Fluorine-Lodged High-Valent High-Entropy Layered Double Hydroxide for Efficient, Long-Lasting Zinc-Air Batteries

Abstract

Efficient and stable bifunctional oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) catalysts are urgently needed to unlock the full potential of zinc-air batteries (ZABs). High-valence oxides (HVOs) and high entropy oxides (HEOs) are suitable candidates for their optimal electronic structures and stability but suffer from demanding synthesis. Here, a low-cost fluorine-lodged high-valent high-entropy layered double hydroxide (HV-HE-LDH) (FeCoNi<inf>2</inf>F<inf>4</inf>(OH)<inf>4</inf>) is conveniently prepared through multi-ions co-precipitation, where F⁻ are firmly embedded into the individual hydroxide layers. Spectroscopic detections and theoretical simulations reveal high valent metal cations are obtained in FeCoNi<inf>2</inf>F<inf>4</inf>(OH)<inf>4</inf>, which enlarge the energy band overlap between metal 3d and O 2p, enhancing the electronic conductivity and charge transfer, thus affording high intrinsic OER catalytic activity. More importantly, the strengthened metal-oxygen (M−O) bonds and stable octahedral geometry (M−O(F)<inf>6</inf>) in FeCoNi<inf>2</inf>F<inf>4</inf>(OH)<inf>4</inf> prevent structural reorganization, rendering long-term catalytic stability. Furthermore, an efficient three-phase reaction interface with fast oxygen transportation was constructed, significantly improving the ORR activity. ZABs assembled with FeCoNi<inf>2</inf>F<inf>4</inf>(OH)<inf>4</inf>@HCC (hydrophobic carbon cloth) cathodes deliver a top performance with high round-trip energy efficiency (61.3 % at 10 mA cm⁻²) and long-term stability (efficiency remains at 58.8 % after 1050 charge–discharge cycles).