Preparation And Electrocatalytic Properties Of Molybdenum Disulfide Quantum Dot Composites

The production of hydrogen and oxygen by electrolytic water splitting is one of the research hotspots in the field of electrocatalysis.Platinum based catalysts,RuO2 and IrO2 are the best catalysts for the generation of hydrogen and oxygen,respectively.However,the high cost and scarcity of these precious metal-based catalysts limits their further large-scale application.Molybdenum disulfide,as a kind of layered semiconductor material,has been widely used as electrocatalyst toward hydrogen evolution reaction(HER),due to its unique mechanical and electronic properties,and excellent catalytic activity.In order to improve its electrocatalytic performance,multiple strategies such as the downsizing of molybdenum disulfide,the doping of heteroatom were adopted to adjust the electronic structure,enhance the conductivity of the catalyst,and increase the active sites,etc.And the main contents are as follows:(1)Molybdenum disulfide quantum dots(MoS2 QDs)with abundant thiols on the surface were first prepared by a rapid microwave method.Then,the Au@MoS2 QDs core-shell nanocomposite was prepared by a simple self-assembly strategy due to the strong interaction between MoS2 QDs and gold nanoparticles(Au NPs).The ultra-small MoS2 QDs(2.5 nm)are tightly distributed on the surface of Au NPs,exposing a large number of active sites.When applied a external current,the electrons would be transferred rapidly from semiconductor quantum dots to the surface of Au NPs.The fast electron transfer and the synergistic effect between Au NPs and MoS2 QDs make the catalytic activity of Au@MoS2 QDs nanocomposite significantly enhanced.The catalyst needed overpotential of 0.112 V vs.RHE to achieve a current density of 10 mA/cm2,The Tafel slope of 83 mV/dec was obtained.After electrolysis for 20 h,the current density of the catalyst almost did not decline.,indicating the excellent electrocatalytic activity and stability of the Au@MoS2 QDs catalyst.(2)Using graphene oxide(GO)and ammonium tetrathiomolybdate[(NH4)2MoS4]as precursors,hydrazine as reducing agent,the oxygen doped MoS2 QDs on reduced graphene oxide(O-MoS2 QDs/RGO)hybrid was synthesized by a rapid microwave method(140?,5 min).In the synthesis process,the use of hydrazine directly regulates the doping content of oxygen in MoS2 QDs.This method is easy to operate and control and is conducive to quickly screening the synthesis conditions for the best hydrogen evolution performance.At the same time,the doping of oxygen atoms can adjust the electron structure on the catalyst surface,which is conducive to the rapid electron transfer.In addition,the doping of oxygen atoms makes the molybdenum edge of molybdenum disulfide have more lewis acid sites,which makes the water molecules adsorbed on the catalyst surface easy to be activated.The abundant peripherally active sites exposed by ultra-small O-MoS2 QDs(5.8 nm)and their chemical synergy with RGO give the catalyst excellent electrocatalytic performance.When the current density is 10 mA/cm2,the overpotential of 0.076 V is needed(vs.RHE).The Tafel slope is 58 mV/dec.Furthermore,the catalyst synthesis method is simple,time-saving,high yield,can be used for industrial large-scale preparation.(3)A novel MoS2 quantum dots/CoSe2 nanosheet(MoS2 QDs/CoSe2)hybrid with 0D/2D heterostructure is developed.The CoSe2 nanosheets(NSs)enabled an excellent oxygen evolution reaction(OER)activity with increasing vacancy configuration on one hand,while the MoS2 QDs served as an eminent hydrogen evolution reaction(HER)catalyst on the other hand.By integrating MoS2 QDs and CoSe2 NSs,the hybrid exhibits excellent electrocatalytic performances in HER and OER.The unique 0D/2D hetero-interface increases the exposed active sites,and facilitates electron transfer,thereby boosting the electrocatalytic activity.Relatively Low overpotentials of 0.082 V and 0.28 V are required to drive the current density of 10 mA/cm2 for HER and OER,with corresponding Tafel slopes of 69 and 78 mV/dec,respectively.Furthermore,this work provides an efficient yet simple approach to construct bifunctional electrocatalysts with enhanced activity and stability.