Study On Molybdenum Disulfide Structure Regulation And Photo/Electrocatalytic Hydrogen Evolution

The development of inexhaustible and clean energy technologies has far-reaching benefits for our society.Owing to its high anisotropy and unique crystal structure,the attractive properties of 2D molybdenum disulfide（MoS₂）can be utilized in a variety of energy conversion and storage（ECS）applications.Therefore,understanding how these properties can be tuned and the tunable properties can be utilized becomes increasingly important.In this paper,we develop synthetic strategies toward preparation of MoS₂ with different structures,and its role in several important renewable energy technologies.We then discuss the relationship between the tuned properties and the performance of MoS₂ in HER applications,offering our perspectives on how to effectively advance the development of MoS₂-based catalysis.The details are summarized as follows:（1）The catalytic activity of molybdenum sulfide（MoS₂）for hydrogen evolution reaction（HER）strongly depends on the number of exposed active edges of MoS₂ nano sheets.Making single or few-layer MoS₂ nanosheets vertically stand on a substrate is a very effective way to maximally expose the edge sites of MoS₂ nanosheets.Vertically standing single or few-layer MoS₂ nanosheets on porous TiO2nanofibers（TiO₂@MoS₂）are successfully prepared via a simple hydrothermal reaction.Due to plenty of pores in the electrospun TiO₂ nanofibers,the MoS₂ nanosheets vertically grow from the inside to the outside,and the growth mode of the MoS₂ nanosheets rooting into the TiO₂ nanofibers endows not only intimate contact between TiO₂ and MoS₂ for fast electrons transfer but also high structural stability of TiO₂@MoS₂ heterostructure.The vertical orientation of MoS₂ nanosheets enables the active edge sites of MoS₂ to be maximally exposed.Without using Pt cocatalyst,the TiO2@MoS₂ heterostructure achieves high photocatalytic hydrogen production rates of 1.68 or 0.49 mmolh^-1g^-1 under UV-vis or visible light illumination,respectively.This high photocatalytic activity arises from the positive synergetic effect between the MoS₂ and TiO₂ components in this novel heterostructure.In addition,the TiO2@MoS₂ heterostructure exhibits a high durability as evidenced by the invariable hydrogen production rate after continuous illumination over 30 h.The work advances the development of highly efficient molybdenum sulfide-based HER catalysts.（2）The scrupulous design and integration of multiple active materials into hierarchical nanoarchitectures is essential for the creation of photocatalytic hydrogen evolution reaction（HER）system that can mimic natural photosynthesis.Here we report the design and preparation of a "cauline leaf"-like structure for highly efficient HER,by decorating TiO₂ nanofibers with vertical arrays of atomically-thin MoS₂ nanosheets and CdS nanocrystals.The unique integrated "cauline leaf" design can promote light trapping and absorption for highly efficient light harvesting and photocarrier generation,and offer unblocked electron transport pathway for rapid charge separation/transport to suppress charge recombination,as well as high surface area and high density of active sites for highly efficient utilization of photo-generated carriers for productive HER.Structural characterizations by transmission electron microscopy show well-integrated nanoarchitectures.Significantly,photocatalytic studies demonstrate rapid HER rates as high as 12.3 or 6.2 mmolh^-1g^-1 under simulated solar light or visible light irradiation,with apparent quantum efficiencies of 70.5%at 365 nm or 57.6%at 420 nm,and excellent long term stability,representing one of the best reported MoS₂ hybrid HER photocatalysts.The study could open new opportunities for the rational design of nanoscale architectures for HER or other application.（3）The metallic 1T-MoS₂ has attracted considerable attention as an effective catalysts for hydrogen evolution reactions（HERs）.However,the fundamental mechanism about the catalytic activity of 1T-MoS₂ and the associated phase evolution remain elusive,largely due to the challenges in preparing highly stable 1T-MoS₂.Herein we report the preparation of highly stable 1T-MoS₂ by hydrothermal exfoliation of MoS₂ nanosheets vertically rooted into rigid one-dimensional（1D）TiO2 nanofibers.The stable 1T-MoS₂ nanosheets presents an ideal model system for investigating the HER catalytic activities as a function of phase evolution.Both the experimental studies and theoretical calculations suggest that the 1T-MoS₂ could be stabilized by strain and sulfur vacancies.Furthermore,the adsorption of H atoms during HER process can irreversibly transform 1T MoS₂ into 1T’ MoS₂ with further enhanced HER activities,resulting in a“catalytic site self-optimization”.（4）As an alternative of Pt,transition metal dichalcogenides（TMDs）have recently received great attention as potential catalysts for HER（hydrogen evolution reaction）.However,Realizing the Volmer-Tafel reaction for the ideal efficient hydrogen evolution reaction based MoS₂ is considerable challenge.Through the structural engineering with hollow nanostructure and electronic structure modulation with S-vacancy and 1T phase,the HER activity of MoS₂ electrocatalysts are expected to be further improved.The MoS₂ nanoscrolls-based electrocatalysts exhibit striking kinetic metrics with onset potential of 103 mV,Tafel slope of 36 mV per decade,performing among the best of current molybdenum disulfide catalysts.The excellent catalytic performance can be ascribed to the abundant active edges provided by defects and phase structure transformation.This approach could lead to tailored geometrically designed electrodes that not only increase the activity of the catalysts but also facilitate the reaction kinetics.