Bifunctionally Electrocatalytic Bromine Redox Reaction by Single-Atom Catalysts for High-Performance Zinc Batteries

Abstract

Aqueous zinc-bromine (Zn||Br<inf>2</inf>) batteries are regarded as one of the most promising energy storage devices due to their high safety, theoretical energy density, and low cost. However, the sluggish bromine redox kinetics and the formation of a soluble tribromide (Br<inf>3</inf>⁻) hinder their practical applications. Here, it is proposed dispersed single iron atom coordinated with nitrogen atoms (FeN<inf>5</inf>) in a mesoporous carbon framework (FeSAC-CMK) as a conductive catalytic bromine host, which possesses porous structure and electrocatalytic functionality of FeN<inf>5</inf> species for enhanced confinement and electrocatalytic effect. The active FeN<inf>5</inf> species can fix the bromine (Br⁰) species to suppress the formation of Br<inf>3</inf>⁻ effectively and bifunctionally catalyze the bromide (Br⁻)/Br° conversion. These free up 1/3 Br⁻ locked by Br<inf>3</inf>⁻ complexing agent for enhanced bromine utilization efficiency and conversion reversibility. Accordingly, the Zn||Br<inf>2</inf> battery with FeSAC-CMK delivers an impressive specific capacity of 344 mAh g⁻¹ at 0.2 A g⁻¹ and superior rate capability with 164 mAh g⁻¹ achieved even at 20 A g⁻¹, much higher than that of inactive CMK (262 mAh g⁻¹ at 0.2 A g⁻¹; 6 mAh g⁻¹ at only 8 A g⁻¹). Furthermore, the battery demonstrates excellent cycling performance of 88% capacity retention after 2000 cycles.