Preparation And Hydrogen Evolution Reaction Of MoS₂-based Core-shell Structured Electrocatalysts

Molybdenum disulfide（MoS2）can be used as a highly efficient and stable electrocatalyst for hydrogen evolution reaction（HER）,but it has the problems of poor conductivity and agglomeration.At present,it is an effective strategy to improve the HER performance by employing the substrates with high activity and excellent conductivity to composite with MoS2 nanosheets.This thesis focuses on the studies of electrocatalytic properties of the composites by using MOFs derivatives as the matrixes.A series of core-shell structured MOFs derivatives@MoS2 composites were constructed through the high-temperature treatment and hydrothermal method.On the basis of systematic characterizations,the electrocatalytic HER performances of the resultant materials were emphasisly investigated.In addition,the relationship between carbonization/phosphating temperatures,MoS2 loading amount,and electrocatalytic performances was discussed in detail.Then,the crucial factors affecting HER activities were revealed,and the enhanced mechanism of catalytic activities for such system was further clarified.The research content of this thesis is as follows:1)ZIF-67 nanocubes were prepared by a co-precipitation method followed by the high-temperature calcination,formingthe Co/NC substrate.Then,the combination of Co/NC matrix and MoS2 nanosheets by a hydrothermal approach afforded the Co/NC@MoS2 composite.The hybrids exhibited a typical core-shell structure,where outer MoS2 nanosheets were uniformly grown on the surface of Co/NC nanocubes.Studies revealed that the Co/NC-800@MoS2sample obtained by carbonizating at800°C exhibited the best HER performance,in terms of an overpotential of 167 m V at a current density of 10 m A cm^-2,a Tafel slope of 37 m V dec^-1,and good durability in acid media.The excellent HER performance of the composite is mainly due to the high dispersion of MoS2nanosheets on the substrate,which can expose a large number of active sites.Besides,the presence of Co/NC can not only significantly improve the electron conductivity of the catalyst,but also provide additional catalytic sites.Furthermore,the unique core-shell structure of the hybrid provides an efficient and fast channel for the transportation of active species and electrons during the HER process.2)MOF-derived Co/NC nanocubes were phosphatized through a high-temperature treatment,resulting in the formation of Cox P/NC.The Cox P/NC@MoS2 composite was constructed under the hydrothermal condition.The formation process of the composite,and the effects of phosphating temperature and MoS2 loading amount on electrocatalytic HER activities were studied.The results indicated that the Cox P/NC@MoS2 composite with a suitable MoS2 loading amount exhibited the best HER performance including an overpotential of 148 m V at the current density at 10m A cm^-2,a Tafel slope(33 m V dec^-1)close to Pt/C catalyst,and A high stability in acid solution.Compared with Co/NC@MoS2,the HER activity of the Cox P/NC@MoS2 composite was significantly improved,which can be attributed to the type of substrates.In the composite structure,Co Px not only exhibited an excellent electron conductivity but also a highly intrinsic catalytic activity.In addition,the core-shell structure can expose more active sites of MoS2nanosheets,meanwhile provide a fast channel for the mass and electron transfer during the catalytic reaction,thereby boosting HER performance.3)CoCo-PBA nanocubes were synthesized by a co-precipitation strategy,and then the corresponding metal phosphide（Co P）was isolated by a high-temperature phosphating.The Co P@MoS2 composite was further constructed by a combination of Co P and MoS2 through ahydrothermal method.The resultant composite showed a typical core-shell structure,in which MoS2 nanosheets are uniformly wrapped on the surface of Co P nanocubes.Compared with pure MoS2 and Co P,the HER performance of the compositeis significantly improved.The low overpotential of 201 m V was achieved at 10 m A cm^-2 together with a Tafel slope of 70.4 m V dec^-1and high stability in acid media.The excellent HER performance of the composite can be attributed to the unique core-shell structure and the synergistic interaction between both components.