# Valence‐Engineering of CeO2 Redox Modulator Boosts the Oxygen Electrocatalysis Performance in Fe/Co Dual‐Atom Catalyst

## TL;DR

Valence-engineered CeO2 improves the performance and durability of Fe/Co dual-atom catalysts in zinc-air batteries by managing oxidative by-products and electron transfer.

## Contribution

Valence-engineered CeO2 is introduced as a redox modulator to enhance the stability and activity of Fe/Co dual-atom catalysts.

## Key findings

- Valence-engineered CeO2 scavenges oxidative by-products during oxygen reduction reaction (ORR), improving durability.
- CeO2 accelerates electron transfer and lowers the Co redox potential during oxygen evolution reaction (OER).
- Zinc-air batteries with FeCo─N─C/CeO2 air electrodes achieved 335 mWcm−2 power density with no significant degradation after 1000 hours.

## Abstract

Dual‐atom nitrogen‐doped carbon catalysts have garnered considerable interest as air electrodes for rechargeable zinc‐air batteries (ZABs), owing to their outstanding bifunctional oxygen electrocatalytic activity. Nonetheless, their practical implementation is hindered by durability issues during the oxygen reduction reaction (ORR), as the active sites are degraded by the oxidative by‐products. Furthermore, the sluggish electron transfer obstructs the oxidation state transitions of Co/Fe centers to limit the oxygen evolution reaction (OER) activity. Here, the valence engineering is performed in CeO2 redox modulator that is composed with Fe/Co dual‐atom catalyst (FeCo─N─C), to resolve the stability and activity issues. The valence‐engineered CeO2 with a fast Ce4+/Ce3+ redox process can efficiently scavenge the highly oxidative by‐products in ORR to improve the durability. In addition, the interaction of CeO2 with FeCo─N─C can accelerate electron transfer and lower the Co redox potential during the OER. The ZABs assembled with optimized FeCo─N─C/CeO2 as the air electrode display a maximum power density of 335 mWcm−2 without significant deterioration after ≈1000 h of continuous cycling. Therefore, compositing with valence‐engineered CeO2 provides a simple and effective solution to resolve the stability and activity issues of FeCo─N─C as an air electrode.

Valence‐engineering of CeO2 redox modulator can remove the highly oxidative by‐products and accelerate the oxidation state transitions of Co/Fe centers in FeCo dual‐atom catalyst during oxygen reduction/evolution electrocatalysis. Therefore, the stability and activity issues are resolved, significantly enhancing the overall performance when used as an air electrode in zinc‐air batteries.