Monolayer germanium monochalcogenides (GeS/GeSe) as cathode catalysts in nonaqueous Li-O₂ batteries

The development of novel cathode catalysts is of great importance to the practical applications of nonaqueous lithium oxygen (Li-O₂) batteries. Here by using first-principles calculations, we revealed the catalytic mechanism and evaluated the catalytic activity of monolayer germanium monochalcogenides (2D-GeXs, X = S/Se) as cathode catalytic materials. For 2D-GeXs, Li₄O₄ with a ring-like structure is the final discharge product. The free energy diagram demonstrates that 2D-GeSe is more energetically favorable than 2D-GeS due to its considerably lower oxygen reduction reaction (ORR) overpotential (0.94 V) and oxygen evolution reaction (OER) overpotential (1.30 V), which originate from its weaker binding with LiO₂ and stronger binding with the inserted Li atom. The analyses on electronic properties elucidate that the final product of Li₄O₄ on 2D-GeSe induces the semiconductor to semi-metal transition. Our results reflect that 2D-GeSe is an excellent candidate as a cathode material in nonaqueous Li-O₂ batteries, while 2D-GeS is not appropriate.