Multiwall carbon nanotubes loaded with MoS2 quantum dots and MXene quantum dots: Non–Pt bifunctional catalyst for the methanol oxidation and oxygen reduction reactions in alkaline solution

We synthesized a novel composite of multiwall carbon nanotubes (MWCNTs) decorated with MoS 2 quantum dots (MoS 2 QDs) and Ti 3 C 2 T x QDs (denoted by MoS 2 QDs@Ti 3 C 2 T x QDs@MWCNTs), of which MoS 2 QDs and Ti 3 C 2 T x QDs were separately prepared by exfoliating MoS 2 and Ti 3 C 2 T x MXene nanosheets by the hydrothermal method. It showed that the as–prepared MoS 2 QDs@Ti 3 C 2 T x QDs@MMWCNTs composite was rich in functional groups and exhibited homogeneous nanotube nanostructure by coupling with good electrochemical activity. Of note, the MoS 2 QDs@Ti 3 C 2 T x QDs@MWCNTs composite exhibited outstanding bifunctional electrocatalytic performances for oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR) in alkaline solution by combining the superior electrocatalytic activity of MoS 2 QDs and Ti 3 C 2 T x QDs and the excellent electrochemical performance of MWCNTs. The MoS 2 QDs@Ti 3 C 2 T x QDs@MMWCNTs catalyst exhibited a superior ORR activity to other non-Pt catalysts, giving a low Tafel slope (90 mV dec −1 ) and high half potential ( E 1/2 , 0.75 V), which was close to those of the commercial Pt/C (20%) catalyst (Tafel slope of 89 mV dec −1 , E 1/2 of 0.80 V). Additionally, the MoS 2 QDs@Ti 3 C 2 T x QDs@MMWCNTs also possessed good electro–oxidation performance for methanol in alkaline solution, giving a maximum methanol oxidation current density at 2.2 V of 160 A·g −1 . The results indicated that the combination of MoS 2 and Ti 3 C 2 T x QDs with MWCNTs can supply a potential for fabricating the bifunctional electrocatalysts for ORR and MOR.