Controllable Preparation And Properties Of Two-dimensional Transition Metal Chalcogenide Quantum Sheet Materials

The development of two-dimensional?2D,monolayer?material-related theories and technologies have led to the rapid development of related basic science and application fields.2D transition metal chalcogenides?TMCs?have characteristics of wide range of band gaps,multi-phases,chemical stability and abundant element reserves.2D TMCs have gained important applications in catalysis,energy storage,field effect transistors,sensors,superconductors,ferroelectrics,wearable electronics,and biomedical applications,etc.Further reduction of the lateral size of 2D materials to quantum dimensions?<10nm?will result in new physical and chemical properties and facilitate the development of related applications.However,at present,research on the regulation and preparation of 2D TMC quantum sheet?QS?materials is very lacking.The difficulty lies in the cognition and regulation of the factors that affect the lateral size of 2D TMCs.The lack of modulation and preparation methods therefore leads to the lack of research on the applications and performance for 2D TMC QS materials.To this end,in this study,the Group 6 TMCs were used as the research objects and the lateral size and 1T phase content of the Group 6 TMCs were effectively regulated via a developed controlled electrochemical Li intercalation plus liquid exfoliation method.With the developed method,2D Group 6 TMC QS materials with high 1T phase content were obtained.The fragmentation mechanism for the developed electrochemical method was deeply studied and a mass production method for preparing 2D 1T-MoS₂ QSs was developed based on the obtained mechanism.Further,the performance of the prepared 2D 1T-MoS₂ QS materials as catalysts for electrocatalytic water splitting hydrogen evolution reaction?HER?and as electrodes for electrochemical supercapacitor energy storage were studied.The research results are as follows:?1?An electrochemical regulation method for preparing 2D 1T-MX₂?M=Mo,W;X=S,Se?QS materials was proposed.Through the control of the electrochemical lithiation rate followed by liquid exfoliation,it was found that the key factor for regulating the phase composition and lateral size for 2D MoS₂ was the intercalated Li amount.With the decrease in the electrochemical lithiation rate,the intercalated Li amount of MoS₂ was improved,and the degree of 2H?1T phase transition and lattice distortion for MoS₂ was increased.After exfoliation,the lateral size of the 2D MoS₂was reduced and the 1T phase content was increased.At the lithiation current density of 0.001 A/g,2H-MX₂?M=Mo,W;X=S,Se?obtained a quasi-full intercalated Li amount?².0?.After exfoliation,single-layered MX₂ QS materials with mean lateral size of 3.0⁵.4 nm and 1T phase content of 92%⁹7%were prepared.?2?A mass production method for preparing 2D 1T-MoS₂ QS materials was proposed.Based on the electrochemical mechanism in?1?that quasi-full Li intercalation induced fragmentation and exfoliation of MoS₂ into 2D 1T-MoS₂ QSs,the2H-MoS₂//LiCoO₂ soft pack battery design was proposed to realize quasi-full Li intercalation for mass MoS₂ powders.After exfoliation,2D 1T-MoS₂ QS materials with1T phase content of up to 93%and lateral size of 6.1±1.1 nm were mass produced.One soft pack battery produces ca.1.2 g 2D 1T-MoS₂ QS materials with a yield of ca.27%.?3?The edge site of the 2D 1T-MoS₂ QS materials was found to be the primary active site for its electrocatalytic activity of HER?including acidic and basic media?.Further,in the alkaline media,the HER activity of the site or interface in the 1T-MoS₂and 1T-MoS₂/Ni?OH?₂ obtained by interfacial engineering on 1T-MoS₂ was confirmed by experimental and theoretical calculations that it follows:edge_1T-MoS2/edge _Ni?OH?2>edge_1T-MoS2>in-plane_1T-MoS2/edge_Ni?OH?2>in-plane_1T-MoS2.The 1T QS/Ni?OH?₂ obtained by interfacial engineering on the 2D 1T-MoS₂ QSs has high density of highly active interface of edge_1T-MoS2/edge _Ni?OH?2,which leads to its higher HER performance than commercial Pt/C.?4?A dense 2D 1T-MoS₂ QS film with pilled brick-like structure was obtained by configuration regulation.As a supercapacitor electrode material,results show that the QS film exhibits excellent capacity and rate performance due to its ultra-high density of ion transport channels and ultra-short ion transport distance.In the electrolytes of0.5M H₂SO₄ and 1M KCl,with electrode thickness of only 14²4?m,the1T-MoS₂QS films can simultaneously achieve area capacitance?>0.6 F/cm²?that meet the practical application standard and high volumetric capacitance?>255 F/cm³?at high scan rates of 1000²000 mV/s.The performance indicates that the 2D 1T-MoS₂ QS film electrodes can meet the actual total capacitance requirement at an ultra-high operating frequency within an very small electrode volume when assembled into an actual capacitors.This study has important scientific and practical significance for further research on the basic physical and chemical properties of 2D 1T-TMC QS materials and the exploration and development of more related applications.This study can provide strong support for the design and preparation of other two-dimensional quantum sheet materials.