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 MoS2 quantum dots (MoS2 QDs) and Ti(3)C(2)Tx QDs (denoted by MoS(2)QDs@Ti(3)C(2)TxQDs@MWCNTs), of which MoS2 QDs and Ti3C2Tx QDs were separately prepared by exfoliating MoS2 and Ti(3)C(2)Tx MXene nanosheets by the hydrothermal method. It showed that the as-prepared MoS(2)QDs@Ti(3)C(2)TxQDs@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 MoS2 QDs and Ti3C2Tx QDs and the excellent electrochemical performance of MWCNTs. The MoS(2)QDs@Ti(3)C(2)TxQDs@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 (E1/2, 0.75 V), which was close to those of the commercial Pt/C (20%) catalyst (Tafel slope of 89 mV dec(-1), E1/2 of 0.80 V). Additionally, the MoS(2)QDs@Ti(3)C(2)TxQDs@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 MoS2 and Ti3C2Tx QDs with MWCNTs can supply a potential for fabricating the bifunctional electrocatalysts for ORR and MOR.