Synthesis And Characterization Of Non-noble MoS₂ And Cobalt-based Nanomaterials And Their Enhanced Performance In Hydrogen Evolution Reaction

Hydrogen,as a promising energy carrier in the hydrogen economy paradigm,is mainly produced from fossil fuels by steam reformation,but increasing concerns over the environment problem make sustainable energy technologies attractive.Recently,water splitting for renewable energy has been proposed as an alternative way for hydrogen production in large scale.The hydrogen evolution reaction(HER)is one key step in the process of water splitting.To achieve a high efficiency,high active electrocatalysts for HER are crucial.Currently,the noble metals,such as platinum,exhibit the highest electroactivity toward HER,but the high cost and scarcity of noble metals may limit their large scale application.Transition-metal chalcogenides,carbides,nitrides and metal alloys have been widely investigated as HER catalysts.Among all these alternatives,molybdenum disulfide(MoS2)with the earth-abundant composition and high activity has received tremendous attention.In this thesis,our research is mainly focus on molybdenum and cobalt based catalyst by combination of controllable design of active sites,as well as doped and functionalized carbon-based support for effective HER electrocatalysts.The details of this dissertation are summarized briefly as follows:1.A facile fabrication of in-situ nitrogenated graphene with few layer MoS2 electrocatalysts with high HER performance has been realized via a combined chemical and hydrothermal reduction of graphene oxide.The MoS2/N-rGO composite exhibited a high current density about 32.4 mA·cm-2 at an overpotential of 200 mV,as well as excellent long-term stability.The excellent HER performance of MoS2/N-rGO composite stemmed from the highly dispersed MoS2 nanosheets,interconnected conductive graphene skeleton with higher N content,dominant concentrations of of pyridinic and graphitic N,and confinement effects on graphene sheets,which accelerated electron transfer from the electrode to the few-layers MoS2 nanosheets and maintained long-term stability.2.A highly and stable electrocatalyst for hydrogen evolution reaction(HER)has been developed on the basis of MoS2 on p-phenylenediamine(PPD)-functionalized reduced graphene oxide/O-containing carbon nanotubes(rGO/O-MWCNT)hybrids via facile and green hydrothermal process.Among the prepared catalysts,the optimized MoS2 /rGO/PPD/O-MWCNT with nanosized and highly dispersed MoS2 sheets provides a large amount of available edge sites and the improved electron transfer in 3D conductive networks.It exhibits excellent HER activity with a low overpotential of 90 mV and large current density of 47.6 mA·cm-2 at 200 mV,as well as excellent stability in an acidic medium.The Tafel slope of 48 mV·dec-1 reveals the Volmer-Heyrovsky mechanism for HER.3.The porous N-rich carbonitride nanotubes(Co@NCN)encapsulated Co particles have been successfully obtained by melamine polymerization,pCN exfoliation,and following decomposition and concurrent reduction of Co2+ by thermal annealing under a NH3 atmosphere.Control experiments reveal that the superior performance should be ascribed to the synergistic effects between embedded Co nanoparticles and N-rich carbonitride nanotubes,which originate from the high pyridinic N content,fast charge transfer rate from Co particles to electrodes via electronic coupling,and porous and bamboo-like carbonitride nanotubes for more active sites in HER.The optimized Co@NCN-800 exhibits outstanding HER activity with an onset potential of-89 mV(vs RHE),a large exchange current density of 62.2 ?A·cm-2,and small Tafel slope of 82 mV dec-1,as well as excellent stability(5000 cycles)in acid media,demonstrating the potential for the replacement of Pt-based catalysts.