER kinetics.

## Abstract

The oxygen evolution reaction (OER) in water splitting involves complex multi-electron–proton transfer processes and represents the rate-determining step limiting overall electrolysis efficiency. Developing non-noble-metal catalysts with high activity and stability is therefore essential. Herein, a heterogeneous synthesis strategy was employed to in situ construct an iron-rich layered sulfate precursor (Fe0.42Co0.58-SO4/NF) on nickel foam, which underwent deep self-reconstruction in alkaline electrolyte to form nanoflower-like Fe0.42Co0.58OOH/NF. The optimized catalyst maintained its iron-rich composition and hierarchical structure, delivering outstanding OER performance with an overpotential of 220 mV at 10 mA·cm−2, a Tafel slope of 31.9 mV·dec−1, and stability exceeding 12 h at 600 mA·cm−2. Synchrotron analyses revealed dynamic transitions between mono-μ-O and di-μ-O Fe–M (M = Fe, Co) oxygen bridges during reconstruction, which enhanced both structural robustness and active-site density. The Fe-rich environment promoted the formation of Fe3+–O–Fe3+ units that synergized with Co4+ species to activate the lattice oxygen mechanism (LOM), thereby accelerating OER kinetics. This work elucidates the key role of oxygen-bridge geometry in optimizing catalytic activity and durability, providing valuable insights into the rational design of Fe–Co-based non-noble-metal catalysts with high iron content for efficient water oxidation.