Accordion-Like Structure MBene with Ordered Metal Vacancies as Catalytic Host Material to Enhance Se Reaction Kinetics in Aqueous Cu-Se Batteries

Aqueous copper-selenium (Cu-Se) batteries have received increasing attention in energy storage research due to their high theoretical specific capacity and inherent safety. However, the sluggish reaction kinetics of the selenium (Se) cathode hinder its development. Herein, an accordion-like structure transition metal boride (Mo_4/3B₂T_z MBene) with ordered metal vacancies is synthesized and employed as Se catalytic host material for aqueous Cu-Se batteries. The Mo_4/3B₂T_z host material exhibits a unique layered structure, abundant active sites, and high electrical conductivity, which significantly improves the kinetic properties of the selenium redox reaction in aqueous Cu-Se batteries. As a result, the Se-Mo_4/3B₂T_z cathode delivers a high discharge capacity of 1010 mAh g⁻¹ at 1 A g⁻¹ and greatly enhances rate performance with a reversible capacity of 693 mAh g⁻¹ at 25 A g⁻¹. Meanwhile, the Se-Mo_4/3B₂T_z cathode maintains an impressive 755 mAh g⁻¹ discharge capacity after 1500 cycles at 20 A g⁻¹. Furthermore, the conversion mechanism of aqueous Cu-Se batteries is illustrated by different characterization methods and density functional theory calculations. This work introduces a distinctive approach to accelerating the reaction kinetics of aqueous Cu-Se batteries via MBene-based catalytic host material.