Defect-engineered exfoliated MoS₂/rGO hybrids for dual-function oxygen electrocatalysis and high-capacity Li-O₂ batteries

Pristine bulk MoS₂ (BMS) and the bulk MoS₂@reduced graphene oxide (BMR) composites are synthesized via a single-step hydrothermal method, while exfoliated MoS₂ (EMS) nanosheets and their respective composites (EMR) with the reduced graphene oxide (rGO) are prepared using a simple sonication-assisted route. The synthesized catalysts are systematically characterized to elucidate their phase composition, defect chemistry and morphology, and were evaluated as bifunctional oxygen electrocatalysts using rotating ring-disk electrode (RRDE) analysis. Among all the catalysts, the exfoliated MoS₂ containing 80 wt% rGO (EMR80) catalyst achieves a positive ORR onset potential of 0.90 V, a high limiting current density of 6.85 mA cm−2, very low OER overpotential of 290 mV, and a low bifunctionality index of 0.21 V. The improved electrocatalytic performance arises from the 1T phase of exfoliated MoS₂, which possesses defect-rich features, such as few MoS₂ layers having reduced crystallite size and increased lattice disorder. When applied as the air cathode in a coin-type Li-O₂ battery (LOB), the EMR80 catalyst delivers an impressive discharge capacity of 17000 mA h g−1 at a current density of 100 mA g−1 with a low charge overpotential of 1 V.